Faculty of Agriculture and Forestry


Recent Submissions

  • Wasonga, Daniel (Helsingin yliopisto, 2021)
    Cassava (Manihot esculenta Crantz) is a staple food for millions of people in the tropics, providing high energy and nutritional value. Problems associated with cassava in the arid tropics are low yield, high cyanide concentration, and low mineral and vitamin A availability in leaves and roots. These factors hinder the utilization of cassava greatly and are highly influenced by the plant water status and potassium (K) availability in the growth environment. The productivity of cassava in such environments could be improved using irrigation strategies not based on full crop water requirements, such as deficit irrigation combined with K nutrition to ensure sustainable quantity and quality production. Additionally, employing systems that can allow non-destructive estimation of plant performance, such as the use of plant imaging techniques, could provide early information on plant performance, which would facilitate phenotyping, as well as assist in the mitigation of abiotic challenges in cassava production. This study investigated how irrigation water, K fertigation and their interactions affect the growth responses of biofortified cassava during the early growth phase. It was also investigated whether K fertigation could improve the nutritional and reduce the anti-nutritional qualities of biofortified cassava growing under typical conditions of water deficit. The ability to use red-green-blue (RGB) and multispectral sensors to detect the effects of water deficit and low K in cassava, and whether the crop quality changes due to low moisture and low K could be observed from the images, were also examined. Pot experiments were conducted at early developmental stages of cassava under controlled greenhouse conditions at the University of Helsinki. Young biofortified cassava plants were established using cuttings. The plants were subjected to three irrigation treatments (30%, 60%, 100% pot capacity) that were split into five K (0.01 mM, 1 mM, 4 mM, 16 mM, 32 mM) application rates beginning 30 days after planting (DAP) and ended at 90 DAP, when plants were harvested. Irrigation treatments and K application rates significantly affected leaf water potential, leaf osmotic potential, net photosynthesis, stomatal conductance, leaf temperature, leaf chlorophyll, water usage, plant leaf area, plant height, tuber number and whole-plant biomass. The interaction was also statistically significant for these properties. Irrigation treatments and K application rates also affected leaf turgor, but the interaction was not statistically significant. Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants. Lowering the K application rate below 16 mM reduced the values further. Most importantly, the growth was decreased least when irrigation was decreased to 60% together with 16 mM K, compared with optimal applications. The combined effect of irrigation treatments and K applications was statistically significant for starch, energy, minerals, total carotenoids, and cyanide, but the interaction was not statistically significant for dietary fibre and crude protein in the leaves and roots. In the leaves and roots, water deficit and lower K applications inhibited starch, carotenoids, crude protein, and fibre synthesis. Water deficit interrupted the uptake of minerals by the cassava roots from the soil and ultimately to the leaves. Improved uptake of calcium, phosphorous, magnesium, zinc, iron, sulphur, and chloride to the leaves was recorded with increased K application regardless of water deficit. K application also mitigated the effect of water deficit at 30% irrigation. Crude protein, carotenoids, and minerals were revealed to be more abundant in the leaves than in the roots, while the inverse was the case for starch content and iron. Cyanide was diminished in the leaves and roots of the cassava with increases in both irrigation and K application rates. Full irrigation (100%) with 16 mM K application produced the highest nutritional quality and the least cyanide concentration. Also, 16 mM K significantly improved the nutritional qualities and diminished the cyanide concentration irrespective of the irrigation treatment. High estimation accuracy (R2 = 0.90) for biomass, chlorophyll, and net photosynthesis were recorded. The estimated leaf area associated strongly (R = 0.98) with the measured leaf area. The estimated biomass also associated strongly with the measured biomass. Starch, energy, total carotenoids, and cyanide were estimated reasonably (R2 > 0.80) and showed strong correlations with the most of spectral indices. The estimation accuracy for all mineral elements was low, and weak relationships existed between the mineral elements and the spectral indices. The regression models identified normalized difference vegetation index, green area index, and simple ratio index as the best estimators of growth and key nutritional traits in cassava. Moreover, irrigation at 30% together with 0.01 mM K reduced all the index values but increased crop senescence index. Regardless of water deficit, increasing K application rate to 16 mM resulted in high values for all the spectral indices but low senescence index. In conclusion, adjusting K fertigation rates in combination with deficit irrigation may improve the growth and dietary quality of young cassava, and reduce cyanide concentration. Findings from this work can be utilized as a foundation to develop agronomic management practices involving K application for cassava growing in water-limited environments. The study also shows that RGB and multispectral sensors can be used to provide indirect measurements of growth and key nutritional traits in cassava, thus representing a tool that breeders may use to facilitate evaluation of cultivars, especially in the developing areas. Information from imaging data may also be used to facilitate corrective measures to avert stress, such as the decision to irrigate or apply fertilizers. Nonetheless, laboratory analysis of plant samples should support sensor estimates, especially under field conditions, when all possible factors affecting plant growth are difficult to forecast. Future studies could place emphasis on field conditions with multiple cassava cultivars and employ different imaging techniques.
  • Njoghomi, Elifuraha Elisha (Helsingin yliopisto, 2021)
    This research focuses on stand dynamics and ecological recovery in miombo woodlands, Morogoro, Tanzania. The study uses the Kitulangalo Permanent Sample Plots (PSPs) to analyse tree species’ site-specific growth, regeneration dynamics, and stand development using empirical and modeling approaches. The high number of tree species in miombo necessitated the formulation of three species groups involving 1) trees that grow relatively rapidly to be dominants in top canopy layers 2) trees that stay mainly in the lower and middle canopy levels and 3) trees that grow slowly but persistently and may eventually rise to dominant and codominant canopy positions applied in studies I and III. Study III also applies three harvesting alternatives, which align with the recommended harvesting practices for these woodlands. Diameter increment varied with the change in basal area growth across species groups, reaching a maximum of 3.2 cm (group 1) during 2008-2016. Density-dependent mortality and ingrowth also varied with species group as higher mortality rates dominated the lower and middle canopy layers due to asymmetrical competitions. Fencing the plots prompted thick grass cover. The drop in the total number of regeneration stems and the simultaneous increase in the number of main stems in fenced areas and dense plots indicated a self-thinning process induced by competition. This is linked to multi-stem regeneration undergoing a morphological transformation into single-stem saplings (main stems) and eventually becoming small trees. Harvesting intensity, density-dependent mortality, and ingrowth regulated stand basal area and therefore stand growth and development during the simulation. Stand structural development was dominated by species groups 1 and 2, indicating sustainability in species composition and structures. Stand development was affected by the addition of new stems of each species in each simulation year. Miombo stands have demonstrated the potential to attain a steady-state condition over the medium-term under-regulated stand conditions and silvicultural treatments. The developed models, treatments, and harvesting alternatives may be limited in application to Kitulangalo and similar lowland miombo woodlands in Tanzania. Future studies concerning stand conditions, silvicultural treatments, and harvesting alternatives are vital for a better understanding of stand dynamics in miombo woodlands in Tanzania. Keywords: Forest disturbance, tree growth and stand dynamics, regeneration dynamics, silvicultural treatment, harvesting alternative, miombo woodlands
  • Haikka, Hanna (Helsingin yliopisto, 2021)
    The aim of this study was to detect usability of genomic prediction for different breeding dilemmas. In order to achieve this aim, breeding data sets from oat and barley were used in the study. The studied lines were genotyped with genome-wide markers. Meanwhile, phenotypes were collected from multiple years and locations of historical breeding data. Together, the data of the line genotypic and phenotypic information formed the training population used in the analysis. The separate studies concerned genomic prediction, genome-wide association study (GWAS) and analysis on genotype by environment (GE) interaction. The studies had in common that they present ‘difficult’ topics within the breeding process. The original publication I concentrated on improving grain yield prediction for oat and barley. Grain yield presents one of the most important traits in breeding, but has low predictability due to low heritability. The prediction of genomic estimated breeding values (GEBVs) was improved by using multi-trait prediction. For this purpose, grain yield was predicted simultaneously with correlated traits. In addition, benefit of trait-assisted prediction was examined. In conclusion for oat and barley, prediction of grain yield was improved by 4% and 9% with multi-trait prediction, and by 9-14% and 11-28% with trait-assisted prediction compared to prediction of grain yield alone, respectively. The original publication II focused on Fusarium head blight (FHB) resistance in oat. FHB resistance is a troublesome trait to breed, since the disease cannot be reliably scored visually, but extensive laboratory analysis is needed to obtain resistance phenotypes. In addition, FHB resistance consists of multiple components. In the study, the correlations between FHB resistance related traits were high. Much lower correlations were seen between FHB resistance related and agronomic traits. No significant associations between FHB related traits and genetic markers were discovered with reasonable correction of population structure and genetic relationship between the studied oat lines. For this reason, using genome-wide marker information to promote resistance breeding should be done solely with genomic selection (GS), where all the marker effects are used to enrich resistance alleles within the breeding population. The original publication III explored the extent of GE interaction within breeding data sets of oat and barley. At first, the genetic correlations between trial locations within year were calculated and used to compute mean across the years. The correlations suggested that data set of oat was not as sufficient as the data set for barley to explore the quantity of GE interaction. The second step of the analysis contained genomic prediction with six different models. The prediction models contained effects due to lines, genetic, environmental covariates, GE interaction and genotype by environmental covariates interaction. The prediction accuracy was increased for both crops when GE interaction was added into the prediction model. The results from the analysis imply that GE interaction exists within the breeding data sets, and should be taken into account upon prediction. All of the conducted studies proved the usability of genomic prediction in solving principal questions in the breeding process. The studies improved prediction of central traits simultaneously enabling the prediction in the early breeding generations, and showed the significance of GE interaction, and most of all, showed that historical breeding data can be used to predict the important traits. These studies present tools for practical breeding in order to meet the demand to accelerate crop improvement.
  • Tuure, Juuso (Helsingin yliopisto, 2021)
    Water scarcity is globally a key reason for crop yield losses. Difficulties in efficient utilization of the total available precipitation cause yield limitations and even total crop failure at rainfed dryland farms. This study assessed two potentially available measures to improve the water balance of dryland agriculture; water recovery through passive dew collection and soil mulching with plant residue. Dew collection field experiments were conducted to evaluate the effectiveness of various plastic materials in dew collection in dryland conditions. The planar dew collectors were of the standard type: a 1 m2 surface tilted at 30◦ in respect to the horizontal. Dew yields were measured daily over a one-year period. The condensing surface temperatures and the meteorological conditions were monitored continuously, to calculate potential dew output. A laboratory method was prepared and tested for evaluating the attributes affecting dew condensation and droplet flow. The condensing surfaces were cooled below dewpoint by utilizing Peltier elements in controlled conditions. Dew yields measured in laboratory conditions were compared with calculated dew outputs, and with dew yields measured in field conditions. Dew occurred throughout the year, even through the dry seasons, and may be considered a small but reliable source of water. Annual dew yields were < 8% of the annual precipitation (322 mm). No significant differences were found between the tested materials. Clear skies, calm winds (0.5–2.5 m s-1), and conditions with dew point close to air temperature (Tdew ≈ Tair) favor dew condensation. Placement in the field affects the airflow characteristics at the condensing surfaces and ultimately the collected dew quantities, thus attention should be paid to the placement of the dew collectors in the field. Based on our results, a more comprehensive laboratory evaluation regime, with specific design and measurements of the airflow characteristics is needed to draw valid conclusions on the differences between the plastic foils. Mulching with plant residue was studied by measuring soil volumetric water content in vertical profiles in bare and plant residue-covered soil during a 100-day period. A one-dimensional model based on Richard’s equation was used to predict the effect of mulch over a two-year period. Compared with bare soil, mulching prolonged the time when continuously measured soil moisture content exceeded the water stress limit of maize. The predicted water-conserving effect increased with mulch thickness. However, plant residue mulch degrades naturally and the availability and competitive uses of plant residues may limit the thickness of the mulch layer. A mulch layer with a thickness of > 1 cm brought clear improvements to the soil moisture conditions and resilience against dry spells compared with bare soil. The presented models were capable of estimating the cumulative dew condensation and soil moisture behavior satisfactorily over time. For further development of the dew condensation model, more specific airflow measurements are needed for calculating the mass transfer for more accurate predictions of nightly dew quantities. This study touched upon the combined effect of irrigation with dew water and mulching on by using modeling to predict the effects on soil moisture. The results indicated that mulching improves the usability of irrigational water recovered from dew by reducing evaporation. The effect increases with layer thickness. Future research steps could include the quantification of the presented water-conserving measures on actual crop yields, especially the combined effect.
  • Silventoinen, Pia (Helsingin yliopisto, 2021)
    The agro-food industry generates annually substantial amounts of side streams, resulting in the loss of high-quality protein and dietary fibre, whereas their incorporation into the food chain would positively contribute to resource sufficiency and healthier diets. However, plant-based ingredients, especially proteins, typically deliver limited performance in certain food applications, such as beverages and spoonable products, when compared with their animal-based counterparts. Therefore, fractionation and functionalisation techniques are investigated and applied to improve the applicability of the plant-origin ingredients in a wider range of food matrices where they can offer alternatives to animal-based ingredients. Dry fractionation provides a sustainable and gentle processing technology, which allows the production of multicomponent hybrid-ingredients, enriched in protein but also containing considerable amounts of dietary fibre or starch, depending on the raw material. The aim of the current work was to investigate the use of dry fractionation, more specifically, dry milling and air classification, for increasing the protein content of cereal side streams, namely, wheat, rice and rye brans, and the barley endosperm fraction. In addition, the objective was to understand the factors affecting the technological functionality and applicability of the protein-enriched ingredients in the relevant food matrices. To facilitate a more efficient fractionation, pre-treatments, including defatting with supercritical carbon dioxide (SC-CO2) for rice bran, moisture removal for wheat and rye brans and mixing with a flow aid for the barley endosperm fraction, were elucidated. The technological functionality of the protein-enriched fractions was examined, and bioprocessing and physical processing approaches for improving the ingredient applicability in high-moisture food systems were investigated with rice and barley fractions. This study revealed that the fat removal, drying and use of flowability aids were effective in enhancing dry fractionation by improving the processability, particle size reduction and dispersability of rice bran, wheat and rye brans, and the barley endosperm fraction, respectively. Pin disc milling and air classification of a SC-CO2-extracted rice bran increased the protein content from 18.5 to 25.7% with 38.0% protein separation efficiency (PSE). Alternatively, a two-step air classification of the defatted rice bran allowed to reach a slightly higher protein content (27.4%) with lower PSE (20.2%) compared with the one-step air classification approach. Air classification of the dried and pin disc-milled wheat and rye brans increased the protein content from 16.4 and 14.7%, respectively, to 30.9 and 30.7%, with PSE of 18.0 and 26.9%. Additionally, soluble-to-insoluble dietary fibre ratios were increased and phytic acid was considerably enriched in bran fractionations. The maximum protein content reached by air classification from the barley endosperm fraction, initially containing 80.0% starch and 8.3% protein, was 28.3% with 21.7% PSE, while reaching a lower protein enrichment level of 22.3% allowed obtaining PSE of 59.4%. The protein-enriched fractions, especially those from rice and wheat, exhibited higher protein solubility than the raw material brans, presumably due to the enrichment of albumin and globulin proteins from the aleurone during air classification, which was also indicated by an altered protein profile and the co-enrichment of phytic acid. When the ultra-fine milling of wheat and rye brans was explored as an alternative to fractionation, the formation of damaged starch and lowered protein solubility were observed. The protein-enriched brans and the ultra-finely milled brans both showed improved dispersion stabilities, whereas pasting viscosities, and water and oil binding capacities were lower for the hybrid ingredients compared with the pin disc-milled raw materials. The protein-enriched fraction from barley, on the other hand, exhibited low protein solubility and limited techno-functional properties. The applicability of the protein-enriched fractions in high-moisture food model systems was tested after ingredient modifications via enzyme treatment, ultrasonication and pH shifting. Phytase treatment of the protein-enriched rice bran fraction improved the behaviour of the ingredient in heat-induced gelation, especially under alkaline conditions. For the protein-enriched barley fraction, ultrasound treatment with or without pH shifting reduced particle size; improved colloidal stability at pH 3, 7 and 9; and increased protein solubility, especially at pH 9. To conclude, dry fractionation of cereal side streams allowed protein enrichment with a concurrent increase in the soluble-to-insoluble dietary fibre ratios of the brans and considerable reduction in the starch content of the barley endosperm fraction. Additionally, this thesis demonstrated for the first time that cereal side stream-derived, protein-enriched hybrid ingredients exhibit improved technological functionalities that can be further enhanced via enzymatic or physical processes that affect, for example, their gelation and dispersion stability. The bioprocessed protein-enriched rice bran fraction could find potential use as a raw material in spoonable food products delivering a good amount of protein and dietary fibre and allowing the use of the nutritional claim that the food is a ‘source of fibre’. The ultrasound-treated barley protein ingredients, on the other hand, should be further studied in the manufacturing of plant-based milk substitutes. In general, these improved ingredient properties suggest the possibility of developing novel side stream-based food ingredients with increased nutritional and technological qualities that simultaneously contribute positively to raw material resource sufficiency.
  • Salin, Siru (Helsingin yliopisto, 2020)
    The research documented in publications I-IV involved studies in dry, late-pregnant Ayrshire dairy cows on grass silage (GS) based diets (I-IV). The principal aim was to investigate the effect of prepartal plasma non-esterified fatty acids (NEFA) level (I) and the effect of prepartal dietary energy intake (II-IV) on the development of insulin resistance (IR) during late pregnancy (I-IV) and changes in insulin resistance in early lactation (II-IV). Detailed, extensive physiological studies were conducted to understand the mechanisms underlying the development of maternal insulin resistance and to investigate the impact of changes in dietary energy level and subsequent changes in plasma NEFA concentration prepartum. The insulin resistance was assessed by interpretation of data from intravenous glucose tolerance test (IVGTT) with minimal model (MM) approach (I-III) and by insulin challenge (IC; I, II) data. Besides insulin resistance, also the impact of prepartal energy intake on metabolic adaptations, tissue deposition and mobilisation as well as dry matter intake (DMI) and lactational performance were investigated in publications III and IV. In publication I, the key objective was to evaluate the effects of increment of plasma NEFA concentration, typically observed during the last weeks of pregnancy and in early weeks of lactation in dairy cows, on glucose tolerance and responsiveness or sensitivity to insulin as assessed by IVGTT and IC. The greater NEFA levels were achieved by abomasal infusion of tallow (TAL) or camelina oil (CAM). Compared with water infusion (CON), infusion of lipids increased basal plasma NEFA concentrations by around 50%, to an equal level than what was found in dairy cows 2 to 1 weeks prepartum on GS-based diets (II-IV). Elevation of plasma NEFA concentration impaired glucose clearance and decreased insulin secretion during metabolic challenges. These data suggest that elevated plasma NEFA concentrations impaired whole-body insulin responsiveness and sensitivity in dry cows in late pregnancy. As assessed by MM indices, both the disposition and the insulin sensitivity indices were greater after CAM than TAL infusion during IVGTT. Compared with TAL infusion, CAM had an insulin-sensitizing effect which was most likely caused by alterations in plasma profiles of major long-chain fatty acid (FA) groups. A 50% increment in the percentage of polyunsaturated FA (C18:2 and C18:3) and a similar decrease in the percentage of monounsaturated FA (C16:1 and C18:1) was found in plasma FA profiles after CAM infusion when compared with TAL. In publication II, the dietary effects on insulin resistance were assessed not only by the level of energy intake but also by comparing tissue responses to glucose and insulin in late pregnancy vs. early lactation. Compared with controlled energy intake (CEI), the effect of prepartal overfeeding and gradual restriction of energy (HEI) had a minor effect on whole-body insulin resistance during the transition period. An attenuated prepartal NEFA response to endogenous insulin was found in HEI cows suggesting a more refractory adipose tissue to insulin than in CEI. After parturition, this effect was reversed. Across the dietary treatments, both basal and stimulated insulin concentration decreased after parturition as a result of a lower response to a similar secretory stimulus than before parturition and due to increased clearance of insulin postpartum. Compared with prepartal IVGTT, glucose disposal was enhanced postpartum across the dietary treatments. A hyperbolic relationship denoted as the disposition index (DI) was observed during the IVGTT. Compared with prepartal glucose and insulin dynamics across the diets, the MM indices point to increased insulin resistance shortly before than shortly after parturition. However, low insulin concentration is the major factor regulating the use of glucose by peripheral tissues in early lactation. The lack of dietary effect on whole-body insulin resistance in publication II was most likely due to minor dietary effect on tissue accretion between treatment groups, although the lower prepartal plasma NEFA concentration in HEI than in CEI cows suggests enhanced lipid deposition in adipose tissue before parturition, facilitated by higher plasma insulin (IV). No dietary effect on plasma hormone and metabolite concentrations or total DMI was found after parturition. High energy intake during the dry period tended to decrease milk yield after calving (IV). In publication III easily applicable diets suitable for loose housing systems were compared. An ad libitum allowance of GS (HEI) induced a more pronounced BW and BCS change prepartum when compared with a GS-diet diluted with wheat straw (CEI). HEI cows demonstrated a compensatory insulin response to glucose in prepartal IVGTT which preserved glucose tolerance of peripheral tissues. The HEI diet reduced and delayed NEFA suppression suggesting decreased insulin sensitivity and responsiveness in adipose tissue prepartum. The high NDF-content in CEI diet probably decreased ruminal propionic acid production as reflected by lower prepartal glucose and insulin CEI cows. Prepartal energy level did not affect metabolic flexibility of transition dairy cows as assessed by the absence of dietary effect on mobilisation of body reserves, plasma metabolites and hormones, and DMI after calving, whereas milk yield was greater from week 5 onward in HEI than in CEI. The moderate negative effects of gradual restriction of prepartal energy and dilution of energy by mixing GS with wheat straw on early lactation production response demonstrated that these feeding practices were not optimal for transition dairy cows. A moderate or ad libitum overfeeding affected peripheral insulin resistance in the level of prepartal lipid metabolism, while ad libitum overfeeding of GS induced changes in prepartal glucose metabolism as well. Both the difference in energy intake and the composition of the diet contributed to the observed effects on glucose and NEFA dynamics orchestrated via changes in insulin concentration in the transition period. Keywords: dairy cow, transition period, grass silage, energy intake, peripheral insulin resistance, adipose tissue lipolysis, plasma hormone and metabolite, milk yield, lipid infusion, plasma NEFA, minimal model
  • Ahlberg, Sara (Helsingin yliopisto, 2020)
    Aflatoxins continue to be a food safety problem globally, especially in developing regions. Prevalent food contaminating aflatoxins are B1 (AFB1) and M1 (AFM1). These are human carcinogens and have potentially severe health impacts. Almost all (99.5 %) milk samples from Nairobi were contaminated with AFM1, highlighting the urgent need to create functional solutions to improve food safety. Based on the aflatoxin levels and milk consumption, risks were calculated: cancer risk caused by AFM1 was lower among consumers purchasing from formal markets (0.003 cases per 100,000) than for low-income consumers (0.006 cases per 100,000) purchasing from informal markets. Overall cancer risk (0.004 cases per 100,000) from AFM1 alone was low. Because of AFM1 in milk, 2.1 % of children below three years in middle-income families, and 2.4 % in low-income families, could be stunted. Overall, 2.7 % of children could hypothetically be stunted due to AFM1 exposure from milk. Based on these results AFM1 levels found in milk could contribute to an average of -0.340 height for age z-score reduction in growth. The exposure to AFM1 from milk is 46 ng/day on average, but children bear higher exposure of 3.5 ng/kg bodyweight (bw)/day compared with adults, at 0.8 ng/kg bw/day. Aflatoxins are produced by Aspergillus flavus fungus, which is prevalent in soils. Certain strains of lactic acid bacteria (LAB) have been reported inhibiting fungal growth. 171 LAB strains were tested against aflatoxin producing A. flavus fungi. The three LAB strains showing the highest antifungal activity were identified as Lactobacillus plantarum. None of the strains was able to completely inhibit fungal growth under conditions favorable for fungi and suboptimal for LAB. The three indigenous LAB Lactobacillus strains and one Lactococcus strains were tested for their AFM1 binding abilities in different conditions and after different treatments along with two reference Lactobacillus strains. The binding of AFM1 by LAB strains varied between 11 to 100 % in the biocontrol solution analysis, being approximately at the level of 40 % throughout the analysis sets. A significant amount of effort and resources have been invested in an attempt to control aflatoxins. However, these efforts have not substantially decreased the prevalence nor dietary exposure to aflatoxins in developing countries. The growth reduction of aflatoxin producing fungi with LAB could be one potential option, but there are still major issues to solve prior to any practical applications. A different approach to control aflatoxins suggesting the usage of binding agents in foods and lactic acid bacteria (LAB) have been studied extensively for this purpose. However, when assessing the results comprehensively and reviewing the practicality and ethics of use, risks are evident, and concerns arise. In conclusion, there are too many issues with using LAB for aflatoxin binding for it to be safely promoted. Arguably, using binders in human food might even worsen food safety in the longer term. A more comprehensive food safety approach has to be taken to solve this ongoing crisis.
  • Zhang, Yuemei (Helsingin yliopisto, 2020)
    The thesis aimed to study the effects and mechanisms of freezing-thawing treatments on myofibrillar protein denaturation and to explore the role of myofibrillar protein denaturation in causing the formation of thaw loss. The freezing-thawing of porcine M. longissimus thoracis et lumborum (LTL) increased the free Ca2+ concentration and the subsequent chilled storage promoted an accelerated decrease of activities of calpain-1 and calpain-2, compared to unfrozen meat. Proteasome activity was observed to be around 40% lower after freezing-thawing. The observed increased purge loss and decreased water-holding capacity (WHC) of myofibrils indicated myofibrillar protein denaturation occurring during the freezing-thawing treatment. In the investigation of freezing-induced denaturation of myofibrillar and sarcoplasmic proteins of LTL in relation to freezing rate, fast frozen samples (cold metal plate/-80°C) had a characteristic freezing time of 12 min, while samples frozen at slow rate (air/-20°C) had a freezing time of around 174 min. Slow freezing led to around 30% larger thaw loss in parallel with reduced WHC and increased surface hydrophobicity of myofibrils, indicating more severe myofibrillar protein denaturation in slow compared to fast freezing. A model is proposed to explain the importance of myofibrillar protein denaturation in relation to the freezing rate in the origin of thaw loss: In slow freezing, protons are accumulated with concentrating solutes in the unfrozen water leading to a decline of pH causing denaturation of structural proteins. In fast freezing small ice crystals might trap protons inducing less decline of pH and thus less myofibrillar protein denaturation and reduced thaw loss when compared with slow freezing. Sarcoplasmic protein denaturation also was shown to occur in freezing-thawing as evaluated by differential scanning calorimetry and tryptophan fluorescence properties of drip, which was, however, independent of freezing rate. The role of decreased pH (from pH 5.5 to 5.2), combined with high ionic strength (2 M KCl), in causing myofibrillar protein denaturation was studied by exposing fresh minced meat to either high ionic strength only or to high ionic strength with decreased pH to mimic conditions estimated to be in the unfrozen water of frozen meat during freezing. Exposure to high ionic strength caused an increase of WHC of the isolated myofibrils, whereas exposure to high ionic strength combined with low pH reduced WHC and increased surface hydrophobicity of the myofibrils. These results suggest that decreased pH combined with increased ionic strength in the unfrozen water of frozen meat largely would explain myofibrillar protein denaturation and thus the thaw loss occurring in frozen-thawed meat. The storage at -3 °C of fast or slow frozen pork prior to final thawing at 2 °C diminished the impact of the freezing rate on myofibrillar protein attributes, and differences between fast and slow freezing were no longer significant for WHC and surface hydrophobicity of the isolated myofibrils when frozen samples subsequently were kept at -3 °C for 7 days. The results suggest that a marked myofibrillar protein denaturation is taking place with extended storage time at -3 °C. In conclusion, freezing-thawing increases water loss in meat and slow freezing causes a higher increase when compared to freezing at fast rate. Myofibrillar and sarcoplasmic protein denaturation occurs in freezing and thawing. The rate of freezing produces a significant effect in the myofibrillar fraction: A slow freezing will develop a more severe protein denaturation than a fast freezing. Consequently, the myofibrillar protein denaturation, related to the freezing rate, is proposed to contribute to the generation of thaw loss. However, a subsequent storage of frozen meat at -3 °C before final thawing seems to diminish the beneficial effects of fast freezing on myofibrillar protein characteristics, compared to slow freezing, due to an additional protein denaturation. Therefore, it is recommended that meat industry adjusts the thawing capacity to minimize the passage time in temperature of -3 °C in meat.
  • Rantala, Tapio (Helsingin yliopisto, 2020)
    This study analyzes the political legitimacy of forest and forest-related nature conservation policies in Finland. Legitimacy is defined here that the forest and nature conservation regimes and related political institutions are perceived as rightful among the people. The major contribution of this study is the comprehensive conceptual framework of legitimacy based on several theories, mainly from political science. The framework analyzes the objects of support, patterns of legitimacy, performance evaluations, and how these relate to one another. In this study, the objects of support refer to forest-related political institutions; these include regulations and public incentives, as well as decision-making processes, political programs, and administrative procedures. The framework is intended to be especially useful in the empirical analyses of pluralistic public political discussion and uses a methodology developed for this purpose. The study also analyses the social values of organized political actors. The empirical part of this study explores a data set from Finnish print media discourse, based on letters to editors in three newspapers and in one journal, along with comments given during the preparation of Finland's National Forest Programme 2010. Another empirical data set consists of qualitative semi-structured interviews and the writings of the organized interest groups. Many different groups of citizens were found to participate in public discussion on forests. Quite a large number of individuals shared the overall publicity, despite the fact that there were some very active writers. Nature conservation organizations, researchers, and politicians were well represented. However, the participation of governmental officials from both the forest and environmental sectors can be characterized as insufficient, considering their importance in the implementation of policies. The study of letters to editors found that groups of common social values served as patterns of legitimacy in the performance evaluations of forest policies. These include welfare and wellbeing derived from forests; values related to nature conservation; democratic values; distributive justice; good governance; core regime principles; and fair markets. Of all performance evaluations, 52% were negative while 26% were positive and 22 % were mixed. Domestic, EU-level, and international legality were commonly perceived as sources of the legitimacy of policies. Finland's good international standing and its role as a moral and economic forerunner were very common principles in the evaluations in both the forest and nature conservation policies, in all parts of data. The same idea was also found central in the national forest programs and strategies. The shared goal of the Finns seems to be that the nation would be best in the world both in forest and nature conservation policies. Keywords: forest policy, nature conservation policy, political legitimacy, democracy, justice, public discussion .
  • Joensuu, Johanna (2020)
    Ozone (O3) and nitrogen oxides (NOx: nitrogen monoxide NO and nitrogen dioxide NO2) are reactive gases with an important role in atmospheric chemistry. Terpenes are a reactive subgroup of BVOCs (biogenic volatile organic compounds) emitted by plants. Needle or leaf surfaces are the first point of contact between the atmosphere and a plant. Boreal forests represent a significant portion of the global land area available for atmosphere-biosphere interactions. The aim of the study was to develop methods for observing the exchange of NOx in field conditions and to explore the roles of terpenes on needle surfaces and nitrate fertilization on the fate of O3 and NOx in plant-soil-atmosphere interfaces. The methods included whole-canopy measurements, shoot-scale chamber measurements, needle sampling and laboratory analyses, utilizing both continuous observations and experimental setups. In the studied low-NOx environment, the shoot-level NOx fluxes were too small to be monitored accurately in field conditions with an automated dynamic chamber. In addition to interference, the signal to noise ratio was low, and a significant proportion of the observed fluxes were to/from chamber walls. No clear NOx fluxes from Scots pine foliage were detected, and there was no effect of nitrogen fertilization on the observed fluxes. It seems unlikely that a fertilization treatment could cause significant NOx emission from boreal pine forests. The fluxes reported in our earlier studies included compounds other than NOx. Shoot terpene emissions and needle wax extracts were both dominated by monoterpenes. There was variation in the terpene spectra of both emissions and wax extracts. The proportion of sesquiterpenes was higher in the epicuticular waxes than emissions, and the observed sesquiterpene compounds were for the most part different in the emissions and wax extracts. The role of direct transport through the cuticle from sites of terpene synthesis may be more important than has been assumed.
  • Alam, Syed Ariful (Helsingin yliopisto, 2020)
    This study focused on modification of rye bran to produce high fibre extruded cereal foods with a good texture and structure. Rye bran addition during extrusion is challenging due to high levels of insoluble dietary fibre, which leads to less expanded products and a hard texture. Bran modification by particle size reduction or fermentation significantly improved both the structural and textural properties of extrudates. Moreover, optimization of the processing parameters such as increasing the screw speed, lowering the water feed rate, as well as the use of in-barrel hydration regimens further improved the textural properties. The applicability of rye bran in extruded products could thus be improved by particle size reduction and fermentation. The extruded food structure and texture had a direct effect on the mastication and bolus formation process in the mouth. A hard and dense extrudate structure required more mastication effort than a crispy structure. Crispy and porous structures easily disintegrated in the mouth and produced smaller bolus particles than a hard and dense structure. A smaller particle size of the bolus was associated with increased starch hydrolysis. The bolus particle size was more effective than the matrix composition in altering the starch digestibility. Increased dietary fibre intake via appealing snack products could help reduce chronic diseases. Knowledge obtained in this thesis on cereal matrix formation and digestion and the effects of added dietary fibre on the structural and textural properties of extruded solid foams will help the food industry to develop healthy and appealing products. Understanding process-structure-digestibility relationships of high fibre extruded matrices is essential for designing health promoting foods.
  • Räty, Mari (Helsingin yliopisto, 2020)
    Grasslands occupy 45% of agricultural land in Finland, but in provinces characterised by grassland-based dairy production the proportion can be 67%. Phosphorus (P) loads from grasslands to inland waters have received relatively little research attention. In the Finnish climate, soils are subjected to frost in winter and snowfall comprises a considerable part of total annual precipitation. Surface runoff is generated by limited infiltration of snowmelt water into partially frozen soil in spring, which is a crucial period for dissolved nutrient and soil particle transport, especially in central and northern Finland. This thesis examined the role of perennial grass vegetation in P dynamics in the soil-plant-water continuum and quantified P losses from grasslands under boreal conditions. Potential contributions of perennial vegetation to P losses were estimated indirectly, by determining changes in nutrient content of aboveground vegetation. Susceptibility of overwintering perennial ley regrowth to deliver P was assessed in a simulated snowmelt-induced surface runoff study. These approaches were complemented with five-year monitoring of a small (3.2 km2) agricultural and forested catchment, representing grassland-based dairy production areas in east-central Finland. Amount and inter-annual variation in P losses and erosion rate were quantified. The results showed that grasslands can release substantial amounts of plant-derived P when exposed to frost, freezing and thawing. Elevated P concentrations and losses of up to 0.69 kg ha-1 were detected in simulated snowmelt-induced runoff outflow. Higher P concentrations were also occasionally measured in early spring runoff at small catchment scale. More frequent freezing/thawing will enhance plant-derived P release, especially under a reduced snow layer and lack of insulating cover. In five-year monitoring of an agricultural sub-catchment with short-terms leys, where some fields were under grassland and others under cereals, mean annual total P (TP) losses were 1.0 kg ha-1 (range 0.6−1.5 kg ha-1). The proportion of this TP load transported as dissolved reactive P (DRP) averaged 44% (range 32−56%) for the agricultural sub-catchment and 34% (28−38%) for the whole catchment area, reflecting low erosion rate under the protective grass cover. Five-year annual soil erosion rate from the agricultural sub-catchment was only 46−287 kg ha-1 (mean 115 kg ha-1 yr-1). The results also suggested that P losses were partly associated with loss of organic material. These results indicate a need for P monitoring based on chemical analysis of water samples, instead of on turbidity measurements. Grasslands are prone to DRP losses, but substantially less susceptible to erosion than arable fields during harvest years. In Finnish short-term ley rotations, grass leys are typically renovated every 3−4 years, often including autumn ploughing, which can increase erosion and particulate P losses. Thus when quantifying P loads to waters from short-term grass leys, erosion and nutrient losses within the whole ley cycle should be considered, including the ley establishment and renewal year. Keywords: phosphorus, erosion, grassland, ley rotation, nutrient loading, surface runoff, winter
  • Córdova, Raúl (Helsingin yliopisto, 2020)
    Smallholder farming is known to be highly vulnerable to climate change and climatic variability, especially in mountainous regions of the developing world, mainly due to high environmental exposure and sensitivity and low adaptive capacity to a variety of climate and non-climate stressors. Maintenance of more sustainable and resilient agricultural systems are essential for guaranteeing sustainable management of land and for securing the livelihoods of millions of rural and urban people. The aim of this study was to study the main socioeconomic and environmental parameters which influence the adaptation of smallholder farmers and their farming systems to climate change and climatic variability. The adaptation opportunities and constraints of smallholder farming systems were determined comparing their biophysical and socioeconomic sustainability (Study I) and their vulnerability to climate change and climatic variability (Study II and Study III). The data was collected by interviewing 60 households (30 agroforestry systems and 30 conventional systems) during 2015–2016. Semi-structured questionnaires were designed to collect primary biophysical, socioeconomic and sustainability data, while a modified Climate Change Questionnaire of the World Overview of Conservation Approaches and Technologies (WOCAT) was used to collect the vulnerability data. The characteristics of the farming system were analysed applying a comparative analysis approach. Qualitative variables were analysed through descriptive statistics (Crosstabs and Chi-square), while Independent Samples t test was applied for the quantitative variables. The main findings highlight the role of agroforestry systems in supporting the sustainability of the systems and farmers’ livelihoods: higher levels of agrobiodiversity, greater diversification of livelihoods, more secure land tenure, higher on-farm incomes, and greater diversification of irrigation sources. In addition, agroforesters and conventional farmers perceived climate change in the same way, as a continuing trend of rising temperatures and decreasing precipitation. Results also indicate that conventional systems had greater exposure to solar radiation, pests, weeds, disease outbreaks and droughts compared to agroforestry systems. By contrast, agroforestry systems presented greater potential to decrease exposure and sensitivity, and greater assets to support farmers’ adaptive capacity, especially in aspects related to social environment, and access to information and production infrastructure. Keywords: Andean smallholder agroforestry and conventional agricultural systems, socioeconomic and biophysical sustainability, exposure, sensitivity, adaptive capacity, traditional knowledge
  • Matkala, Laura (Helsingin yliopisto, 2020)
    The growing conditions in northern boreal forests have remained similar for millennia. However, amplified climate change may cause higher mean annual temperatures and precipitation sums, longer growing seasons, along with increased occurrence of extreme weather events (drought, heavy rain, or summertime frost) in the region. The relationship that forest vegetation has with soil nutrients and the exchange of carbon dioxide (CO2) between the forest and atmosphere may change. This dissertation focuses on quantifying the baseline status of northern boreal forests from these aspects, to be able to predict theupcoming changes more precisely. Soil total phosphorus (P) and nitrogen (N) contents were important factors in explaining the community composition of understory vegetation in the study site. The site was located in a region near a phosphate ore, where soil nutrient contents are highly variable. The number of herb, grass, and sedge species increased with N and P contents in the humus, especially with P. The increasing P content, on the other hand, positively correlated with downy birch (Betula pubescens Ehrh.), which was the dominant tree species of the research plot. The understory vegetation had an important role in the CO2 exchange rates of a northern boreal Scots pine (Pinus sylvestris L.) forest site. The annual CO2 dynamics varied between the canopy and understory, so that when the canopy began photosynthesizing in the spring, the understory was still under snow cover. The cumulative temperature sum had a higher positive correlation with photosynthesis than the total ecosystem respiration (TER) rate of the pine site. Overall, the pine site was a weak carbon sink during the growing season, although it temporarily turned into a carbon source during a cold and rainy summer. Extreme weather events, and their effects on the CO2 dynamics of forests, were studied on a Scots pine site and a Norway spruce (Picea abies (L.) Karst.) site. Both sites had experienced extreme summers during the studied times, but the CO2 flux rates in the Norway spruce site responded more clearly to them. The TER rates of the Norway spruce forest declined when it was warm and dry. This likely happened because of decreased decomposition of organic matter. The decline was, however, only temporary, and TER returned to normal when the temperature and precipitation returned to their average levels. Thus, the studied forest sites seemed to, so far, be rather resilient towards extreme weather events. Several studies have found that N availability will increase because of warmer temperatures, which speeds up decomposition and nutrient mineralization. However, decomposition may potentially slow down in some spruce forests due to heat. Local variation may thus be high when it comes to the availability of nutrients or to the CO2 dynamics of forests. While modeling studies are important for predicting the responses of northern forests to climate change on the large scale, our research reminds that local-scale studies are also inevitable for gaining a more precise picture.
  • Martikainen, Katja (Helsingin yliopisto, 2020)
    Inbreeding increases homozygosity, which in turn increases the frequency of harmful recessive alleles and decreases advantageous heterozygosity, resulting in inbreeding depression. Inbreeding depression on fertility decreases the lifetime milk production of cows and increases the need for veterinary treatments, inseminations and involuntary cullings, which has a negative impact on the profitability, sustainability and animal welfare of the dairy sector. The main goal of this thesis was to estimate the effect of inbreeding on female fertility in Finnish Ayrshire cattle. More specifically, this study aimed to estimate inbreeding depression using different metrics based on pedigree and genomic information, and to dissect inbreeding depression to chromosomes, chromosomal segments and specific homozygous genotypes. Moreover, it identified specific ROH genotypes that had detrimental effect on female fertility and milk production traits. The data used included over 12 000 genotyped cows with corresponding phenotypic records of fertility and milk production traits. The fertility traits studied included the non-return rate at 56 days after first insemination (NRR), number of inseminations per conception (AIS), interval from calving to first insemination (ICF) and interval from first to last insemination (IFL). Milk production traits included milk, protein and fat yields. Inbreeding coefficients were estimated based on pedigree (FPED), percentage of homozygous SNPs (FPH) and runs of homozygosity (ROH; FROH). FPED was not found to be associated with inbreeding depression in any of the fertility traits. However, statistically significant inbreeding depression was observed when using genomic measures of inbreeding (FPH and FROH) in the model. For example, a 10% increase in FROH was associated with 4 and 6 days longer IFL in heifers and first-parity cows, respectively. When FROH was used to estimate inbreeding depression separately for each autosomal chromosome, a 10% increase in FROH on chromosomes 2, 18 and 22 was observed to increase IFL in heifers by 1.6, 0.9 and 0.7 days, respectively. Similarly, a 10% increase in FROH on chromosome 15 was associated with the lengthening of IFL in second-parity cows by 2.3 days. Haplotype analysis for the detected regions revealed haplotypes that, when occurring as homozygous, were associated with the lengthening of IFL of approximately 4 and 8 days in heifers and second-parity cows, respectively. Finally, an analysis of unique ROH genotypes revealed several ROHs with unfavourable effects on fertility and milk production traits. The estimated effects of ROHs with the highest statistical significance varied between parities from 13 to 38 days longer IFL, from 9 to 17 days longer ICF and from 0.3 to 1.0 more AIS. For milk production traits, the ROHs with the highest statistical significance resulted in reductions of 208 kg for milk yield, 7 kg for protein yield and 16 kg for fat yield. In addition, this study found regions in which inbreeding is particularly harmful due to ROHs displaying unfavourable effects across multiple traits. The detrimental effects of inbreeding observed in this study highlight the importance of managing the levels of inbreeding in the Finnish Ayrshire breeding programme. The findings of this study can be utilized for more efficient control of inbreeding depression as well as investigations of the mechanisms of inbreeding depression by examining the identified regions showing inbreeding depression.
  • Bhattarai, Mamata (Helsingin yliopisto, 2020)
    Galactoglucomannans (GGMs) are principal hemicelluloses in softwood tissues. Spruce GGM obtained from different recovery approaches are currently studied for applications as emulsifiers and stabilizers of dispersed systems. Natural polysaccharides, owing to their origin from a complex matrix, have an intrinsic affinity for the association. Their associative properties are affected by the recovery approach since it influences purity and intrinsic characteristics (e.g., molar mass, degree of substitution). Understanding the impact of the GGM recovery approach on its associative behavior, currently limited, is essential to comprehend the stabilization mechanism of GGM in dispersed systems as well in the expansion of its functional applications. This doctoral project investigated the associative behavior of GGM at a semi-dilute concentration of 1% in an aqueous medium and its effect in an oil-in-water emulsion system, with GGM recovered from spruce sawdust/wood chips using pressurized hot water extraction, BLN process (modified pressurized hot water extraction process), and effluent of the thermo-mechanical pulping process. All studied GGM samples existed in the form of polysaccharide molecules and supramolecular fraction. It was observed that the recovery approach and sample purity affected the molar mass of the polysaccharide fraction as well as the share and structural properties of the supramolecular fraction. The supramolecular fraction was observed to be either colloidal aggregates, agglomerates, solid particles, or a combination in varying proportions. Next, these samples were studied in emulsions. Differences in the macromolecular state of samples were found to influence interfacial morphology and stability of emulsions. Following, the associative behavior of purified GGM obtained from the pressurized hot water extraction process was studied at acidic, neutral, and alkaline pH and upon addition of sodium chloride. Associative behavior of the sample displayed a positive correlation with acidic pH condition and time, improving emulsion stability. The sample exhibited an upper limit of GGM to oil ratio for efficient emulsification and stabilization ability, implying the presence of a limited amount of active emulsifying component. Currently, novel biomaterials are being developed from wood biomass. The findings of this study contributed to the characterization of colloidal properties of GGM at a nanometric scale, thereby enhancing its scope of future applications. These findings regarding the solubility of GGM would also be relevant in existing operations of paper and pulping industries, as well as for aspiring biorefineries in identifying optimal GGM recovery approach.
  • Mattila, Antti (Helsingin yliopisto, 2020)
    Natural products are small metabolites produced by living organisms with versatile chemical structures and diverse bioactivities. Bacteria are a rich but yet underexplored source of natural products. Natural product biosynthetic pathways encode a huge array of biosynthetic enzymes which can catalyze stereospecific and regiospecific modification of intermediates to produce complex natural products from simple precursors. The biosynthetic mechanisms underlying the production of natural products vary substantially. Cyanobactins are synthesized through the post-translational modification of precursor peptides and represent one of the most abundant natural product classes produced by cyanobacteria. Cyanobactins have a macrocyclic or linear structure with antimicrobial and cytotoxic bioactivities, although their ecological function is unclear. In this study, genome mining was used to catalog the genetic diversity of cyanobactin biosynthetic pathways from bacterial and archaeal genomes. Bioinformatic analysis of microbial genomes was used to identify cyanobactin biosynthetic pathways. New cyanobactin biosynthetic pathways were studied using a combination of bioinformatics, molecular biology, microbiology, biochemistry and structural chemistry. Bioinformatic predictions of cyanobactin biosynthetic gene clusters were performed based on DNA sequence data. Subsequently, candidate strains identified based on the predictions were grown in the laboratory and subjected to mass spectrometric analysis and heterologous expression. Novel cyanobactin natural products were discovered and the enzymes underpinning their biosynthesis were characterized. In the first part of the study, the muscoride biosynthetic gene cluster was described and a new muscoride variant was discovered. Two specific prenyltransferases from the muscoride biosynthetic gene cluster, which were biochemically characterized, catalyzed the regiospesific prenylation of the N- and C-termini of the linear polyoxazole muscorides. In the second part of the study, genome mining revealed a truncated cyanobactin biosynthetic gene cluster across the bacterial and archaeal domains for the production of structurally unusual cyanobactins. In the third part of the study, a regiospecific prenyltransferase was discovered, belonging to the anacyclamide cyanobactin pathway and catalyzing the N-prenylation of the tryptophan residue of the substrate peptide. The main aim of this work was to uncover novel cyanobactin biosynthetic gene clusters from bacteria and expand knowledge regarding the biosynthetic potential of cyanobactin pathways. The results from this thesis broaden the chemical diversity of the cyanobactin family and expand upon the biosynthetic logic underlying cyanobactin biosynthesis.
  • Saha, Shreya (Helsingin yliopisto, 2020)
    Potato Virus A (PVA), which belongs to the family Potyviridae, is a significant agricultural plant virus that causes crop loss worldwide. Most potyvirus resistance is recessive and occurs due to the loss of interaction between the viral protein genome linked (VPg) and the host eukaryotic initiation factor [eIF4E/(iso)4E]. This interaction has been demonstrated in many cultivated plants that are susceptible to potyviruses. Studies on potyvirus resistance have shown that minute changes in either eIF4E/(iso)4E or VPg can cause the interaction to fail, resulting in the development of viral resistance. However, the detailed mechanisms underlying the significant effects of this interaction during potyvirus infection remain unclear. The central domain of the PVA VPg contains an eIF(iso)4E-binding consensus motif, Tyr-X-X-X-X-Leu-phi (YXXXLΦ). The function of this motif during the VPg–eIF(iso)4E interaction, in the context of PVA infection, was investigated in the present study. The tyrosine and the leucine residues at the binding site were replaced with alanine residues in PVA infectious cDNA (icDNA, PVAVPgmut) and in a VPg expression construct (VPgmut). The results showed that PVAVPgmut was capable of replicating inside the host cell, but overall gene expression remained low, similar to the levels observed for a replication-deficient virus. Systemic infection in PVAVPgmut-infected plants only occurred upon reversion to the wild-type PVA, which occurred in 26% of PVAVPgmut-infected plants by 15 days postinfection. Although VPg typically stabilises viral RNA (vRNA) and 3’ renilla luciferase (RLUC) expression, as published previously, the VPgmut failed to perform these functions. The helper component proteinase (HCPro) induces the generation of PVA-induced granules (PGs) during infection and the assembly of vRNA within these PGs to safeguard vRNA from being silenced. Plants infected with PVAVPgmut showed an increased number of PG-like foci in infected cells as compared to the plants infected with PVAWT. However, in compare to the PVAWT the percentage of PVA RNA colocalising with PGs was significantly low in PVAVPgmut infected leaf samples. The host eIF(iso)4E is thought to bind to the PVA VPg via the YXXXLΦ motif, and this interaction is considered to be essential for PVA RNA stabilisation, the transfer of RNA to the RNA silencing suppression pathway, and RNA translocation to polysomes for viral protein synthesis. In the second study, an alternative mechanism was explored involving the production of large quantities of coat protein (CP), which is a multi-functional protein. Tight control over CP production is necessary, depending on the stage of virus infection. Increased CP concentrations have been shown to represses potyviral gene expression. Therefore, CP concentrations are maintained at low levels during active gene expression in the early infection stage through a host-mediated degradation system. During later infection stages, CP is required at high quantities for the production of a large number of stable particles. The present study showed that ectopically expressed VPg enhances reporter expression more pronouncedly from the 3' side of the genome than from the 5’ side. A similar phenomenon was observed towards the later stages of the infection, in which the 3’ CP cistron and the 3’ reporter cistron were expressed more pronouncedly than the central cylindrical inclusion (CI) cistron and the 5’ reporter cistron. The 3’CP and 3’ reporter protein showed different production/accumulation dynamics than were observed for the rest of the genome. CP expression levels were observed to increase in the presence of overexpressed VPg, during both the early infection stage and towards the later infection stage. This process could represent the mechanism through which potyviruses increase CP production for sufficient virion formation. In the third study of this thesis, whether the stabilisation of CP was necessary for successful virion formation was investigated. These results revealed the function of PVA HCPro during CP stabilisation and virion formation. HCPro was found to be unable to stabilise CP in a virus-free system. A number of additional host and viral factors are necessary to produce stable particles. CP stability by HCPro is unrelated to its capacity for silencing suppression and, therefore, cannot be complemented by other viral silencing suppressors. Together, the findings described in this dissertation revealed important mechanisms that underlie potyvirus recessive resistance and the factors that affect stable virion formation.
  • Kairenius, Piia (Helsingin yliopisto, 2020)
    The objective of the research described in this thesis was to provide new information on the ruminal biohydrogenation of long-chain n-3 polyunsaturated fatty acids (PUFA), such as 20:5n-3, 22:5n-3 and 22:6n-3, for altering bovine milk fatty acid (FA) composition, with the potential to improve human health. Emphasis was not only placed on the potential to increase milk fat n-3, but also to modulate ruminal lipid metabolism and to explore the mechanisms driving milk fat synthesis and its regulation in lactating cows in order to understand the mechanisms and metabolic pathways underlying the diet-induced changes in milk fat depression (MFD), milk FA composition and specific FA intermediates and end products associated with MFD. Experiments documented in I–IV encompassed detailed investigations of ruminal (I-III) and mammary (IV) lipid metabolism. Experiment reported in I was conducted to build up methods for the analysis of long-chain 20- to 22-carbon FA intermediates formed during ruminal biohydrogenation of n-3 PUFA. The detailed analysis of fish oil (FO) and omasal digesta of lactating cows fed FO enabled the structure identification of 27 previously unidentified 20- to 22-carbon FA intermediates, containing at least one trans double bond. No conjugated 20-carbon FA were detected in omasal digesta. Results demonstrated that the hydrogenation of 20:5n-3, 22:5n-3 and 22:6n-3 in the rumen proceeds via two principal mechanisms that involve sequential reduction or isomerisation of cis double bonds closest to carboxyl group and provided clear evidence of extensive biohydrogenation of 20:5n-3, 22:5n-3 and 22:6n-3 in cows fed FO. Experiments documented in II-IV involved two physiological studies in which, the effects of dietary FO supplements alone (II; IV) or in combination (III) with sunflower (rich in 18:2-6; SFO) or linseed (rich in 18:3n-3; LFO) oil on animal performance (II-IV), ruminal lipid metabolism (II; III), microbial ecology in the rumen (II; III) and milk fat composition (IV) were investigated in lactating cows. Dietary FO supplements increased the intakes of 20:5n-3, 22:5n-3, 22:6n-3 and total FA (II; III), whereas decreased dry matter intake (II; III). Dietary oil supplements decreased (II) or had no effect (III) on ruminal volatile FA concentrations, but FO at high amounts (II) or when supplemented with plant oils (III) promoted an increase in molar proportions of propionate (II; III) and butyrate (II) at the expense of acetate (II; III). Supplements of FO modified ruminal metabolism of 16- and 18-carbon PUFA, causing increases in trans 16:1, trans 18:1 and trans 18:2 flow and a decrease in 18:0 at the omasum, and at high amounts promoted trans-10 18:1 accumulation at the expense of trans-11 18:1. Dietary FO had no substantial influence on ruminal outflow of conjugated linoleic acid (CLA). Extensive ruminal biohydrogenation of 20:5n-3, 22:5n-3 and 22:6n-3 resulted in increases in numerous 20- and 22-carbon PUFA containing at least one trans double bond at the omasum. Relative to FO, ruminal metabolism of 22:6n-3 was more extensive on diets containing plant oils, whereas the biohydrogenation of 22:5n-3 and 20:5n-3 showed no difference between FO and diets containing plant oils (III). The inhibitory effects of FO on the reduction of 18-carbon PUFA to 18:0 were influenced by the source of 18-carbon PUFA in SFO and LFO. The ruminal outflow of 18:0 was lower and accumulation of trans 18:2 and 20- to 22-carbon FA intermediates greater for LFO than SFO. Supplements of SFO and LFO caused trans-10 and trans-11 18:1 to accumulate, trans-10 18:1 being the most abundant FA intermediate in SFO. Alterations in the ruminal metabolism of FA were not associated with substantial changes in rumen protozoal counts or analysed bacterial populations known to be capable of biohydrogenation (II; III), but lowered Butyrivibrio spp. numbers in response to increasing levels of FO (II). Supplements of FO decreased milk fat yield and content and increased 20:5n-3, 22:5n-3 and 22:6n-3 concentrations in milk fat (IV). Enrichment of milk long-chain n-3 PUFA was associated with decreases in 4- to 18-carbon saturated FA and several-fold increases in CLA, trans FA and PUFA concentrations. Dietary FO resulted in the appearance of 37 unique 20- and 22-carbon FA in milk. FO-induced MFD (up to -40.6 % reduction in milk fat synthesis) was associated with changes in the concentrations of multiple FA in milk, in particular increases in milk fat trans-10 18:1 and cis-11 18:1 concentrations, but not with changes in the amount of trans-10,cis-12 CLA in milk and omasum or estimated milk fat melting point (IV). The negative relationship between ruminal outflow of trans-10 18:1 and milk fat secretion confirmed that a shift in ruminal biohydrogenation of 18-carbon FA toward trans-10 pathway has a role in the regulation of milk fat synthesis during FO-induced MFD. A decrease in 18:0 supply in combination with increased mammary uptake of cis-11 18:1, trans-10 18:1, and trans 20- and 22-carbon FA intermediates originating from the rumen may contribute to the reduction of milk fat observed during FO-induced MFD. The dietary supplements of FO alone or in combination with plant oils increased the ruminal outflow of FA intermediates containing at least one trans double bond and enriched long-chain n-3 PUFA in bovine milk with associated changes in the abundance and distribution of FA. These changes may have implications for the host metabolism and the nutritional quality or ruminant-derived foods. Keywords: biohydrogenation, rumen, fish oil, plant oil, sunflower oil, linseed oil, lactating cow, polyunsaturated fatty acid, n-3 fatty acid, conjugated linoleic acid, milk fat, trans fatty acid, Butyrivibrio, microbial ecology, gas chromatography, mass spectrometry, silver-ion thin-layer chromatography
  • Assmuth, Aino (Helsingin yliopisto, 2020)
    Forests play a vital role in mitigating climate change, as they sequester and store large quantities of carbon. This dissertation examines how carbon storage may be increased by changing forest management at the stand level. To extend the economics of forest carbon storage beyond single-species even-aged stands, this dissertation develops a bioeconomic model framework that incorporates the size and species structure of the stand, and the optimal choice between continuous cover forestry and forestry based on clearcuts. The studies apply empirically estimated growth models for boreal conifer and broadleaf tree species. The dissertation consists of a summary section and three articles. The first article presents an analytically solvable economic model for timber production and carbon storage with optimized management regime choice between continuous cover and rotation forestry. Continuous-time optimal control theory is utilized to solve the thinning path and the potentially infinite rotation age: if no optimal finite rotation age exists, thinnings are performed indefinitely while maintaining continuous forest cover. The second article extends this model by applying a size-structured growth model for Norway spruce (Picea abies (L.) Karst.), road-side pricing of sawlog and pulpwood, variable and fixed harvesting costs, and several carbon pools. The timing and intensity of thinnings, the rotation age, and the management regime are optimized numerically. In the third article, the optimization approach of the second article is extended to mixed-species size-structured stands. Species mixtures include the commercially valuable Norway spruce and birch (Betula pendula Roth and B. pubescens Ehrh.), and other broadleaves (e.g. Eurasian aspen, Populus tremula L., and maple, Acer sp.) that have no market value. Optimal rotation age is shown to either increase or decrease with carbon price depending on interest rate and the speed of carbon release from harvested wood products. Given empirically realistic assumptions, carbon pricing increases the rotation period and eventually causes a regime shift from rotation management to continuous cover management. Hence, carbon pricing heightens the importance of determining the management regime – continuous cover or rotation forestry – through optimization. Optimal thinnings are invariably targeted to the largest size classes of each tree species. Carbon pricing postpones thinnings and increases the average size of harvested and standing trees, hence increasing mean stand volume. Without carbon pricing, commercially non-valuable other broadleaves are felled during each harvesting operation. When carbon storage is valued, some of the other broadleaves are retained standing until they are large, thus increasing tree species diversity and deadwood quantity. The results suggest that moderate carbon price levels increase timber yields, especially of sawlog that may be used for long-lived products. Increasing carbon storage through changes in forest management is shown to be relatively inexpensive, and the marginal abatement cost is the lower, the higher the number of tree species in the stand.

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