Fungal pathogens infecting moss green roofs in Finland

Abstract

Green roofs play an important role for cities in mediating some problems caused by urbanization. Mosses are ecologically important plants and capable of tolerating harsh conditions, and thus their use for greening building surfaces has become more common. There is only a little information concerning moss-associated microbes, especially those found in green roof environments. Moss-associated microbes might have significant role on the welfare of green roofs as they might induce both beneficial as well as adverse effects on mosses. In this study, the occurrence of fungal populations was studied on green roofs in Finland. A total of 94 samples were collected from nine different green roofs, and 64 fungal isolates and one oomycete were obtained from the brown, necrotic parts of the collected green roof mosses. The most general isolated fungal genus was Trichoderma, comprising 25 different fungal isolates. The second most common genus was Fusarium, with 15 fungal isolates. The third most common genus was Mucor, with nine fungal isolates. Most of the Trichoderma isolates were described as T. harzianum, whereas most of the Fusarium isolates were described as F. acuminatium. In addition, the genera Phoma and Mortierella were frequently present. Fifty-two of 65 isolates caused symptoms in the model plant Physcomitrella patens. The most harmful Trichoderma isolates were described as T. atroviride, T. viride, T. koningiopsis and T. hamatum, all of which caused severe damage to the protonema, stem and leaves. The most harmful Fusarium isolates were F. acuminatium, F. avenaceum and F. tricinctum. The genera Mucor and Mortierella were isolated but they did not cause detectable symptoms in P. patens. These results indicate that many fungal isolates belonging to different genera are able to colonize mosses on green roofs and some of them cause severe damage to the mosses.