Seedborne mycoflora of faba bean (Vicia fabae L.) and evaluation of plant extract and Trichoderma species against mycelium growth of selected fungi

Abstract

Fungal diseases are among the biotic factors limiting the production of faba bean in Ethiopia. The objective of this study was to isolate and identify seedborne mycoflora associated with faba bean seed samples, determine their effects on seed germination and disease transmission, and evaluate the antimicrobial activities of seven plant extracts and four Trichoderma spp. against the pathogen isolated from the seed. Fifty seed samples were collected from different farmers’ saved seeds of five major faba bean-producing varieties of the Ambo district and were tested by agar plate methods as recommended by the International Seed Testing Association (ISTA). A total of 7 fungal species belonging to 6 genera, viz. Fusarium oxysporum (Schlechlendahl), Fusarium solani (Mart.) Sacc, Aspergillus spp. Penicillium spp. Botrytis spp. Rhizoctonia solani (Kühn) and Alternaria spp. were isolated and identified. Among these, Fusarium spp., Aspergillus spp, and Penicillium spp. were the most predominant fungi in all seed samples. Seed-to-seedling transmission test results confirmed that F. oxysporum, F. solani and R. solani were major causal pathogens that caused root rot and damping-off disease in faba beans and were transmitted from seeds to seedlings. A higher germination rate was observed in Golja-GF2 (97%), and a lower germination rate was observed in Kure Gatira-KF8 (81%). A study on in vitro evaluation of plant extract and Trichoderma spp. against F. oxysporum, F. solani and R. solani revealed that plant extracts at 5%, 10% and 20% concentrations significantly inhibited the mycelial growth of all tested fungi. Inhibitory effects on the three tested fungi (R. solani, F. solani and F. oxysporum) were recorded on T. longibrachiatum (87.91%), T. atroviride (86.87%), Trichoderma virens (86.16%) and T. harzianum (85.45%). The inhibitory effect of the aqueous plant extracts on mycelial growth increased with an increase in concentration, and the hot water extracts showed higher effects compared to the cold water extract in all tested fungi. This study showed that the highest inhibitory effect of Allium sativum L. extracted at a 20% concentration against mycelial growth inhibition of the three test fungi (F. oxysporum, R. solani and F. solani) was 84.60%, 83.61% and 83.47%, respectively. However, Nicandra physalodes (L.) Gaertn.) extracts at the same concentration showed the lowest inhibitory effects on the three tested fungi (74.94%, 73.94% and 73.24%).