Antifungal Potential of Extracellular Metabolites Produced by Drechslera spp. against Phytopathogenic Fungi (original) (raw)

Culture filtrates of nine Drechslera isolates (D. australiensis, D. cactivora, D. cynodontis, D. ellisii, D. hawaiensis, D. maydis, D. neergaardii, D. poae and D. spicifera), used at 30, 50 and 70%, were evaluated in-vitro against mycelial growth and spore germination of eight plant pathogenic fungi (Alternaria solani, Botrytis cinerea, Botrytis fabae, Fusarium oxysporum, Fusarium solani, Rhizoctonia solani, Sclerotinia sclerotiorum and Sclerotium cepivorum). Among the tested culture filtrates, only D. cynodontis was a highly effective growth inhibitor against all tested fungi; it reducing the fungal growth from 51.1 to 86.7%, and was the strongest inhibitor of spore germination, inhibiting spore germination of all tested fungi by 92 to 98%. The chloroform extract of D. cynodontis was the best growth inhibitor against all tested fungi: it inhibited fungal growth from 66.7% to 88.9% at 30 mg/ml and also highly effectively suppressed spore germination of all tested fungi at all concentrations. In greenhouse experiments, the chloroform extract was most effectively controlled damping-off disease caused by F. solani and S. sclerotiorum on bean. The ethyl acetate extract was the second best for S. sclerotiorum and R. solani. Two sesquiterpenes, dihydrobipolaroxin (1) and sorokinianin (2), were isolated from the chloroform extract of D. cynodontis and identified by EI-MS, 1 H-NMR, 13 C-NMR, DEPT, COSY, HMQC and HMBC experiments. Compound (1) was a highly effective growth inhibitor against A. solani, F. oxysporum and S. sclerotiorum at 100 μg/ml. Compound (2) decreased the growth of all tested fungi between 22.2 and 61.1%. Compound (1) greatly decreased spore germination of A. solani and F. solani. Compound (2) highly effectively suppressed spore germination of F. solani at 100 μg/ml.