Prevalence of fungi associated with soybean seeds and pathogenicity tests of the major seed-borne pathogens.
An investigation to detect the seed borne fungi of soybean and the pathogenicity tests of two major seedborne fungal pathogens against soybean was conducted in the Microbiology Laboratory of Plant Pathology Department, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, during 2005 to 2006. A total of 33 soybean seed samples were collected from four different locations namely Gazipur (BARI), Mymensingh (BAU), Meherpur (local farmer) and Noakhali (local farmer) representing three varieties and 16 genotypes. Blotter method was used for detection of the associated fungi of soybean seeds. Altogether, ten fungi comprising nine genera namely Alternaria alternata, Aspergillus flavus, Aspergillus niger, Chaetomium globosum, Colletotrichum dematium, Curvularia lunata, Fusarium oxysporum, Macrophomina phaseolina, Penicillium sp. and Rhizopus stolonifer were found to be associated with the tested soybean seed samples. The germination of seed samples varied from 16-98%. Germination of seeds was directly related to the prevalence of fungi associated with the seed. The pathogenicity test was performed with 25 isolates of C. dematium and 33 isolates of F. oxysporum against the variety Shohag in pot culture. All the tested isolates of both the pathogens were found to be pathogenic. Among the tested 25 isolates of C. dematium two isolates namely C19 and C20 collected from Noakhali district from variety Shohag were appeared to be virulent. Twelve were appeared to be moderately virulent while rest of the 11 isolates was found to be weak pathogen. Among the tested isolates of F. oxysporum, three isolates namely F21, F22 and F23 were appeared to be highly virulent. Seven isolates were found to be virulent, 13 isolates showed moderately virulence reaction and 10 isolates were appeared to be weak pathogens.