The Isolation and Identification of Soybean Pod and Stem Blight in Taiwan

Phomopsis seed decay (PSD) caused by Diaporthe phaseolorum var. sojae (Lehman) Wehmeyer, Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. caulivora Athow & Caldwell, and Phomopsis longicolla Hobbs reduces quality of soybean (Glycine max (L.) Merr.) seed when it is wet and warm condition during seed maturation period. To study of the PSD in Taiwan in March 2008, three unidentified fungal isolates (isolate1, isolate2 and isolate3) were isolated from soybean stems infected with pod and stem blight which is associated with seed decay. Based on their morphological and genotypic characteristics, three isolates were regarded as Diaporthe phaseolorum var. sojae. For PSD assay, we found that the best condition for the fungal isolates growth was on potato dextrose agar (PDA) media at 24°C temperature for 24 or 15 hr photoperiod. Leaf- stem and pods of soybean were inoculated by an atomizer with two isolates among three isolates to investigate PSD infection. In the result of two inoculation parts with two isolates, there was no significant difference in degree of pod infection and seed infection rate (%) between isolate2 and isolate3, but there was a tendency that pod inoculation than leaf- stem inoculation caused higher level of seed infection. These isolates obtained in this study would be applicable to screening of PSD resistant soybean germplasms in the breeding program.