SOIL-BORNE DISEASES AND ECOLOGY OF PATHOGENS ON SOYBEAN ROOTS IN INDONESIA

Studies on root diseases and causal fungi on soybean in Indonesia were carried out. Missing plants due to damping-off of seedlings occurred frequently. In addition, the average infection rates of root rots amou nted to 60% of all the surviving plants toward the pod filling stage. The more severe root rot was, the lower the yield of soybean seeds. Th e isolates from the seedlings showing damping-off belonged mainly to e ither Pythium apanidermatum, Sclerotium rolfsii, anastomosis groups (A G) 4 and 7 of Rhizoctonia solani, AG-E and other AGs of binucleate Rhi zoctonia spp. As time went on, the severity of the root rot symptoms i ncreased rapidly and Fusarium spp. and binucleate Rhizoctonia were pre dominantly isolated from rotten roots in the great majority of the fie lds, except for one field where root rot disease caused by Cylindrocla dium sp. occurred. All the isolates of S. rolfsii, R. solani AG-4 and AG-7, binucleate Rhizoctonia AG-E, P. aphanidermatum, P. myliotylum an d Pythium sp. caused damping-off as well as root rot on soybean, where as the isolates of F. solani and C. floridanum from soybean were patho genic to the plants in the middle or late stage of growth. A new root rot disease caused by C. floridanum and damping-off disease caused by AG-7 and AG-E of Rhizoctonia spp. were detected for the first time in soybean fields in Indonesia.