Soybean reaction to Races 1 and 2 of Heterodera glycines

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is a serious pest of soybean [Glycine max (L.) Merr.] in the USA and worldwide. A current cl assification system has designated 16 different races of SCN populations. I n the Southern USA, SCN Races 1 and 2 are becoming more prevalent. It is im portant to identify soybean accessions with resistance to these races. The objective of this study was to bioassay 32 soybean plant introductions (PIs ) for resistance to SCN Races 1 and 2 together with standard host different ials and a susceptible control. The bioassays were performed for each of th e two races during 1997 to 1998 in thermoregulated water baths in the green house. The results indicated that 25 PIs had resistance to Race 1 and 24 Pl s had resistance to Race 2. PIs which were resistant to Race 1 and either m oderately resistant or moderately susceptible to Race 2 included PIs 468915 , 494182, 507354, 507422, and 509100. PIs 467327, 468903, and 507471 were r esistant to Race 2 and additionally were either moderately susceptible or m oderately resistant to Race 1. Soybean PIs that were yellow seeded and had various levels of resistance to both races included PIs 494182, 507354, 507 422, and 507471. These are the most desirable sources for development of so ybean cultivars with resistance to SCN Races 1 and 2. These soybean lines a re being fingerprinted by means of microsatellites to identify unique types to allow broadening the diversity of resistance gene introgression.