Survey of soybean cyst nematode races in tennessee.

Cordell soybean is a newly released cultivar resistant to Heterodera glycines (SCN) races 3 and 5. The hectarage infested with these races and with other races that can parasitize Cordell in Tennessee is not known. A survey of races in Tennessee soybean fields with sampling weighted by soybean hectarage on a county basis was conducted in 1988. The SCN race plus female development on Bedford and Cordell soybeans were determined in a greenhouse for 21 field populations. Races 2, 3, 4, 5, 6, and 9 were 14%, 5%, 10%, 38%, 19%, and 14% of these populations, respectively. The SCN female indices on the differentials that were sources of SCN resistance in Bedford and Cordell were not accurate indicators of female development on these cultivars. The female index was < 10 on PI 90763 for 19 populations, but four of these populations had an index > 30 on Cordell, which derives SCN resistance from PI 90763. The index was < 10 on PI 88788 for seven populations, but two populations had an index > 40 on Bedford, which derives resistance from PI 88788. When recommending cultivars to be planted by soybean producers, SCN reproduction should be determined on the cultivars, instead of on race differentials.