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Genetic Diversity Among Isolates of Heterodera glycines and Sources of Resistance in Soybeans. A. P. Rao-Arelli, Plant Science Unit, University of Missouri-Columbia Delta Center, Portageville 63873. J. A. Wrather, and S. C. Anand. Plant Science Unit, University of Missouri-Columbia Delta Center, Portageville 63873. Plant Dis. 76:894-896. Accepted for publication 7 March 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0894.

Populations of the soybean cyst nematode (Heterodera glycines) (SCN) are extremely variable. A recent nematode classification system includes 11 new races, for a total of 16. Little is known about newly described races 4, 613, 15, and 16. We have attempted to examine the genetic diversity among isolates of H. glycines, isolate sources of resistance in soybeans, and identify soybean differentials for describing intrarace variation of SCN. Thirty-two field isolates of H. glycines collected from 10 states were evaluated in the greenhouse for female maturation on soybean (Glycine max) genotypes Peking, Pickett, Custer, Bedford, Lee, PI 209332, PI 404166, PI 404198B, PI 437654, PI 437690, PI 438489B, PI 438496B, PI 438503A, PI 88788, PI 89772, and PI 90763. Among the isolates tested, 3.1, 6.2, 43.7, 9.3, 25, 6.2, and 6.2% were races 1, 2, 3, 5, 6, 9, and 14, respectively, according to standard race determination scheme. Race 2 isolates were separated by their ability to multiply on PI 437690. Race 3 isolates were better characterized by their ability to mature on Custer and PI 438503A. Custer, Bedford, PI 209332, PI 404166, PI 404198B, PI 437690, and PI 438496B were useful in describing variation in race 6 field isolates. Race 14 isolates were separated according to their response to soybean lines PI 404166, PI 404198B, PI 438489B, PI 438503A, and PI 89772. None of the additional hosts further separated race 9 isolates. The additional hosts used in this study are genetically stable in reaction to nematode and, therefore, may be useful in describing variability among SCN isolates. PI 437654 is recommended as a resistant control of race determination. We found soybean lines PI 437654, PI 438489B, PI 438503A, and PI 89772 resistant to all isolates of newly designated SCN races 6 and 9. Additional resistance to isolates of race 9 was found in PI 209332 and PI 404166. Soybean line PI 89772 has agronomically desirable traits and may be used as an alternate source of SCN resistance in breeding soybean cultivars.