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Variation in Parasitic Potential of Heterodera glycines Populations

University of Missouri, Delta Center, P.O. Box 160, Portageville, MO 63873

^* Corresponding author. (agrosam{at}mizzou1.missouri.edu).

A great deal of variation in parasitic potential has been observed among the soybean cyst nematode (SCN) Heterodera glycines Ichinohe populations in the USA. To best utilize sources of genetic resistance to SCN, this variation needs to be characterized. Fifty-eight populations of the SCN were collected from 10 major soybean producing states. These populations were compared for infraspeeific variation in parasitic potential on soybean [Glycine max (L.) Merr.] genotypes ‘Peking’, ‘Pickett’, Plant Introduction (PI) 88788, PI 90763, and ‘Lee 68’. Race structure, genes for parasitism (capability of a nematode population to produce at least one cyst on a resistant genotype), and levels of parasitism (percentage of cysts that developed on resistant genotypes compared with the susceptible cultivar Lee 68) were assessed. Race was present in 45% of locations; it was the most widespread population. Race 6 was present in 19% of the locations. Frequency of occurrence of other races (Races 1, 2, 5, 9, and 14) ranged between 3 and 9%. On the basis of reproduction on genotypes, 83% of the populations tested had genes to parasitize Pickett. All populations from Arkansas, Florida, Georgia, Iowa, North Carolina, and South Carolina produced cysts on this genotype. Average level of parasitism was greatest on Pickett and lowest on PI 90763; 91% of SCN populations tested had <10% level of parasitism on PI 90763. The SCN gene frequencies demonstrated that nematode populations with predominant genes for parasitism on Pickett and Lee 68 were widespread especially in the southern soybean producing states in the USA. Cultivation of varieties with resistance derived from Peking and Pickett in these regions should not be very effective. For management of SCN-caused yield losses, cultivation of soybean varieties with resistance derived from P190763, PI 88788, and PI 437654 should be encouraged.

Received for publication February 17, 1994.