Changes in Reproduction of a Heterodera glycines Race 5 Isolate Cultured on 'Cordell' and 'Bedford' Soybean.

Isolates from a race 5 field population of Heterodera glycines were cultured separately on soybean cultivars 'Bedford' (resistance derived from Peking and plant introduction [PI] 88788) and 'Cordell' (resistance derived from 'Peking', PI 88788, and PI 90763) for 10, 12, and 14 generations. Reproduction was measured of the 10th, 12th, and 14th generations on Bedford and Cordell and on Peking, 'Pickett', PI 88788, PI 90763, and 'Lee' (the soybean lines that are used to determine H. glycines race). The isolate cultured on Bedford remained race 5, whereas the isolate cultured on Cordell changed to race 14, to which Bedford is moderately resistant. Cordell probably derived its race 5 resistance from either Peking or PI 90763 because the isolate resulting from culture on Cordell reproduced on the H. glycines race differentials in a pattern similar to those of other isolates selected on PI 90763 in previous studies. Rotation of cultivars with pedigrees similar to Bedford and Cordell may be effective in managing H. glycines to prevent yield suppression in soybean and the development of new races.