DNA MARKERS FOR RESISTANCE TO HETERODERA-GLYCINES .1. RACE-3 IN SOYBEAN CULTIVAR PEKING

Ninety F-2:3 progeny from a cross of resistant cultivar Peking and sus ceptible Essex and near-isogenic lines, NC55, and Lee, were employed i n transmission, bulk, and segregation analyses to identify molecular m arkers associated with resistance to soybean cyst nematode (SCN) race 3, SCN bioassays were performed in a greenhouse using a race 3 isolate . Progeny response to SCN was characterized by Female Index (FI). Thre e morphological traits, 108 restriction fragment length polymorphisms (RFLPs), and 400 random amplified poll-morphic DNAs (RAPDs) were emplo yed, The i locus for seed coat color showed highly significant associa tion with resistance to race 3 SCN (R(2) = 0.25, P = 0.0001). Two inde pendently inherited RFLP markers, pA 136 and pA635, (linkage groups A and C, of the USDA-ARS/ISU soybean RFLP map) and three RAPD markers, E 01c (LG A), G15d (LG F), and S07a (LG A), explained 32.5 % of the tota l phenotypic variation for SCN response in F-2 progeny. Two-way ANOVA indicated significant interaction of i locus with pA136, pA635, S07a, and E01c (P= 0.0001) suggesting that a quantitatire trait locus (QTL) on LG A interacts with other QTLs for SCN resistance in the genome, Th e dominant QTL was localized 0.6 cM from i locus using MAPMAKER/QTL 1. 1. Twenty-six combinations of the identified molecular markers were us ed in selection for SCN resistance. Combination of 4 markers (pA 136, S07a, G15d, and E01c) explained 67 % of total variation among. selecte d resistant and susceptible individuals.