DNA MARKERS ASSOCIATED WITH RESISTANCE TO JAVANESE ROOT-KNOT NEMATODEIN SOYBEAN

Javanese root-knot nematode [Meloidogyne javanica (Treub) Chitwood) (M j) is a pathogen of soybean [Glycine max (L). Merr.] in the southern U SA. Although breeding for root-knot nematode resistance is an importan t objective in many plant breeding programs, progress in selection for nematode resistant lines is hampered by laborious screening procedure s. The inheritance of resistance to Mj is quantitative and has a moder ate to high heritability (0.48-0.76). The objectives of this study wer e to use restriction fragment length polymorphism (RFLP) markers to id entify quantitative trait loci (QTL) conditioning resistance to Mj and to determine the genomic location and the relative contribution to re sistance of each QTL. Eighty-four F-2 progeny from a cross between ''C NS'' and a root-knot nematode resistant soybean plant introduction, PI 230977, were used to map 86 RFLP markers and three morphological trait s. The 89 markers converged on 18 linkage groups spanning a total of 1 053 centimorgan (cM). Sixty-eight of the 84 F-2:3 families were assaye d for Mj galling in the greenhouse. Analysis of variance and interval mapping were used to identify QTL associated with galling. Two QTL wit h alleles derived from PI230977 conditioning resistance to Mj were ide ntified on two Linkage Groups (LG). Marker B212-1 on LG-F accounted fo r 46% of the variation in gall number, whereas A725-2 on LG-D1 account ed for 13%. The additive model best fit the data, and together the two markers accounted for 54% of the variation in gall number. Marker B21 2-1 is within a cluster of seven other disease resistance loci that sp an a 5- to 10-cM region on LG-F.