DNA marker analysis of loci conferring resistance to peanut root-knot nematode in soybean

Peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood] (Ma) is a serious pathogen of soybean, Glycine max L. Merrill, in the southern USA. Breeding for root-knot nematode resistance is an important objective in many plant breeding programs. The inheritance of soybean resistance to Ma is quantitative and has a moderate-to-high variance-component heritability on a family mean basis. The objectives of the present study were to use restriction fragment length polymorphism (RFLP) markers to identify quantitative trait loci (QTLs) conferring resistance to Ma and to determine the genomic location and the relative contribution to resistance of each QTL. An F-2 Population from a cross between PI200538 (Ma resistant) and 'CNS' (Ma susceptible) was mapped with 130 RFLPs. The 130 markers converged on 20 linkage groups spanning a total of 1766 cM. One hundred and five F-2:3 families were grown in the greenhouse and inoculated with Ma Race 2. Two QTLs conferring resistance to Ma were identified and PI200538 contributed the alleles for resistance at both QTLs. One QTL was mapped at 0-cM recombination with marker B212V-1 on linkage group-F (LG-F) of the USDA/ARS-Iowa State University RFLP map, and accounted for 32% of the variation in gall number, Another QTL was mapped in the interval from B212D-2 to A111H-2 on LG-E, and accounted for 16% of the variation in gall number. Gene action for the QTL located on LG-F was additive to partially dominant, whereas the gene action for the QTL on LG-E was dominant with respect to resistance. The two QTLs, when fixed on the framework map, accounted for 51% of the variation in gall number in a two-QTL model. The two QTLs for Ma resistance were found in duplicated regions of the soybean genome, and the major QTL for Ma resistance on LG-F is positioned within a cluster of eight diverse disease-resistance loci.