RFLP mapping of resistance to southern root-knot nematode in soybean

In the USA, the southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] (Mi) is a serious pathogen of soybean [Glycine max (L.) Merrill]. The objectives of this study were the following: (i) to use restriction fragment length polymorphism (RFLP) to identify markers associated with quantitative trait loci (QTL) conferring Mi resistance, (ii) to estimate the relative contribution to resistance of each QTL, and (iii) to locate each QTL on the molecular map of the soybean genome. PI96354, a plant introduction with a high level of resistance to Mi, was crossed with 'Bossier', a highly susceptible cultivar, and 110 Fz plants were produced and mapped with 121 RFLP markers. A greenhouse screening procedure was used to determine the level of galling for the F-2:3 lines. Data were analyzed using single-factor and two-factor analysis of variance and interval mapping. Two QTL were identified which mapped to LG-O and LG-G of the USDA/ARS-Iowa State Univ. (USDA/ARS-ISU) soybean RFLP Map. Results showed a major resistance QTL (R-2 = 31%) linked to marker G248A-1 on LG-O. The second QTL (R-2 = 14%) was located on LG-G in the interval from K493H-1 to Cs008D-1 and was dominant with respect to resistance. The two QTL explained 39% of the variation in Mi galling in a multiple QTL model. Marker G248A-1 may be closely linked to the Rmi1 gene. When galling data was classified into three distinct classes, it mapped distally to G248A-1 on LG-O. Mi resistance also was linked to G248A-1 through simulated marker analysis. The root-knot nematode resistance QTL identified were found in duplicated DNA segments.