INHERITANCE OF RESISTANCE TO THE SOUTHERN ROOT-KNOT NEMATODE IN SOYBEAN

The inheritance of resistance to the southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] in soybean [Glycine max (L.) Merrill] was determined for crosses of a susceptible cultivar, Bossier, with two resistant plant introductions, PI96354 and PI417444. Each F-1, F-2, and/or F-3 generation was screened in a greenhouse for resistance to gall formation. In the PI96354 x Bossier population the number of galls per F-2 plant and F-3 family mean gall numbers were continuously distributed. The PI417444 x Bossier F-3 family mean gall numbers were also distributed continuously. For both crosses, each F-2 and/or F-3 distribution indicated that resistance was quantitatively inherited. Variance component heritability estimates on a mean and plot basis for both crosses ranged from 0.79 to 0.93. The parent-progeny (F-2-F-3) correlation calculated for PI96354 x Bossier was 0.73. The uniqueness of resistance genes was determined for crosses among 'Forrest' (resistant), PI96354, and PI417444. F-3 progeny from crosses of PI96354 x Forrest and Forrest x PI417444 exhibited transgressive segregation. Individual F-3 plants and F-3 families were identified with more galls than Forrest, PI96354, and PI417444. Some F-3 plants had the same number of galls as Bossier, the susceptible check. These data indicate that Forrest differs from PI96354 and PI417444 for resistance to M. incognita by at least one gene. For PI96354 x PI417444, the similarity of F-1, F-2, and parental means and variances indicated that PI96354 and PI417444 have resistance genes at the same loci. Soybean breeders can use this information to develop strategies for using these plant introductions to improve the level of M. incognita resistance in adapted cultivars.