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

The inheritance of resistance to the southern root-knot nematode [Melo idogyne incognita (Kofoid and White) Chitwood] in soybean [Glycine max (L.) Merrill] was determined for crosses of a susceptible cultivar, B ossier, 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 co ntinuously distributed. The PI417444 x Bossier F-3 family mean gall nu mbers were also distributed continuously. For both crosses, each F-2 a nd/or F-3 distribution indicated that resistance was quantitatively in herited. 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 uni queness of resistance genes was determined for crosses among 'Forrest' (resistant), PI96354, and PI417444. F-3 progeny from crosses of PI963 54 x Forrest and Forrest x PI417444 exhibited transgressive segregatio n. Individual F-3 plants and F-3 families were identified with more ga lls 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. i ncognita by at least one gene. For PI96354 x PI417444, the similarity of F-1, F-2, and parental means and variances indicated that PI96354 a nd PI417444 have resistance genes at the same loci. Soybean breeders c an use this information to develop strategies for using these plant in troductions to improve the level of M. incognita resistance in adapted cultivars.