Combining Ability Analysis of Resistance of Southern Root‐knot Nematode in Red Clover

Abstract

Production of red clover, Trifolium pratense L., is reduced in areas infested with root‐knot nematodes (RKN) in the southeastern USA. Although progress has been made in improving RKN resistance in red clover through recurrent selection, little information is available on the mode of inheritance of red clover resistance to any of the RKN species. This study was conducted from 1993 to 1995 in Florida to determine the mode of inheritance and relative importance of general combining ability (GCA) and specific combining ability (SCA) effects in controlling resistance to Meloidogyne incognita (Kofoid & White) Chitwood Race 3 in red clover. By means of a breeding population selected for low root galling and egg mass production when infested with M. incognita, four red clover plants were identified as resistant, three as intermediate, and two additional susceptible individuals were selected from ‘Kenstar’. These individuals were cloned and used as parents in a diallel genetic study. Forty‐eight progeny from each of 36 F1 crosses, without reciprocals, were evaluated under greenhouse conditions during 1995 for response to inoculation with 1500 M. incognita eggs per plant. Eight weeks after inoculation, the number of galls and egg masses on roots of each plant were counted under low power magnification (10–20 ✕). Resistant genotype 119 produced progeny with the least M. incognita reproduction and galling. Crosses involving the two susceptible genotypes, N1 and K4, resulted in the highest numbers of galls and egg masses. The GCA effects were significant for both traits, whereas SCA effects were not significant. These results indicate that for this set of parents, breeding procedures that utilize GCA effects to maximize exploitation of additive gene action should be most effective in improving resistance to M. incognita galling and reproduction.