Combining Ability Analysis of Resistance in White Clover to Southern Root‐Knot Nematode

Abstract

White clover (Trifolium repens L.) is an important forage crop worldwide and also in the southeastern United States. Root‐knot nematodes (RKN; Meloidogyne spp.) can be a major factor limiting white clover production and persistence. This study was conducted to determine the genetic basis of resistance to M. incognita race 4 in white clover. Eight parents composed of three resistant, two intermediate, and three susceptible clones were crossed in a partial diallel design, and progeny of those 28 crosses were evaluated for egg mass score, gall score, eggs per gram of dry root weight, eggs per plant, shoot weight, and root weight. Progeny were arranged in a randomized complete block design with five replications each consisting of 14 individual plants. Two weeks after germination, plants were inoculated with approximately 500 M. incognita race 4 eggs. To serve as a noninoculated control, cross progeny were arranged in another randomized complete block design with three replications each consisting of seven plants. The analysis of egg mass score, gall score, eggs per gram dry root weight, and eggs per plant showed that both general combining ability (GCA) and specific combining ability (SCA) were significant in the expression of those variables. The GCA effects were related with previously classified resistance reaction to the southern RKN.