[Development and expression process of inheritance of resistance to cotton worm (Prodenia litura) in soybeans]

Cotton worm [Prodenia litura(Fabricius)] was one of the major leaf-feeders for soybeans in Southern China. Resistance to leaf-feeders has been recognized as one of the major breeding target traits in the National Soybean Breeding Program. This paper deals with the study of inheritance of resistance of soybeans to cotton worm [Prodenia litura(Fabricius)]. P1, P2, F1, F2, F2:3 of four susceptible x resistant crosses, i.e. N21297 x N1178-2-2, N21266 x N23860, N119-1 x N1178-2-2 and N21266 x N3039, were used in the study. The materials were planted in net room under artificial infestation in 1996-1998. The data of defoliation percentage of successive development stages, during cotton worm damage period were obtained and collected for genetic analysis. The segregation analysis methods for major genes plus polygene mixed inheritance model developed by Gai et al. were used to identify the genetic system of resistance. The results from joint analyses of multiple segregating generations as well as from analyses of single F2 or F2:3 generations of the four crosses showed a two major genes plus polygene mixed inheritance model at fully developed stages of resistance while one or two major genes with or without polygene were observed at other stages. Between the two major genes, the additive effect of one locus was from 1.56 to 9.89(%, defoliation), another from -3.79 to 3.75(%, defoliation). The heritability values of major genes were estimated as 70.40%-99.21%, greater than those of polygene which were only 0.00%-22.29%. Therefore, in the improvement of resistance to cotton worm, major gene resistance should be considered at first.