Genertion Mean Analysis of Resistance to Race 3 of Soybean Cyst Nematode
- L. M. Mansur,
- A. L. Carriquiry and
- A. P. Rao-Arelli
The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is a serious pest of soybean [(Glycine max (L.) Merr.]. Most genetic studies of resistance in soybean to SCN have used qualitative models, although continuous distributions of phenotypes from zero to many cysts have been observed. We investigated the mode of inheritance for resistance to Race 3 of SCN by weighted least squares regression analysis of generation means for genetic models having additive and dominance parameters. Reaction to SCN was determined by counting the white females present on plant roots 30 d after inoculation. Four crosses, including one reciprocal, were made between resistant and susceptible genotypes. The ancestry of the resistant genotypes (‘A20’, ‘Jack’, and ‘Cordell’) traces to different sources of SCN resistance. Six generation means (P1, P2, Fl, F2, BCp1, and BCP2) in three of the crosses, and four in one (Pl, P2, F1, F2), were used to estimate the genetic effects contained in the means. The data were transformed for analysis because they were not normally distributed. The results indicated that an additive genetic model was sufficient to explain most of the genetic variation for resistance to Race 3 in each cross. Analysis of the pooled data from all crosses, however, indicated the presence of dominance effects as well. Recovery of parental phenotypes in the F2 and backcross populations indicated that no more than four genes were involved in the inheritance of the trait. Estimates for broad sense heritabilities on single plant basis ranged from 0.48 to 0.81. The relatively high heritability and additive genetic control indicate that breeder should be able to select genotypes with an intermediate level of resistance.
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