Mixed inheritance model for resistance to agromyzid beanfly (Melanagromyzasojae Zehntner) in soybean

A quantitative trait could be controlled by a few major genes and many poly genes. Distinguishing the effects of major genes from polygenes and/or envi ronments is important for understanding the expression of a major gene in r elation to its genetic background, and for predicting the segregation of a cross in breeding. Our objective was to re-analyze the resistance of soybea n to agromyzid beanfly by a mixed inheritance model. Number of insects in s tem (NIS) was used as an indicator of resistance. The previous result from the segregation ratio of resistance and susceptibility was that resistance was controlled by one dominant gene. The major results from the mixed inher itance model were (1) the inheritance of resistance was controlled by one m ajor gene along with minor genes; (2) Additive and dominance effects of min or genes were generally less than those of the major gene and varied among crosses, indicating different minor gene systems; (3) Heritability was high er for the major gene than for the minor genes; (4) The F-2 plants and F-2: 3 lines were classified into appropriate genotypes according to their poste rior probabilities and the critical value to distinguish resistant and susc eptible plants was given for NIS based on the classification. These results indicated that mixed major gene and polygene genetic analysis was superior to the frequently used classical Mendelian method.