The genetics of rust resistance in sugar cane seedling populations

The inheritance of rust resistance was studied in sugar cane seedling populations using a factorial mating design over 1 summer and 2 winter seasons. Frequency distributions for rust infection pooled over 2 winter seasons for resistant x resistant parents were highly skewed with the majority of progenies grouped towards the resistant classes, whereas crosses between susceptible x highly susceptible parents tended to be skewed with the majority of progenies grouped towards the susceptible ones. Both categories of crosses produced transgressive segregants at either extremes. Distribution of infection within progeny of the selfed resistant parent 'R 570' and distribution in the majority of crosses tended to support the hypothesis of a major gene with a dominant effect for resistance. However, the action of other minor genes acting in a quantitative way is also suggested. The female (F) and male (M) variance components were very important, and FM interaction indicated the existence of non-additive genetic effects. FS, MS and FMS interaction mean squares were generally low or insignificant. Broad-sense heritability for the individual season ratings and for the combined ratings was high (0.75-0.90), whereas narrow-sense heritability was generally moderate (0.40-0.52) with the additive genetic effects accounting for 44-68% of the total genetic variation. The implications of these findings in the breeding for rust resistance in the local programme are discussed.