Inheritance of resistance to damage byThrips tabaci Lindeman (Thysanoptera: Thripidae) in Cabbage

Summary

The inheritance of resistance in cabbage (Brassica oleracea var.capitata) to damage caused byThrips tabaci Lindeman was studied in progeny from four crosses between resistant and susceptible inbred lines. In two families sharing the same susceptible parent, the narrow-sense heritability was calculated to be high (>90%), using the Warner method of calculation (Warner, 1952). The other two families, also sharing a susceptible parent, had very low narrow-sense heritability (0–11%). In three of the four families, however, the validity of the Warner calculations were called into question due to significant epistatic interactions. In all four families, the F₁ populations approached or exceeded the susceptibility of the susceptible parent, indicating that susceptibility is generally dominant. The importance of epistasis and dominance suggests that tests of hybrid combinations to determine combining ability for thrips resistance may be required, rather than selecting only on the basis of thrips damage to the inbred lines. The technique of planting wheat upwind from the cabbage test plot did generate adequate levels of thrips pressure, but the infestation was uneven in two of the four blocks, so that reasonable replication of tests is required.