Inheritance of Resistance to Clubroot (Plasmodiophora brassicae Wor.) in Kale (Brassica oleracea ssp. Acephala)

Abstract

For kale (Brassica oleracea ssp. acephala L.), the inheritance of resistance and that of tolerance to clubroot (Plasmodiophora brassicae) were studied. Six homozygous lines belonging to the half marrow-stem and green curly kale groups were intercrossed in a diallel F1 mating design. Inheritance of resistance was assessed from a glasshouse test on young plants and from a field trial on adult plants. A Disease Index was used to estimate the behaviour of each progeny. Tolerance to clubroot was denned as the ratio of yield produced by a progeny on a clubroot-infected part of the field compared with its yield on an uninfected soil. Resistance to clubroot on young and adult kales is mainly controlled by genetic effects. The broad sense heritability assessments are greater than 0.8 for the 2 trials. Resistance inheritance is characterized by a predominance of additive genetic effects with incomplete dominance. Yet, the additive components have less relative importance compared to dominance effects in the inheritance of resistance of adult kales (h2ns= 0.55 compared to 0.78 for young kales). Many dominant alleles control resistance. The phenotypic and genetic values calculated for resistance are not correlated with those of tolerance. The dominance genetic effects control a great part of the genetic variation for tolerance (h2ns= 0.16). Breeding programmes are proposed to increase clubroot resistance level in the kale group. A maternal individual recurrent selection on progenies could be undertaken.