Kale population improvement and cultivar production

Abstract

Marrow-stem kale (Brassica oleracea var. acephala L.) is grown in the United Kingdom, New Zealand and similar climates, for feeding cattle and sheep during autumn and winter. Population improvement by half-sib family selection for higher digestibility and digestible organic matter yield, lower levels of antimetabolites, and clubroot resistance is described and analysed as a selection experiment. The foundation population consisted of 120 clubroot resistant plants from the 16 most resistant marrow-stem cultivars in an assessment of 96 cultivars of Brassica oleracea. At the end of the first generation of selection adequate resistance had been achieved. After five generations, dry-matter content and digestible organic matter yield had been increased, the latter without an undesirable increase in height. Indolyl glucosinolate (source of goitrogenic thiocyanate ion) content had been reduced, but not S-methylcysteine sulphoxide (the haemolytic factor) content. Selection differentials each generation were small and heritabilities of family means were moderate to low, making improvement per generation slow. It was demonstrated that faster progress could be made by switching from half-sib to full-sib family selection, as expected from theory. Multiplication of the half-sib family with the highest digestibility (DOMD%) achieved an improvement in this trait, without a reduction in digestible organic matter yield, and was marketed as cultivar Grampian.

Plant Breeding: Past, Present and Future

“…Genetic variation was achieved by including cultivars of diverse geographic origin, but restricted to the marrow-stem type for eventual ease of producing a cultivar with the necessary uniformity for National Listing (Bradshaw and Wilson 2012). As clubroot (Plasmodiophora brassicae) is the most serious disease of kale and other Brassicas, 120 resistant plants were chosen from the 16 most resistant cultivars out of 96 assessed.…”

“…In contrast, with characters of low heritability, improvement should be faster with family selection than with single plant selection, because replicated trials allow the effects of environmental and genotype  environmental interaction variation to be reduced. Kale examples are referred to in the paper by Bradshaw and Wilson (2012), but it is time to return to an economically more important crop, maize. Likewise, it is important to take into account practical considerations when comparing selection schemes, such as the time in years to complete one cycle and the ease of seed production.…”

“…Certainly in kale it seemed best to focus on around six important traits, and this was borne out in practice (Bradshaw and Wilson 2012). In the absence of objective economic weights, equal weights in terms of phenotypic standard deviations were used (1/σ P ), although it could be argued that these should be multiplied by the number of standard deviations required to equal control cultivars or to exceed them by a desired amount.…”

“…In the kale programme mentioned above this was done after five generations by selecting and separately multiplying six half-sib families (Bradshaw and Wilson 2012). In the kale programme mentioned above this was done after five generations by selecting and separately multiplying six half-sib families (Bradshaw and Wilson 2012).…”

“…Subsequently, for greater uniformity and ease of production of relatively cheap seed, open-pollinated cultivars Caledonian and Grampian were bred from a population of marrow-stem kales from different parts of the world (Bradshaw and Wilson 2012). Subsequently, for greater uniformity and ease of production of relatively cheap seed, open-pollinated cultivars Caledonian and Grampian were bred from a population of marrow-stem kales from different parts of the world (Bradshaw and Wilson 2012).…”