Kale population improvement and cultivar production

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.