Quantative inheritance in Lucerne, Medicago sativa L. I. Inheritance and selection for winter yield

Spaced plants of lucerne, Medicago sativa L., derived from 10 strains and 44 F1's, grown in the field at Canberra, exhibited discontinuous variation in winter growth. Some were completely dormant, others grew at over 40 per cent. of their summer rate. Strains differed with respect to combining ability for growth rates, both in summer and in winter, but differences between strains in combining ability were much more evident in minter than in summer. The correlation between winter and summer growth rates was markedly affected by differences in winter dormancy. Thus the Canadian Creeping-rooted strain, which had the highest combining ability for summer growth, was among the poorest for winter growth. Within strains or crosses, winter and summer growth rates were strongly correlated (r = 0.77), presumably because genotypes within such lines were relatively homogeneous with respect to winter dormancy. The Hairy Peruvian strain, and to a lesser extent Hunter River, Provence, and an Australian selection, showed high combining ability for winter growth. In other experiments winter dormancy was broken by either increased temperatures (heated glass-house) or by supplementing the natural day length with low-intensity artificial light. These treatment effects were supplementary without interaction. In one set of material a highly significant genotype (clone) X temperature interaction, and the absence of a genotype X day length interaction, indicated that genetic differences in dormancy could be determined largely by the response to low temperatures. For the present neither short days nor low temperatures alone seem sufficient to distinguish between winter-active and winter-dormant genotypes. The growth rates of some genotypes in winter provide encouragement for the introduction, selection, and management for increased winter production of lucerne and other species. The behaviour of the strains in the field, and published evidence on this and other species with a temperate-subtropical distribution, indicates that genes for winter activity are most likely to be found in the warmer parts of the distribution.