The Effect of Water Deficits during Flowering and Seed Production on Cultivars of Subterranean Clover and Annual Medic

In improved pastures in inland southern Australia, the persistence and growth of annual pasture legumes depends in part on their ability to produce and conserve abundant seed for regeneration and production. For near-maximum seed production in spring, adequate soil water is needed for at least 70 days in subterranean clover (Trifolium subterraneum) and medic (Medicago) species. Water deficits during spring are a common occurrence, and they appear to be increasing in frequency. The effect of relatively short periods of water deficit during reproductive development has received some attention but the findings conflict. The present experiment was conducted to examine further the responses of subterranean clover to water deficits imposed during the reproductive phase, and to compare the response of medic to that of subterranean clover. The flowering of two early strains of subterranean clover (Northam, Daglish) was synchronised with two early-flowering cultivars of annual medic (Cyprus barrel medic and Harbinger strand medic). Seed production parameters were observed on four watering treatments (nil, early, mid and late deficits during the reproductive phase). Notable differences occurred between the two genera and between the water treatments in their effect on reproductive development. A highly significant interaction favouring medic was recorded between the legumes (clover, medic) and the early deficit treatment, in that the individual seed weight of medic was slightly enhanced by water stress and clover was significantly depressed. In the mid- and late-stress treatments, a significantly lower proportion of viable seed was recorded with clover versus medic. The implications of the findings for the use of adapted annual legumes are discussed. This research was supported by a Reserve Bank Research Fellowship