Responses of a standard Australian and a Mexican wheat to temperature and water stress

Abstract

Single plants of Gabo, an Australian spring wheat, and Pitic 62, a Mexican semi-dwarf one, were grown at 20°C in a growth cabinet until anthesis. They were then transferred to glasshouses at 18/13, 21/16 and 24/19°C day/night temperatures and supplied with 20, 60 and 100% of their ad lib. water requirements. In terms of water use, dry matter production and grain yield, patterns of response to temperature and water stress were very similar for the two varieties. Highest yields were obtained at 21/16°C. Efficiencies of water use increased as water supply decreased; they were lower at 18/13°C than at higher temperatures. The amounts of dry matter produced after the treatments were imposed were taken as biological indexes of the nine environments. Over the entire range of those values, the grain yields of Pitic 62 were consistently higher than those of Gabo. Significant features of Pitic 62 that contributed to its higher yields were that: (1) by anthesis it had produced larger ears from a given weight of supporting shoot tissues; (2) after anthesis it mobilized a higher percentage and amount of stem and leaf material that apparently contributed to grain production. Two broad categories of shoots were distinguished. The first four shoots of both varieties were very tolerant of water stress, producing 50% of their potential grain yield on 20% of ad lib. water supplies. These shoots experienced water stress only after anthesis. Younger shoots experienced the stress treatments from an earlier stage of development; they were very sensitive to water stress and their grain yields were related linearly to water supply. Harvest index values varied with the category of shoot selected and with size of shoot or plant. Implications of relationships between grain weight and shoot weight for crop selection are discussed.