GROWTH AND YIELD OF WHEAT LINES WITH DIFFERING OSMOREGULATIVE CAPACITY AT HIGH SOIL-WATER DEFICIT IN SEASONS OF VARYING EVAPORATIVE DEMAND

Wheat Lines with differing capacities for osmoregulation were grown on a full profile of soil water at sowing in seasons of contrasting evaporative demand. Watered experiments were also included. Across seasons the relative increase in dry weight and yield associated with high osmoregulation was positively correlated with cumulative pan evaporation during the period of most rapid growth before anthesis. In experiments showing the most extreme responses to osmoregulative capacity there was no association with the overall soil water deficit at anthesis or harvest suggesting a direct effect of evaporative demand. This was further confirmed by correlations between vapour pressure deficit and leaf water potential and differences in turgor pressure. Significant differences in turgor were, in turn, associated with significant differences in dry weight. It was therefore concluded that osmoregulative effects on growth were mediated through leaf or shoot responses to leaf water stress rather than through root responses to soil water deficit, and that it was necessary to screen lines specifically for osmoregulation rather than for growth responses to soil water deficit.