Relative Contributions of Tolerance and Avoidance to Drought Resistance in Dry-Matter Production of Different Rice Cultivars at Different Fertilization Levels.

Abstract

Relative contributions of drought tolerance and drought avoidance to drought resistance in the dry-matter production of different rice cultivars at different fertilization levels were evaluated based on a pot experiment with three cultivars subjected to drought and fertilization treatments and in a field experiment with 10 cultivars subjected to drought treatments. Drought tolerance was expressed as leaf water potential(LWP) at which dry-matter production declined to 50% or 20% of that under flooded conditions. The cultivar difference in drought tolerance was about O.21MPa, and the difference in fertilization levels was 0.74MPa in midday LWP, indicating that the fertilization effect is larger than the cultivar effect. However a large cultivar difference was observed in leaf death and plant survival. The cultivar difference in the avoidance in field experiment, defined as LWP maintained under drought conditions, was about 0.29MPa in the midday LWP, which was more than about 50% larger than that in the tolerance. In the pot experiment, the avoidance was about twice as large as the tolerance. These facts revealed that differences in dry-matter production in the field experiment were closely correlated with diffrerences in the avoidance. And a close relation was revealed between yields and dry weight at harvest under continuous drought conditions. Because differences in drought avoidance were more than about 50% larger than in drought tolerance, LWP is suggested to be a good index of drought resistance.