Transpirational Cooling as a Screening Technique for Drought Tolerance in Oil Seed Brassicas

Abstract

Twenty-two genotypes of five Brassica species (oilseed rape and mustard), consisting of two different maturity groups and differing in plant morphology, were grown on sandy soil without post-sowing irrigation during 1982–83 winter season. Canopy temperature (Tc minus air temperature (Ta, stomatal conductance ($) and osmotic adjustment were studied on two different dear days corresponding to the siliqua formation stage in early duration (137–150 d) and late maturing genotypes (151–165 d) of oilseed Brassicas. The absolute mid-day values of transpirational cooling (Tc–Ta) were relatively higher in B.juncea and B. carinata than in B. tomifortii, B. napus and B. campestris. Tc-Tm showed a genetic variability ranging from 0-5 to 4 °C for early maturing genotypes, and from 0–5 to 5 °C for late maturing genotypes. Mid-day Tc–Ta showed significant positive correlation with Kh osmotic adjustment and seed yield in Brassica cultivars. Early genotypes out-yielded the late maturing ones, despite the lower values of AT, and Tc–Ta at siliqua formation in the former rather than later group of cultivars. It is suggested that average mid-day Tc–Ta as observed with an infrared thermometer, could effectively be used as a technique to screen Brassica genotypes for drought tolerance under receding soil moisture conditions.