MEASUREMENT OF CANOPY TEMPERATURE FOR HEAT TOLERANCE IN UPLAND COTTON: VARIABILITY AND ITS GENETIC BASIS

The present study was conducted with the objective to assess germplasm of American cotton for heat tolerance using canopy temperature. For this purpose seventy varieties/lines of Upland cotton were screened out at flowering stage. Analysis of variance revealed significant differences among the germplasm lines. Three tolerant (MNH552, FH1000 and NIAB111) and three susceptible lines (Cedix ST-362 (GL), LRA5166 and 4F) were selected. The tolerant and susceptible genotypes were crossed to develop F1 seed of the three crosses. Six generations i.e. F1, F2, BC1 and BC2 of each cross were grown along with their parents under normal and high temperature in the field following RCBD with three replications. At flowering stage, canopy temperature was measured in both the temperature regimes. Indices of heat tolerance were calculated for genetic investigation. Generation means analysis of the data revealed that additive, dominance and epistatic component were involved in the inheritance of canopy temperature. However genetic variance analysis showed that canopy temperature was predominantly controlled by additive genes, and thus estimates of h2ns were high. These results suggest that rapid improvement in reducing canopy temperature of the plant material is possible through breeding and selection in F3 population.