Sugarcane for water-limited environments. Variation in stomatal conductance and its genetic correlation with crop productivity.

Stomatal conductance (g(s)) and canopy temperature have been used to estimate plant water status in many crops. The behaviour of g(s) in sugarcane indicates that the internal leaf water status is controlled by regular opening and closing of stomata. A large number of g(s) measurements obtained across varying moisture regimes, locations, and crop cycles with a diverse sugarcane germplasm composed of introgression, and commercial clones indicated that there is a high genetic variation for g(s) that can be exploited in a breeding programme. Regardless of the environmental influences on the expression of this trait, moderate heritability was observed across 51 sets of individual measurements made on replicated trials over 3 years. The clone×water status interaction (G×E) variation was smaller than the clone (G) variation on many occasions. A wide range of genetic correlations (r(g)= -0.29 to 0.94) between g(s) and yield were observed across test environments in all three different production regions used. Canopy conductance (g(c)) based on g(s) and leaf area index (LAI) showed a stronger genetic correlation than the g(s) with cane yield (tonnes of cane per hectare; TCH) at 12 months (mature crop). The regression analysis of input weather data for the duration of measurements showed that the predicted values of r(g) correlated with the maximum temperature (r=0.47) during the measurements and less with other environmental variables. These results confirm that the g(c) could have potential as a criterion for early-stage selection of clones in sugarcane breeding programmes.