Genotypic variation in intrinsic transpiration efficiency correlates with sugarcane yield under rainfed and irrigated field conditions.

Intrinsic transpiration efficiency ( TE), the ratio of photosynthesis (A) to stomatal conductance (g ), is considered a useful trait for improving productivity; however, higher TE with high A is more desirable than that with low g . This study dissects TE of 20 sugarcane genotypes to understand its relationship with total dry matter (TDM) and cane yield (TCH) under irrigated and rainfed conditions. Water stress reduced mean A and g by 56 and 61%, and mean TDM and TCH by 55 and 59%, respectively; however, genotype × irrigation treatment interaction was smaller than genotype variance. Mean TE increased from 117.4 μmol mol in the irrigated treatment to 130.6 μmol mol in the rainfed treatment. In irrigated conditions, TE had high heritability (H  = 0.67) and significant genetic correlation with TDM (r  = 0.58) and TCH (r  = 0.72). Under water stress, at g below 0.1 mol m  s , non-stomatal limitation to A was evident and TE had low heritability (H  = 0.2). Whereas in the g range of 0.1-0.4 mol m  s , heritability of TE (H  = 0.63) and its genetic correlation with TDM (r  = 0.78) and TCH (r  = 0.75) were maximised. There was significant genotypic variation in photosynthetic capacity (A ), and the differences were related to TDM and TE. Selecting genotypes with higher TE and A could offer potential for improving productivity without the unfavourable effect of low g .