LAUSR

Abstract Intrinsic transpiration efficiency (i TE), the ratio of photosynthesis (A) to stomatal conductance (g s), is considered a useful trait for improving productivity; however, higher i TE with high A is more desirable than that with low g s. This study dissects i 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 s 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 i TE increased from 117.4 μmol mol−1 in the irrigated treatment to 130.6 μmol mol−1 in the rainfed treatment. In irrigated conditions, i TE had high heritability (H 2 b = 0.67) and significant genetic correlation with TDM (r g = 0.58) and TCH (r g = 0.72). Under water stress, at g s below 0.1 mol m−2 s−1, non‐stomatal limitation to A was evident and i TE had low heritability (H 2 b = 0.2). Whereas in the g s range of 0.1–0.4 mol m−2 s−1, heritability of i TE (H 2 b = 0.63) and its genetic correlation with TDM (r g = 0.78) and TCH (r g = 0.75) were maximised. There was significant genotypic variation in photosynthetic capacity (A c), and the differences were related to TDM and i TE. Selecting genotypes with higher i TE and A c could offer potential for improving productivity without the unfavourable effect of low g s.