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) .