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

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 (H² _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 (H² _b  = 0.2). Whereas in the g_s range of 0.1-0.4 mol m^-2  s^-1 , heritability of _i TE (H² _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 .