Transpiration efficiency of sorghum [Sorghum bicolor(L.) Moench] in relation to plant type and genotype

Sorghum is a major crop in dry land farming systems where grain yield is limited by water availability around anthesis. Genotypic differences in transpiration efficiency (TB) have been reported for sorghum, but it is unclear whether the TE of tall double dwarf (2d) genotype's is different to that of short triple dwarf (3d) ones. The objectives of this study are to determine whether (i) plant type in terms of plant stature has a significant effect on TE, and (ii) genotypic differences in TB are associated with leaf conductance or photosynthetic capacity. Individual plants of seven tall 2d genotypes and 14 short 3d genotypes were grown in lysimeters. Plants were well watered and harvested 5 +/- 1 days after flowering of the main shoot. At harvest, total transpiration (T), leaf area and biomass were measured. TB, photosynthetic capacity and conductance were calculated. The TE did not differ between 2d and 3d plant types. Differences in TE among genotypes of both sorghum plant types were observed. These differences were associated with differences in photosynthetic capacity, rather than conductance and were not linked to stay-green expression. As stay-green expression can be a consequence of plant size, it indicates that TE and plant size are potentially independent traits of drought adaptation, highlighting the possibility of simultaneous selection for these two traits.