EPICUTICULAR WAX LOAD AND WATER-USE EFFICIENCY IN BLOOMLESS AND SPARSE-BLOOM MUTANTS OF SORGHUM-BICOLOR L

A mutation breeding approach was utilized to obtain near-isogenic lines of sorghum [Sorghum bicolor (L.) Moench.] with altered epicuticular wax. Seeds of three bloomless mutants (bm-15, bm-22 and bm-38) and one sparse-bloom mutant (h-19) were obtained from the M(4) generation, and responses of mutants were compared to their corresponding normal, non-mutant sib lines (designated N-15, N-22, N-38 and N-19). Net CO2 assimilation rate, stomatal conductance, transpiration rate and water-use efficiency were measured on the uppermost, fully expanded leaves in irrigated and non-irrigated 43-day-old plants using a LiCor LI-6200 portable photosynthesis system. Epicuticular wax load (EWL) and cumulative water loss from excised leaves (CWL) were measured, and the relationships among EWL, CWL and water-use efficiency were assessed. Differences in response to irrigation lever varied among the four lines. Among irrigated plants, h-19 exhibited a higher water-use efficiency than N-19. Among non-irrigated plants, bm-15, bm-22 and h-19 exhibited lower water-use efficiencies than N-15, N-22 and N-19, respectively. Water-use efficiency measured in non-irrigated bm-22, a mutant line with no visible wax structures on the abaxial leaf surface, was more than 40% below that measured in N-22. The water loss from excised leaves was greater in bloomless and sparse-bloom lines than in normal lines. Water-use efficiency varied linearly with epicuticular wax load under irrigated (r=0.72) and non-irrigated (r=0.94) conditions.