Genetic and physiological analysis of an irradiated bloomless mutant (epicuticular wax mutant) of sorghum

An irradiation-induced bloomless mutant of sorghum [Sorghum bicolor (L.) Moench.], KFS2021, which visually exhibits an absence of white fluffy epicuticular wax in leaf and sheath, was characterized using a combination of genetic and physiological approaches. Study of the phenotypic segregation for the bloomless trait in F-2 and F-2:3 populations from a cross between KFS2021 and BTx623 (a cultivar with bloom showing profuse deposition of white epicuticular wax) suggests that bloomless is controlled by a single nuclear recessive gene. The bloomless parent (KFS2021) and F-2 individuals had lower frequency of guttation, leakier epidermal layer (based on percentage of chlorophyll leaching), and higher rate of seedling water loss than the BTx623 and F-2 bloom individuals. Bloomless F-2 individuals showed 3- to 6-fold higher nighttime transpiration rates relative to F. bloom individuals based on nighttime conductance. Correlation analysis showed significant negative associations between leaf epicuticular wax load with epidermal permeability and nighttime conductance, which indicate the important role of epicuticular wax in these traits. These results suggest that epicuticular wax may enhance water use efficiency of sorghum by regulating nighttime water loss.