Comparing the Water-Use Efficiency of Bloom and Bloomless Sorghum.

ABSTRACT

Sorghum (Sorghum bicolor L. Moench) is an important crop grown for both fodder and food specially in Africa and Asia. The bloomless (bm) type which visually exhibit an absence of white fluffy epicuticular wax in leaf sheath is known to be highly digestible compered to bloom (Bm) type. However, the bloomless trait has been associated with low stress tolerance, but this conclusion is based on a narrow pool of bloomless alleles. The purpose of this study was to determine if the Bm type water use advantage over the bm mutants. Greenhouse experiments were conducted at College Station, TX, in 2015 using BC₂F6 bloom and bloomless near isogenic lines (NILs) derived from ethylmethanesulfonate (EMS) mutagenized Tx623, a heavily bloom inbred line. A second set of F4 derived from a cross of Stg4 (bloom) X M1789 (EMS-induced bloomless). Two types of treatments were applied, well watered (WW) and water deficit (WD). In each treatment, a complete randomized block design was used in with four replications per treatment (pots) and two plants per pot for each of the bloom and bloomless line. Intrinsic measurements were taken for gas exchange, stomatal conductance (C), canopy temperature, vapor pressure deficit (VPD) and humidity. Whole plant water use was determined by change in weight per pot every 2 d from emergence to heading when non grain total biomass is expected to plateau. Integrated WUE was determined as the ratio of total dry biomass to whole plant evapotranspiration for each genotype in each treatment. The means were computed separately for F4 bloomless and F4 bloom and separately for bloom NILs and bloomless NILs. Results showed that in the WW treatment, the F4 bloom type had significantly higher WUE than F4 bloomless, but not difference under WD conditions. There was no significant difference between the bloom NILs and their bloomless counterparts under both conditions. These results suggest that the bloomless sorghum types can have equal potential to accumulate high biomass comparable to their bloom wildtype counterparts under stress. This may be important in breeding the highly digestible bloomless genotypes for livestock feed under dry conditions.

Key words: Sorghum Bicolor L., bloom, bloomless, water-use efficiency