Genetic diversity of transpiration efficiency in sorghum

Abstract

Sorghum is the fifth most important grain crop and is becoming increasingly important as a biofuel feedstock due to its superior tolerance to water-deficit stress. Sorghum is commonly grown under rain-fed conditions in the Southern Plains in the U.S.A. and other semi-arid regions in the world. Thus, its production is strongly affected by the availability of soil water during the growing season. Enhancing transpiration efficiency (TE), defined as biomass accumulation per unit water transpired, may be an effective approach to increasing sorghum yield in arid and semi-arid regions under no or limited irrigation. In this report, we surveyed 341 sorghum accessions for variation in TE. A selection of 25 lines was used to confirm the initial survey and these accessions were studied in a greenhouse experiment over 2 years. TE in these selected lines varied from year to year; however, similar rank was observed in both studies. Several accessions with consistent high or low TE were identified. TE based on biomass production was strongly correlated with increased biomass accumulation rather than with reduced water use. Gas-exchange analysis indicated that low internal CO 2 concentration and enhanced photosynthetic capacity may be a factor accounting for the high TE in some lines; other physiological processes also contribute to the TE based on integrated biomass. The result suggests that considerable genetic variation in TE exists in the sorghum germplasm collection and that TE is strongly influenced by environment. The sorghum lines with contrasting TE may serve as an important genetic resource for identification of physiological mechanisms regulating TE and for improvement of this trait in sorghum breeding.