On the extent of genetic variation for transpiration efficiency in sorghum

Abstract

A glasshouse study examined 49 diverse sorghum lines for variation in transpiration efficiency. Three of the 49 lines grown were Sorghum spp. native to Australia; one was the major weed Johnson grass (Sorghum halepense), and the remaining 45 lines were cultivars of Sorghum bicolor. All plants were grown under non-limiting water and nutrient conditions using a semi-automatic pot watering system designed to facilitate accurate measurement of water use. Plants were harvested 56–58 days after sowing and dry weights of plant parts were determined. Transpiration efficiency differed signficantly among cultivars. The 3 Australian native sorghums had much lower transpiration efficiency than the other 46 cultivars, which ranged from 7·7 to 6·0 g/kg. For the 46 diverse cultivars, the ratio of range in transpiration efficiency to its l.s.d. was 2·0, which was similar to that found among more adapted cultivars in a previous study. This is a significant finding as it suggests that there is likely to be little pay-off from pursuing screening of unadapted material for increased variation in transpiration efficiency. It is necessary, however, also to examine absolute levels of transpiration efficiency to determine whether increased levels have been found. The cultivar with greatest transpiration efficiency in this study (IS9710) had a value 9% greater (P < 0·05) than the accepted standard for adapted sorghum cultivars. The potential impact of such an increase in transpiration efficiency warrants continued effort to capture it. Transpiration efficiency has been related theoretically and experimentally to the degree of carbon isotope discrimination in leaf tissue in sorghum, which thus offers a relatively simple selection index. In this study, the variation in transpiration efficiency was not related simply to carbon isotope discrimination. Significant associations of transpiration efficiency with ash content and indices of photosynthetic capacity were found. However, the associations were not strong. These results suggest that a simple screening technique could not be based on any of the measures or indices analysed in this study. A better understanding of the physiological basis of the observed genetic differences in transpiration efficiency may assist in developing reliable selection indices. It was concluded that the potential value of the improvement in transpiration efficiency over the accepted standard and the degree of genetic variation found warrant further study on this subject. It was suggested that screening for genetic variation under water-limiting conditions may provide useful insights and should be pursued.

Stay-green quantitative trait loci's effects on water extraction, transpiration efficiency and seed yield depend on recipient parent background

“…Differences in TE have been reported in sorghum, although generally under well-watered conditions (Hammer et al, 1997;Xin et al, 2009). Other reports also show the existence of genotypic variation in TE under differing water regimes (Donatelli et al, 1992;Balota et al, 2008) in a work that included Tx7078, a genotype with low TE and assumed to be tolerant to pre-flowering drought (Tuinstra et al, 1998).…”

“…Van Oosterom and colleagues (2006) have also hypothesized that stay-green could be the consequence of water saving from having higher water use efficiency. Differences in transpiration efficiency (TE) have been reported under fullyirrigated conditions in sorghum germplasm (Hammer et al, 1997;Xin et al, 2009). …”

Role of leaf photosynthesis and stomatal conductance in determining the genotypic variation in whole-plant Transpiration Efficiency (TE) in Sorghum

“…2.2) (Hammer, 2006; Turner, 2004). In addition, TE can play an important role in increasing biomass and grain yield under water limitation (Hammer et al, 1997; Krishnamurthy et al, 2007;Xin et al, 2009). As mentioned previously, TE at the plant (or crop) level is the emerging consequence of inter-dependent processes taking place at the leaf level.…”

“…The components that determine higher TE are under genetic control and result in genotypic variation in TE amongst crop species and among genotypes within species. Hence, to select for increased crop TE, genotypic variation in TE at the plant level should be present (Borrell et al, 2006).Genotypic variation in TE has been reported for a number of crop species such as wheat (Condon et al, 1990), rice (Impa et al, 2005), peanut (Sheshshayee et al, 2006;Wright et al, 1994) and sorghum (Hammer et al, 1997;Xin et al, 2009). However, to better understand the cause of these plant-level TE differences, it is useful to investigate the underlying physiological processes at the leaf level, and their associations with the environment (Jackson et al, 2016).…”

“…At the plant level, TE is the amount of plant biomass produced (g) per unit of water captured for transpiration (kg) (Hammer et al, 1997), typically measured over a few months. At the leaf level, what is termed intrinsic TE is the ratio of instantaneous rates of CO2 assimilation (photosynthesis) and leaf conductance to water (Condon et al, 2002; Tuberosa, 2012), which is measured over a few seconds to a few minutes.Genotypic variation in TE has been reported in various crops, including wheat (Condon et al, 1990), rice (Impa et al, 2005), peanut (Wright et al, 1994), sunflower (Lambrides et al, 2004), maize (Pilbeam et al, 1995;Ryan et al, 2016a) and sorghum (Hammer et al, 1997;Mortlock and Hammer, 1999;Vadez et al, 2011;Xin et al, 2008). This genetic variation is suggestive of greater scope for further development of more drought-tolerant and water-efficient sorghum varieties (Borrell et al, 2006).…”