Is the Stay‐Green Trait in Sorghum a Result of Transpiration Sensitivity to Either Soil Drying or Vapor Pressure Deficit?

Abstract

Persistence of green leaves during seed fill, referred to as a stay‐green trait, has been investigated in sorghum [Sorghum bicolor (L.) Moench] as an approach to increasing yields under water‐limited conditions. An hypothesis to explain the observation of stay green in some sorghum genotypes and not in others is that the genotypes expressing the trait employ mechanisms to increase availability of soil water during seed fill. In this study, the expression of two mechanisms resulting in soil water conservation to allow greater water availability during seed fill was explored among 12 sorghum genotypes. One mechanism is an earlier decrease in transpiration with soil drying so that the rate of soil water loss is decreased earlier in the soil drying cycle. The second mechanism is a limitation on transpiration rate at high vapor pressure deficit (VPD) so that soil water is conserved on days when midday VPD is high. Field studies were undertaken to identify seven genotypes that consistently expressed the stay‐green trait and five genotypes that did not exhibit this trait. The range of the threshold for the decrease in transpiration rate with soil drying was similar among the two sets of genotypes. Similarly, the expression of the limited transpiration rate under high VPD was found for both sets of genotypes. There was no evidence in these studies that the stay‐green trait was closely linked with either mechanism of water conservation.

Measurement of transpiration restriction under high vapor pressure deficit for sorghum mapping population parents

“…The light flux 450-500 l mol m -2 s -1 was maintained above the canopy level. The TR subjected to increasing VPD was measured as described in the earlier studies in sorghum by Gholipoor et al (2010), Choudhary et al (2013) and Shekoofa et al (2014). During the transition time, the pots are measured by a gravimetric method using 0.01 precision balances (FBK, Kern & Sohn GmbH, Balingen, Germany).…”

“…First of these mechanisms is the expression of a limited transpiration rate under increasing vapour pressure deficit (VPD) conditions and the second is a decrease in transpiration at high soil moisture conditions when subjected to progressive soil drying conditions. These two mechanisms were first studied in a few genotypes of sorghum (Gholipoor et al 2012;Choudhary et al 2013), where significant genetic variation was found among the genotypes. This phenomenon was also experimented in a series of crops by several researchers and existence of genetic variation for transpiration rate at different vapor pressure deficit levels (Fletcher et al 2007;Devi et al 2010;Kholova et al 2010;Gilbert et al 2011;Zaman-Allah et al 2011).…”

Stay‐green alleles individually enhance grain yield in sorghum under drought by modifying canopy development and water uptake patterns

“…The stay-green drought adaptation trait has been a focus of sorghum crop improvement programmes in Australia and the USA for over 30 yr (Rosenow, 1977;Henzell et al, 1992;Jordan et al, 2012). The physiological basis of stay-green remains unclear, although a number of studies in sorghum have increased our understanding of this complex trait (Borrell et al, 2000a,b;Harris et al, 2007;van Oosterom et al, 2011;Vadez et al, 2011;Jordan et al, 2012;Burke et al, 2013;Choudhary et al, 2013). Earlier research focused on the nitrogen status of plants during terminal water deficit (Borrell & Hammer, 2000;Borrell et al, 2001), but later studies also evaluated the role of plant water management (Hammer, 2006;Vadez et al, 2011;Choudhary et al, 2013).…”

Variation Among Maize Hybrids in Response to High Vapor Pressure Deficit at High Temperatures

“…One approach to achieve water conservation is to have TR lim under high atmospheric VPD as a result of partial closure of stomata. Partial stomatal closure would occur when water transfer to guard cells cannot match the transpiration rate (TR) that results from fully open stomata (Brodribb and Jordan, 2008; Yang et al, 2012; Shekoofa et al, 2013; Choudhary et al, 2013). A simulation study of maize production in the US (Messina et al, 2015) illustrated the regions and probability of yield increase that could be expected from the TR lim trait.…”