Terminal drought-tolerant pearl millet [Pennisetum glaucum (L.) R. Br.] have high leaf ABA and limit transpiration at high vapour pressure deficit

Abstract

It was previously shown that pearl millet genotypes carrying a terminal drought tolerance quantitative trait locus (QTL) had a lower transpiration rate (Tr; g cm−2 d−1) under well-watered conditions than sensitive lines. Here experiments were carried out to test whether this relates to leaf abscisic acid (ABA) and Tr concentration at high vapour pressure deficit (VPD), and whether that leads to transpiration efficiency (TE) differences. These traits were measured in tolerant/sensitive pearl millet genotypes, including near-isogenic lines introgressed with a terminal drought tolerance QTL (NIL-QTLs). Most genotypic differences were found under well-watered conditions. ABA levels under well-watered conditions were higher in tolerant genotypes, including NIL-QTLs, than in sensitive genotypes, and ABA did not increase under water stress. Well-watered Tr was lower in tolerant than in sensitive genotypes at all VPD levels. Except for one line, Tr slowed down in tolerant lines above a breakpoint at 1.40–1.90 kPa, with the slope decreasing >50%, whereas sensitive lines showed no change in that Tr response across the whole VPD range. It is concluded that two water-saving (avoidance) mechanisms may operate under well-watered conditions in tolerant pearl millet: (i) a low Tr even at low VPD conditions, which may relate to leaf ABA; and (ii) a sensitivity to higher VPD that further restricts Tr, which suggests the involvement of hydraulic signals. Both traits, which did not lead to TE differences, could contribute to absolute water saving seen in part due to dry weight increase differences. This water saved would become critical for grain filling and deserves consideration in the breeding of terminal drought-tolerant lines.

Water: the most important ‘molecular’ component of water stress tolerance research

“…Indeed, under similar environmental conditions, two genotypes with the same leaf area exhibiting differences in leaf canopy conductance would lose different amounts of water. For example, pearl millet genotypes varied with respect to leaf canopy conductance under fully irrigated conditions despite exhibiting a similar leaf area (Kholová et al 2010a), and this appeared to be related to higher leaf ABA content in genotypes with low leaf canopy conductance (Kholová et al 2010b). Similar results were obtained in chickpea (Zaman-Allah et al 2011b) and cowpea (Belko et al 2012), where the canopy conductance differed among genotypes.…”

“…Similar results were obtained in chickpea (Zaman-Allah et al 2011b) and cowpea (Belko et al 2012), where the canopy conductance differed among genotypes. In the research reported by Kholová et al (2010b), Zaman-Allah et al (2011b) and Belko et al (2012), the leaf canopy conductance was calculated as the ratio of gravimetric transpiration measurements at the wholeplant level divided by the leaf area and the time that plants were allowed to transpire (either an entire day or one-hour time periods across an entire day). Thus, it was ensured that the leaf area index of the plants was <1, such that there was a lack of (or limited) mutual shading of leaves.…”

“…Squire 1979;Turner et al 1984;Grantz 1990), and it ensures maximum transpiration at times of the day when the VPD crosses a threshold. However, genotypic variation has only recently been revealed in different species such as soybean (Fletcher et al 2007;Sadok and Sinclair 2009), chickpea (Zaman-Allah et al 2011b), cowpea (Belko et al 2012), peanut (Devi et al 2010) and cereals such as sorghum (Gholipoor et al 2010) and pearl millet (Kholová et al 2010b). Crop simulation analysis has shown that this maximum rate of transpiration would have a beneficial effect on yield and also that it would lead to water saving and a higher TE (Sinclair et al 2005).…”

Transpiração e crescimento foliar de plantas de mandioca em resposta ao deficit hídrico no solo

“…Alguns trabalhos com soja (Fletcher et al, 2007), sorgo (Gholipoor et al, 2010) e milheto (Kholová et al, 2010) têm mostrado que há variabilidade genética na resposta da transpiração, em diferentes condições de demanda evaporativa da atmosfera. Essas constatações poderiam explicar a variabilidade, obtida no presente trabalho, entre as Figura 3.…”

“…Esse fato poderia levar à limitação do fluxo transpiratório com um conteúdo de água maior no solo, ou seja, poderia resultar em maiores valores de FATS crítica, mas essa hipótese não se confirmou em seu estudo com dois híbridos de milho, que não apresentaram variação significativa nos valores de FATS crítica entre os tratamentos de DPV (11,20,29 e 36 hPa). No entanto, alguns trabalhos indicam que a transpiração aumenta com o aumento do DPV, e que as respostas variam entre espécies e entre genótipos da mesma espécie (Fletcher et al, 2007;Sinclair et al, 2008;Wherley & Sinclair, 2009;Gholipoor et al, 2010;Kholová et al, 2010).…”