Abstract
AbstractDedicated non‐food bioenergy crops like poplar are needed as sustainable, low‐input feedstocks for renewable energy in a future drier climate, where they can be grown on marginal soils. Such plants should have a low water, carbon, and chemical footprint. Capturing natural variation in traits associated with water use efficiency (WUE) is the first step to developing trees that require less water and may be adapted to drier environments. We have assessed stomatal conductance (gs) and leaf carbon isotope composition (δ13C, an indirect indicator of leaf WUE) in two Populus species, P. deltoides and P. trichocarpa and their F2 progeny, grown in the United Kingdom and in Italy. Populus deltoides leaves showed lower δ13C than P. trichocarpa, suggesting a higher WUE in P. trichocarpa, although without drought preconditioning, gs of P. trichocarpa was less responsive to dehydration and abscisic acid treatment than P. deltoides, suggesting that leaf anatomy may also contribute to δ13C in Populus. Quantitative trait loci (QTL) were identified for δ13C on eight linkage groups (LG) and two QTL for gs. From these. QTL and differential gene expression in response to drought from microarray data, we focused on three hotspots and identified 23 novel candidate genes on LG VI, X, and XVI. We have begun to unravel the genetic basis of WUE in bioenergy Populus revealing important underpinning data for breeding and improvement in poplar genotypes for a future drier climate.
Highlights
There remains a pressing need to better understand the links between water supply and the genetic basis of plant drought tolerance – a complex trait, difficult to quantify and highly variable (Passioura 2012)
There is evidence to suggest that enough genetic diversity exists across the genus for targeted selection and breeding for drought tolerance, with wide variations reported in traits such as intrinsic water use efficiency, leaf carbon isotope discrimination, stomatal conductance, stomatal density (Monclus et al 2006), and differences in gene expression and metabolic changes in response to drought in Populus identified (Street et al 2006)
The excised and ABA-treated leaves of P. deltoides first shortly decreased in temperature – the “Iwanoff effect” (Iwanoff 1928), which is due to a sudden loss in epidermal turgor (Kaiser and Grams 2006), showed a rise in temperature indicating stomatal closure (Fig. 1B and see video available in the Video S1) stabilizing after ~10–15 min while those of P. trichocarpa did not change, even after 2 h
Summary
There remains a pressing need to better understand the links between water supply and the genetic basis of plant drought tolerance – a complex trait, difficult to quantify and highly variable (Passioura 2012). There is evidence to suggest that enough genetic diversity exists across the genus for targeted selection and breeding for drought tolerance, with wide variations reported in traits such as intrinsic water use efficiency, leaf carbon isotope discrimination, stomatal conductance, stomatal density (Monclus et al 2006), and differences in gene expression and metabolic changes in response to drought in Populus identified (Street et al 2006). Populus euphratica was found in highly saline and arid environments such as the Negev desert (Brosche et al 2005) Quantifying this genetic diversity and understanding the physiological traits associated with genetic variation provides the first step to identifying superior plants for drought tolerance that will underpin breeding efforts for these bioenergy species
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