Physiological traits for improving wheat yield under a wide range of conditions

Abstract

A better understanding of relatively simple crop-physiological attributes that determine yield in a wide range of conditions may be instrumental for assisting future breeding. Physiological traits may be selected either directly or through the use of molecular-biology tools. Physiological and breeding literature frequently distinguishes between yield under potential, stress-free conditions and under the pressure of stress, mostly abiotic. Although the rationale behind the idea that the different physiological attributes contribute to yield under these contrasting conditions may be sound, in practice there is a large body of evidence pointing out the other way around. For instance, genotypes with physiological attributes conferring higher yield potential usually also perform better under stress conditions, at least when excluding extremely severe environments. As breeders normally need to release improved cultivars to be grown in different sites throughout several seasons and subjected to a wide range of management decisions, identifying physiological traits that may confer simultaneously high yield potential and constitutive tolerance to stress would be critical. These traits must allow the plants to capture more resources or to use them more efficiently. A well-known attribute conferring high yield potential and widely studied physiologically has been semi-dwarfism. Semi-dwarf cultivars normally yield better than tall ones in a wide range of stressful conditions (at least if seedling emergence is not a major inconvenience). This is because reducing height to a certain level does not alter the ability of the crop to capture resources, whilst improving markedly the efficiency with which the resources are used to produce yield. This trait is not further useful as modern cultivars possess already a stature within the ranges optimizing yield. Two other traits that may also be associated with improved performance in a wide range of conditions may be the discrimination against 13C (?13C) and a lengthened stem elongation phase at the expense of previous phases. Although more research is needed before conclusions may be robust, physiological evidence supports the hypothesis that increasing ?13C and lengthening the stem elongation phase would result in an improved performance over a range of environmental conditions