Phenotyping genotypic performance under multistress conditions: Mediterranean wheat as a case study

Abstract

Context or problem: While crop breeding represents a key factor in terms of effectiveness and affordability in the adaptation of agriculture to stress conditions, phenotyping is perceived as a major bottleneck to achieving genetic advance. Crops in the field experience the simultaneous occurrence of multiple stresses, which vary depending on the location, year and management conditions. Even under the so-called “optimal agronomic conditions”, crops under field conditions may experience some degree of stress. Objective or research question: The review addresses the methodology of field phenotyping in environments with multiple stresses where genotype by environment (and even by management) interactions are common, the ideotypes that may work, and the phenotypic traits that characterise such ideotypes that are the most useful for identifying better adapted genotypes. Mediterranean wheat is taken as a case study. Methods: Integrative phenotypic traits have intrinsic value in terms of information about crop adaptability to growing conditions in a wide sense, thus inherently accounting for the occurrence of “hidden” stresses. Indeed, this has implications when considering genotype by environment interactions. Thus, such integrative traits, when evaluated under real (i.e. field) conditions, account for the crop’s performance under scenarios where the interaction between environmental growing conditions is the norm. Three categories of traits may comprise the ideotypic characteristics when phenotyping wheat for Mediterranean environments: phenology, water status and plant growth. While these characteristics are not fully independent of each other, they should represent the crop’s performance reasonably well over a wide range of Mediterranean scenarios. Results: It is in such a context that this review examines the case of wheat and other small grain cereals growing under Mediterranean conditions and illustrates how a few phenotyping traits, related to crop growth, water status and phenology, may define ideotypes well adapted to a wide range of environmental conditions, where non-crossover interactions exist. This is despite the fact that across such a range of environmental conditions, multistressors are present and are variable in nature, intensity and timing. Thus, for a wide range of Mediterranean conditions, the genotypes chosen correspond to ideotypes that exhibit more effective use of water and stronger growth. Conclusions: It is not only the characteristics of the ideotypes, but also the appropriate phenotypic traits characterising these ideotypes that are integrative in nature, meaning that they inform about crop performance over time (e.g. stable carbon isotope composition) and/or at the highest organisational level (e.g. canopy assessed via remote sensing). Implications or significance: At the functional level, these traits guide improvements in the capture of resources such as water or radiation, rather than how efficiently these resources are being used.