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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. 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. 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. 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. 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). 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. • Crops in the field experience simultaneous occurrence of multiple stresses. • Ideotypes can be formulated based on characters phenotyped with integrative traits. • A few traits may define wheat ideotypes that are well adapted to a wide range of Mediterranean conditions. • Classical ways to display GxE interaction help to assess trait performance across growing conditions. • These traits guide improvements in the capture of resources, rather than how efficiently they are being used. [ABSTRACT FROM AUTHOR]

Highlights • Genetic gain of durum wheat in Spain slowed after the green revolution until reach a plateau in the last decade. • However, genetic gain was positively related with the mean and maximum daily temperatures of the testing sites. • The genetic advance was related to improvement in kernels m−2 and kernels spike−1. Abstract This paper addresses the question of whether there has been any genetic gain in yield for durum wheat released in Spain after the Green Revolution and assesses the agronomical and physiological traits associated with evolution of the crop during this time. Field experiments were carried out with a wide range of durum wheat cultivars (released in Spain from 1980 to 2009) and were conducted in different sites embracing a wide range of growing temperatures and water regimes at Aranjuez and Zamadueñas during three consecutive growing seasons (2013/14, 2014/15, 2015/16) under rainfed and supplemental irrigation and at Coria for two consecutive seasons (2014/15 and 2015/16) under rainfed conditions alone. Grain yield increased with the year of release of cultivars at a rate of 24 kg ha−1 y−1 (0.44% y−1) from 1980 to 2003, with no clear additional improvements thereafter. The moderate grain yield improvement from 1980 and 2003 was associated with kernels m−2 and kernels spike−1, with an increase of 117 kernels m−2 y−1 and 0.24 kernels spike−1 y−1, respectively. Moreover, aerial biomass at harvest and grain nitrogen yield increased with the year of release of cultivars for the entire period. However, no differences were found for thousand kernel weight, number of spikes m−2, days to heading, plant height, harvest index, canopy temperature depression, carbon isotope discrimination or grain nitrogen concentration. Overall, these results indicated that the rate of genetic progress in the yield of durum wheat in Spain after the Green Revolution has been low and has even stopped during the last decade, while no clear trend in some grain quality traits (TKW and grain N concentration) was recorded. However, the absolute and relative genetic gains estimated for yield were positively associated with the average mean and maximum daily temperatures from sowing to harvest of the testing site, which suggest that breeding has been performed under high-temperature environments. [ABSTRACT FROM AUTHOR]

Identifying traits conferring high yield in target environments has become a main concern of wheat breeders. This is particularly relevant for the current Mediterranean conditions as well as for the expected scenarios driven by climate change for central and northern Europe. The objective of this study was to identify breeding traits conferring adaption of high-yielding European wheat cultivars to actual Mediterranean conditions. Twelve elite winter wheat cultivars from different European (northern, central and southern) regions were grown under Mediterranean continental conditions across three consecutive crop seasons and three different topdressing nitrogen fertilization levels. Phenology was assessed throughout the crop cycle. At maturity, grain yield (GY), grain number and thousand kernel weight (TKW) were determined. Further, carbon (δ13C) and nitrogen (δ15N) stable isotope compositions and nitrogen concentration (N) were analyzed in mature grains as proxies for water and nitrogen status, respectively. The nitrogen fertilization effect was minor for GY compared with the season and genotypic effects. Concerning genotypic performance, the effect of phenology varied across seasons, with longer crop durations being associated with higher GY under the wettest season (2017–2018), no effect under mildly wet conditions (2019–2020) and being negatively associated with GY under dry conditions (2018–2019). Furthermore, the relative duration of each phenological stage had an effect on genotypic performance, particularly during the dry season (2018–2019). Moreover, regardless of the season considered, the highest-yielding genotypes were associated with better water status (lower δ13C). Under wet season conditions, northern European genotypes had 6 % higher yields, whereas in the dry season, southern European genotypes had 2 % higher yields. The differences in GY among the top wheat cultivars originating from different European regions were fairly minor across the seasons and across the N fertilization levels recommended in the region. The study suggests that, depending on the season, selection for the high-yielding conditions of central and northern Europe also delivers genetic increases in grain yield under Mediterranean conditions. • Recommended N topdressing levels place wheat fertilization in the saturation zone. • Genotypic yield performance is associated with higher grain number rather than weight. • Crop duration and phenology are key to adapting genotypes to Mediterranean conditions. • Regardless of the season, the best genotypes exhibit better water status (lower δ13C). • Some northern European wheat cultivars are well adapted to Mediterranean conditions. [ABSTRACT FROM AUTHOR]

Crop performance is very dependent on roots because they determine the capture of water and nutrients, and the crop's subsequent growth and productivity. Durum wheat is a major crop in the Mediterranean region, where water and nitrogen availability limit its productivity. Therefore, the focus of this study was to uncover the response of root and shoot traits in durum wheat to different Mediterranean growing conditions and how they relate to better growth and yield performance. For this purpose, crop performance was evaluated in a set of modern durum wheat cultivars grown during four consecutive seasons and under contrasting water regimes, temperatures and nitrogen supplies, totalling 12 different growing conditions. Grain yield, biomass, other crop-growth traits (plant height, PH, and the Normalised Difference Vegetation Index, NDVI), together with physiological indicators of water (carbon isotope composition, δ13C, and canopy temperature depression, CTD) and nitrogen (nitrogen isotope composition, δ15N, and grain nitrogen yield, GNY) status were assessed. In addition, root architecture and distribution were measured using shovelomics and soil coring, and the provenance of the water captured by roots was determined by comparing the oxygen (δ18O) and hydrogen (δ2H) isotope compositions of water at the base of the stem, with water in different soil sections. Water and nitrogen status indicators combined with shovelomic traits allowed development of yield-prediction models. while higher yields were associated in most cases with better water status, root architecture was very responsive to different growing conditions. Overall, genotypes better adapted to rainfed conditions exhibited roots favouring deeper water extraction, whereas under support irrigation, the root system enabled water extraction from the topsoil as from deeper soil sections. Our study also highlights the limitation of shovelomics and soil coring as phenotyping approaches and proposes the δ18O of stem water as a promising functional phenotypic approach. [Display omitted] • Water availability is the main environmental factor limiting durum wheat yield. • Durum wheat root architecture shows high plasticity under Mediterranean conditions. • Under rainfed conditions, higher yields are associated with deeper roots. • Under irrigation, higher yielding crops combined shallow and deep roots. • We propose the δ18O of stem water as a phenotypic trait informing about soil water uptake. [ABSTRACT FROM AUTHOR]