Abdelhalim Elazab

Contribution of the ear and the flag leaf to grain filling in durum wheat inferred from the carbon isotope signature: Genotypic and growing conditions effects

The ear, together with the flag leaf, is believed to play a major role as a source of assimilates during grain filling in C3 cereals. However, the intrusive nature of most of the available methodologies prevents reaching conclusive results in this regard. This study compares the carbon isotope composition (δ(13)C) in its natural abundance in the water-soluble fractions of the flag leaf blade and the ear with the δ(13)C of mature kernels to assess the relative contribution of both organs to grain filling in durum wheat (Triticum turgidum L. var. durum). The relative contribution of the ear was higher in landraces compared to modern cultivars, as well as in response to nitrogen fertilization and water stress. Such genotypic and environmentally driven differences were associated with changes in harvest index (HI), with the relative contribution of the ear being negatively associated with HI. In the case of the genotypic differences, the lower relative contribution of the ear in modern cultivars compared with landraces is probably associated with the appearance in the former of a certain amount of source limitation driven by a higher HI. In fact, the relative contribution of the ear was far more responsive to changes in HI in modern cultivars compared with landraces.

Physiological traits contributed to the recent increase in yield potential of winter wheat from Henan Province, China

This experiment aims to test the traits responsible for the increase in yield potential of winter wheat released in Henan Province, China. Seven established cultivars released in the last 20 years and three advanced lines were assayed. The results showed that grain yield was positively correlated with harvest index (HI), kernel number per square meter, and aboveground biomass. In addition, the HI and aboveground biomass showed an increasing trend with the year of release. Therefore, we can conclude that bread wheat breeding advances during recent decades in Henan Province, China, have been achieved through an increase in HI, kernel number per square meter, and aboveground biomass. A higher δ(13)C seems also to be involved in these advances, which suggests a progressive improvement in constitutive water use efficiency not associated with a trend towards lower stomatal conductance in the most recent genotypes. However, genetic advance does not appear related to changes in photosynthesis rates on area basis when measured in the flag leaf or the spike, but only to a higher, whole-spike photosynthesis. Results also indirectly support the concept that under potential yield conditions, the spike contributed more than the flag leaf to kernel formation.

Root traits and δ13C and δ18O of durum wheat under different water regimes

Plant growth, root characteristics and the stable carbon (δ13C) and oxygen (δ18O) composition were studied in durum wheat. Four recombinant inbred lines with good agronomic adaptation were grown under well watered (WW) and water stress (WS) conditions until mid-grain filling in lysimeters. Gas exchange was measured in the flag leaf just before harvest and then the aerial dry matter (Aerial DM), root weight density (RWD) and root length density (RLD) and the specific root length (SRL) were evaluated and the δ13C and δ18O of the roots, the flag leaf blade and the spike were analysed. Water stress decreased stomatal conductance, plant accumulated transpiration and Aerial DM, whereas δ13C and δ18O increased. Genotypic differences were found for all gas-exchange and root traits and isotope signatures. Aerial DM was positively correlated with RLD, regardless of the water regime, whereas it was negatively correlated with δ13C and δ18O, but only under WW conditions. Moreover, RWD and RLD were negatively related to both δ13C and δ18O under the WW regime, but no clear pattern existed under WS. Our study supports the use of δ13C and δ18O as proxies for selecting root traits associated with higher growth in the absence of water stress.

Low-cost assessment of wheat resistance to yellow rust through conventional RGB images

RGB imagery is a low-cost approach for field phenotyping of rust tolerance in wheat.It performs better than chlorophyll content and gas exchange of individual leaves.Hue, Green Fraction, Greener Fraction, a and u are the most effective color traits. Establishing low-cost methods for stripe (yellow) rust (Puccinia striiformis f. sp. tritici) phenotyping is paramount to maintain the breeding pipeline in wheat. Twelve winter wheat genotypes were grown to test rust resistance and yield performance. Physiological traits, including leaf chlorophyll content (Chl), net photosynthesis rate (Pn), stomatal conductance (gs), transpiration rate (E) and canopy temperature depression (CTD), together with diverse color components derived from Red, Green and Blue (RGB) images, were measured at different crop stages. Grain yield (GY) and grain yield loss index (GYLI) were assessed through comparison with the previous normal planting year. Genotypes exhibited a wide range of resistance to yellow rust, with GYLI values ranging from about -3% for the more resistant (Zhoumai 22) to 89% for the most susceptible (Lankao 298) genotypes. Moreover yellow rust reduced Chl and to a lesser extent, Pn, while traits related to water status were lower (gs) or not affected (E and CTD). The color parameters Green Fraction, Greener Fraction, Hue, a and u measured during grain filling were much better correlated with GY and GYLI (r2 ranging between 74% and 81%) than the set of photosynthetic and transpirative traits (Chl, Pn, gs, E, CTD) measurements in the same stage. Conventional digital imaging appears to be a potentially affordable approach for high-throughput phenotyping of yellow rust resistance.

Interactive effect of water and nitrogen regimes on plant growth, root traits and water status of old and modern durum wheat genotypes

AbstractMain conclusionsThe selection of the ideal root drought adaptive traits should take into account the production and maintenance of root tissues alongside the capacity to capture soil resources. Ten old and modern Spanish durum wheat (Triticum turgidum L. var durum) genotypes were grown in lysimeters under two contrasting water and nitrogen regimes to study the effect of such growth conditions on: (1) the aerial biomass, (2) the growth and structure of the roots and (3) the relationships of the root structure with aerial biomass, photosynthetic and transpirative characteristics and water use efficiency. Both high water and nitrogen regimes significantly increased aerial biomass. Root dry biomass and root length increased and decreased in response to improved water supply and nitrogen regimes, respectively. No significant correlations were detected between aerial biomass and any root trait under well-watered conditions. Under water stress aerial biomass was negatively correlated with root dry biomass, root length and root weight density and positively correlated with the specific root length, particularly for the subset of old genotypes. The high nitrogen regime significantly enriched the carbon isotope composition of the flag leaf (δ13CFL) and hindered the effect of the high water regime on decreasing δ13CFL enrichment. Thus, positive correlations of aerial biomass with δ13CFL were detected regardless of the water regime. The study revealed: (1) the importance of root traits for higher aerial biomass under the low water regime; (2) that the interaction between nitrogen and the water regime may affect the predictive nature of the δ13C in drought breeding programs; and (3) the selection of the ideal root system structure should take into account the metabolic costs of the production and maintenance of root tissues alongside the capacity of capturing resources.

Wheat ear carbon assimilation and nitrogen remobilization contribute significantly to grain yield

The role of wheat ears as a source of nitrogen (N) and carbon (C) in the grain filling process has barely been studied. To resolve this question, five wheat genotypes were labeled with 15 N-enriched nutrient solution. N remobilization and absorption were estimated via the nitrogen isotope composition of total organic matter and Rubisco. Gas exchange analyses showed that ear photosynthesis contributed substantially to grain filling in spite of the great loss of C due to respiration. Of the total kernel N, 64.7% was derived from the N acquired between sowing and anthesis, while the remaining 35.3% was derived from the N acquired between anthesis and maturity. In addition, 1.87 times more N was remobilized to the developing kernel from the ear than from the flag leaf. The higher yielding genotypes showed an increased N remobilization to the kernel compared to the lower yielding genotypes. In addition, the higher yielding genotypes remobilized more N from the ears to the kernel than the lower yielding genotypes, while the lower yielding genotypes remobilized more N from the flag leaf to the kernel. Therefore, the ears contribute significantly toward fulfilling C and N demands during grain filling.

Agronomic and physiological responses of Chinese facultative wheat genotypes to high-yielding Mediterranean conditions

Nine wheat genotypes, bred for the high-input agronomical conditions of Henan Province (China), were tested under the high-yielding Mediterranean conditions of Spain. Two cultivars widely grown in the zone were included as controls. Crop growth and leaf chlorophyll (Chl) content, leaf stomatal conductance ( g s ) and canopy temperature (CT) were measured during the crop cycle and stable carbon (C), oxygen (O) and nitrogen (N) isotope compositions ( δ 13 C, δ 18 O and δ 15 N) were analysed on different plant parts. The lower yield of the Chinese genotypes compared with the controls was due to fewer grains/unit area, associated with lower tillering and a plant height clearly below the optimal range. Moreover, Chinese wheat exhibited a lower spike fertility index than the controls, and this was associated with a less compact spike structure. The physiological characteristics that were related to better performance under high-yielding Mediterranean conditions consisted of a higher green aerial biomass, particularly during the reproductive stage, together with more favourable water conditions (higher g s and lower CT and δ 13 C), the capacity to take up water during grain fill (higher δ 18 O) and a more efficient uptake (lower δ 15 N) and utilization (lower leaf N and Chl content) of N fertilizer. It is concluded that Chinese genotypes exhibited a low acclimation capacity to the moderate stress typical of the high-yielding Mediterranean conditions.

New Technologies for Phenotyping

Improvements in agronomical practices and crop breeding are paramount responses to the present and future challenges imposed by water stress and heat (Lobell et al. 2011a, b; Cairns et al. 2013; Hawkins et al. 2013). On what concerns breeding, constraints in field phenotyping capability currently limit our ability to dissect the genetics of quantitative traits, especially those related to yield and water stress tolerance. Progress in sensors, aeronautics and high-performance computing is paving the way. Field high throughput platforms will combine non-invasive remote-sensing methods, together with automated environmental data collection. In addition, laboratory analyses of key plant parts may complement direct phenotyping under field conditions (Araus and Cairns 2014). Moreover, these phenotyping techniques may also help to cope with spatial variability inherent to phenotyping in the field.