Jordi Bort

Quantitative Trait Loci for Grain Yield and Adaptation of Durum Wheat (Triticum durum Desf.) Across a Wide Range of Water Availability

Grain yield is a major goal for the improvement of durum wheat, particularly in drought-prone areas. In this study, the genetic basis of grain yield (GY), heading date (HD), and plant height (PH) was investigated in a durum wheat population of 249 recombinant inbred lines evaluated in 16 environments (10 rainfed and 6 irrigated) characterized by a broad range of water availability and GY (from 5.6 to 58.8 q ha−1). Among the 16 quantitative trait loci (QTL) that affected GY, two major QTL on chromosomes 2BL and 3BS showed significant effects in 8 and 7 environments, with R2 values of 21.5 and 13.8% (mean data of all 16 environments), respectively. In both cases, extensive overlap was observed between the LOD profiles of GY and PH, but not with those for HD. QTL specific for PH were identified on chromosomes 1BS, 3AL, and 7AS. Additionally, three major QTL for HD on chromosomes 2AS, 2BL, and 7BS showed limited or no effects on GY. For both PH and GY, notable epistasis between the chromosome 2BL and 3BS QTL was detected across several environments.

The Photosynthetic Role of Ears in C3 Cereals : Metabolism, Water Use Efficiency and Contribution to Grain Yield

This review concerns ear photosynthesis and its contribution to grain filling in C3 cereals. Ear photosynthesis is quantitatively important to grain filling, particularly in dry areas where source (i.e., assimilate) limitations can occur. Compared to the flag leaf, ear photosynthesis exhibits higher water stress tolerance. Several factors could be involved in the ears “drought tolerance.” First, although degree of C4 metabolism in ear parts has been reported, current evidence supports only typical C3 metabolism. Second, recycling of respired CO2 (i.e., refixation) could have considerable impact on final crop yield by preventing loss of CO2. Because refixation of CO2 is independent of atmospheric conditions, water use efficiency (measured as total ear photosynthesis divided by transpiration) could be higher in the ear than in the flag leaf. Moreover, ear parts (in particular awns) show higher relative water content and better osmotic adjustment under water stress compared to the flag leaf. This capacity, in addition to persistence of photosynthetic components under drought (delayed senescence), might help the ear to continue to fix CO2 late in the grain filling period.

Detection and Quantification of Unbound Phytochelatin 2 in Plant Extracts of Brassica napus Grown with Different Levels of Mercury

The mercury (Hg) accumulation mechanism was studied in rape (Brassica napus) plants grown under a Hg concentration gradient (0 μm–1,000 μm). Hg mainly accumulated in roots. Therefore, the presence of phytochelatins (PCs) was studied in the roots of the plants. The high stability of the PC-Hg multicomplexes (mPC-nHg) seems to be the main reason for the lack of previous Hg-PC characterization studies. We propose a modification of the method to detect and quantify unbound PC of Hg in plant extracts via high-performance liquid chromatography coupled to electrospray tandem mass spectrometry and inductively coupled plasma mass spectrometry in parallel. We separated the PC from the Hg by adding the chelating agent sodium 2,3-dimercaptopropanesulfonate monohydrate. We only detected the presence of PC after the addition of the chelating agent. Some multicomplexes mPC-nHg could be formed but, due to their large sizes, could not be detected. In this study, only PC2 was observed in plant samples. Hg accumulation was correlated with PC2 concentration (r2 = 0.98).

A panel of elite accessions of durum wheat (Triticum durum Desf.) suitable for association mapping studies

The effectiveness of association mapping (AM) based on linkage disequilibrium (LD) is currently beingtestedinanumberofcrops.AnimportantprerequisitefortheapplicationofAMistheavailabilityofcollectionsofaccessionswithasuitablelevelofgeneticvariationfortargettraitsandwith limited spurious LD due to the presence of population structure. Herein, the results of a genomewide molecular characterization of a collection of elite durum wheat accessions well-adapted to Mediterranean environments are presented. Ninety-seven highly polymorphic simple sequence repeats and 166 amplified fragment length polymorphism markers were used to characterize 189 durum accessions, mainly cultivars and advanced breeding lines. Genome-wide significant and sizeable LD indices at a centimorgan scale were observed, while LD mainly decayed within 10cM. On the other hand, effects due to spurious LD were notably lower than those previously observed in a durum wheat collection sampling durum gene pools of more diverse origin.

Comparative performance of δ13C, δ18O and δ15N for phenotyping durum wheat adaptation to a dryland environment

Grain yield and the natural abundance of the stable isotope compositions of carbon (δ13C), oxygen (δ18O) and nitrogen (δ15N) of mature kernels were measured during 3 consecutive years in 10 durum wheat genotypes (five landraces and five modern cultivars) subjected to different water and N availabilities in a Mediterranean location and encompassing a total of 12 trials. Water limitation was the main environmental factor affecting yield, δ13C and δ18O, whereas N fertilisation had a major effect on δ15N. The genotypic effect was significant for yield, yield components, δ13C, δ18O and δ15N. Landraces exhibited a higher δ13C and δ15N than cultivars. Phenotypic correlations of δ13C and δ18O with grain yield were negative, suggesting that genotypes able to sustain a higher water use and stomatal conductance were the most productive and best adapted; δ15N was also negatively correlated with grain yield regardless of the growing conditions. δ13C was the best isotopic trait in terms of genetic correlation with yield and heritability, whereas δ18O was the worst of the three isotopic abundances. The physiological basis for the different performance of the three isotopes explaining the genotypic variability in yield is discussed.

Relationships between early vigour, grain yield, leaf structure and stable isotope composition in field grown barley

Abstract Fast growth and early development in barley are used in breeding programmes to improve the water use efficiency and transpiration efficiency of this crop in Mediterranean conditions. Here, we examine the use of several simple traits based on the structure and stable isotope composition of seedling leaves to assess differences in early vigour, phenology and grain yield, and also the interaction with low temperatures in barley. A set of 260 F8 lines of two-row barley (Hordeum vulgare L.) derived from the cross of Tadmor and WI 2291 were cultivated in two locations in northwest Syria. Total chlorophyll content on an area basis (SPAD) and specific leaf dry weight (SLDW) were measured in recently fully expanded intact leaves of seedlings. Total leaf area and total dry weight per seedling were evaluated in the same seedlings. The stable isotope compositions of carbon and nitrogen (δ13C and δ15N, respectively) were analyzed in the same leaves on a subset of 75 genotypes. Number of days from planting to heading and grain yield were recorded at both sites. The grain yield measured at both locations was positively correlated with the SPAD value of seedlings, but showed no relationship with SLDW. Days to heading was negatively correlated with SPAD values. Regarding early vigour, a negative relationship between the SLDW and the total leaf area of seedlings was observed. However, no relationship between the δ13C of seedlings and early vigour was observed, except when only the genotypes most resistant to low temperatures (i.e. showing the highest SPAD values) were considered. This subset of genotypes showed negative relationships between δ13C and either total leaf area or total dry weight. In addition, δ15N was negatively correlated with SPAD only within the high-SPAD genotypes. This suggests that within the genotypes resistant to low temperatures, those with higher chlorophyll content assimilate more nitrogen from nitrate.

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.

Immunocytochemical localization of phosphoenolpyruvate carboxylase and photosynthetic gas-exchange characteristics in ears of Triticum durum Desf.

The presence and distribution of phosphoenolpyruvate carboxylase (PEPCase) in the glumes and immature grains of durum wheat (Triticum durum Desf.) were studied by electron-microscopical immunolabeling of PEPCase with polyclonal antibodies followed by protein A-gold. Plants were grown under mediterranean field conditions and samples were obtained two weeks after anthesis. In the kernels, high gold label was associated with the unstained areas of the protein bodies of aleurone cells, whereas labeling in the cytoplasm and chloroplasts of the pericarp was slight, although significantly above the background. In the glumes, high gold label was only located in cytoplasmic granules (vesicles) of the mesophyll cells, although labeling in the cytoplasm and chloroplasts was also significantly above the background. These observations in immature kernels and glumes are in accordance with the anaplerotic role of this enzyme, as evidenced in C3 plants. Measurements of apparent photosynthesis and its O2 dependence and CO2 compensation concentration were made on ears and flag leaves of durum wheat. In addition, an analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxy-phosphinoylmethyl-2-propenoate, was used to inhibit PEPCase and, thereby, to assess the contribution of the PEPCase to photosynthesis in detached ears. There was no effect of the inhibitor on the apparent photosynthesis of ears. Whereas inhibition of apparent photosynthesis by 210 mL · L−1 O2 in flag leaves was typical of C3 species, inhibition in ears was even greater. The CO2 compensation concentrations in different ear parts were similar to or higher than in flag leaves and the O2 dependence was also comparable (about 70%). Therefore, gas-exchange data give further support to the assumption that a C4 cycle is absent or limited to very low rates in ears of durum wheat.

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.

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.