Genetic basis of variation for root traits and response to heat stress in durum wheat

Durum wheat is the second most important wheat species worldwide and the most important crop in several Mediterranean countries including Italy. Durum wheat is primarily grown under rainfed conditions where episodes of drought and heat stress are major factors limiting grain yield. The research presented in this thesis aimed at the identification of traits and genes that underlie root system architecture (RSA) and tolerance to heat stress in durum wheat, in order to eventually contribute to the genetic improvement of this species. In the first two experiments we aimed at the identification of QTLs for root trait architecture at the seedling level by studying a bi-parental population of 176 recombinant inbred lines (from the cross Meridiano x Claudio) and a collection of 183 durum elite accessions. Forty-eight novel QTLs for RSA traits were identified in each of the two experiments, by means of linkage- and association mapping-based QTL analysis, respectively. Important QTLs controlling the angle of root growth in the seedling were identified. In a third experiment, we investigated the phenotypic variation of root anatomical traits by means of microscope-based analysis of root cross sections in 10 elite durum cultivars. The results showed the presence of sizeable genetic variation in aerenchyma-related traits, prompting for additional studies aimed at mapping the QTLs governing such variation and to test the role of aerenchyma in the adaptive response to abiotic stresses. In the fourth experiment, an association mapping experiment for cell membrane stability at the seedling stage (as a proxy trait for heat tolerance) was carried out by means of association mapping. A total of 34 QTLs (including five major ones), were detected. Our study provides information on QTLs for root architecture and heat tolerance which could potentially be considered in durum wheat breeding programs

Prioritizing quantitative trait loci for root system architecture in tetraploid wheat

Optimization of root system architecture (RSA) traits is an important objective for modern wheat breeding. Linkage and association mapping for RSA in two recombinant inbred line populations and one association mapping panel of 183 elite durum wheat (Triticum turgidum L. var. durum Desf.) accessions evaluated as seedlings grown on filter paper/polycarbonate screening plates revealed 20 clusters of quantitative trait loci (QTLs) for root length and number, as well as 30 QTLs for root growth angle (RGA). Divergent RGA phenotypes observed by seminal root screening were validated by root phenotyping of field-grown adult plants. QTLs were mapped on a high-density tetraploid consensus map based on transcript-Associated Illumina 90K single nucleotide polymorphisms (SNPs) developed for bread and durum wheat, thus allowing for an accurate cross-referencing of RSA QTLs between durum and bread wheat. Among the main QTL clusters for root length and number highlighted in this study, 15 overlapped with QTLs for multiple RSA traits reported in bread wheat, while out of 30 QTLs for RGA, only six showed co-location with previously reported QTLs in wheat. Based on their relative additive effects/significance, allelic distribution in the association mapping panel, and co-location with QTLs for grain weight and grain yield, the RSA QTLs have been prioritized in terms of breeding value. Three major QTL clusters for root length and number (RSA-QTL-cluster-5#, RSA-QTL-cluster-6#, and RSA-QTL-cluster-12#) and nine RGA QTL clusters (QRGA.ubo-2A.1, QRGA.ubo-2A.3, QRGA.ubo-2B.2/2B.3, QRGA.ubo-4B.4, QRGA.ubo-6A.1, QRGA.ubo-6A.2, QRGA.ubo-7A.1, QRGA.ubo-7A.2, and QRGA.ubo-7B) appear particularly valuable for further characterization towards a possible implementation of breeding applications in marker-Assisted selection and/or cloning of the causal genes underlying the QTLs

International Journal of Farming and Allied Sciences The effects of water deficit stress on seed yield and quantitative traits of Canola cultivars

ABSTRACT: Concerning the importance of oilseeds cultivation, especially canola in addition to the growing trend of its cultivated land and limited water resources in the world, this experiment was undertaken in split plot based on randomized complete block design (RCBD) with four replications in order to evaluate the effects of the water deficit stress on seed yield and quantitative traits of canola cultivars to determine the tolerant and sensitive cultivars. The main plots included two canola cultivars (RGS003 and Sarigol) and sub plots were five irrigation levels including; I 1 , irrigation during full season (control); I 2 , water deficit stress in stemming stage; I 3 , water deficit stress in budding stage; I 4 , water deficit stress in flowering stage and I 5 , water deficit stress in ripening stage. Mentioned treatments were selected in order to evaluate the canola relative resistance to water deficiency in these stages. During conducting the experiment, important traits of canola cultivars were measured including plant height, number of branches per plant, number of siliqua per plant, seed yield and volume of the consumed water in all irrigation treatments for both Sarigol and RGSoo3 cultivars. The highest water consumption efficiency was obtained for the cv. RGS003 and from water deficit stress treatment in ripening stage that was 0.682 ha -1 , while the least water consumption efficiency rate was 0.482 ha -1 for the cv. Sarigol and from water deficit stress in flowering stage. The interaction effect of irrigation and canola cultivars indicated that the most seed yield reduction from water deficit stress was in budding stage and for cv. Sarigol was 2858 kg ha -1 . So, the overall performance of the cultivars for seed yield indicates that under water deficit stress, the cv. RGS003 is superior to other cultivar. Hence, it can withstand low levels of water regimes

Genetic variation for aerenchyma and other root anatomical traits in durum wheat (Triticum durum Desf.)

Variation in root anatomical traits influences whole plant physiology and crop adaptation to adverse soil conditions and thus impacts yield and its stability. A typical component of anatomical root traits is the arrangement of cells and tissues as observed by microscopy sections. In this study, we investigated the phenotypic variation of 11 root anatomical traits including aerenchyma-like features in ten elite durum wheat cultivars and found significant differences among cultivars for several traits. Trait heritability ranged from 0.12 (number of xylem vessels) to 0.72 (number of aerenchyma-like lacunae). While area and number of aerenchyma-like lacunae were highly correlated, neither trait correlated with other root features, suggesting an independent physiological and/or genetic control in respect to the other root anatomical traits. The old Italian founder cultivar Cappelli was shown to have a significantly higher portion of root aerenchyma-like structures of all the modern cultivars. These results show for the first time the presence of sizeable genetic variation in root anatomical traits in cultivated tetraploid wheats, prompting for additional studies aimed at mapping the quantitative trait loci governing such variation and to test their role in the adaptive response of durum wheat to abiotic stresses as related to soil conditions

Prioritizing quantitative trait loci for root system architecture in tetraploid wheat

Optimization of root system architecture (RSA) traits is an important objective for modern wheat breeding. Linkage and association mapping for RSA in two recombinant inbred line populations and one association mapping panel of 183 elite durum wheat (Triticum turgidum L. var. durum Desf.) accessions evaluated as seedlings grown on filter paper/polycarbonate screening plates revealed 20 clusters of quantitative trait loci (QTLs) for root length and number, as well as 30 QTLs for root growth angle (RGA). Divergent RGA phenotypes observed by seminal root screening were validated by root phenotyping of field-grown adult plants. QTLs were mapped on a high-density tetraploid consensus map based on transcript-associated Illumina 90K single nucleotide polymorphisms (SNPs) developed for bread and durum wheat, thus allowing for an accurate cross-referencing of RSA QTLs between durum and bread wheat. Among the main QTL clusters for root length and number highlighted in this study, 15 overlapped with QTLs for multiple RSA traits reported in bread wheat, while out of 30 QTLs for RGA, only six showed co-location with previously reported QTLs in wheat. Based on their relative additive effects/significance, allelic distribution in the association mapping panel, and co-location with QTLs for grain weight and grain yield, the RSA QTLs have been prioritized in terms of breeding value. Three major QTL clusters for root length and number (RSA_QTL_cluster_5#, RSA_QTL_cluster_6#, and RSA_QTL_cluster_12#) and nine RGA QTL clusters (QRGA.ubo-2A.1, QRGA.ubo-2A.3, QRGA.ubo-2B.2/2B.3, QRGA.ubo-4B.4, QRGA.ubo-6A.1, QRGA.ubo-6A.2, QRGA.ubo-7A.1, QRGA.ubo-7A.2, and QRGA.ubo-7B) appear particularly valuable for further characterization towards a possible implementation of breeding applications in marker-assisted selection and/or cloning of the causal genes underlying the QTLs