Date Published: February 27, 2019
Publisher: Public Library of Science
Author(s): Rosa Mérida-García, Guozheng Liu, Sang He, Victoria Gonzalez-Dugo, Gabriel Dorado, Sergio Gálvez, Ignacio Solís, Pablo J. Zarco-Tejada, Jochen C. Reif, Pilar Hernandez, Roberto Papa.
Climatic conditions affect the growth, development and final crop production. As wheat is of paramount importance as a staple crop in the human diet, there is a growing need to study its abiotic stress adaptation through the performance of key breeding traits. New and complementary approaches, such as genome-wide association studies (GWAS) and genomic selection (GS), are used for the dissection of different agronomic traits. The present study focused on the dissection of agronomic and quality traits of interest (initial agronomic score, yield, gluten index, sedimentation index, specific weight, whole grain protein and yellow colour) assessed in a panel of 179 durum wheat lines (Triticum durum Desf.), grown under rainfed conditions in different Mediterranean environments in Southern Spain (Andalusia). The findings show a total of 37 marker-trait associations (MTAs) which affect phenotype expression for three quality traits (specific weight, gluten and sedimentation indexes). MTAs could be mapped on the A and B durum wheat subgenomes (on chromosomes 1A, 1B, 2A, 2B and 3A) through the recently available bread wheat reference assembly (IWGSC RefSeqv1). Two of the MTAs found for quality traits (gluten index and SDS) corresponded to the known Glu-B1 and Glu-A1 loci, for which candidate genes corresponding to high molecular weight glutenin subunits could be located. The GS prediction ability values obtained from the breeding materials analyzed showed promising results for traits as grain protein content, sedimentation and gluten indexes, which can be used in plant breeding programs.
Durum wheat (Triticum durum) is one of the most important crops in the Mediterranean diet. It is mainly grown in the Mediterranean basin (Italy, Turkey, Algeria and Spain, providing 50% of the world’s production [1, 2]) and North America (Canada, Mexico and USA). The genetic dissection of agronomic and quality traits is essential for durum breeding programs. The identification of QTLs related to quality and yield is important as an entry point for marker assisted selection (MAS) . Association mapping (AM) is an integrated analysis to determine genotype-phenotype correlations in a germplasm collection  based on the linkage disequilibrium (LD). AM mapping resolution depends on the number and density of markers , on the ability to correctly measure the target trait and the traits of the population under study, and on an efficient field design . It has been used to dissect several agronomic traits of great importance in bread and durum wheat, such as yield or yield-related traits [7, 8], quality [9, 10], biotic stress resistance [11, 12] and abiotic stress tolerance [13, 14].
Field experiments for the assessment of yield and quality traits under rainfed conditions were carried out at five sites in Southern Spain. These Mediterranean environments present unpredictable water deficit and heat stress during the final stages of wheat development, affecting the mentioned traits. A strong effect of maximum temperatures on yield was observed at final stage (S2A Fig), while thermal sum (GDD) presented a moderate to minor effect (S2B Fig).
Association mapping and genomic selection approaches were applied using the same genotyped and phenotyped collection of experimental lines and varieties of durum wheat. The main aim of AM was to detect specific loci on the wheat genome which were directly related with phenotypic character variations, while GS uses statistical models to predict genomic values for the assessed lines.