The stripe or yellow rust (YR) disease, caused by Puccinia striiformis f. sp. tritici (Pst), severely threatens grain yield of durum wheat. Unusual and severe epidemics of YR were observed on several continents in the last years, as a consequence of climate changes. Urgent is the exploration of new genetic variability to discover novel resistance genes in both modern durum wheat cultivars and its wild progenitor (T. dicoccoides) which is known to carry useful alleles for several traits. This search of novel sources of resistance to YR has been carried out through genome wide association mapping (GWAS) and QTL analysis. In the first case, a wide collection of wild emmer accessions of 285 lines, genotyped using the Axiom 35k array, has been evaluated at plantlet stage for reaction to three YR isolates (Pstv14, Pstv37, Pstv40), and in open field in Southern Italy for two years in natural infection conditions. A similar field evaluation has been carried out for the RIL population derived from the cross between the two modern durum wheat cv. Cirillo and Neodur (150 lines). The GWAS and QTL analysis identified a number of resistance loci widespread through the genome. Some of them were of particular interest, as an example, a QTL mapped to chromosome 1B explained resistance in both controlled and field conditions, and QTLs mapped to chromosome 1A, 1B and 5A were involved in the reaction to two or three YR races in the wild emmer wheat collection. QTLs on chromosomes 2B, 6B and 7B were identified in the Cirillo x Neodur segregating population. These QTLs were projected onto the durum reference genome (cv Svevo) thus evidencing the overlapping with known genes as well as novel resistance loci. The QTLs were also projected to the wild emmer (Zavitan) and durum wheat (Svevo) reference genomes to identify putative candidate genes. Resistant loci identified in durum wheat RIL populations can be easily transferred to other elite cultivars, while genes for resistance carried by wild emmer wheat are useful in prebreeding programs for their introgression in cultivars of interest.
This study was supported by the Italian Ministry of Foreign Affairs and International Cooperation, with the special grant RES-WHEAT.
