Identification of genetic factors governing drought tolerance in wild and domesticated tetraploid wheat

Germplasm characterization and gene identification are essential first steps in developing drought-resilient cultivars. Evaluation of diverse tetraploid wheat accessions representing cultivated and wild species under severe drought stress using an in-house protocol identified three extremely tolerant genotypes including the CIMMYT-bred durum (Triticum turgidum ssp. durum) variety Altar 84 and the two wild emmer (T. turgidum ssp. dicoccoides) accessions PI 478742 and PI 481521. Chromosome substitution lines involving individual pairs of chromosomes from PI 478742 and PI 481521 substituted for homologous pairs of chromosomes in drought sensitive durum variety Langdon 16 were evaluated to identify chromosome(s) carrying loci controlling drought tolerance. The 11 chromosome substitution lines available for PI 478742 (2A, 3A, and 3B substitution lines were not available) were all sensitive to drought suggesting tolerance may be conferred by a locus on one of the chromosomes not evaluated. All 14 possible chromosome substitution lines were available for PI 481521, and among these, 13 were drought sensitive. The substitution line involving chromosome 3A (LDN-DIC 3A(521)) was tolerant to drought. QTL mapping in a durum inter-varietal population of 138 recombinant inbred lines (RILs) derived by crossing Altar 84 and Langdon 16 identified a major QTL on the short arm of chromosome 4B explaining 26% of phenotypic variation (PVE). This QTL spans large physical region of approximately 265.52 Mb in the Svevo RefSeq v1.0 genome. Sequence analysis of TRITD4Bv1G024340, an orthologue of drought tolerance gene (TaWD40-4B.1) cloned and previously reported from same genomic region in hexaploid wheat, suggested that QTL identified in this study in Altar 84 is governed by a different genomic region. Additionally, two drought tolerance regions identified (on chromosome 3A and 4BS) in this study are two independent QTLs originated from different sources, and hence they might have different genetic tolerance mechanism. Drought tolerant lines and the genomic regions identified in this study serve as valuable resources for developing drought-resilient durum wheat varieties.