QTL Mapping and Candidate Gene Analysis for Wax Trait of Stem and Leaf in Durum Wheat (Triticum turgidum L. ssp. durum (Desf.))

The waxy cuticle on plant surfaces, comprising a cutin polymer matrix and complex very long chain fatty acids, figure in protective barrier against water loss and environmental damage. In this study, we employed a F₂ population (comprising of 237 individual plants) constructed by the crossing of HX128 (female parent without cuticular wax) with HX027 (male parent with significant cuticular wax). Two extreme phenotypic bulks were constructed according to the variation of wax trait in F₂ population, and bulked segregant RNA-seq (BSR-seq) was implemented to decipher the molecular underpinnings of waxiness trait in durum wheat. The QTL related to waxiness was mapped between 0.8 and 23.4 Mb on chromosome 2B. According to the differential sequence information of target interval between the parents, polymorphic primers were designed to screen F₂ population. The QTL of waxiness trait was further narrowed down between 6.8 and 10.1 Mb using the composite interval mapping tool. The LOD value was 129.53, with phenotypic variance explained (PVE) up to 44.65%. The annotation and expression analysis of the genes in the QTL region entailed selection of 15 potential candidate genes. Among which, eleven new genes with four previously reported genes were found that seem to be a gene cluster mediating wax synthesis at W1 loci. This study provides important insights into fine mapping and cloning of genes involved in wax synthesis with improved efficacy.