Abstract
Representative, broad and diverse collections are a primary resource to dissect genetic diversity and meet pre-breeding and breeding goals through the identification of beneficial alleles for target traits. From 2,500 tetraploid wheat accessions obtained through an international collaborative effort, a Global Durum wheat Panel (GDP) of 1,011 genotypes was assembled that captured 94–97% of the original diversity. The GDP consists of a wide representation of Triticum turgidum ssp. durum modern germplasm and landraces, along with a selection of emmer and primitive tetraploid wheats to maximize diversity. GDP accessions were genotyped using the wheat iSelect 90K SNP array. Among modern durum accessions, breeding programs from Italy, France and Central Asia provided the highest level of genetic diversity, with only a moderate decrease in genetic diversity observed across nearly 50 years of breeding (1970–2018). Further, the breeding programs from Europe had the largest sets of unique alleles. LD was lower in the landraces (0.4 Mbp) than in modern germplasm (1.8 Mbp) at r2 = 0.5. ADMIXTURE analysis of modern germplasm defined a minimum of 13 distinct genetic clusters (k), which could be traced to the breeding program of origin. Chromosome regions putatively subjected to strong selection pressure were identified from fixation index (Fst) and diversity reduction index (DRI) metrics in pairwise comparisons among decades of release and breeding programs. Clusters of putative selection sweeps (PSW) were identified as co-localized with major loci controlling phenology (Ppd and Vrn), plant height (Rht) and quality (gliadins and glutenins), underlining the role of the corresponding genes as driving elements in modern breeding. Public seed availability and deep genetic characterization of the GDP make this collection a unique and ideal resource to identify and map useful genetic diversity at loci of interest to any breeding program.
Highlights
Durum wheat [Triticum turgidum L. ssp. durum (Desf.) Husn.] is the 10th most important crop worldwide with an annual production of over 40 million tons (Sall et al, 2019)
Three distinct phases can be identified in the human-driven tetraploid wheat evolution process: (i) domestication, (ii) continued evolution under domestication and (iii) improvements achieved by modern breeding (Maccaferri et al, 2019)
The limited number of landraces that were used as founder lines of the modern gene pool and the “best × best” strategy traditionally used by breeders to drive the genetic gain (Hoisington et al, 1999; Maccaferri et al, 2003; van Ginkel and Ortiz, 2018) are the two main causes of this phenomenon
Summary
Durum wheat [Triticum turgidum L. ssp. durum (Desf.) Husn.] is the 10th most important crop worldwide with an annual production of over 40 million tons (Sall et al, 2019). Genetic erosion of the durum wheat cultivated gene-pool in comparison with wild relatives and landraces has been reported, analogously to other crop species (Tanksley and McCouch, 1997; Gur and Zamir, 2004; Raman et al, 2010; Royo et al, 2010; Laidò et al, 2013; Kabbaj et al, 2017; Maccaferri et al, 2019), and it represents a real concern for breeders as it might lead to a lack of novel beneficial alleles for selection, yield stagnation, and/or increased susceptibility to biotic and abiotic stresses. Germplasm collections have been characterized with the Illumina iSelect 90K SNP (Maccaferri et al, 2016; Mangini et al, 2018; Saccomanno et al, 2018) and
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