Abstract
A panel of 172 Mediterranean durum wheat landraces and 200 modern cultivars was phenotyped during three years for 21 agronomic and physiological traits and genotyped with 46,161 DArTseq markers. Modern cultivars showed greater yield, number of grains per spike (NGS) and harvest index (HI), but similar number of spikes per unit area (NS) and grain weight than the landraces. Modern cultivars had earlier heading but longer heading-anthesis and grain-filling periods than the landraces. They had greater RUE (Radiation Use Efficiency) up to anthesis and lower canopy temperature at anthesis than the landraces, but the opposite was true during the grain-filling period. Landraces produced more biomass at both anthesis and maturity. The 120 genotypes with a membership coefficient q > 0.8 to the five genetic subpopulations (SP) that structured the panel were related with the geographic distribution and evolutionary history of durum wheat. SP1 included landraces from eastern countries, the domestication region of the “Fertile Crescent.” SP2 and SP3 consisted of landraces from the north and the south Mediterranean shores, where durum wheat spread during its migration westward. Decreases in NS, grain-filling duration and HI, but increases in early soil coverage, days to heading, biomass at anthesis, grain-filling rate, plant height and peduncle length occurred during this migration. SP4 grouped modern cultivars gathering the CIMMYT/ICARDA genetic background, and SP5 contained modern north-American cultivars. SP4 was agronomically distant from the landraces, but SP5 was genetically and agronomically close to SP1. GWAS identified 2,046 marker-trait associations (MTA) and 144 QTL hotspots integrating 1,927 MTAs. Thirty-nine haplotype blocks (HB) with allelic differences among SPs and associated with 16 agronomic traits were identified within 13 QTL hotspots. Alleles in chromosomes 5A and 7A detected in landraces were associated with decreased yield. The late heading and short grain-filling period of SP2 and SP3 were associated with a hotspot on chromosome 7B. The heavy grains of SP3 were associated with hotspots on chromosomes 2A and 7A. The greater NGS and HI of modern cultivars were associated with allelic variants on chromosome 7A. A hotspot on chromosome 3A was associated with the high NGS, earliness and short stature of SP4.
Highlights
Durum wheat (Triticum turgidum ssp. durum) is an important cereal crop grown on around 17 million ha worldwide with a global production of 33.6 million tons in 2020
The combination of natural selection for traits that augment fitness to the diverse agro-ecological zones existing within the Mediterranean Basin (Cleveland and Soleri, 2007), and farmer-mediated selection for traits deemed of interest resulted in the local establishment of landraces
SP5 included 16 modern cultivars, 15 of them from USA and Canada and the French cultivar “Auroc” (q = 0.949), which is very likely genetically related with the north-American germplasm pool. These results revealed a different origin for each subpopulation i.e., SP1, SP2, and SP3 containing landraces from eastern, northern and western Mediterranean countries, respectively, SP4 grouping modern cultivars derived from the international centers CIMMYT and ICARDA, and SP5 grouping modern northAmerican cultivars (Figure 2)
Summary
Durum wheat (Triticum turgidum ssp. durum) is an important cereal crop grown on around 17 million ha worldwide with a global production of 33.6 million tons in 2020 (http://www. agr.gc.ca/eng/industry-markets-and-trade/canadian-agrifood-sector-intelligence/crops/reports-and-statistics-datafor-canadian-principal-field-crops/?id=1378743094676). Wheat was domesticated ∼10,000 years BP in the mountainous areas of southwest Asia and Iran, Turkey, Syria, Lebanon, Israel, Palestine and Jordan, in the region often referred to as the “Fertile Crescent” (Vavilov, 1951; Harlan, 1992). From this area, wheat spread to the west of the Mediterranean Basin about 3,000 years ago to reach the Iberian Peninsula (Feldman, 2001; MacKey, 2005). Mediterranean landraces hold a rich genetic diversity for many traits, including for those which are considered economically important in today’s agricultural production systems, which makes them invaluable sources of biodiversity within the species (Nazco et al, 2012; Lopes et al, 2015)
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