Abstract
Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao) is a semi-wild hexaploid wheat resource that is only naturally distributed in the Qinghai-Tibet Plateau. Brittle rachis and hard threshing are two important characters of Tibetan semi-wild wheat. A whole-genome linkage map of T. aestivum ssp. tibetanum was constructed using a recombinant inbred line population (Q1028×ZM9023) with 186 lines, 564 diversity array technology markers, and 117 simple sequence repeat markers. Phenotypic data on brittle rachis and threshability, as two quantitative traits, were evaluated on the basis of the number of average spike rachis fragments per spike and percent threshability in 2012 and 2013, respectively. Quantitative trait locus (QTL) mapping performed using inclusive composite interval mapping analysis clearly identified four QTLs for brittle rachis and three QTLs for threshability. However, three loci on 2DS, 2DL, and 5AL showed pleiotropism for brittle rachis and threshability; they respectively explained 5.3%, 18.6%, and 18.6% of phenotypic variation for brittle rachis and 17.4%, 13.2%, and 35.2% of phenotypic variation for threshability. A locus on 3DS showed an independent effect on brittle rachis, which explained 38.7% of the phenotypic variation. The loci on 2DS and 3DS probably represented the effect of Tg and Br1, respectively. The locus on 5AL was in very close proximity to the Q gene, but was different from the predicted q in Tibetan semi-wild wheat. To our knowledge, the locus on 2DL has never been reported in common wheat but was prominent in T. aestivum ssp. tibetanum accession Q1028. It remarkably interacted with the locus on 5AL to affect brittle rachis. Several major loci for brittle rachis and threshability were identified in Tibetan semi-wild wheat, improving the understanding of these two characters and suggesting the occurrence of special evolution in Tibetan semi-wild wheat.
Highlights
Cereal crops, the world’s primary food source, have been domesticated from a diverse array of grass species
The effect of several major genes for brittle rachis and threshability were identified in Tibetan semi-wild wheat by using the inclusive composite interval mapping (ICIM) analysis
Three loci on 2DS, 2DL, and 5A simultaneously controlled brittle rachis and threshability, which could explain the significant correlation between brittle rachis and threshability
Summary
The world’s primary food source, have been domesticated from a diverse array of grass species. Wild wheat shows characteristic traits such as brittle rachis, tough glume, and hard-threshing features, which help the wild species survive and multiply in nature. A major modifier gene for a domestication-related trait (q gene) has been identified on the long arm of chromosome 5A; this gene affects brittle rachis, tough glume, and hard-threshing features [2,3,4,5,6,7,8,9,10,11]. The brittle rachis trait is primarily controlled by Br gene, which was mapped on homoeologous group 3 chromosomes [17,18,19,20,21,22] and chromosome 2A [23]. Unlike Tg, Br is not linked with threshability and showed an independent effect on brittle rachis [23]
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