Development of an integrated linkage map of einkorn wheat and its application for QTL mapping and genome sequence anchoring
In temperate grasses, such as wheat (Triticum sp.) and barley (Hordeum vulgare L.), earliness per se (eps) is defined as the intrinsic difference in flowering time of fully vernalized plants grown under long day conditions. The main task of our investigations was to confirm and refine the chromosomal position of the previously mapped Eps-3A m locus in einkorn wheat (Shindo et al. in Genome 45:563–569, 2002; Hori et al. in Breed Sci 57:39–45, 2007). To this end, 110 recombinant inbred lines (RILs) were phenotypically and genotypically evaluated. The population had been obtained from a cross between an early flowering X-ray mutant KT3-5 (T. monococcum L.) of cultivated spring type and a wild wheat line KT1-1 of T. boeoticum Boiss. (winter type). Heading time evaluations under greenhouse conditions resulted in a 10-day difference (P = 0.008) between the mapping parents and a range of 49 days for the RIL population. Quantitative trait locus analyses of heading time, anthesis time, spikelet number and spike length showed the best linkage with marker loci close to the telomeric region of the long arm of chromosome 3A. The highest LOD values for heading time, anthesis time, spikelet number and spike length were 5.96, 5.40, 3.33 and 5.10, respectively (LOD threshold 2.0, P < 0.05). Linkage analysis of 51 molecular markers delimited the new Eps-3A m interval to 0.9 cM, including 14 newly developed markers using collinearity with rice (Oryza sativa L.) and Brachypodium distachyon L. The present study marks a further step towards the molecular elucidation and functional analysis of Eps-3A m in wheat and other small grain cereals.