Detailed Mapping of the Species Cytoplasm-Specific (scs) Gene in Durum Wheat

The compatibility-inducing action of the scsti (species cytoplasm-specific gene derived from Triticum timopheevii) and Vi (vitality) genes can be observed when a durum (T. turgidum) nucleus is placed in T. longissimum cytoplasm. These two genes restore compatibility between an otherwise incompatible nucleus and cytoplasm. The objective of this study was to localize the scsti gene on a linkage map of chromosome 1A, which could eventually be used to clone the gene. The mapping population consisted of 110 F2 individuals derived from crossing a Langdon-T. dicoccoides chromosome 1A substitution line with a euplasmic (normal cytoplasm) line homozygous for the scsti gene. Through a series of testcrosses the genotypes of the 110 individuals were determined: 22 had two copies, 59 had one copy, and 29 had no copy of the scsti gene. Data from RFLP, AFLP, and microsatellite analysis were used to create a linkage map. The flanking marker loci found for the scsti gene were Xbcd12 and Xbcd1449-1A.2 with distances of 2.3 and 0.6 cM, respectively. Nearly 10% of individuals in this population were double recombinant for a genetic interval of <3 cM. A blistering phenotype reminiscent of the phenotype observed in maize brittle-1 mutable was also evident in these individuals. The higher frequency of double recombination within this region and seed-blistering phenotype could be an indication of a transposable element(s) in this locus.