Linkage between the centromere and a gene producing nucleocytoplasmic compatibility in durum wheat

Species cytoplasm specific (scs) genes on chromosome 1A (1A(scs)) derived from Triticum timopheevii Zhuk. and chromosome 1D (1D(scs)) derived from common wheat improve compatibility between the durum wheat (T. turgidum L. var. durum) nucleus and Aegilops longissima S. and M. (lo) cytoplasm. The (lo) scs durum lines thus produced are male sterile and when crossed with durum produce viable plump seeds carrying scs and inviable shriveled seeds without scs. Objectives of the present study were to determine centromere-scs linkage distances and viability and transmission of female gametes carrying one or both scs genes. The (lo) scs durum heterozygous for 1A/1A(scs) was crossed with the Langdon (LDN) durum disomic substitution line 1D(scs)(1A) in which the 1A chromosome pair is substituted by a 1D(scs) pair. Two types of 1A + 1D double monosomic F₁s were recovered, (lo) durum 13'' + 1'1A(scs) + 1'1D(scs), and (lo) durum 13'' + 1'1A + 1'1D(scs), which were confirmed in progeny tests with normal durum. For centromere mapping, these lines were crossed with LDN double ditelosomic 1A (LDN dDt 1A; 2n = 30; 13'' + t''1AS + t₁AL) and progeny examined for meiotic chromosome constitution. No telocentric t1AL(scs) arising from recombination with 1A(scs) was detected, indicating that scs is tightly linked to the centromere on chromosome 1A. To determine the transmission of female gametes carrying one or both scs genes, (lo) durum 13'' + 1'1A(scs) + 1'1D(scs) was crossed with LDN dDt 1A and control durum. The functional female gametes carried one or both scs genes. Crosses of (lo) durum 13'' + 1'1A + 1'1D(scs) to LDN dDt 1A produced several plants with a T1AL.1DL translocation chromosome. The formation of this chromosome was coupled with strong selection for the scs gene on 1DL.