Chromosome elimination of hexaploid common wheat mediated by interaction between Chinese Spring cytoplasm and a genetic factor(s) on chromosome arm 1BL of wild emmer

To create recombinant substitution lines from chromosome arm substitution lines (CASLs) of wild emmer, the common wheat cultivar ‘Bethlehem’ (BLH) was crossed with 4 CASLs of group 1 and the resulting F 1 s were backcrossed with corresponding BLH ditelosomic (DT) lines to produce monotelosomic plants (BC 1 F 1, 2n = 6x = 41 + t). For each cross combination, about 100 BC 1 F 2 plants derived from 47 to 49 BC 1 F 1 plants were analyzed for their chromosome number and constitution. The frequencies of plants with 42 or 41 + t chromosomes in [DT1BS × (BLH × CASL1BL)] progenies were much lower than in crosses involving CASLs 1AS, 1AL and 1BS; while the frequency of [DT1BS × (BLH × CASL1BL)] progeny plants with 41 chromosomes was high. A total of 49 (BLH × CASL1BL) BC 1 F 1 plants could be clearly classified into three types based on chromosome constitution of their 461 BC 1 F 2 progenies. In type I (21 BC 1 F 1 plants), 95 % of BC 1 F 2 plants possessed 42 chromosomes (counting the telosomic chromosome as an entire chromosome). In type III (24 BC 1 F 1 plants), most BC 1 F 2 plants (75.6 %) had 41 chromosomes and no telosomic chromosome. In type II (4 BC 1 F 1 plants), the expected number of ~48 % of BC 1 F 2 plants had the telosomic chromosome, but about 70 % had fewer than the expected 42 chromosomes. All type III BC 1 F 1 plants were confirmed to have experienced elimination of telosomic chromosome 1BS. Observation of BC 1 F 1 seedling mitosis revealed that the elimination of 1BS occurred most probably during embryogenesis. However, type II BC 1 F 1 plants experienced the elimination of different chromosomes, which was deduced to occur during meiosis. Reciprocal crosses indicated that both types of chromosome elimination occurred only when BLH DT1BS, which has Chinese Spring cytoplasm, was used as female parent. Collectively, these results reveal a genetic system on chromosome arm 1BL of wild emmer that interacts with the CS cytoplasm to cause chromosome elimination.