A strategy for enhancing recombination in proximal regions of chromosomes.

As a rule, recombination in bread wheat (Triticum aestivum L.) is low in proximal and high in distal regions of chromosomes. Recombination may be enhanced in proximal regions by using deletion (del) chromosomes deficient for a distal part of a chromosome arm. The chromosome del5BL-11 derived from Chinese Spring (CS) is missing 41% of the distal long arm. This line was made polymorphic by crossing with a stock in which chromosome 5B of CS (5B(CS)) is substituted for chromosome 5B of T. turgidum ssp. dicoccoides origin (5B(T.dic)). Three recombinant del5BL-11 (del5BL-11(rec)) lines were isolated, all resulting from localized recombination between loci Xbcd926 and XksuH1. In del5BL-11(rec), the centromere to fraction length (FL) 0.53 (C-FL0.53) segment is derived from 5B(T. dic) and the distal region of FL 0.55-0.59 is from 5B(CS). Genetic recombination for the C-FL 0.53 interval was assayed in segregating progenies from 5B(CS)/5B(T.dic) and del5BL-11/del5BL-11(rec) crosses using polymorphic markers and for the FL 0.55-0.59 interval in del5BL-11/del5BL-11(rec) cross from chiasma counts. The pairing data and comparative mapping of normal 5B and del5BL-11 indicated that the increase in recombination was restricted to the FL 0.55-0.59 interval of the del5BL-11 chromosome. No significant increase in recombination in more proximal regions was observed although the order of several markers that cosegregated in the normal 5B map was resolved in the del5BL-11 map. The presented data show that recombination in proximal, usually low-recombination, regions can be increased by placing them close to the chromosome end.