CHROMOSOME CONDITIONS IN THE SECOND AND THIRD GENERATIONS OF PENTAPLOID WHEAT HYBRIDS

Abstract

The numbers and mating capabilities of the chromosomes were determined in a good many F₂plants and their offspring in two crosses between common (42-chromosome) wheat and emmer (28-chromosome) types. In general the results confirmed those of Kihara and supported his conclusions. Chromosome numbers were much nearer those of the parental types than was to be expected if all germ cells were capable of functioning and all zygotes of developing. A large number of expected chromosome types did not appear at all. A high percentage of F₂had only 14 bivalent chromosomes and zero to seven univalents. These tended to revert rapidly to the 14-bivalent condition of emmers. F₃in this group did not have more than 14 bivalents nor more univalents than their F₂parents. A chromosome formula for all of the group of F₂with more than 14 bivalents may be written (14+x) bivalents +(7−x) univalents. Thesetended to revert to the 21-bivalent condition of common wheat. F₃in this group did not have fewer bivalents nor more univalents than their F₂parents. Occasional plants were exceptions to these rules.