CHROMOSOME NUMBER AND BEHAVIOUR IN A PLANT BREEDER'S SAMPLE OF PENTAPLOID WHEAT HYBRID DERIVATIVES

Abstract

Meiosis was studied in Triticum vulgare vars. Marquis, Marquillo, Hope, and R.L. 729, in T. durum var. Iumillo, and in 336 rust resistant selections from their pentaploid hybrids. R.L. 729 contains some plants that are unstable cytologically. In the fifth to seventh generation material, in fifty lines that had been subjected to rigorous selection, plants were found with 28, 38, 39, 40, 41, 42, and 43 chromosomes. Less than 42% of the plants had 42 chromosomes—the Vulgare number.Fifty per cent of the plants were heterozygous for the arrangement of one or more chromosome segments. The chromosome aberrations detected were, in order of frequency: inversions, translocations, deficiencies, and duplications. All types of aberration were transmitted from F₇to F₈in some cases. One chromosome deficient for a complete arm arose from an isochromosome, and one isochromosome arose from a chromosome deficient for a complete arm.The incidence of natural crossing in the aberrant plants is much higher than in normal wheats.It is suggested (1) that plant breeders use as parents only those plants known to be stable cytologically; (2) that a more intensive cytological analysis of hybrid derivatives would be invaluable to the plant breeder; and (3) that the plant breeder should not overlook hybrid derivatives with specific chromosome rearrangements since such plants may be the means of breaking the linkage between "desirable" and "undesirable" genes.