Heterochromatin, aberrant endosperm nuclei and grain shrivelling in wheat-rye genotypes

Abstract

Evidence is presented leading to the conclusion that there is, in wheat-rye genotypes, a causal link first, between the presence of late replicating segments of heterochromatin on rye chromosomes and the occurrence of chromosome bridges at anaphase and of other aberrant nuclei in coenocytic endosperm, and second, between the frequency of occurrence of aberrant nuclei in young endosperms and the degree of grain shrivelling at maturity. Bridges in coenocytic endosperm of wheat-rye genotypes are caused at anaphase by the failure of rye chromosomes to separate at the telomeres where late replicating DNA is known to be located. The frequency of occurrence of aberrant nuclei in endosperms of the seven disomic chromosome addition lines of King II rye to Holdfast wheat fixed at the end of the coenocytic stage is significantly lower in three addition lines lacking a large telomeric block of terminal heterochromatin on one arm (due to its deletion) than in the remaining four addition lines without deletions of terminal heterochromatin. Evidence is presented showing a significant positive correlation between the proportion of aberrant nuclei in endosperms of six hexaploid triticales during the first 4 days after pollination, and the degree of grain shrivelling scored at maturity. It is concluded that the reduction or elimination of segments of late replicating DNA from rye chromosomes should be a major object in the breeding of economically useful triticales, and the means of achieving this goal are discussed.