Cytogenetic Analysis of the Basis of Tall Off-Types in Semi-Dwarf Spring Wheat (Triticum aestivum)

Wheat, one of the most important food crops in the world, is an allohexaploid (2n = 6x = 42), and thus a large genome having 16x10⁹ base pairs per chromosome. It is estimated that more than 80% of this is repetitive DNA. The crop is relatively tolerant to aneuploidy, a condition that may result in off-types within populations. We are evaluating the cause of tall mutants that arise naturally in the semi-dwarf spring wheat cultivar ‘Rollag’ using cytogenetic-based approaches. Our working hypothesis is that the tall off-types are aneuploids. We are using chromosome squashes to evaluate semi-dwarf spring wheat population of the Rollag background in an effort to assess the ploidy level of the tall off-type genotypes.  All the genotypes evaluated thus far, except RT7-2-4, had 2n=42 chromosomes. The genotype RT7-2-4 had 2n=43 chromosomes. The additional chromosome in this genotype was acrocentric and appeared to be rearranged, possibly a deletion. Work is underway to evaluate the progenies of RT7-2-4 in an effort to determine the segregation pattern. We anticipate that a chromosome present in a single copy remains univalent during meiosis and is only transmitted to about 25% of the offspring. This work, ultimately, will bring us closer towards formulating a solution to issues that may arise in seed certification and farmers acceptance of new cultivars. Funding: USDA-NIFA Triticeae Coordinated Agricultural Project