Genetic analysis of a grass dwarf mutation induced by wheat callus culture.

Genetic variation induced by passage through tissue culture (somaclonal variation) has been characterized for many agronomic traits of wheat. The study presented here was conducted to genetically and phenotypically characterize a mutation influencing plant height that was induced by wheat callus culture. Dwarf plants were identified in the progeny of a tall plant regenerated from immature embryo-derived callus tissue of the hard red winter wheat 'TAM 105'. The dwarfs are significantly shorter, later in heading, and have a greater number of tillers, fewer seeds per spike, lower grain yield per plant, and lower floret fertility than 'TAM 105'. The dwarfs also exhibit branching at the aerial nodes when grown under cool temperatures (<20°C) and short daylengths (<12h). We hypothesize that a single, partially dominant gene which acts in a complementary manner with the grass-dwarf gene D1 is responsible for this phenotype. Based on phenotype and the dominance relationship between mutant and wild-type alleles, we hypothesize that the mutation is a new allele at either the D2 or D4 grass-dwarfism locus. The utilization of genotypes lacking any of the grass-dwarfism alleles would greatly reduce the chance of recovering these undesirable genotypes by mutations arising during tissue culture. It is also important to recognize the grass-dwarf phenotype. If transgenic plants, somatic hybrids, or regenerants from in vitro selection strategies have a grass-dwarf phenotype, they can be induced to enter reproductive development by long daylengths (>14 h) and high temperatures (>26°C).