Dormancy in white-grain mutants of Chinese Spring wheat (Triticum aestivumL.)

Red wheats (Triticum aestivum L.) are generally more dormant and sprout res istant than white wheats. Whether this is caused by pleiotropic effects of the red grain colour genes (R) on dormancy and coat colour, or to tight lin kage between R and dormancy genes has not been fully resolved. To directly determine the effect of the R1 allele on dormancy, mutations were induced w ith sodium azide in a pure line selection of the red genotype (R1R1r2r2r3r3 ) Chinese Spring wheat. Two white mutants (CSW01, CSW02) were recovered fro m M-3 caryopses derived from approximately 20,000 M-2 plants. Both mutants were shown to be allelic to a domestic white genotype (r1r1r2r2r3r3). Excep t for seed coat colour, CSW01 and CSW02 are morphologically indistinguishab le from the wild type and are presumed to be near isogenic lines of Chinese Spring. Freshly harvested grains produced under four different environment s were evaluated for post-harvest dormancy. In all environments, intact car yopses of all three isolines exhibited high temperature dormancy typical of cereal species, although the red wild type consistently exhibited greater dormancy than the white mutant isolines. Dormancy was dissipated by afterri pening in dry storage at 37 degrees C in a similar manner for the red and w hite isolines. Excised embryos of the three isolines exhibited similar leve ls of dormancy and sensitivities to exogenous abscisic acid. These results indicate a functional R1 allele is not absolutely required for dormancy in wheat, but does enhance its expression in caryopses with dormant (sensitive ) embryos.