II.3 Rye dwarf gene introgression into barley.
L.S. Bates*, K.A. Mujeeb*, R. Rodriguez R.+, and R.F. Waters*. *Department of Grain Science and Industry, Kansas State University, Manhattan, Kansas 66506. +International Maize and Wheat Improvement Center, Apdo. Postal 6-641, Mexico 6, D.F. "R"
An intergeneric Hordeum vulgare (var. CM 67) x Secale cereale (dwarf cultivar Snoopy) cross and progeny through F5 have been studied to determine if the dwarf progeny were the result of introgressive hybridization or other factors. The cross was made by the chemical suppression technique of Bates et al. (1974) and is believed subsequently to involve chromosome elimination and spontaneous somatic doubling of the resultant haploid. Because illegitimate fertilization by a dwarf rye or because mutation of the maternal barley parent produces dwarfness, those events had to be excluded as possibilities through field observations and controlled laboratory experiments.
Illegitimate outcrossing by barley or other species can be excluded because we have observed segregation for plant height only. The dwarfs are nearly identical copies of the normal six-rowed CM 67 maternal parent. The progeny differences are constant and include a shorter flag leaf and average 12 fewer florets per spike than CM 67. Extensive phenotypic variation would be expected in the progeny from mating CM 67 with dwarf barley or any other compatible species.
Mutation also can be excluded for several reasons: 1) We have been unable to induce dwarf or chlorophyll mutants with the chemical suppressants by M3 in controlled field experiments, hydroponics, or seed treatments. We found no cytological abnormalities in mitosis or meiosis under the same conditions. 2) A wheat (6x) x Snoopy rye cross with presumably similar chromosome elimination and somatic doubling in Fl also produced dwarf progeny by F3 and further dwarfs by F5. The complexity of dwarf gene action suggests interactions of wheat and rye genes are involved in this polyploid hybrid in contrast to the single gene expression in the dwarf diploid barley. 3) As in barley, we have been unable to induce chemically macro or micro mutations or cytological abnormalities in hexaploid wheat. Furthermore, the rate of spontaneous mutations in barley is considerably less than the dwarf frequency of our crosses.
Consequently, introgression that has required no backcrossing must be explained as a function of the chemicals. We do not clearly understand the mechanisms yet. The chromosomes are lost early-on during embryo formation but whether by reported elimination processes (Subrahmanyam and Kasha, 1973; Barclay 1975) or by some chemically induced system is unknown. Chromosome doubling of the introgressed haploid occurred without colchicine treatment, presumably via endomitosis. We believe gene insertion or similar somatic exchange has resulted in rye gene(s) incorporation into the barley genome. The phenomena are under continued investigation.
References:
Bates, L.S., A. Campos V., R. Rodriguez R., and R.G. Anderson. Cereal Science Today 19:283 (1974).
Subrahmanyam, N.C., and K.J. Kasha. Chromosoma 42:111 (1973).
Barclay, I.R. Nature 256:410 (1975).