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Homozygous Variation in Rice Somaclones: Nonrandom Variation Instead of Mitotic Recombination

Dep. of Plant Pathology and Crop Physiology

J. H. Oard

Dep. of Agronomy, Louisiana Agric. Exp. Stn., Louisiana State Univ. Agric. Center, Baton Rouge, LA 70803-1720

^* Corresponding author.

Mitotic recombination has been postulated by some researchers as a mechanism to explain the lack of segregation for certain traits in plants derived from tissue culture. Three genetic marker lines were used to examine whether mitotic recombination could be detected from plants regenerated from rice (Oryza sativa L.) tissue culture. One line, CI 11014, had two dominant genes An (awned) and Gl (pubescence) in linkage group 12. The other two, CI 11020 and CI 245714, had two corresponding recessive genes an (awnless) and gl (glabrous). A total of 1788 R₁ plants regenerated from immature panicles of F₁ plants from the crosses CI 11020 x CI 11014 and CI 245714 x CI 11014, and from the parental lines, were evaluated from 1988 to 1990 in the greenhouse, and 360 R₂ lines derived from these F₁ plants and parental lines were evaluated in the field. No mitotic recombination occurred for the genes investigated in this experiment. A high somaclonal variation frequency (47.5%) for the awnless characteristic was observed. The variation was not due to mutation of the dominant gene An, but was apparently caused by mutation of an inhibitor gene. Results from these experiments suggested that somaclonal variation was not always random and that specific loci had higher mutation rates during the somaculture procedure. Previous suggestions that changes in DNA methylation pattern caused by the tissue culture process were not random were consistent with the data from our studies.

Received for publication May 2, 1994.