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Spectrum of Variation in Somaclones of Triploid Ryegrass¹

Ryegrass (Lolium spp.) plants regenerated from callus culture were investigated for variation in morphology, chromosome number and fertility. More than 4000 plants were produced from successive subculture of a single callus initiated from a triploid (2n = 21) embryo of hybrid origin, 2x (Lolium multiflorum Lam.-perenne L.)x 4x (L. perenne L.). The first group of plants regenerated from the callus were triploid. However, those obtained from successive callus subculture had chromosome number of 2n = 20,19,18,16,14, and still later regenerates were neartetraploids with 2n = 30, 29, 28, 27, and 26 chromosomes. A number of plants were mosaics with 2n = 21/20,20/19,27/28, 20/30, and 29/30 chromosomes. Some plants had pollen mother cells with variable chromosome number of 2n = 20,40,60,200 and 2n = 19, 38, 57. Meiotic study suggested the presence of reciprocal translocations, deletions, inversions, chromosomal fragmentation and elimination, and polyploidy. Regenerated plants showed wide variation in leaf shape and size, floral development, vigor, and survival. Some plants had novel phenotypes, not produced by conventional breeding. An albino mutant sector of callus produced only albino plants. Regenerated plants originated both via differentiation of shoot primordia and somatic embryogenesis. It is concluded that the observed variation among the regenerated plants resulted primarily from chromosomal instability in the callus subcultures.

Key Words: Lolium multiflorum Lam. • Lolium Perenne L. • Chromosomal changes • Tissue culture • Somatic embryogenesis

² Research geneticist.

Received for publication November 17, 1982.