Cytogenetic abnormalities in cotton (Gossypium hirsutum L.) cell cultures

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Abstract
High frequencies of somaclonal phenotypic and cytogenetic variation have been observed previously among regenerants from cotton (Gossypium hirsutum L., 2n = 4x = 52). In this study we endeavored to determine if cytogenetic abnormalities would be detectable in cotton cell cultures and if so, whether or not the observed abnormalities would parallel those expected on the basis of previous cytogenetic analyses of cotton somaclones. Paired samples from suspension cultures established from 21-month-old 'Coker 312' and 8-month-old 'Coker 315' calli were pretreated or not pretreated with colchicine to detect cytogenetic abnormalities at metaphase or anaphase–telophase, respectively. Cell cultures established from both calli were found to vary in chromosome number. Hypoaneuploidy was common, but hyperaneuploidy and polyploidy were rare. Modal chromosome numbers for the 'Coker 312' and 'Coker 315' cultures were 46 and 50, respectively. Bridges at anaphase and telophase were frequent in the 'Coker 312' cultures but rare in the 'Coker 315'cultures. Cytogenetic differences between the cultures could be due to effects of culture age, genotype, their interaction, or other factors. Very small chromosomes, presumably centric fragments, as well as ring chromosomes and putative bridges between metaphase chromosomes occurred at low frequencies. The prevalence of hypoaneuploidy and rarity of hyperaneuploidy and polyploidy in cultures paralleled previous results on cotton somaclones, indicating that cytogenetic abnormalities arising in vitro probably contribute significantly to cotton somaclonal variation. The occurrence of hypoaneuploidy and bridges, including multiple bridges within single cells, is concordant with the hypothesis that breakage–fusion–bridge cycles may accumulate during in vitro culture of cotton.Key words: cotton, Gossypium, tissue culture, cytogenetics.