Investigations on the Sporting Process in Greenhouse Chrysanthemums

Abstract

The chromosome numbers of 56 varieties of greenhouse chrysanthemums were determined. Fifty-one varieties belonged to 10 'families' of sports and the chromosome numbers of the sports were compared with those of their vegetative parents. Sporting, mostly flower colour mutation, was accompanied by the gain or loss of a few chromosomes in about 30 per cent of the cases. Two plants with different chromosome numbers but with the true varietal flower colour were found.The most frequent chromosome number in the authors' material was 2n = 57. The range was 2n = 45–64. Mitotic irregularities and chromosome number variation within individuals were observed. Attempts to induce sporting by hot water treatment failed.Varieties with large inflorescences had higher chromosome numbers (2n = 58–64) than varieties with medium or small inflorescences (2n = 54–58), but in most of the material varieties with small inflorescences differed little in chromosome number from those with medium-sized inflorescences. Five additional varieties with very small inflorescences had lower chromosome numbers (2n = 45–55).

Plantlets from Petal Segments, Petal Epidermis, and Shoot Tips of the Periclinal Chimera, Chrysanthemum morifolium 'Indianapolis'

“…The shoot tip cultures, on the other hand, are always organized into meristematic areas and the new shoots are from axillary buds rather than from adventitious origin. Sampson et al (1958) observed chromosomal bridges in cells during mitosis in chrysanthemum root tips. Perhaps a breakagefusion-deletion cycle is occurring naturally in the 'Indianapolis' cultivars and tissue culture aggravates this anomaly so that during each cell division some genes are lost to one of the daughter cells.…”

“…tions "tend to promote abnormalities in the mitotic spindle as evidenced by the increased frequencies of multipolar separations and lagging chromosomes ... polyploidization by spindle failure may occur." Sampson et al (1958) observed chromosomal bridges in cells during mitosis in chrysanthemum root tips. This could explain the greater abnormalities found in plants originating from petal callus, as opposed to shoot tip cultures.…”

“…Earle and Langhans (1974a) obtained multiple shoots from single shoot tips of chrysanthemum. This has led many workers, including Dorwick (1953), Sampson et al (1958), Weaver (1963), and Stewart and Dermen (1970), to study the possible chimeral nature of these chrysanthemums. White' shoot tips CULTIVARS of Chrysanthemum moriioiium are among the most important flowers in commercial floriculture.…”

“…They suggest the change to yellow, which is seen so often naturally, and is described in Weaver's (1963) work, is due to loss of a chromosome carrying a suppressor for yellow. Chromosome bridges and lagging chromosomes are reported in chrysanthemum (Sampson et al 1958, andDorwick, 1953) and may be involved in the sporting to yellow.…”

“…The frequency of this phenomenon is too great to be accounted for by somatic mutation alone. This has led many workers, including Dorwick (1953), Sampson et al (1958), Weaver (1963), and Stewart and Dermen (1970), to study the possible chimeral nature of these chrysanthemums. The 'Indianapolis' series was studied extensively by Stewart and Dermen (1970).…”