Artificial induction of polyploidy in orchids by the use of colchicine
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1960
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University of Hawaii at Manoa
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Abstract
The study of chromosome numbers of p1.ants has shown the occurrence of a large number of natural polyploids. In :related species of plants entire series of polyploids have been revealed. Muntzing (1) indicates that at least 50 per cent and probably more of the angiosperms are polyploids and that they have played an important role in the evolution of plant species. Presumably, polyploids were able to invade new habitats because of unusual vigor, growth, and general adaptability. Plant breeders and geneticists have become aware of the increased fertility of the naturally occurring amphidiploids over their ancestral hybrids. Cytological investigations have demonstrated that many plants selected from the wild for domestication are polyploids. These were selected because of specific, superior values even though the ploidy of these plants were unknown at that time. With increased knowledge of the nature of polyploids and the realization of their importance in plant improvement programs and in genetic studies, breeders have specifically bred for polyploid types. They have concluded that in many instances polyploids are superior to their diploid counterparts in vigor, size, quality, texture, and other characteristics. In the orchid industry, polyploidy has come to assume a prominent role in the production of superior types. Kamemoto (32) has shown that the award winning Cattleya hybrids such as C. Balmar, C. Bow Bells, and C. Joyce Hannington were triploids. Storey (57, 58) and. Kamemoto (33, 34) showed that superior selections of hybrids in the vandaceous group were triploids, tetraploids, and pentaploids. Kosaki (36) working with Dendrobiums, showed that a number of superior plants were triploids and tetraploids. Polyploid plants developed in the early years of orchid breeding originated through a number of avenues. Many occurred through spontaneous doubling in the somatic tissues and non-reduction of gametes, while others were the result of polyspermy and polyploidization of gametes. Many present day advance generation hybrids are the results of hybridization of these polyploids. In the course of an extensive breeding program in orchids, relatively high sterility among intergeneric hybrids and to a lesser degree among interspecific hybrids was encountered. The cytological basis for such sterility in orchids is largely that of non-homology of the chromosomes (32, 57, 58, 33, 34). Because of the highly sterile nature of many diploid hybrids as well as triploid strains, it was found desirable to overcome this sterility barrier in order to advance the breeding program. Previous workers have demonstrated with plants other than orchids that this sterility barrier could be removed by doubling the chromosome numbers of the sterile types, and that certain chemicals such as colchicine are effective in inducing such changes. Thus far, attempts that have been made both here and in other areas indicate considerable difficulty in inducing polyploidy artificially in orchids. Furthermore, no studies have been conducted on the behavior of such induced polyploids in orchids, and very little work has been done relative to comparison of morphological differences between diploids and induced polyploids. Following upon the above considerations, the thesis as presented here involved three major objectives. The first objective was to devise practical methods for inducing polyploids in selected orchid groups by the use of colchicine. The second objective entailed the study of the characteristics of the induced polyploids, with these types being compared with their diploid counterparts in respect to morphological differences. The third objective involved an attempt to analyze and explain the induction of cytochimeras found among most of the induced polyploids.
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Orchids, Polyploidy, Colchicine
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Theses for the degree of Doctor of Philosophy (University of Hawaii (Honolulu)). Biomedical Sciences (Genetics - Cell, Molecular and Neuro Sciences); no. 22
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