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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Techniques to Induce Polyploid Daylillies

Authors
item Sakhanokho, Hamidou
item Cheatham, Christopher
item Pounders, Cecil

Submitted to: Southern Nursery Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 10, 2004
Publication Date: December 10, 2004
Citation: Sakhanokho, H.F., Cheatham, C.L., Pounders Jr, C.T. 2004. Evaluation of techniques to induce polyploid daylillies. Southern Nursery Association Proceedings Vol. 49 pg592-594.

Interpretive Summary: Consumers generally prefer the vigor and improved horticultural traits of tetraploid daylily clones. Tetraploid daylilies are obtained by doubling the basic chromosome number through chemical treatments, such as colchicine treatment. Techniques of daylily conversion include in vitro tissue culture method, exposure of germinating seeds or the meristematic area to a conversion chemical, and injection of conversion chemical into the meristematic region with a hypodermic needle. The objective of the current study was to evaluate some of the techniques used to convert diploid daylilies into tetraploids. Results obtained in this study suggest that techniques currently used by daylily hybridizers to convert diploid germplasm to the tetraploid level produce predominantly mixaploids. This means that the converted daylilies are actually chimeric plants consisting of diploid, tetraploid (doubled chromosome number), and octoploid (quadrupled chromosome number) materials. This phenomenon could account in part for the higher levels of sterility in progeny of hybrids utilizing newly converted clones reported in catalogues of many daylily breeders. Additional research is needed to identify an easy and dependable conversion technique that will efficiently produce tetraploids to increase genetic diversity while maintaining fertility.

Technical Abstract: Most daylily species are diploid (2n = 22), with the exception of some triploids which are generally sterile as pod parents, but consumers generally prefer the vigor and improved horticultural traits of tetraploid (2n = 44) daylily clones. Tetraploid daylily cultivars are the result of doubling the basic chromosome number by breeders through chemical treatments, such as colchicine treatment. The genetic diversity within such modern daylily tetraploids is rapidly decreasing because breeders have focused on only a limited number of tetraploid genotypes with unique flower traits. This situation could have serious consequences as pest and environmental changes occur. The recent introduction of daylily rust has demonstrated how devastating a new pest can be to clones commonly marketed by the nursery industry. There is a need to expand the pool of daylily tetraploid germplasm through conversion of more genetically diverse diploid clones for use in tetraploid breeding programs. We evaluated several daylily conversion techniques using two diploid daylily cultivars. The treatments were: 1) injection with water (control); 2) injection with 0.4% colchicine; 3) exposure of the meristem to 0.4% colchicine for 48 hours; 4) exposure of the meristem to 0.4% colchicine + 10% glycerol for 48 hours; and 5) injection of the meristem with 0.4% colchicine + 10% glycerol. The results obtained suggest that techniques currently used by daylily hybridizers to convert diploid germplasm to the tetraploid level produce predominantly mixaploids. This could account in part for the higher levels of sterility in progeny of hybrids utilizing newly converted clones reported in catalogues of many daylily breeders. Additional research is needed to identify an easy and dependable conversion technique that will efficiently produce tetraploids to increase genetic diversity while maintaining fertility.

Last Modified: 8/30/2014
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