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Substitution of Cotton Cytoplasms from Wild Diploid Species for Cotton Germplasm Improvement¹

The purpose of this investigation was to initiate a program of cytoplasm introgression from the wild diploid species into cultivated cotton (Gossypium hirsutum L.) and then use the semigametic trait of Pima cotton (G. barbadense L.) to develop homozygous cytoplasmic-substituted lines for evaluation and commercial release. It was determined that the in situ pattern of ovule and embryo growth in the wild species is similar to the cultigens but that the wild relatives have a shortened period of boll development, show reduced seed size and weight, have fewer seeds per boll, and in some cases require specific light conditions in order to initiate flowering. Three new interspecific hybrids with wild species cytoplasms were recovered by using four different pollen parent sources, a single application of GA₃, at 3.5 mmol L^–1 to the flower at anthesis, and embryo rescue techniques. Results indicated that the success of fertilization and embryo development was strongly influenced by the paternal species used to make the cross, and secondly, that the degree of hybrid embryo development may be a more important factor than the age or size at the time of embryo rescue. Immature embryos rescued prior to 15 days post-anthesis failed to show further development or undergo precocious germination. The optimum time for embryo rescue and recovery occurred between 15 and 25 days after anthesis. Cytogenetic analysis of the hybrids verified that they were true interspecies crosses. Observations of meiotic metaphase chromosomes indicated the degree of relatedness between species. As expected, chromosome pairing indicated a very close homoeology between the G. trilobum DC. ex Skov. (D₈) genome and the D subgenome of G. hirsutum. The E genomes of G. stocksii Mast ex Hook. (E₁) and G. somalense (Gürke) Mayer (E₂) exhibited little homoeology to either the A or the D subgenome of G. hirsutum or the A genome of G. arboreum L. Cytogenetic observations by others on the reciprocal hybrids of these species closely agree with our data on chromosome associations. Thus, there does not appear to be a significant effect of cytoplasm on chromosome pairing in the primary hybrids.

Key Words: Interspecific hybridization • Embryo rescue • Cytogenetics

² Scientist, Cetus Madison Corporation, Middleton, WI 53562. Formerly, research associate, Dep. Plant and Soil Science, Univ. of Tennessee and plant physiologist, USDA-ARS, Dep. Plant and Soil Science, P.O. Box 1071, Knoxville, TN 37901-1071.

Received for publication November 20, 1984.

This article has been cited by other articles:

				J. Zhang, J. M. Stewart, and T. Wang Linkage Analysis between Gametophytic Restorer Rf2 Gene and Genetic Markers in Cotton Crop Sci., January 1, 2005; 45(1): 147 - 156. [Abstract] [Full Text] [PDF]