The Southern corn leaf blight crisis of the 1970s has taught plant breeders and geneticists the danger of genetic uniformity in a crop species. What was a minor disease for many years turned into an epidemic in the corn industry simply because the seed companies were using a male sterile cytoplasm, which was highly susceptible to a race of leaf blight, in their hybrid seed production. Although there has been greater awareness on maintaining some levels of genetic diversity since that time, this precaution is not always heeded.
Currently, the cotton industry, with its overwhelming acreage of transgenic cultivars, shares a resemblance to the corn industry of the 1970s. Most transgenic cotton cultivars are developed through a two-step process; the transgene is first “engineered” into embryonic cells that are capable of regenerating into plants and then introduced into the desired cultivars using backcross breeding. In cotton, the ability to produce embryogenic cells is genotype dependent with only a few genotypes known to be capable of regenerating plants from cell culture. Because of this limitation, most transgenic cultivars are produced by inserting the transgene into the highly embryogenic but obsolete cultivar, Coker 312, and then introduced into the desired cultivars through backcrossing. Therefore, a majority of the transgenic cultivars are closely related with one of their parents tracing back to Coker 312.
The limited number of regenerable cotton varieties has not only further narrowed the genetic base of cotton, but remains a major obstacle for cotton transformation programs. Realizing the importance to expand the current panel of cotton varieties that is conducive to somatic embryogenesis, we collaborated in-house with Dr. Lloyd May (then cotton breeder with UGA) and Dr. Peggy Ozias-Akins (Horticulture Dept.) to evaluate elite breeding lines developed by the UGA cotton breeding program for somatic embryogenesis. The results showed that somatic embryogenic ability is present in four elite lines (Sakhonokho et al. 2003); the one with the greatest embryo production, GA98033, was later released as public germplasm line (May et al. 2004).
Enhancing the regeneration potential of GA98033 by phenotypic selection and tissue culture manipulation is currently underway. Also, recovered somatic embryos from this line are being utilized to optimize our particle bombardment gene transformation procedure using the green fluorescent protein gene.