⋅ BY PENG W. CHEE AND DONALD C. JONES ⋅
UNIVERSITY OF GEORGIA
For most crop species, it usually requires 10 to 12 growing seasons of generation advancement and selective breeding to produce a new variety. Winter nurseries are, therefore, essential to crop breeding programs as they allow breeders to grow more than one crop per calendar year, enabling multiple cycles of selection within the same time frame.
This accelerates genetic gain, allowing breeders to develop superior genotypes more quickly and advance them through the breeding pipeline. Winter nurseries also serve as counter-season locations to increase the seed supply of advanced breeding lines for further testing.
Ultimately, this helps shortening the time from initial crossing to bring new cultivars to market. For these reasons, winter nurseries have been established for all major crops grown in the United States.
70 Years Strong
The Cotton Winter Nursery was established in Mexico nearly 70 years ago, but in 2015 it was relocated to a new facility five miles northwest of Liberia, Costa Rica. The location was chosen primarily because of the suitable cotton-growing environment, affordable labor force, available water and reliable flights.
Mr. Alfonso Palafox, who had 10 years of previous CWN experience in Mexico, is the manager of the facility and operations. He has been instrumental in establishing the farm and building the facility to what it is today. The nursery provides services that include advancing generations, increasing seeds and making crosses for public and private breeding programs.
How does the CWN benefit the U.S. cotton industry? It serves two critical purposes to ensure cotton production in the United States remains profitable and sustainable.
First Benefit To U.S. Cotton
The first is preservation and characterization of the U.S. Department of Agriculture National Cotton Germplasm Collection currently housed at College Station, Texas.
The CWN serves as an in-situ preservation and characterization site. The nearly 10,000 accessions in the collection serve as reservoirs of genetic material. An accession is a unique genotype in the germplasm collection. If the U.S. cotton germplasm collection has 1,000 accessions, it means that there are 1,000 different genotypes in the collection.
The reservoirs of genetic material have a wide array of traits that provide the foundation for breeders to develop improved cotton varieties with better yield, fiber quality and disease resistance.
Because a significant portion of the germplasm collection is day-length sensitive and would not flower during the U.S. mainland’s long daylength-conditions in summer, conducting plant characterizations and seed increases during the winter months is efficiently done in the short day CWN environment.
Second Benefit To U.S. Cotton
COURTESY OF DR. JAMES FRELRELICHOWSKI
The second purpose is development of germplasm and cultivars. Virtually all cotton germplasm or cultivars developed by public breeding programs have had their developmental journey pass through the CWN.
Though often overlooked, many important native traits that commercial breeding companies offer have come from public research endeavors. The initial germplasm in which these traits were discovered were likely grown in the CWN.
For example, bacterial blight and root-knot nematode resistance — two agronomically important traits growers seek in elite cultivars —were discovered by public breeders, with considerable pre-breeding taking place in the CWN before being utilized by commercial seed companies. More recently, FOV4 resistance in cotton would not have been achieved without the generation advancement and seed increases that occurred in the CWN.
UGA Explains Its Stake
Like most public cotton breeding programs in the United States, the University of Georgia’s cotton breeding program relies on the CWN to accelerate germplasm development. Each summer they create about 100 new hybrid combinations by crossing elite breeding lines to initiate a new breeding cycle.
The resulting seeds are sent to the CWN soon after harvest in the fall. There, Palafox and his team grow the seeds from each hybrid, carefully self-pollinating every flower to ensure genetic purity. The seedcotton produced from each plant is harvested, delinted and returned to Georgia in time for spring planting.
This usually results in a good seed supply, allowing them to make plant observations and begin the first cycle of selecting new experimental breeding lines with desirable traits such as higher yield potential, improved fiber quality and disease resistance. While this process may seem trivial, it provides an extra growing season, effectively allowing two breeding cycles within a single year.
UGA Graduate Students
The CWN is also an indispensable resource for our graduate students, enabling them to create and advance genetic populations for their research. Typically, M.S. students have two years and Ph.D. students three years to complete their research and course of study.
Gaining an additional growing season — whether to advance generations in a segregating population or to generate sufficient seeds for field testing — can be the difference between graduating on schedule or having to stay an additional growing season to collect enough data for their research.
Funding to support the maintenance and operation of the CWN includes user fees and financial support from Cotton Incorporated, USDA and the Southern Association of Agricultural Experiment Station Directors.
Although these costs are significant, the CWN provides a steady stream of breeding innovations, ensuring that cotton producers have continued access to high-performing varieties that are more productive, of high quality and less vulnerable to environmental stresses and diseases.
This helps maintain the profitability and sustainability of U.S. cotton production.