A New Method of Evaluating Cotton Cultivar Performance In the Southeast US.

For several years prior to 2010, approximately 85% of the cotton acreage in Georgia was planted to a single cultivar, DP 555 BR. This cultivar portrayed later maturity than most modern cultivars at the time, affording it with the capacity to recover from drought periods and continue to develop harvestable bolls when favorable conditions returned, whereas other cultivars ceased blooming during adversely dry conditions. As a result of this characteristic, DP 555 BR was touted to outperform nearly all other cultivars especially in dryland environments in Georgia, which comprise nearly half of the total cotton acreage in this state. Due to the expiration of the EPA registration for single-gene Bt technologies, DP 555 BR was only planted on a limited basis in 2010, and was not available for planting in 2011 and beyond. Growers in this region therefore are searching for a replacement for DP 555 BR, with most concern given to dryland acres. Official Variety Testing (OVT) in Georgia provides a valuable resource for evaluating cotton cultivars. This program is conducted using small-plot trials for both early and late maturity, as well as for both irrigated and dryland environments. However, due to the extensive labor requirements and number of entries in this program, these experiments are conducted in only a few locations or environments. Beginning in 2010, the University of Georgia Extension Cotton Agronomists launched a program for evaluating new cotton cultivars at the county / on-farm level, which was named the UGA Uniform Cotton Variety Performance Evaluation Program. This program established replicated large-plot trials in a very wide range of environments across the cotton belt in Georgia. This program was also used for training county agents on cultivar selection, as well as to provide local growers with data relevant to their local environments. Additionally, this program consisted of list of top-performing cotton cultivars, chosen by seed manufacturers, to ensure uniformity of cultivars in all of the replicated trial environments. It was apparent that there was not going to be another single cultivar that would be planted to the proportion of Georgia’s cotton acreage that DP 555 BR previously comprised, as there was no one cultivar that performed as consistently as DP 555 BR. This program however, illustrated the importance of placing cultivars in yield environments where they would outperform most other cultivars. Due to the extremely wide range of yield environments captured by this program, growers now have a tool to evaluate stability and consistency of cotton cultivars across environments, and can also determine which cultivars are better adapted for particular environments versus others. As opposed to combining yield data over similar environments, yield data derived from this program was shown for individual locations in ascending order based on trial averages, and then combined over locations. Top-performing cultivars were highlighted in each individual trial, which clearly illustrated stability characteristics of each cultivar, as well as which type of environment each cultivar would need to out perform others. This program effectively complimented Official Variety Testing for cultivar evaluation in Georgia.