Investigation of cotton mega-environment based on fiberstrength selection and GGE biplot

Environmental interactions with genotype have heightened among plant breeders and/or extension agronomists the exploration and application of useful traits in the discrimination of genetic differences among candidate genotypes and similarities to average performances in target regions. GGE biplot with "which-wins-where" view has been a useful technique in graphical display and visualization of interrelation between environments and genotypes, and of mega-environment investigations. However, first two principal component restrictions in GGE biplots have led to uncertainties in terms of fitting degree optimizations of GGE models. Therefore a GGE biplot analysis was adopted in exploring and investigating possible mega-environments in a target cotton planting region. The region included fifteen test sites (Anqing, Nanyang, Huanggang, Jingzhou, Wuhan, Xiangfan, Changde, Yueyang, Nanjing, Nantong, Yancheng, Jiujiang, Jianyang, Shehong and Cixi) for cotton fiber strength selection in 27 independent test sets of cotton variety trials in the Yangtze River Valley for the period 2000-2010. The information ratio (IR) adjustment method was used as a validation tool to ensure that sufficient and necessary principal component scores were selected in the GGE biplot analysis. The study showed that the average effective fitting degree of the GGE biplot analysis of cotton fiber strength selection was 68.4%, with 13 exception records of over-fit or lost-fit. The counterpart fitting degreet of the IR-adjusted GGE model was 73.7%, with 6.0% improvement. This showed that optimization and adjustments to the GGE biplot using IR obviously enhanced the reliability of mega-environment investigations. Based on the GGE biplot analysis, the cotton planting region in the Yangtze River Valley was subdivided into four mega-environments for fiber strength selection ― the first mega-environment included Anqing, Xiangfan, Nantong and Yueyang; the second comprised of Changde, Jiujiang and Wuhan; the third included Cixi, Nanjing, Huanggang, Jingzhou and Yancheng; and the forth also included Nanyang, Jianyang and Shehong. Based on the IR-adjusted GGE model, however, the cotton planting region more distinctively consisted of three mega-environments ― the main mega-environment contained eleven out of fifteen test sites (Anqing, Wuhan, Jiujiang, Xiangfan, Nanyang, Yueyang, Changde, Huanggang, Jingzhou, Nanjing and Cixi), the minor mega-environment consisted of two test sites (Nantong and Jianyang), and the other minor mega-environment also consisted of two test sites (Yancheng and Shehong). Compared with the results of GGE biplot mega-environment analysis, IR-adjusted results were more reliable with distinct geographical characteristics for cotton fiber strength selection. Cotton plants in the Sichuan Basin and Jiangsu Coastal Regions were not suitable for fiber strength selection. It was therefore recommended to target the whole cotton planting region in the Yangtze River Valley. On the basis of the mega-environment investigation and above divisions, scientific decision-makings on cotton fiber strength selection, new cultivar breeding and policy registration for the Yangtze River Valley were recommended.