Genotype x Environment Interaction and Stability Analysis of Performance, and Mega- Environment Identification of Fruit Yield and Yield Components in Watermelon [Citrullus lanatus(Thumb.) Matsum & Nakai] Tested in Multiple US Locations

One of the major breeding objectives for watermelon [Citrullus lanatus (Thumb.) Matsum & Nakai] is improved fruit yield. High yielding genotypes have been identified, so our objective was to evaluate genotypes for stability of fruit yield and yield components over diverse environments. The success of any breeding program depends on several factors, including understanding and selection of suitable breeding and test locations. The objectives of this study were to (i) evaluate the influence of years and locations on yield of watermelon genotypes, (ii) identify genotypes with high stability for yield, (iii) determine whether locations belong to a single mega-environment, or a diverse set, and (iv) rank locations based on discriminating ability and representativeness. A set of 40 genotypes was tested over 3 years (2009, 2010, and 2011) and 8 locations across the southern United States in replicated, multi-harvest trials. The genotypes included new vs. old releases, small vs. large fruit size, round vs. elongate fruit shape, striped vs. solid rind pattern, resistant vs. susceptible to anthracnose, eastern vs. western adapted, and inbred vs. hybrid type. Yield traits were summed over harvests, and measured as marketable yield, fruit count, % cull fruit, % early fruit, and fruit size. There were strong effects of environment and genotype x environment interaction (GEI) on watermelon yield traits. There was a significant advantage of hybrids over inbreds for performance of yield components and responsiveness to favorable environments. Four genotypes, including 'Fiesta F1', 'Stars-N-Stripes F1', 'Stone Mountain' and 'Calhoun Gray' had high trait means and high stability: high marketable yield, high fruit count, low % cull fruit, above average % early yield, and medium fruit size. Inbreds 'Big Crimson' and 'Legacy' would be good for development of cultivars having high yield and stability. Two locations including, Florida and Clinton, NC were consistently represented as key centers of two mega-environments for marketable yield, fruit count, and % early fruit. The entire southern US should be considered one mega-environment for breeding watermelon for fruit size. Identification of separate mega-environments in the watermelon production region of the US has several implications for future breeding objectives and genotype evaluation, including deployment of different genotypes in different areas for optimum performance.