Adaptive potential of a watermelon collection for performance indicators

Purpose and Objectives. To select highly adaptable watermelon starting material by the main indicators of the performance (yield and average marketable fruit weight). Materials and Methods. The watermelon collection was investigated: 101 cultivars and lines from 9 countries (55 accessions from Ukraine, 23 - from Russia, 8 - from China, 5 - from the USA, 3 - from Moldova, 2 - from Kazakhstan, Thailand and the Czech Republic each, and 1 - from Italy). A Ukrainian cultivar, Maks Plus, was taken as the check accession. The following parameters were calculated: Vi - general adaptive capacity (GAC), σ2SACi - specific adaptive capacity (SAC), Sgi - genotype stability, bi - regression coefficient of the genotype's response to changing conditions (plasticity), and GBVi – genotype breeding value. AV Kilchevskyi and LV Khotylyova’s method was applied to estimate the parameters of adaptive capacity and stability of the genotypes. The environmental plasticity coefficients (bi) were calculated according to SA Eberhart and WA Russel algorithm. Data were statistically processed, as BA Dospekhov recommended. Results and Discussion. The adaptive potential of the watermelon collection was evaluated for the following traits: total yield, marketable yield, and average marketable fruit weight. The variation amplitude (Am) of the "total yield" trait based on the averaged three-year data on the collection was 51.26; the variation range was 15.07 - 66.33 t/ha. In the check accession, Maks Plus, the mean total yield across the 3 years was 64.72 t/ha. For further work, we selected 31 collection accessions, basing on the total yield” trait. The adaptability parameters of the collection watermelon accessions for the "marketable yield" trait differed somewhat from those for the “total yield” trait. From the averaged three-year data, the variation amplitude (Am) of the "marketable yield" trait was 51.15 t/ha; the variation range of this trait was 13.19 - 64.34 t/ha. The variation amplitude of the "average marketable fruit weight" trait based on the averaged three-year data was 3.00 kg. The variation range of this trait was 0.99–3.99 kg. The average fruit weight in the sample across the 3 years was 2.14 kg. In the check cultivar, Maks Plus, the average fruit weight was 2.50 kg. For the breeding for the characteristics under investigation, accessions of practical value, with high values of the general adaptive capacity, stability, and genotype breeding value were selected. By the environmental plasticity coefficient bi, the collection watermelon accessions were categorized as low-, mid- and highly plastic in terms of the characteristics under investigation: intensive accessions with enhanced responses to growing conditions, accessions with moderate levels of the environmental plasticity, and highly plastic accessions, which slightly respond to changes in growing conditions.