International Journal of Horticulture, 2024, Vol.14, No.2, 78-88 http://hortherbpublisher.com/index.php/ijh 79 Figure 1 Strawberry production in the US and Europe (1961-2021) Figure 2 shows the cumulative marketable fruit yields of modern short-day and day-neutral cultivars (hybrids) grown in coastal areas of California during the 2015—2016 and 2016—2017 growing seasons. The estimated marginal means (EMMs) depict the yield variations among different varieties at different locations. In Figure A, we observe the production of short-day varieties in the Oxnard region during 2016—2017, showing some variation in annual yields with a generally increasing trend. Notably, varieties such as Fronteras and Victor exhibited significant production increases. Figures B and C display the yields of day-neutral varieties in the Santa Maria and Prunedale regions. These varieties show a very significant trend of increasing annual production, with varieties like Royal Royce and Valiant demonstrating exceptional productivity. Figure D compares the yields of day-neutral varieties between the two years in these regions, showing that the production was relatively stable over the years, with the Royal Royce variety performing exceptionally well. Overall, day-neutral varieties exhibit higher yields than short-day varieties, especially in specific areas like Santa Maria, and this trend remains consistent across different years. This likely relates to the genetic characteristics of the varieties and their adaptability to specific regional climate conditions. These findings are crucial for improving strawberry breeding and cultivation management strategies. Figure 3 displays the genetic diversity among early and modern strawberry hybrids. The first two principal components (PC1 and PC2) from principal component analysis (PCA) illustrate the genetic relationships among three groups of genotype individuals based on 28,513 single nucleotide polymorphisms (SNPs) in 1,406 hybrid varieties, ranging from the years 1775-2016. Blue dots represent 405 elite × elite hybrid varieties that have been phenotypically tested for fruit yield and quality; coral dots represent 131 elite × exotic and 8 exotic × exotic
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