International Journal of Horticulture, 2024, Vol.14, No.2, 78-88 http://hortherbpublisher.com/index.php/ijh 83 Therefore, over time, there have been significant changes in the breeding values of traits such as yield, number, weight, and firmness in strawberry breeding. The predicted change point years represent a turning point in strawberry breeding, possibly related to the introduction of specific breeding techniques or changes in crop management practices. Additionally, changes in quality traits and disease resistance indicate the diversity of strawberry germplasm in these traits and the direction of strawberry breeding may have shifted over time with the accumulation and change of selective pressures. These data are valuable for understanding the historical process of strawberry breeding and for formulating future breeding strategies. Figure 6 displays the additive genetic correlations between strawberry fruit traits and disease resistance traits. These correlations are derived from the genomic estimated breeding values (GEBVs) of 796 genotyped individuals and 5646 non-genotyped individuals, whose individual birth years range from 1775 to 2015. Part A of the figure (lower triangle area) shows the estimated additive genetic correlations for all individuals from 1775 to 2015; Part B (upper triangle displays estimates before 1954, and the lower triangle shows estimates after 1954). The color gradient from red to blue represents the change in correlation from positive (+1) to negative (-1). The figure illustrates strong genetic correlations between some traits. For instance, fruit yield correlates positively with the number, weight, and firmness, suggesting that these traits are often improved simultaneously in breeding programs. In contrast, correlations with total soluble solids (TSS), titratable acidity (TA), and other quality traits are weaker, indicating that productivity improvements and quality enhancements might need to be selected independently in breeding. Additionally, disease resistance traits, such as Phytophthora crown rot (PhCR) and Verticillium wilt (VW) resistance, show low or negative genetic correlations with productivity-related traits, suggesting that increasing yield and improving other agronomic traits could impact plant disease resistance. Thus, the figure underscores the complex genetic links between different strawberry traits, which is crucial for future breeding strategies, especially when aiming to simultaneously enhance strawberry yield, quality, and disease resistance. This information aids breeders in choosing parents for hybridization, balancing traits to achieve optimal breeding goals. Figure 6 Additive genetic correlations Figure 7 graphically summarizes the important milestones in strawberry domestication from 1715 to the present. The development of strawberries is depicted in watercolor, with each letter representing a specific stage of development. A: Post-1715, spontaneous hybrids between F. chiloensis subsp. chiloensis and F. virginiana subsp. virginiana emerged in Western European cultivation. B: Between 1715 and 1766, the earliest interspecific hybrid varieties appeared and were exchanged and cultivated in Western European botanical gardens such as the Versailles Gardens. C: Post-1766, Antoine Nicolas Duchesne discovered the interspecific hybrid origin of F. × ananassa and began producing early cultivated varieties through artificial hybridization and selection from interspecific offspring. D: In the early 1800s, iconic early cultivated varieties like Keen’s Seedling and Downtown
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