Blueberry plants require large quantities of pollen deposited on stigmas to produce commercial-quality fruit. Like many agricultural crops, the interaction between pollen-source variety and pollen-recipient variety can be a major determinant of fruit quality in blueberries. However, little information exists to guide growers in optimising fruit set and quality. Using five commonly grown blueberry varieties, I determined whether crossing between varieties (inter-varietal) increased fruit mass

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... decreased developmental time relative to crossing within a variety (intra-varietal), and if so, what the best crossing combinations are. While intra-varietal pollination often produced fruit, for certain varieties the fruit set and fruit mass were highly reduced compared to inter-varietal pollination. Furthermore, intra-varietal pollination resulted in longer fruit developmental time in comparison to pollination between varieties. For the same pollen-recipient variety, inter-varietal crosses typically outperformed intra-varietal crosses in fruit mass and developmental time; however, the extent to which inter-varietal crosses outperformed intra-varietal crosses differed between pollen-donor varieties. This result suggests that combinations of varieties are not trivial as some inter-varietal combinations may outperform others. Furthermore, some varieties appear to be more susceptible to the negative effects of intra-varietal crosses than others and that less susceptible varieties may be better suited to conditions where pollinator movement is poor. While our study can guide growers in determining optimal co-planting schemes for the varieties tested, for example in South Africa where these varieties are frequently grown. It also serves as a blueprint for similar compatibility studies that can easily be performed prior to planting to determine the best inter-varietal combinations.