Mapping of quantitative trait loci corroborates independent genetic control of apple size and shape

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• Fruit size, length, and diameter followed Gaussian distributions and they are polygenic qualitative traits.
• Both fruit size and shape were significantly correlated with fruit length and diameter, but no significant correlation was detected between fruit size and shape.
• We found that fruit size and shape are under independent genetic control.

Fruit size and shape are important external quality traits in commercial crops. To determine the genetic relationship between the size and shape of apple fruits, quantitative trait loci (QTLs) for apple size (average weight), length, diameter, and shape (length/diameter ratio) were identified and mapped in progeny of a ‘Jonathan’ × ‘Golden Delicious’ cross. Fruit size, length, and diameter followed a normal distribution. There was no correlation between apple size and shape, but both variables were significantly correlated with length and diameter. Forty-five QTLs for apple size, length, diameter, and shape were mapped to 13 chromosomes of the two parent cultivars. Of these, 12 QTLs for fruit length and diameter either overlapped or were closely associated with QTLs for fruit size, whereas three co-localized with QTLs for fruit shape. No QTLs for fruit size mapped to the same or neighboring regions as QTLs for fruit shape, suggesting that size and shape are under independent genetic control.