Analysing fruit shape in sweet cherry (Prunus avium L.)

Abstract Fruit shape in sweet cherry ( Prunus avium L.) was described using an objective procedure based on image and regression analysis. Digitised images of individual fruit in front view (onto ventral suture) and side view were obtained by image analysis, the Cartesian coordinates of the fruit contour extracted and subsequently normalised for differing fruit size by dividing by fruit height. Normalised fruit contour data of 40 mature cv. Sam fruit were transformed into polar coordinates and a third-order polynomial was fitted. Coefficients of determination ( r 2 ) were r 2 =0.98 and 0.99 for front and side view, respectively. Statistical analysis of regression coefficients revealed symmetry of left and right half of fruit contour in front view, but asymmetry in side view. There was no significant change in fruit shape in front view between 57 and 71 days after full bloom (DAFB; cv. Sam). Fruit contour of 24 sweet cherry cultivars in front view was equally well-described by the third-order polynomial with a mean r 2 =0.98 (range 0.96–1.00). By cluster analysis of regression coefficients cultivars were grouped according to fruit shape. There was little similarity between cluster membership of cultivars and their respective fruit shape rating in the cultivar description or the five standard fruit shape categories (FSCs) (FSC1: kidney-shaped; FSC2: flat-round; FSC3: round; FSC4: oblong; FSC5: cordate) that are used as a reference for rating fruit shape in sweet cherry cultivars. Principle component analysis identified the ratio of fruit height to width and the depth of pedicel cavity relative to fruit height as two important determinants of fruit shape. The procedure described maybe useful in analysing effects of environmental and genetic factors on fruit shape in sweet cherry fruit.