Quantitative evaluation of cucumber fruit texture and shape traits reveals extensive diversity and differentiation

Abstract

For many years, cucumber (Cucumis sativus L.) has been genetically improved by breeders to meet consumer demands. A wide variety of cucumber cultivars, differing in fruit qualities such as texture and shape, are grown around the world, and several major cucumber types have been developed in different regions. We used several computer-aided evaluation methods to assess the diversity in fruit texture and shape traits among a wide variety of world cucumber cultivars. Firmness of fruit skin, placenta and flesh and crispness of flesh were evaluated quantitatively and objectively by analysis of puncture-test data (force-deformation curves). Fruit shape was also evaluated quantitatively and objectively by using elliptic Fourier descriptors (EFDs) and principal component analysis (PCA). Fruit firmness and crispness clearly differed among cultivars and growth stages. Flesh crispness scores were significantly higher in Japanese F1 hybrid cultivars, which maintained relatively high crispness even at maturity; in contrast, the crispness of the other type cultivars remained low at all stages. PCA of EFDs detected three major components of fruit shape variation: the ratio of length to diameter, the amount of swelling at the fruit ends and the shape of the stem end. Significant differences were detected in these shape components among cultivars and cucumber types. These results indicate that quantitative differentiation has occurred in the fruit texture and shape traits of cucumber during domestication and subsequent breeding.