The relationship between fruit shape and internal fruit characteristics in 'No Mai Tsz' litchi fruits

In litchi (Litchi chinensis Sonn.) fruit, seed size and flesh weight vary greatly depending on the cultivars and even within a cultivar. It is well-known that seed traits such as seed number and size affect fruit shape in some fruit crops. In litchi, seed size is often regarded as a very important characteristic because it determines the edible flesh amount. Additionally, other internal fruit characteristics, such as sweetness and acidity, are also very important. However, no studies have been carried out to understand the relationship between fruit appearance and internal fruit characteristics in litchi. This study evaluated the relationship between fruit shape and internal fruit characteristics of the commercial litchi cultivar 'No Mai Tsz' in Taiwan. Fruit image data were obtained by photographing each fruit from three different sides, peduncle side, suture line side and the opposite side of suture line side. Several internal fruit characteristics of each fruit were recorded. The obtained contour of each fruit image was quantified by elliptical Fourier descriptors (EFDs) using the SHAPE program. The obtained data were subjected to the principal component analysis (PCA). Then, relationships between the PC scores and the fruit internal characteristics were investigated. We obtained several PCs that show significant difference between fruits containing large and small seed. Of these PCs, one PC representing fruit length-to-diameter ratio showed moderate correlation with some internal fruit characteristics. In conclusion, although litchi fruit appearance may possibly correlate with internal fruit characteristics such as seed size and flesh weight, further fine dissection of fruit images will be required to unveil the relationship between fruit shape and fruit internal characteristics.