Comprehensive evaluation of biological characteristics and fruit traits in early and mid-ripening sweet cherry varieties

【Objective】Sweet cherry (Prunus avium L.) is a popular fruit tree known for its unique flavor and rich nutrition. However, with the development of logistics cold chain transportation and the rise of e-commerce, the sales of sweet cherries have expanded to all parts of the country. The existing main varieties can no longer meet the needs of the national market development. The market demand is shifting towards bright fruit color, high hardness, excellent flavor, high quality, and storage and transportation resistance. Tianshui area has unique natural environmental conditions suitable for planting sweet cherry. In this study, the growth characteristics and quality features of different cultivars planted in this area were investigated in order to screen the excellent sweet cherry cultivars suitable for local planting. 【Methods】Under the same planting management mode, the phenology of 8-year-old and early- or midseason sweet cherry trees of Heizhenzhu, Chelan, Luyu, Sparkle, Glenred, Brooks, Скороспелка, Caiyu and Hanxiang growin Tianshui area were investigated. Periods of budding, the beginning of flowering, full bloom, the end of flowering, fruit ripening and defoliation were recorded according to the Specification and Data Standards for Cherry Germplasm Resources Description. Leaf morphological characteristics including color, shape, tip, base, edge, hairiness on lower side, and gland shape, color, number and size were also observed. Fruit flesh firmness was measured using a fruit hardness tester (probe diameter: 6.0 mm), while peel firmness was determined using a texture analyzer at three points on each fruit surface. A colorimeter was used to measure the L*, a*, and b* values at three locations on each fruit surface. A handheld refractometer was employed to determine the soluble solids content. The titratable acid content was measured following the method in GB/T 12456—2008. The membrane leakage or relative electrical conductivity, total sugar, total phenol, and vitamin C contents of each sweet cherry cultivar were also determined.【Results】Morphological characteristics, biological features, appearance quality, functional nutrient content, fruit shape index and single fruit quality varied among cultivars. The tree types of the test cultivars were all common, and the tree bodies of Chelan, Luyu, Glenred and Скороспелка were open, and Heizhenzhu and Brooks were semi-open, while Sparkle, Caiyu and Hanxiang were upright. Sparkle, Brooks, and Caiyu had relatively stronger growth potential; Chelan and Скороспелка had relatively weaker growth potential. The skin color of the branches of Brooks was light brown, and that of the rest was brown. The leaf color of most sweet cherry cultivars was rich green, and the color and shape of the leaf glands was red and reniform, respectively. However, Caiyu had green leaf glands and Hanxiang had circular leaf glands. The fruit shape of Sparkle, Glenred and Brooks was reniform, while that of the rest cultivars was heart- shaped. Brooks and Hanxiang had the highest single-fruit weight; Glenred had the heaviest pit weight and lowest flesh recovery, while Chelan had the lightest pit weight and highest flesh recovery. The sweet cherries were all brightly colored. The peel color of Heizhenzhu and Glenred was purple red; that of Chelan and Hanxiang black purple; Luyu and Caiyu had a yellow background with a reddish hue; and the others were red. In contrast to the red flesh of most cultivars, Caiyu had a milky white flesh color. All the cultivars were sour-sweet and tasty and rich in nutrients. Glenred and Hanxiang had the highest titratable acid and total sugar and relatively high soluble solids; Скороспелка and Hanxiang had the highest phenolic and vitamin C contents; Brooklyn had the lowest vitamin C content; and Скороспелка had very low total sugar and soluble solids.【Conclusion】There are differences in tree and fruit morphological characteristics, leaf traits, appearance quality, functional nutrient content, fruit shape index, and single fruit quality among the 9 tested sweet cherry varieties. In the shallow mountains of Tianshui area about 1200 m above sea level, Chelan, Sparkle, Glenred, Brooks and Hanxiang with large fruit, beautiful color, delicious taste, high flesh recovery, and good nutritional quality, have a great potential economic value and are suitable for the development of planting. Among the yellow varieties, Luyu has a better overall performance and can be developed appropriately in areas with few yellow varieties in the market. Although Caiyu is more distinctive, with its yellow skin and milky white flesh, its overall performance is average in Tianshui area. Like Heizhenzhu and Скороспелка, it is not recommended for large scale planting.