Study on the fruit phenotypic characters diversity of Litchi chinensis var. fulvosus

Abstract:【Objective】Litchi chinensis Sonn. var. fulvosus Y. Q. Lee (LF) is a wild variety of litchi that originated in Yunnan province. It has many special characteristics, such as very easy flowering, high fruit-setting rate, high yield, early maturity, sour taste pulp, and so on. In the litchi industry, LF is mostly used as rootstocks. In recent years, some trees of LF has been cut down to grow other crops with high economic value or distroyed by the drought in spring in some areas, which led to the loss of its genetic diversity. Therefore, it is urgent to strengthen the investigation of the germplasm resources to preserve the genetic diversity of LF. In this study, we investigated the wild LF resources extensively in Yunnanprovince and collected the fruits from 93 single plants. The characteristics of these fruits were measured, evaluated, and analyzed to provide a certain basis for further research and utilization of LF. 【Methods】LF distributed in 10 counties of Yunnan province were extensively investigated, and 93 single LF plants were recorded, with at least 50 meters apart from each other. At least 15 matured fruits were picked from each plant. A total of 16 descriptive traits were measured according to the description standard and the 8 quantitative traits were also determined based on the standard methods. The distribution frequency, coefficient of variation, and diversity index of these characters were analyzed. The LF plants were classified by systematic cluster analysis according to both the descriptive and quantitative index, and the principal component analysis was carried out.【Results】(1) The main fruit descriptive traits of LF were determined. Most LF plants had fruits with crooked-heart shapes, reddish with yellowish pericarp, oblique fruit shoulder, convex, and obtuse shape of fruit tip, smooth shape of fruit skin segments with hairy-tip shape of protuberances, and inconspicuous suture line. The fruits from most LF germplasm resources had waxy-white pulp with a little brown inner membrane or absence of color. The fruit pulp usually showed a tender texture, sour and sweet, and slightly astringent taste with no fragrance. All the 93 LF plants born fruits with large, oval-long, and light brown skin seed, except one plant had aborted seed. The diversity index (DI) of the 16 fruit descriptive traits varied from 0.46 to 2.29. Among them, the highest DI was the peel color (2.29), and the distribution frequency of reddish and yellowish was 41.94% , followed by the shape of fruit skin segments, the DI of it was 1.79, the smooth distribution frequency was 49.46%. The suture line had the lowest DI (0.46). (2) The average single fruit mass of 93 LF germplasm resources was 3.95-28.38 g, the longitudinal diameter was 22.28- 45.36 mm, the transverse diameter was 16.56-34.62 mm, the lateral diameter was 12.13-31.48 mm, the pericarp mass was 1.09-6.41 g, the seed mass was 0.26-7.25 g, the total soluble solids content (TSS) was 7.65%-21.95%, and the edible rate was 38.42%-69.74%. The DIs of the 8 quantitative indexes ranged from 2.83 (fruit transverse diameter) to 2.98 (seed weight), indicating that their variation range was lower than that of the descriptive indicators. The coefficient of the variation of single fruit weight, longitudinal diameter, transverse diameter, lateral diameter, pericarp weight, seed weight, soluble solid content, and edible rate were 29.76% , 14.39% , 13.17% , 14.37% , 38.36% , 32.14% , 14.54% , and 11.69%, respectively. (3) The results of cluster analysis with 16 fruit descriptive traits showed that the LF fruits could be divided into four categories, among them the fourth category had better flavor. Based on the 8 quantitative characters, the LF plants could be divided into five categories, among them the fruit size of Class Ⅴ was larger than those of others, and the edible rate of the Class Ⅱ were the highest. Each category contained resources from multiple regions. The principal component analysis (PCA) showed that the first principal component factor reflected the fruit size and weight, and the second principal component factor reflected the fruit descriptive traits. The comprehensive scores of each LF plant were calculated. The higher the score was, the larger the fruit, the higher the TSS content, and the higher the edible rate. (4) One plant with aborted seed in fruit was found, and two excellent plants with good descriptive were screened out from the collected litchi resources according to the score of PCA.【Conclusion】The fruit characters of LF are rich in phenotype diversity, which could be used as materials for breeding new litchi varieties.