Comprehensive evaluation on fruit traits of local pear germplasm resources in Shandong

Abstract: 【Objective】Pear is one of the important fruit crops in Shandong province, not only being rich in variety resources but also having a long history of cultivation. In the long process of production, the people have continuously created and domesticated a large number of excellent local cultivation varieties of pears, which have rich genetic diversity and are valuable materials for cultivating new excellent varieties. However, in recent years, the loss of local variety resources has been serious, and it is urgent to collect, preserve and research. Therefore, the fruit characteristics of 107 pear germplasm resources in Shandong province were screened and evaluated, which laid the foundation for breeding new varieties.【Methods】107 local pear germplasm resources in the Core Demonstration Garden of Shandong Pomology Research Institute were used as test materials to investigate and analyze the fruit quality traits, including sensory evaluation, appearance quality and internal quality. The pears were harvested based on their maturation stage, and then those parameters including single fruit weight, longitudinal diameter, transverse diameter, sugar and acid contents, and so on were measured. The GC-MS method was used to determine aroma contents and composition. We also analyzed the distribution frequency and coefficient of variation of fruit characteristics. The fruit traits of 107 germplasm resources were classified by Q-type and R-type cluster analysis, and fruit traits were analyzed by the principal component analysis.【Results】(1) Among 107 pear varieties, 84.11% of fruit types belonged to medium and large sizes. Most of the fruits were oval and round, and the fruit-shape index was about 1. The longitudi-nal and transverse diameters of most fruits distributed between 60-90 mm and 65-85 mm, respectively. (2) Most fruits exhibited such characteristics as yellow green skin, white flesh, sourness and sweetness, abundant juice, and a slight aroma. (3) 34.58% fruit hardness were moderate and ranged from 3 kg·cm^-2 to 6 kg· cm^-2 . The distribution range of titratable acid and solid/acid ratio were 0.06%-1.27% and 9.04- 188.57, respectively. (4) A total of 339 kinds of aroma substances were detected by GC-MS, and there were great differences in the types and contents of aroma substances among different varieties. The content of esters was significantly higher than that of other aroma substances. The aroma of the fruit was mainly slightly fragrant, followed by fragrant and not fragrant. (5) The variation coefficients of titratable acid, aroma content, aroma type, solid/acid ratio, single fruit weight, longitudinal diameter, transverse diameter, hardness, soluble solids content and fruit-shape indexs were 101.80%, 71.05%, 28.86%, 52.53%, 48.74%, 21.04%, 18.15%, 33.33%, 20.97% and 11.00%, respectively. (6) The correlation analysis of fruit quality by the multivariate correlation analysis found that single fruit weight and transverse diameter and longitudinal diameter, correlation coefficients greater than 0.8, were highly correlated, and significantly and negatively correlated with fruit hardness. The ratio of TSS to TA showed a significant positive correlation with the single fruit weight, longitudinal and transverse diameter and fruit shape index, and a significant negative correlation with the titrable acid content. Hardness showed a significant negative correlation between single fruit weight and longitudinal and transverse diameter. There was a very significant positive correlation between the soluble solid content and the titratable acid content. The aroma types and the aroma contents were significantly and positively correlated. (7) Q-type and Rtype cluster analysis showed that the group clustering germplasm had certain characteristics and most of them showed pairwise correlation. (8) Principal component analysis showed that the contribution rate of each trait was scattered and the trait variation was rich. Positively increasing the first principal component factor would help improve the appearance quality of the fruit. The second principal component of positive growth was beneficial to improve the quality of fruit aroma, and the third principal components of positive growth contributed to improve the nutritional quality of the fruit.【Conclusion】The local germplasm resources of pear in Shandong province were rich and diverse, 84.11% of them belonged to medium or large fruit type, the fruit was mostly oval or round, and the fruit shape index was about 1. The distribution of fruit characteristics, such as single fruit weight, longitudinal diameter, transverse diameter, fruit type index, fruit hardness and soluble solid content, were consistent with normal distribution. A total of 339 kinds of aroma substances were detected by GC-MS, and the types and contents of aroma substances were different among the varieties. The content of ester was the main component of aroma substances. The coefficient of variation of fruit traits was very different. Q-type and R-type cluster analysis showed that the germplasm of group clusters had certain common characteristics, and most of the traits were correlated with each other. The germplasm resources with high contents of soluble solids and aroma, including Wendeng Shishengzhong, Qixi Daxiangshui, Yaguang pear, Laiyang Qiubai pear, Gaomi En pear, Changyi Xiansuizi and Damahou pear, were identified as valuable parental materials for breeding new excellent varieties.