Distribution and phenotypic diversity analysis of pear germplasm resources in Qinghai province

【Objective】Qinghai Province is endowed with abundant pear germplasm resources due to its unique natural environment. These resources may carry valuable genetic traits—such as cold tolerance, drought resistance, and distinctive fruit quality that are adapted to plateau conditions. However, systematic research on the distribution patterns and phenotypic diversity of these resources remains inadequate. This study aimed to clarify the distribution patterns and phenotypic variation characteristics of pear resources in Qinghai, so as to provide a scientific foundation for biodiversity conservation and the sustainable development of the local pear industry.【Methods】A province- wide field survey and sampling campaign was conducted across the main distribution regions of miscellaneous fruit trees in Qinghai. To improve sample representativeness and reduce selection bias, sampling sites were selected through an integrated approach that combines purposive typical site selection with random sampling. Occurrence records of pear resources obtained from the survey were compiled into a distribution dataset and imported into MaxEnt (Maximum Entropy) for ecological niche modeling. Model performance and variable importance were evaluated using the Jackknife procedure to test the contribution and weight of environmental predictors. The MaxEnt outputs were further processed using ArcGIS for spatial overlay analysis and thematic map production. A suitability map of potential distribution areas for pear resources in Qinghai was generated, and the relative contributions of major climatic factors were calculated. These climatic contributions were interpreted in combination with environmental conditions to explore the ecological drivers shaping the observed distribution pattern. Finally, following the‘Descriptors and Data Standards for Pear Germplasm Resources’, external phenotypic traits were recorded for 19 representative germplasm accessions, including fruit shape, single fruit weight, fruit equatorial diameter, fruit longitudinal diameter, transverse diameter of the fruit core, fruit base color, degree of fruit dot visibility, depth of stalk cavity, bulge degree at the stalk base, attitude of fruit stalk, ridge degree on fruit surface, sepal persistence, relief of the area around the calyx basin, depth of the calyx basin, position of the fruit core, seed shape, flesh color, degree of fruit skin smoothness, and comprehensive evaluation of fruit appearance. Flesh firmness and soluble solids content were measured using a GY-4 digital fruit firmness tester and a refractometer, respectively. Titratable acidity was determined with an automatic intelligent potentiometric titrator, after which the soluble solids-to-acid ratio was calculated.【Results】The results showed that pear resources in Qinghai were unevenly distributed spatially, concentrated mainly in the river-valley zones of the Yellow River Basin and the Huangshui River Basin, with only a small proportion occurring in the hilly areas on both sides of the valleys. The counties with relatively abundant distributions include Minhe, Ledu, Xunhua, and Hualong in Haidong, as well as Guide in Hainan Autonomous Prefecture and Jianzha in Huangnan Prefecture. Counties (cities) with fewer recorded occurrences include Xining, Datong, Huzhu, Huangzhong, and Tongren, while Guinan, Tongde, Gonghe, and Xinghai have the fewest records. Evaluation of the contributions of different environmental factors indicated that precipitation of the driest month, annual precipitation, precipitation seasonality (coefficient of variation), and mean temperature of the coldest quarter together contributed more than 90% cumulatively. This highlights the important influence of temperature and precipitation on the distribution of pear germplasm resourcein Qinghai. Pear germplasm showed abundant genetic variation in phenotypic traits, and its overall appearance quality generally reached a medium level or above. Statistical analyses of quantitative traits showed that the distribution patterns of single fruit weight, fruit equatorial diameter, fruit longitudinal diameter, and transverse diameter of the fruit core differed, but all four traits followed normal distributions. The highest frequency of single fruit weight occurred at 75 g. Pyrus betulifolia had the lightest single-fruit weight (at 1.00 g, whereas Huangguan had the heaviest (at 284.00 g, with an extremely significant difference between the two. Huangguan had the largest mean transverse diameter (8.10 cm), while P. betulifolia had the smallest (1.09 cm). Zaosu pear had the largest mean longitudinal diameter (9.02 cm), and P. betulifolia again had the smallest (1.18 cm). Fruit shape comprised eight types and was the most variable qualitative trait, followed by fruit color with six types. For internal quality traits, flesh firmness, soluble solids content, and titratable acidity all showed extremely significant differences among accessions (P＜0.001). Heiba pear had the highest flesh firmness, while Piteguo had the lowest, with a difference of 11.09 kg· cm-2 . Zaosu (Ledu) pear had the highest soluble solids content (12.82%), whereas Bingtang pear had a lower content, with a difference of 4.57 percentage points between the two cultivars. Woli had the highest titratable acidity, while Shenbuzhi had the lowest; the acidity of Huangjinguo was 57.27 times as much as that of Shenbuzhi. Accordingly, Shenbuzhi exhibited the highest soluble solids-to-acid ratio (315), while Huangjinguo had the lowest (7.14). Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) showed that cultivars including Huangguan, Zaosu (Ledu), Dongguo, Shuijing, Heibali, and Huangjinguo had higher single fruit weight, soluble solids content, fruit transverse diameter, and fruit longitudinal diameter, as well as superior external morphology, flavor, and texture characteristics.【Conclusion】Pear trees in Qinghai are unevenly distributed, with no representative distribution center, and their main distribution areas are relatively scattered. Most suitable habitats are concentrated in the river-valley regions of the Yellow River Basin and the Huangshui River Basin, with a small proportion located in the hilly areas on both sides of the valleys. Precipitation-related variables and extreme low-temperature conditions are the major climatic factors shaping their distribution. This germplasm exhibits extensive phenotypic variation in both external morphology and internal quality traits, indicating a high level of phenotypic diversity. These findings would provide valuable germplasm resources for the selection and efficient utilization of superior materials.