Diversity of fruit traits of Quercus variabilis from different geographic provenances in north China

This study investigated the geographical variation patterns and climatic drivers of fruit phenotypic traits in Quercus variabilis across different provenances.

The fruits of 27 Q. variabilis provenances distributed in north China were systematically analyzed by means of variance analysis, cluster analysis, correlation analysis and principal component analysis.

The variation in fruit phenotypic traits of Quercus variabilis was predominantly manifested in fruit weight and size, nutshell thickness, fruit shape, as well as starch content and amylose content. Among the morphological traits, the fresh weight exhibited the highest mean coefficient of variation (CV) of 29.62%, while the fruit length showed the smallest CV of 9.79%. Regarding nutritional components, soluble sugar content had the highest mean CV of 22.13%, whereas starch content had the lowest CV of 3.88%. Cluster analysis classified 27 provenances of Q. variabilis into five clusters. The amylose content in group I was the highest, while the fruit weight and starch content were second only to those in group V. Among these, the heaviest fruits were found in group V from Xintai City, Shandong Province. The thickest fruit nutshells were from Xichuan County, Henan Province, while their amylose content was low. Starch and amylose content showed a significant positive correlation with fruit weight and size. Nutshell thickness was significant negatively correlated with amylose and soluble sugar content. Precipitation, longitude, and altitude were significant negatively correlated with fruit weight and size. Fruit shape and nutshell thickness were significant positively correlated with temperature during hot and humid season while negatively correlated with equivalent latitude. Starch and amylose content was significant positively correlated with equivalent latitude, while soluble sugar content showed a negative correlation with it. Interestingly, starch content and amylose content exhibited significant negative correlations with precipitation during the coldest quarter of 2021, while showing significant positive correlations with soluble sugar content. Additionally, starch content was significant positively correlated with precipitation seasonality of 2022 but negatively correlated with quarterly precipitation and mean temperature.

The variation in fruit traits of Q. variabilis showed significant differences among provenances. Group I exhibited prominent advantages for fruit utilization, while Group V demonstrated distinct superiority for forage purposes. Both soluble sugar content and amylose content showed significant negative correlations with fruit shell thickness. Soluble sugar content also exhibited a significant negative correlation with endocarp thickness. Fruit weight and size were predominantly influenced by longitude, precipitation, and altitude, whereas nutshell thickness was mainly governed by temperature and latitude, indicating distinct geoclimatic drivers between these two trait categories.