Analysis of phenotypic diversity of nuts in wild walnut (Juglans cathayensis Dode) in Xinjiang

Abstract:【Objective】Xinjiang wild walnut is ancestor of the cultivated walnuts and is characterized by high degree of genetic variation, unique quality and rich nut types through long-term natural selection. Therefore, collection, preservation and investigation of the wild walnut resources in Xinjiang are of great significance for the study of the evolution and improvement of walnut. The objective is to analyze the phenotypic diversity of the nuts of Xinjiang wild walnut in order to provide a foundation basis for the utilizations of the species.【Methods】In this study, 34 wild walnut samples were investigated from the wild walnut nature reserve, 10 mature fruits were randomly selected from the periphery of the crown of each sample for index determination. 16 descriptive traits and 11 quantitative traits of air-driednuts of 34 walnut germplasm were determined. Two state standards of the quality grade of walnut and germplasm resources description and data standards were referenced. Related traits of 16 characters of the wild walnut were recorded by description and observation method. 11 quantitative characters of the wild walnut were measured. Clustering analysis and correlation analysis were employed to analyze the phenotypic traits of the nuts of the wild walnut.【Results】The distribution range of the wild walnut in Xinjiang is relatively narrow, but its morphological variation of the nuts is significantly rich. There were clearly significant differences among different wild walnut germplasm in Xinjiang. The variation of nut size in 34 wild walnut accessions tended to become smaller. Among the 16 description characters of 34 samples the elliptocytosis and oval shape of the nuts, accounted for 58.8% and 29.4%, respectively. The smooth nuts accounted for 91.2%. Sandy beige and brown color accounted for 50% and 26.5%respectively. Blunt and sharp shape of the nut top and shoulder accounted for 38.2% and 20.6% respectively. The flat and round end of nuts accounted for 50% and 41.2% respectively. The kinds of core shell groove-intensive germplasm accounted for 58.8%. The samples of inpocketed-membranous wall and diaphragm-membrane accounted for 85.3% and 58.8%, respectively. The full kernel rate accounted for 88.2%, the kernel output with 1/8 kernel accounted for 55.9%. The yellow kernel color accounted for 58.8%. The smell of the kernel was normal, the suture was close and shell developed well. The average coefficient of variation of 11 quantitative characters was 9.92%. Among them, the coefficient of variation of single kernel weight was the largest (19.98%) , and the coefficient of transverse diameter variation was the smallest (5.22%) . Correlation analysis showed that there were high correlations between the 11 quantitative traits, 29 of them were extremely significantly and positively correlated, and 2 were significantly and positively correlated. 1 was significantly and negatively correlated, and 1 was negatively correlated. By cluster analysis, 34 accessions of the wild walnut in Xinjiang were divided into 8 groups.【Conclusion】The phenotypic traits of nuts of Xinjiang wild walnut have abundant genetic diversity. The fruit weight, kernel weight, fruit shape index, seed shell carcass, kernel rate, kernel shell thickness could be used for walnut quality evaluation. The variation of phenotypic traits of nuts of Xinjiang wild walnut have a trend to become smaller compared with those 20 years ago due to the changes in the local environment and human activities. The specific reasons for the trend of being narrow of the variation of nut sizes in the wild walnut needs further study.