High-quality Germplasm Screening And DNA Fingerprint Construction Of The Core Germplasm Of Juglans Sigillata In Guizhou

Juglans sigillata belong to the genus Juglans of the Juglandaceae.Guizhou is one of the central distribution areas of J.sigillata in the world and belongs to the walnut in southwest China.J.sigillata is abundant in germplasm resources,but the breeding methods is not uniform and causing confusion in varieties.Walnut is a characteristic economic forest tree species in Guizhou.It has been cultivated for more than 2000 years.This area has diverse topography,rich climate changes and a wide variety of plants.The complex and changeable natural climatic conditions and traditional breeding and cultivation technology have resulted in a various walnut germplasm resources.However,a wide variety of ecological and farm varieties have been formed under the influence of long-term natural selection and different site conditions.people named walnuts according to certain characteristics in the long-term production practice.Although these common names play a certain role in production,it is impossible to find out the main characteristics for classification because there wasn’t a comprehensive investigation and analysis of the characteristics of walnuts.Therefore,the phenomenon of homonym and synonym are often found.In this study,through field investigation,the phenotype and quality diversity of nuts of high-quality walnut germplasm resources in Guizhou were analyzed and comprehensively evaluated.Based on the surveyed quantitative traits,different sampling strategies and overall sampling ratios were used to explore the appropriate methods for the construction of Guizhou walnut core collections.The fingerprint map of the core germplasm of walnut in Guizhou was preliminarily established by ESTSSR molecular marker technology,the results will provide a reference for the correct identification of walnut germplasm resources in Guizhou.It provides basic data support for the improvement of walnut resource database,and sustainable utilization of resources and protection strategies in Southwest China.The main findings were as follows:(1)The distribution and characteristics of walnut seedling types in Guizhou were ascertained,and walnut resources and related data in 21counties(cities,districts)in Guizhou were investigated.The results showed that Guizhou walnuts were abundant in germplasm resources.A total of more than 500 samples were investigated,and 289 excellent individual plants were selected for the construction of core germplasm according to the breeding objectives and excellent characters,Guizhou walnut seedling resources could be classified into 4 ecological types.(2)The nut morphological diversity of walnut seedling types were analyzed in Guizhou,there were phenotypic traits variation among and within populations of walnut seedling types in the region,which indicated that walnut resources in this area were rich in phenotypic diversity and nut phenotypes.Walnuts were divided into three major categories in region,namely the southwest,northeast and northwest,central and east of Guizhou by clustering.Geographical regions and site conditions significantly affected the classification of walnut germplasm resources,indicating that the geographical environment was an important factor that influenced on the differentiation of walnut populations.(3)The analysis of nut quality diversity of walnut seedlings in Guizhou area showed that the 8 influencing factors of 289 walnut germplasm resources in 6 main producing areas were reduced to 3principal components,and the cumulative contribution rate of variance reached 66.56% in principal component analysis.The collected walnut germplasm resources were divided into 3 categories: fresh walnut,kernel walnuts,walnuts for oil,walnuts for milk(powder),walnuts for leisure nuts.289 walnut germplasm resources were classified into two categories through cluster analysis,the first category was mainly produced in Weining county,Hezhang county,Qixing-guan district and Shuicheng district,while the remaining walnut samples from 17counties(cities)in Guizhou were grouped into another category.The results indicated that the phenology changed greatly in Guizhou.Altitude,average annual temperature,average annual rainfall and average annual sunshine time had a certain impact on the nut quality of walnut in Guizhou.From the perspective of directional breeding,when selecting walnuts for oil,the fat content index is mainly considered.(4)By analyzing quantitative characters of walnut resources in Guizhou and selecting the deviation degree sampling strategy,the overall sampling ratio was 5%.20 copies walnut core germplasm resources were constructed.It could better represent the heterogeneity,diversity and representativeness of the original germplasm,avoiding the redundancy of germplasm resources,and which was a more suitable method to construct the core germplasm of walnut germplasm resources.(5)Using EST-SSR molecular marker technology,20 DNA fingerprints of core germplasm resources of Guizhou were drawn,and the selected primers were identified with high efficiency and easy to distinguish between germplasm resources.The results can provide scientific basis for the identification of germplasm resources,variety protection and utilization and molecular-assisted breeding of walnut in Guizhou.