Study On Evaluation Of Germplasm Diversity Of Corylus Kweichowensis Hu.in Dabie Mountains

Corylus kweichowensis Hu.is one of Chinese endemic species in Corylus.It is an economically and ecologically important nut crop that is widely distributed,particularly in southern provinces in China.However,the distribution,genetic diversity and phenotypic traits of C.kweichowensis are rarely studied.The germplasm resources of C.kweichowensis are declining due to climate change,species competition and humanity’s destruction.Therefore,the protection of genetic diversity is indispensable.This paper analyzed geographic distribution pattern and climatic conditions by referring to the existing document literature,herbarium,local chronicles,meteorological data and field investigation using Kira’s index,Holdrige’s index,Xu’s index and so on.Furthermore,the genetic diversity and genetic structure of C.kweichowensis populations at different altitudes in Dabie Mountains were assessed using SSR marker.Moreover,the phenotypic diversity of C.kweichowensis germplasm resources in Dabie Mountains was comprehensively evaluated,and the candidate superior individuals were chosen by Factor analysis method.Through the above studies,our results will provide theoretical reference and technical practice guidance for protection strategy and utilization of C.kweichowensis.The main results are as follows:（1）Clarifying the modern distribution pattern and climatic water-temperature conditions of C.kweichowensis.C.kweichowensis resources mainly distributed in 15 provinces（autonomous regions and municipalities）in China,with the horizontal distribution ranging from 102°06’to 121°59’in longitude and 25°11’to 37°38’in latitude,whereas the vertical distribution varied from 200 to 2500 m of which the elevation of 500¹000 m was the concentrated area.In Dabie Mountains area,the distribution area of C.kweichowensis mainly located on east longitude 114°05’¹16°29’and north latitude 30°35’³1°48’.Its vertical distribution elevation was 284¹200 m and the concentrated distribution elevation was600⁸00 m.（2）Appropriate cultivation regions of C.kweichowensis were designated.The principal component analysis indicated that low temperature was the first factor among numerous climatic conditions to constrain the geographical distribution of C.kweichowensis.Therefore,mean temperature in January,Kira’s coldness index,extreme low temperature,frostless period and annual mean temperature should be primarily considered when C.kweichowensis was cultivated.The value of optimal range were-2.25⁶.69℃,-18.73⁵.27℃·month^-1,186.20²83.75d,11.24¹7.72℃,respectively.According to Holdrige’s classification system and Kira’s warmth index,C.kweichowensis was a tree species of humid forest life zone type in warm temperate and subtropical zones.By building a regression equation among the latitude（LAT）,longitude（LON）and Kira’s warmth index（WI）,Kira’s cold index（CI）and Xu’s humidity index（HI）,the results indicated that there was a significant correlation.The appropriate cultivation regions were located in east longitude 102°06’¹21°25’and north latitude 28°46’³4°30’,of which the north boundary lied in Meixian county,Weinan county of Shanxi province and Zhouqu county of Gansu province.Its south boundary was located in Wuyi county of Zhejiang province,Sangzhi county of Hunan province and Meigu county of Sichuan province.（3）C.kweichowensis populations had a relatively high genetic diversity.A total of 15microsatellite loci were used to study the genetic diversity of 20 C.kweichowensis populations in Dabie Mountains.The mean value of the allele number（Na）,Shannon’s information index（I）,Observed heterozygosity（HO）,Expected heterozygosity（He）and Polymorphism Information Content（PIC）were 18.867,2.131,0.653,0.814 and 0.798,respectively.The results showed that the genetic diversity of C.kweichowensis had a relatively high level.Among 20 C.kweichowensis populations,some populations showed a relatively high genetic diversity,including JZS population,YXH population,YXB3 population,SCW population and MCSH population,while the lowest genetic diversity population was JZB.The results of FST and AMOVA indicated that the variation within populations accounted for over 90%of the total variation.The mean value of gene flow was 2.990,which neutralized the effect of the genetic drift.The cluster results of UPGMA,STRUCTURE and PCoA revealed that 20 C.kweichowensis populations were clearly divided into two clusters.Results from the Mantel test indicated that there were no significant positive correlation between Nei’s genetic distance and geographic distance（km）among 20 populations.（4）The genetic diversity of C.kweichowensis was affected by altitude.With the increasement of altitude,the genetic diversity level took on low-high-low variation trend.One of all altitudinal groups,there was a level of the highest genetic diversity in the medium altitude（600⁸00m）.The analysis of UPGMA,STRUCTURE and PCoA showed a similar result that 15 C.kweichowensis populations and four groups were divided into two clusters,and the dividing line of the two clusters was 600m.Mantel test revealed a weak but positive correlation between Nei’s genetic distance and altitude（m）（R=0.234,P=0.040）.（5）18 qualitative traits and 25 quantitative traits of 200 C.kweichowensis individuals in Dabie Mountains were analyzed to evaluate the variation and diversity of phenotypic traits.The results indicated that there was a relatively abundant variation of some qualitative and quantitative traits which could be used as priority evaluation index,including nut seed coat colour,nut shape,Kernel fineness,shell thickness,leaf width,nut transverse diameter,nut size,nut weight,kernel longitudinal diameter and kernel size.There were some differences among phenotypic traits,and the genetic diversity index of quantitative traits was higher than that of qualitative traits.The variation and diversity of phenotypic qualitative and quantitative traits of C.kweichowensis in Dabie Mountains were clarified.The main quantitative traits of C.kweichowensis:nut weight ranged from 0.45 to 3.27g,with an average of 1.50g;kernel weight varied from 0.19 to 1.54g,with an average of 0.49g;the mean value of kernel mass percentage was 34.05%,ranged from 18.15 to 71.75%;shell kernel clearance varied from 0 to3.92mm,with an average of 0.78mm;the mean value of shell thickness was 1.74mm,ranged from 0.63 to 2.90mm.There were obvious differences between diversity of phenotypic qualitative traits and that of quantitative traits.The diversity of quantitative traits（H’=1.97）was higher than that of qualitative traits（H’=0.68）.Based on quantitative traits,building thirteen grading index system and ten superior individuals were chosen by Factors analysis methods.（6）According to the results of the genetic diversity of C.kweichowensis in Dabie Mountains area,the results showed that there were a relatively high genetic diversity level among some populations,especially over an altitude of 600m,such as JZS population,YXH population,YXB3 population,SCW population and MCSH population.We suggest that these populations should be protected in situ and ex situ.Meanwhile,the superior individuals and study of C.kweichowensis will be carried out.Furthermore,improving the awareness of C.kweichowensis to reduce man-made destruction phenomenon of wild resources.