Genetic diversity analysis and DNA fingerprint construction of litchi germplasms based on fruit traits and ISSR molecular markers

Objective This study aimed to conduct an analysis of genetic diversity and a cluster analysis of 34 litchi germplasms based on fruit traits and ISSR molecular markers， and construct a DNA fingerprint map， in order to provide theoretical references for the classification， identification， evaluation and innovative utilization of litchi germplasm resources.Method 34 litchi germplasms from the China were selected as the research objects. Their fruit traits such as average single fruit weight， soluble solid content， fruit shape， shape of scute-like segments and distinctness of suture were observed. Variation analysis， diversity analysis and correlation analysis were conducted and the cluster analysis was performed based on fruit shape and ISSR molecular markers， respectively. Finally， a DNA fingerprint map was constructed based on the ISSR molecular marker detection results.Result The single fruit weight of the 34 litchi germplasms ranged from 17.0 to 57.5 g， and the soluble solid content ranged from 13.0% to 20.7%. The fruit shapes included cordate， orbicular shape， oval shape， elliptical shape and oblique cordate. The shape of scute-like segments included swelling， sharp-pointed and smooth. The sutures were either clear or unclear. The Shannon-Weaver diversity index of fruit traits ranged from 0.67 to 1.97， with the lowest was shown in the suture distinctness and the highest shown in the soluble solid content. The single fruit weight had a significantly negative correlation with the soluble solid content （P<0.01）， and the fruit shape had a significantly negative correlation with the shape of scute-like segments （P<0.05）. The cluster analysis based on fruit traits showed that： when the Euclidean distance was 8， the tested materials were divided into four groups； the clustering results of fruit traits showed a strong correlation with the distinctness of the fruit suture in litchi germplasms； and clustering results of fruit shape and shape of scute-like segments showed that each category included germplasms from different regions， indicating that the clustering results had no obvious correlation geographical distribution. A total of 191 bands were amplified using 17 ISSR primers， of which 165 were polymorphic bands， with an average polymorphism ratio of 86.39%. The polymorphism ratios of primers UBC835， UBC846 and UBC879 were as high as 100%. The number of alleles （Na） ranged from 1.6875 to 2.0000， with an average of 1.8422. The effective number of alleles （Ne） ranged from 1.2498 to 1.7177， with an average of 1.4470. Nei’s gene diversity index （H'） ranged from 0.16 to 0.40， with an average of 0.26. Shannon’s information index （I） ranged from 0.2616 to 0.5746， with an average of 0.4015. The cluster analysis based on ISSR molecular markers showed that： the genetic similarity coefficient of the 34 litchi germplasms ranged from 0.5916 to 0.8691， with an average of 0.7359； at a genetic similarity coefficient of 0.7100， the tested materials were divided into 4 groups， each group included germplasms from multiple regions， and the clustering results were not significantly correlated with geographical distribution， but were correlated with the fruit maturity period. The ISSR primer UBC857 could be used to construct the DNA fingerprint map of the 34 litchi germplasms.Conclusion The genetic diversity of fruit traits of the 34 litchi germplasms is relatively rich， but as the genetic similarity coefficient is relatively high， the genetic basis is rather narrow. The clustering results based on fruit traits and ISSR molecular markers are only partially consistent， and both showed no obvious correlation with geographic distribution， but are correlated with fruit suture distinctness and fruit maturity period of litchi germplasm， respectively. The primer UBC857 could be used to distinguish the 34 litchi germplasms.