Authors' Contribution MUA designed the study, conducted the surveys, executed experimental work and prepared the manuscript. SAK supervised the work. NJ provided technical assistance. AUM analyzed the data.

In this study, we analyzed the genetic diversity by using ISSR markers in four populations with 37 DNA samples of Youxi Kucha. In total, 66 alleles were amplified using 8 ISSR primers. A total of 66 bands were detected, of which 63 bands were polymorphic with a polymorphic proportion of 95.24 %. At the population level, the average PPL of the four populations of Youxi Kucha is 76.19 %, and the average values of Nei's gene diversity index (H) and Shannon diversity index (I) are 0.204 5 and 0.367 7 respectively. At the species levelm the H and I are 0.305 1 and 0.465 0 respectively respectively. Youxi Kucha maintained a relatively high genetic variability at the population level and species level bothly. The genetic differentiation within the population was significantly higher than that between populations，but the genetic differentiation between the populations has also reached higher level (Φst = 0.17> 0.15), the differentiation is extremely significant (P <0.01). A mantel test indicated there was no significant relationship between genetic distance and geographic distance among the populations studied. Correlation analysis shows that the diversity index has little relationship with altitude. This study carried out the molecular identification of the germplasm resources of Youxi bitter tea accurately, which can provide a theoretical basis for the protection of Youxi bitter tea and the breeding of improved tea varieties.