Analysis of genetic diversity and environmental associations of wild citron (Citrus medica L.) in northeast India

Abstract

Citron (Citrus medica L.) is a major citrus fruit crop known for its medicinal, nutritional, and aromatic uses. Native to northeast India, Myanmar, and south China, citron is cultivated mostly in the Mediterranean and South Asian countries. The truly wild populations of citron are found in the hills and valleys of northeast India. The extent of genetic diversity in wild citron in relation to environmental variables has not been documented. In the present study, we analyzed genetic diversity and environmental association of wild populations of C. medica in northeast India using 15 polymorphic nuclear SSR (simple sequence repeat) markers and 21 environmental variables. SSR profiling revealed a moderate genetic diversity (Ho = 0.40; He = 0.41; I = 0.70). Neighbor-joining (NJ) and principal coordinate analysis (PCoA) grouped 16 natural populations into two genetic clusters. Bayesian structure results showed two genetic populations with a high admixture of individuals. Analysis of molecular variance (AMOVA) revealed low genetic differentiation (Fst = 0.14; P < 0.001), indicative of high gene flow (Nm = 1.53) in citron. The isolation by distance (IBD) analysis showed a weak correlation, indicating that geographic distance was not a determining factor for genetic distance in C. medica populations. The higher metrics of outcrossing rate (tm > 0.9) revealed outbreeding nature of the species. The genetic diversity of citron showed a positive correlation with precipitation of driest month and precipitation of coldest quarter, but negative with mean diurnal range and isothermality. Overall, the results of the present study could benefit the conservation and management of citron resources and their natural habitat in northeast India. Genetically highly diverse populations identified in the present study can be used for conservation and utilization of citron genetic resources.