Ex-situ evaluation of curry leaf (Murraya koenigii (L.) Spreng) germplasm to unravel the genetic diversity of leaf essential oils

The present study was conducted with the objective of studying the genetic diversity of essential oils (EOs) in curry leaf (CL) ex-situ. Chemometric methods and pattern analysis were employed to assess the genetic diversity of EOs and to characterise diverse sets of CL germplasm into different chemotypes. The study revealed a huge genetic diversity for EO yield and its composition among the tested genotypes. Cultivated types had significantly higher EO yields and showed a greater degree of genetic divergence compared to wild types. In total, 80 different compounds were identified in the EOs of CL and classified into major (6) and minor (74) compounds. The major compounds alpha-pinene, gamma-terpinene, and alpha-selinene and 14 minor compounds were highly variable among the tested genotypes. They may play an important role in the formation of different chemotypes. Other important compounds, such as trans-caryophyllene and alpha-humulene, were more widely distributed among the tested genotypes and indicated their predominant occurrence in the EOs of CL. Some major compounds, such as valencene and gamma-terpinene, showed a significant regional correlation, indicating the role of geographic factors in the evolution of different chemotypes. Furthermore, some compounds such as alpha-pinene, bornyl acetate, and camphene had significantly higher concentrations in wild types compared to cultivated types, indicating the influence of domestication through human selection on the composition of EOs in CL. A total of 4 major chemotypes were characterised, of which three new chemotypes are being reported for the first time in CL.