Genetic Diversity and Structure of Higher-Resin Trees of Pinus oocarpa Schiede in Mexico: Implications for Genetic Improvement

Pinus oocarpa Schiede is the most widely distributed conifer in the Americas. In Mexico, it inhabits diverse environments and is the primary pine species utilized for resin production, prompting the establishment of a genetic improvement program (GIP). Preserving a broad genetic diversity is fundamental to the success of the GIP. This study aimed to assess the genetic diversity and structure of trees selected for their high resin yield. A total of 146 trees from 15 provenances within three populations (MX-MIC, MX-MEX, and MX-OAX) constituting the selection population of the GIP were evaluated. Five SSR microsatellite markers (PtTX3013, NZPR1078, PtTX2146, PtTX3107, and PtTX3034) were used to determine key indicators of genetic diversity and structure. All three populations exhibited high genetic diversity; however, the heterozygosity observed was lower than the expected heterozygosity. Genetic structure analysis revealed the presence of two distinct genetic groups: the Transverse Volcanic Axis (MX-MIC and MX-MEX) and the Sierra Madre del Sur (MX-OAX). Most of the genetic diversity (87.42%) was found within provenances. Gene flow was high among provenances within the same genetic group but limited between provenances from different groups. The findings suggest that GIPs should be tailored to each genetic region, with a focus on within-provenance selection to maintain genetic diversity.