Fine-Scale Genetic Differentiation and Population Structure of Erysiphe quercicola in Mountainous Rubber Plantations of Xishuangbanna, Yunnan

Rubber tree powdery mildew caused by Erysiphe quercicola is the most widespread and destructive foliar disease in China’s rubber-growing regions. This disease frequently occurs in severe epidemics during winter–spring each year, delaying rubber tapping by 1–2 months and causing substantial yield losses, and has become a critical bottleneck for stable natural-rubber production. Xishuangbanna is China’s core planting region for natural rubber and a typical representative of mountainous rubber plantations in Yunnan. More than two-thirds of local rubber plantations are located on mountain slopes steeper than 15°. However, the population-genetic background of E. quercicola in this region remains poorly understood. A total of 188 samples of rubber powdery mildew were recovered from nine sampling sites belonging to three geographic populations (Mengla, Menghai, Jinghong). Ten SSR loci were used to analyse the genetic diversity, genetic differentiation and population structure of the tested samples. The results revealed that E. quercicola in Xishuangbanna rubber plantations exhibited high overall genetic diversity. Most samples possessed unique genotypes even at a fine spatial scale, and the Mengla population showed higher genetic diversity than the other populations. Analysis of molecular variance (AMOVA) revealed that the genetic variation of E. quercicola in Xishuangbanna was predominantly partitioned within sampling-site subpopulations. Significant pairwise genetic differentiation was detected among the three geographic populations, although all pairwise ΦPT values were less than 0.1, indicating a pattern of significant yet limited genetic differentiation at fine geographic scales. PCoA and STRUCTURE analyses further confirmed obvious population genetic structure in this region. The results of this study provide a theoretical basis for the epidemic monitoring of rubber powdery mildew in the Xishuangbanna rubber plantation area.