Diversity, pathogenicity, fungicide sensitivity, and field management of the circular leaf spot pathogen complex on rubber trees in Vietnam

Abstract

Circular Leaf Spot (CLS) has recently emerged as a significant foliar disease affecting Hevea brasiliensis in Vietnam. This study investigated the causal agents, their morphological and molecular characteristics, and evaluated effective disease management approaches. A total of 188 fungal isolates were obtained from infected rubber leaves, comprising 94 isolates of Pestalotiopsis spp. and 94 isolates of Colletotrichum spp. Morphological observations and rDNA-ITS sequencing identified Pestalotiopsis microspora (divided into three intraspecific groups) and three Colletotrichum species complexes: C. gloeosporioides, C. siamense, and C. acutatum. Pathogenicity tests on detached leaves and potted rubber clones confirmed that all isolates were pathogenic, with mixed inoculations causing significantly more severe symptoms than single isolates (p < 0.01). In vitro assays demonstrated that propiconazole, tebuconazole, and tetramycin effectively inhibited mycelial growth of both pathogens. A field trial was established to evaluate an integrated disease management model, incorporating sanitation, biological residue treatment, nutrition-based fertilisation, and targeted fungicide application. The model significantly delayed disease onset, reduced CLS incidence and severity, improved canopy density, and resulted in a 12.3% reduction in management costs and an 11.3% increase in latex yield compared to the control. The study highlights the complex etiology of CLS involving both Pestalotiopsis and Colletotrichum spp., and demonstrates the effectiveness of an integrated approach for sustainable disease management in rubber plantations.