Etiology of Leaf Scorch Disease on Almond: Pathogen Identification, Molecul, and Pathogenicity Tests

Abstract

Leaf scorch disease of Almond has recently emerged as a serious constraint affecting tree vigor, canopy health, and nut productivity in several production regions. The present study was undertaken to elucidate the etiology of leaf scorch disease through pathogen identification, molecular characterization, and pathogenicity confirmation. Symptomatic leaf samples exhibiting marginal scorching, chlorosis, necrotic browning, and progressive leaf desiccation were collected from affected almond orchards. The associated pathogen was isolated on suitable culture media and purified through repeated sub-culturing. Morphological characterization was carried out based on colony features, mycelial growth pattern, and reproductive structures. Molecular identification was performed using PCR amplification and sequencing of conserved genomic regions, followed by comparison with reference sequences in public databases. Phylogenetic analysis confirmed the taxonomic placement of the isolate within a closely related pathogenic group associated with woody perennial hosts. Pathogenicity tests were conducted on healthy almond seedlings under controlled conditions, where inoculated plants reproduced typical leaf scorch symptoms, thereby fulfilling Koch’s postulates. Re-isolation of the same pathogen from artificially infected tissues further validated its causal role. The study demonstrates that a specific fungal pathogen is responsible for leaf scorch disease in almond and highlights its pathogenic potential under conducive environmental conditions. The integration of morphological, molecular, and pathogenicity approaches provides a robust framework for accurate disease diagnosis. These findings are essential for developing effective disease management strategies, including early detection, orchard sanitation, and integrated control measures to reduce the impact of leaf scorch on almond production systems.