Paecilomyces maximus as the causal agent of canker disease on Eucalyptus camaldulensis in Hormozgan Province, Iran

During a survey, a severe canker disease outbreak affecting Eucalyptus camaldulensis was found in various parts of Hormozgan Province, the south of Iran. The disease symptoms manifested through dark brown necrotic lesions, extensive cankers, longitudinal trunk cracks, wood discoloration, twig dieback, gummosis, and death. The disease incidence in the studied regions was 81%. This study aimed to characterize the disease, ascertain its etiological agent, and validate its pathogenicity using Koch’s postulates. Fungal isolations from symptomatic tissues yielded colonies consistent with a Paecilomyces sp., subsequently identified as P. maximus based on morphological traits and molecular analysis of the internal transcribed spacer nrDNA region and β-tubulin (tub2) gene. Pathogenicity tests demonstrated lesion development on healthy branches inoculated with mycelium plugs from P. maximus, confirming the association between the fungus and observed symptoms. Small brown lesions appeared on the inoculated branches during 15 to 18 days, proving that the fungus is the cause of the disease. P. maximus was only re-isolated from the inoculated symptomatic tissue. Notably, this study represents the first documentation of P. maximus causing canker disease on eucalyptus trees in Iran and globally.