First molecular confirmation of Lasiodiplodia theobromae causing grapevine trunk disease in southern Egypt.

Grapevine trunk diseases constitute a significant phytopathological concern in Egyptian viticulture, with ongoing debates regarding their origin and transmission dynamics. These complexities are attributed to the heterogeneous manifestation of symptoms and the involvement of multiple wood-associated pathogens, both suspected and confirmed. This study investigates the mycological aspects of grapevine trunk diseases, focusing on Lasiodiplodia theobromae as a causal agent. The pathogen was associated with vascular cankers, dark brown trunk discoloration, pycnidia formation on necrotic tissues, and grapevine dieback. Identification of L. theobromae was achieved through morphological characteristics and molecular analysis targeting the β-tubulin gene and Internal Transcribed Spacer (ITS) region. Pathogenicity tests were conducted by inoculating detached canes, leaves, petioles, and entire branches with mycelial plugs of L. theobromae. The resulting symptoms closely resembled those observed in naturally infected grapevines in the field. The pathogen was then re-isolated and identified, confirming Koch's postulates. A disease index (DI) ranging from 60 to 100% provided strong evidence of the high pathogenic potential of L. theobromae under experimental conditions.