Unravelling the colonization mechanism of Lasiodiplodia brasiliensis in grapevine plants

Botryosphaeriaceae cause the degenerative disease Botryosphaeria dieback in many woody hosts, including grapevine. These pathogens penetrate host plants through pruning wounds, and colonize vascular tissues causing necrotic lesions, cankers, and eventually plant death. Colonization processes by Botryosphaeriaceae and their interactions with their hosts has been understudied. The colonization mechanisms were examined for Lasiodiplodia brasiliensis, a common pathogen causing Botryosphaeria dieback in Mexican vineyards. Lasiodiplodia brasiliensis MXBCL28 was inoculated onto grapevine ‘Cabernet Sauvignon’ plants, and after 2 months, infected tissues were observed with microscopy using histological techniques. Lasiodiplodia brasiliensis was also cultured on different carbon sources representing cell walls and non-structural plant components, to complement histology data. The host responded to wounding by developing xylem vessel occlusions with tyloses and deposition of suberin in cambium and ray parenchyma. Infection response also included deposition of suberin in pith tissues, reinforcement of cell walls with phenolic compounds, and lignin deposition in xylem vessels and ray parenchyma. The pathogen could overcome host compartmentalization mechanisms and colonize wood tissue causing extensive necrosis. The fungus was visualized in host cambium, vascular bundles, xylem vessels, and pith, and infected tissues were depleted in starch in the ray parenchyma. Cellulose, hemicellulose, and lignin in cell walls were also degraded, supporting in vitro data.