Histopathological studies on grapevine die-back

Histopathological investigations of Botryodiplodia theobromae Pat., Phomopsis viticola Sacc. and Fusarium solani (Mart.) Sacc. on artificially inoculated grapevine shoots revealed the induction of various cytological and histological defects. Immediately after inoculation (ai), the investigated sections exhibited similar structure in both inoculated and non-inoculated shoots. Seven days after inoculation (dai), B. theobromae induced disorganized epidermal and cortical cells with a dark brown color consisting of plasmolysis cells and tissues. No such disorders were noticed in case of Pb. viticola or E solani. The above mentioned pathogenic fungal hyphae were clearly noticed 21 dai in both xylem parenchyma and xylem vessels causing necrosis at these tissues. Not only the pathogenic fungi caused necrosis in xylem parenchyma and xylem vessels, but also colonized the tissues with their hyphae and dark inclusions bodies as well as abundant production of tyloses were clearly noticed. There was a correlation between the histological changes and symptom development. At the time of inoculation, the shoots appeared vigorously green colored and erect. The inoculated shoots 7 dai were paler, less vigorous, and less-rigid than that of non-inoculated ones. Twenty-one dai, the inoculated shoots were drooped, flaccid, yellow in color and signs of wilting began to appear and finally shoots were dead, and turned brown in color.