Comparative ultrastructural analysis of Botrytis cinerea infection in inflorescences and peels of grapevine varieties (Reveals organ-specific responses)

Botrytis bunch rot or gray mold caused by Botrytis cinerea, is a significant disease affecting grapevine clusters. While previous studies focused on leaf resistance, this research delves into the ultrastructural changes of grape inflorescence and fruit infected with Botrytis cinerea. Here, we investigated four grape varieties: a highly resistant Chinese wild grapevine, Vitis amurensis ‘Beibinghong’ (BH), a resistant grapevine, Vitis labrusca × Vitis vinifera ‘Shine Muscat’ (SM), a susceptible grapevine, Vitis vinifera ‘Daqing’ (DQ), and a highly susceptible Vitis vinifera ‘Red Globe’ (RG). Using light microscopy (LM), stereo microscope (SM), scanning electron microscopy (SEM), and Diaminobenzidine (DAB) staining of inoculated grape inflorescences and peels, we observed and compared the prevalence of B. cinerea infection in RG, DQ, SM, and BH, following the order: BH > SM > DQ > RG. After 72 h of inoculation, RG exhibited the highest mycelium count, accompanied by inflorescence and peel decay. In contrast, BH showed minimal mycelium on inflorescences and peels, maintaining a relatively intact epidermis. DAB staining of inflorescences revealed distinct H₂O₂ accumulation in susceptible varieties within 24 h of inoculation, whereas disease-resistant varieties showed minimal staining. Notably, highly resistant BH displayed H₂O₂ accumulation only after 72 h of inoculation. Overall, these results provide insights into the intricate interactions between the grape inflorescences, peels, and B. cinerea. Moreover, the study underscores the potential of highly resistant Chinese wild mountain grapes for developing new varieties with robust gray mold resistance.