Characterizing the interaction between Botrytis cinerea and grapevine inflorescences

Botrytis cinerea causes bunch rot in grapevine that affects both fruit quality and yield. The pathogen is difficult to manage due to asymptomatic infections that often occur during flowering. It is believed that after early colonization of the flowers, the fungus enters a quiescent phase until the onset of ripening. At that time, the infection then becomes active by further colonizing the ripening berry without visible signs and eventually displaying visible signs of rot. In order to characterize the molecular mechanisms associated with the grapevine/fungus interaction, inflorescences of Vitis vinifera ('Pinot Noir') were inoculated with B. cinerea at the cap falling stage (EL25/26). Floral samples were collected at 24 and 96 h post inoculation (hpi) and either plated on selective medium, or subjected to polyphenol and RNA sequence analyses. A microscopic examination of the infection process was also conducted. B. cinerea produced appressoria in grapevine flowers and penetrated the flower cuticle (gynoecium) within 24 hpi but there was no apparent disease progress afterwards even though the presence of the pathogen on flowers/fruitlets was confirmed by plating tissues on selective media. The analysis of phenols indicated a significant increase of several stilbenoids, including oligomeric ones, in samples that had been inoculated. A much larger number of genes (1193) appeared to be modulated in the inoculated samples at 24 hpi than at 96 hpi. Based on GO enrichment and VitisNet analyses, there were more enriched classes, including those involved in plant pathogen interaction, at 24 hpi than at 96 hpi. Additionally, a greater number of B. cinerea genes were detected at 24 hpi than at 96 hpi. These data suggest that within 96 hpi, the pathogen enters into a quiescent phase.