The effect of temperature and wetness duration on infection of Vitis vinifera inflorescences (from "inflorescence clearly visible" to "end of flowering" stages) and young berry clusters (at "fruit swelling" and "berries groat-sized" stages) by Botrytis cinerea was investigated. Artificial inoculations were carried out using conidial suspensions of eight B. cinerea strains belonging to the transposon genotypes transposa and vacuma. Infection incidence was significantly affected by strain but not by transposon genotype (transposon genotype accounted for only 6.5% of the variance). Infection incidence was also affected by the interaction between strain and growth stage of the inflorescence or berry cluster (overall accounting for approximately 57% of the experimental variance). Thus, under our experimental conditions, the ability to cause infection was a strain rather than a transposon genotype attribute. Across all strains, infection incidence was lowest when inflorescences were clearly visible or fully developed, highest at flowering (from beginning to end of flowering), and intermediate at the postflowering fruit stages (fruit swelling and berries groat-sized). One transposa strain, however, was highly virulent on all grapevine growth stages tested. The effects of temperature and wetness duration on infection incidence were similar for all fungal strains and grapevine growth stages; infection incidence was highest at 20°C and lowest at 30°C, and was also low at 5°C. Similar results were obtained for mycelial growth and conidial germination. Based on the pooled data for all strains and grapevine growth stages, an equation was developed that accounted for the combined effects of temperature and wetness duration on relative infection incidence. This equation should be useful for developing decision-making systems concerning B. cinerea control at early grapevine growth stages.
