Table grapes are highly susceptible to Botrytis cinerea infections during the bloom period. After reaching the flower development stage, B. cinerea remains quiescent until berry ripening or gives rise to blossom blight under specific climate conditions. A research study was conducted on the Chilean Central Valley during the 2018-2019 growing season. Flowers of Vitis vinifera cv. Thompson Seedless were collected and B. cinerea was isolated together to a second and morphologically different species, characterized by white mycelium and low to no sporulation (11.4% of total isolates). Three randomly selected isolates within this population were genetically examined and identified as Botrytis prunorum based on a phylogenetic multilocus approach using partial regions of genes RPB2, HSP60, and G3PDH or NEP1 and NEP2. Pathogenicity tests showed that B. prunorum infects and causes wilting in healthy table grape flowers. B. prunorum isolates were able to infect Thompson Seedless berries, inducing lesions between 13.11 and 41.53% with respect to the lesion diameter generated by B. cinerea B05.10. The fungicide sensitivity was evaluated. The three genetically characterized isolates were sensitive to boscalid and to cyprodinil/fludioxonil mixture with a mean EC₅₀ value of 5.5 µg/ml and 0.065 µg/ml, respectively. However, loss of sensitivity to fenhexamid was determined, with a mean EC₅₀ value of 5.13 µg/ml. Our understanding about blossom blight in V. vinifera has been limited to B. cinerea. Here we associated B. prunorum as a second causal agent of this disease in Chile. This data represents a first approach to the epidemiological characteristics of B. prunorum associated with blossom blight in table grapes.

Claudia Carreras

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