Development of a detached leaf assay to evaluate Hydrangea macrophylla cultivars for susceptibility to Botrytis cinerea

Hydrangea macrophylla is an economically important ornamental plant widely cultivated for its colorful, large inflorescences and attractive foliage.
However, Botrytis spp., destructive fungal pathogens with a broad host range, causing gray mold disease, severely affect its production.
While Botrytis has been extensively studied in other crops, interactions between B. cinerea and H. macrophylla remain underexplored.
This study aimed to develop a detached leaf assay using plug inoculation for the rapid and efficient screening of H. macrophylla cultivars.
This method facilitates accurate evaluation of susceptibility to B. cinerea, supporting breeding efforts to enhance disease resistance.
To establish the assay, leaves of H. macrophylla cultivars were inoculated with a specific strain of B. cinerea and incubated under various conditions, including temperature and light variations.
Lesions were measured at different time points post-inoculation, and significant differences in lesion size were investigated.
At 21°C with 16 h of light, clear groupings between cultivars were observed based on their lesion sizes.
Two cultivars constantly displayed small lesions, indicating low susceptibility, while eight cultivars showed large lesions, suggesting high susceptibility.
Our assay allows us to differentiate between cultivars against B. cinerea based on lesion size and progression.
It provides initial data on cultivar responses, with future research aimed at validating these results through an in vivo infection assay using whole plants.

International Symposium on Biotechnological Tools in Horticulture

E. Fatemi, L. Fazlikhani, J. Schumacher, F. Engel, C. Tränkner

gray mold, bigleaf hydrangea, plant-pathogen interaction, susceptibility assessment, resistance breeding

https://doi.org/10.17660/ActaHortic.2026.1454.26