Different tolerance responses against Botrytis cinerea in Hydrangea macrophylla

Botrytis cinerea is an important necrotrophic fungal pathogen with a broad host range and causes devastating economic losses. Although B. cinerea has been well studied in different plant species, there is limited information related to the tolerance and susceptibility of Hydrangea macrophylla cultivars to B. cinerea infection. In this study, spore germination, germ tube growth and the distribution of hydrogen peroxide (H₂O₂) in infected plant tissues were studied over a time frame from 6 to 72 h post inoculation (hpi) in two susceptible and two tolerant H. macrophylla cultivars. Leaf samples were stained with 3,3’-diaminobenzidine (DAB) and the fluorescent dye Uvitex 2B and analyzed at microscopic level. Results revealed no significant differences regarding the germination rates of the B. cinerea spores in tolerant and susceptible cultivars. However, shorter germ tubes and less acceleration of H₂O₂ were observed in tolerant cultivars. These results give first evidences on plant defense mechanisms involved in the tolerance reaction of H. macrophylla against B. cinerea infection.