Changes in susceptibility of bean leaves (Phaseolus vulgaris) to Sclerotinia sclerotiorum and Botrytis cinerea by pre-inoculative ozone exposures

Abstract

The effects of ozone on the susceptibility of leaves ofPhaseolus vulgaris toSclerotinia sclerotiorum andBotrytis cinerea have been investigated. Seedlings of one ozone-sensitive (‘Pros’) and five relatively ozone-insensitive cultivars (‘Gamin’, ‘Precores’, ‘Groffy’, ‘Narda’, ‘Berna’) were exposed to different ozone concentrations (0, 120, 180 and 270 μg m−3) for 8 h. One day after the exposures, primary leaves were detached and immediately inoculated with spores of either pathogen suspended in water or in a 62.5 mM KH2PO4 (Pi) solution. Visible ozone injury differed between the cultivars and increased with increasing ozone concentration. On the leaves of non-exposed plants, spores of the pathogens suspended in water caused very few lesions, whereas fungal pathogenicity was stimulated by addition of Pi to the inoculum. Ozone-injured leaves of all cultivars exhibited lesions after inoculation of the leaves with the pathogens suspended in water, and the number of lesions was positively correlated with the level of ozone injury for either pathogen and cultivar. The increase in susceptibility of bean leaves in response to increasing ozone concentrations was greater forB. cinerea than forS. sclerotiorum when spores were suspended in water, but was similar when the spores were suspended in Pi.