Changes in photosynthesis of Lycopersicon spp. plants induced by tomato powdery mildew infection in combination with heat shock pre-treatment

Effect of economically important powdery mildew fungus Oidium neolycopersici on photosynthesis in tomato leaves was investigated during 9 days after inoculation using CO2 exchange measurement and chlorophyll fluorescence imaging. In both moderately resistant (Lycopersicon chmielewskii) and susceptible (Lycopersicon esculentum cv. Amateur) genotypes the infection caused only minimal impairment of photosynthesis. When the plants were pre-treated by heat shock (40.5 °C, 2 h) before inoculation, resistance response of L. chmielewskii was not affected, whereas in L. esculentum chloroses/necroses developed and rate of CO2 assimilation and maximal quantum yield of photosystem II photochemistry (FV/FM) decreased in infected leaves. We hypothesise that these changes could be associated with cell-wall invertase activation amplified by an increased demand for carbohydrates in heat shock-induced defence reactions.