Differential physiological and molecular responses of susceptible and resistant tomato genotypes to Alternaria solani infection

Early blight caused by Alternaria solani is a prominent tomato, Solanum lycopersicum, disease that destroys a significant part of tomato production worldwide. Cultivating resistant cultivars is notably important in reducing damage caused by early blight disease. Therefore, comprehending the response of different genetic backgrounds to pathogen infection could enhance understanding of the mechanisms involved in plant defense systems against pathogen invasion. In the present study, the differential response of susceptible and resistant tomato genotypes to A. solani was investigated from molecular and physiological aspects. The results showed that soluble sugar content in the resistant genotype increased after pathogen inoculation. Although photosynthetic pigments such as carotenoid, chlorophyll a, and chlorophyll b content decreased in susceptible and resistant genotypes, fluorescence chlorophyll indices differed in resistant and susceptible genotypes. Also, transcription analysis revealed that in the resistant genotype, the expression of SlWRKY1 was 2.58 times more than the control at 48 hpi (hours post inoculation). However, in the susceptible genotype, the expression of the SlNAC1 was 69.12 times more than in control at 24 hpi. The findings of this research provide an improved understanding of tomato plant defense mechanisms against early blight disease.