Bacterial spot disease caused by Xanthomonas campestris pv. vesicatoria (Xcv) negatively affects tomato crop, resulting in significant losses in production and yield. Plant extracts have previously revealed a key role in inducing resistance of plants to the harmful pathogens. The current study aimed at investigating the efficacy of neem (Azadirachta indica L.) extract in inducing the resistance of hydroponically grown tomato plants to bacterial spot disease. Results showed that the infection of hydroponically grown tomato plants with Xcv decreased the gas exchange parameters, relative water content, nutrients uptake and levels of chlorophyll, carotenoids, soluble protein and sugar in tomato plants, in comparison to control plants. Furthermore, infection of tomato plants with Xcv boosted the contents of flavonoids, phenols, electrolyte leakage, malondialdehyde, hydrogen peroxide, glycine betaine, proline, reduced glutathione, oxidized ascorbate, ascorbate, antioxidant enzymes (CAT, APX, SOD) and expression of antioxidant genes in tomato plants. On the other hand, neem extract application markedly decreased disease severity levels and oxidative stress biomarkers in Xcv-infected plants, in comparison to Xcv-infected plants. Furthermore, neem extract application markedly increased the gas exchange parameters, nutrients uptake and levels of chlorophyll, carotenoids, soluble protein and sugar, phenols, flavonoid, glycine betaine, proline, reduced glutathione, oxidized ascorbate, ascorbate, antioxidant enzymes (CAT, APX, SOD) and expression of antioxidant genes in Xcv-infected plants, as compared to Xcv-infected plants. In conclusion, this study proved the efficacy of neem extract in enhancing bacterial spot resistance in tomato plants.
Key words: Neem extract; tomato; soilless culture; antioxidants; bacterial spot; genes expression.
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