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This research was conducted in 2022 at the Department of Plant Protection in the Faculty of Agricultural Engineering at the University of Damascus. It aimed to study the effect of alcoholic extracts from Eucalyptus camaldulensis Dehn., Inula viscosa L., and Lavandula angustifolia Mill., as well as certain fungicides (chlorothalonil, Thiram + Carboxin, Difenoconazole) and a combination of fungicides and plant extracts in inhibiting the growth of the fungus Ascochyta rabiei, which causes ascochyta blight in chickpeas, in the laboratory. The results showed that the alcoholic extracts from the studied plants significantly inhibited fungal mycelium growth compared to the control, with the alcoholic extract of lavender and Inula showing the highest inhibition percentages. The half-maximal inhibitory concentration (EC50) values were 579.05 ppm for lavender, 782.93 ppm for Inula, and 996.06 ppm for eucalyptus, respectively. Meanwhile, the fungicides Carboxin + Thiram and Difenoconazole demonstrated the highest efficacy in inhibiting the mycelium of Ascochyta rabiei, with EC50 values of 13.60 ppm and 18.71 ppm, respectively. Additionally, the mixture of the alcoholic extract of lavender and Inula with half the concentration of the fungicides Carboxin + Thiram and Difenoconazole caused complete inhibition of the fungus Ascochyta rabiei. A lack of compatibility was found between the fungicides and the plant extracts with the biocontrol fungus Trichoderma harzianum in the laboratory. The alcoholic extracts of Inula and lavender did not show phytotoxicity when sprayed or treated on chickpea seeds, whereas the alcoholic extract of eucalyptus exhibited toxicity on chickpea seedlings and plants. Fungicides, biocontrol fungi, and plant extracts have proven effective in reducing disease severity through foliar spraying or seed treatment, and they improved plant growth and productivity compared to infected plants. Additionally, mixtures of fungicides with plant extracts at the EC50:EC50 concentration provided higher efficacy than using fungicides or plant extracts alone and increased plant growth and productivity without showing toxicity to the plants. As a result, plant extracts and the biocontrol fungus Trichoderma harzianum can be used to reduce the severity of infection by the fungus Ascochyta rabiei.
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