Growth Potential of Different Fungicide Resistant Alternaria solani Isolates of Tomato Leaf Blight Pathogen, under In Vitro, in the Presence of Different Fungicide, Growth Temperature and pH Ion Concentration

Evolution of fungicide resistance in plant pathogens and cross resistance to other fungicides in such pathogens is one of major concerns in sustainable plant disease management. Frequent and unwarranted use of fungicides to control plant diseases not only pollute the earth soil and environment, but also causes the development of fungicide resistance in the plant pathogens, which makes it difficult to manage the plant disease. In India, particularly in western Maharashtra, Alternaria leaf blight pathogen of tomato developed resistance and cross resistance to various fungicides. How these fungicide resistant isolates grow in the different fungicidal environment is reported in the present investigation. Eight different fungicide resistant isolates of Alternaria solani responsible for causing leaf blight in tomato crop were tested for their growth potential, under in vitro condition, on the potato-dextrose-agar(PDA) growth media amended with different fungicides viz. Dithane M-45, Blitox, Kavach, Ridomil, Nativo, Bavistin, Captaf and Score. Different fungicide resistant isolates showed different pattern of growth i.e. complete inhibition of growth, reduced growth or enhancement of growth on different fungicide amended PDA media. The growth of Dithane M-45 resistant isolate was enhanced by fungicide Kavach and Bavistin while reduced by fungicide Blitox. The growth of this fungicide resistant isolate was completely inhibited by fungicide Ridomil, Nativo, Captaf and Score. The maximum enhancement of growth was for Nativo resistant isolate to Bavistin amended PDA media. Bavistin resistant isolate had decreased growth on all fungicides amended PDA media. The minimum reduction in growth was recorded for Kavach resistant isolate on Dithane M-45 fungicide amended PDA media. The growth rate (cm/day) of these fungicide resistant isolates was maximum at 220C temperature as compared to 25 and 300C temperature on the routine PDA growth medium. Captaf resistant isolate produced more growth followed by Nativo, Dithane M-45 and score resistant isolate. The minimum growth was observed for Blitox resistant isolate. As the temperature increases, the growth rate decreased. The growth of fungicide resistant isolates was favored by neutral pH of 7.0 and decreased toward the acidic and alkaline condition. Captaf resistant isolate produced more growth followed by Nativo and score resistant isolates. The minimum growth was produced by Blitox resistant isolate. More growth of fungicide resistant Alternaria isolate means production of more inoculum for disease initiation and spread which is favored at 22 °C temperature and further indicate which fungicide should be used to restrict/manage the growth of particular Alternaria fungicide resistant isolate.