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.
Crop cultivation in controlled environment is significantly increasing all over the world due to erratic climatic conditions and climate change. Under controlled environment, the plant pathogens particularly from seed borne infections, develop very quickly infecting the crop and causes substantial losses. Control of these pathogens and diseases with pesticide application in controlled environment has its own limitations due to persistance of pesticidal residues over a long period owing to its non depletion in the controlled environment. Traditional homa treatment as non-chemical treatment was used to manage the fungal pathogen Alternaria solani in tomato and potato crop and bacterial pathogen Xanthomonas campestris pv. vesicatoria in tomato crop under controlled polyhouse condition. It was observed that homa therapy effectively reduced the incidence of early blight disease of potato and tomato and bacterial blight disease of tomato in polyhouse and it also reduced the environmental pathogenic microflora around 70 per cent. Thus homa therapy can be used as an alternate solution for chemical pesticides in protected cultivation and also be used in integrated pest management.
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