Symptomatology of purple blotch disease of onion and exploration of fungicides, phytoextract and bio-agents against causal fungus Alternaria porri

Symptomatology of purple blotch disease of onion and exploration of fungicides, phytoextract and bio-agents against causal fungus Alternaria porri

2014

E10127

In field, Onion blight / purple botch symptoms development starts from tip of the older leaves as small, whitish, sunken, oval shaped lesions which later On became elliptical or oblong, which brown to purple at the centre and surrounded by a light brown area. Further, the lesions coalesce and spread rapidly on leaf blade and affected leaves show drying from tip downward. The leaves break at the affected area and hang down. Concentric light and dark rings were observed on the infected leaves. In older spots, the conidia were produced abundantly on bunch of conidiophores. Brown lesions with reddish-purple margins resembling bull’s eye were also noticed. Affected leaves and stems turn yellowish white and die. On inoculated plant, blight symptoms were visible within 4 - 5 days of inoculation as small, water soaked sunken more or less oval shaped spots on leaves whichenlarged, became elliptical to oblong, zonate and turned brown to purple surrounded by yellow halo extending upwards and downwards with light to dark concentric rings. Lesions usually girdle leaves, causing them to fall over or hang down.Within 25 - 27 days after inoculation the affected plant showed complete drying of leaves. Under natural / field and artificial inoculation, symptoms induced by A. porri, causing blight (purple blotch) were recorded. All the fungicides tested in vitro against the pathogen were found effective in inhibiting the mycelial growth. Propiconazole 25% EC (0.1%) and combi product of iprodione 25% + Carbendazim 25% WP (0.1 and 0.05%) completely inhibited the mycelial growth of A. porri. Among the different plant extract testet against A. porri maximum per cent inhibition of mycelial growth was achieved with 10 per cent Cinnamon extract (72.22%), followed by Soapnut (64.77%) and Jatropha (64.44%). Among the various bio-agents tested, complete inhibition of A. porri was achieved by Trichoderma hargianum and Aspergillus niger, followed by T. viride and pseudomonas flourescens.

11(31):63-69, SPECIES

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