Onionpurpleblotch

Department of plant pathology

1. COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai Dam, Theni-625 562 Onion Purple blotch Student Course teacher A. Sowbejan Dr. Parthasarathy . S 2015021122 Assistant Professor (Plant Pathology)

2. Name of disease Common name: Purple blotch of onion Pathogen name: Alternaria porri

3. Occurrence The disease was first time reported from Bombay ( Ajrekar , 1921). Since then has been reported from many states of the country like Maharashtra, Gujarat,Tamilnadu , Rajasthan, Haryana and Punjab ( Pandotra , 1964). Inventor : Alternaria porri ( Ellis) Hosts : Onion, shallot, leek

4. KINGDOM Fungi PHYLUM Ascomycota CLASS Dothideomycetes ORDER Pleosporales FAMILY Pleosporaceae GENUS Alternaria SPECIES A . porri

5. Economic Importance These pathogens reportedly cause storage yield. The disease causes 20-25 per cent losses to the onion seed crop.

6. Symptoms The characteristic symptoms of the disease appear as a small, light coloured , sunken lesions, which become zonate with purplish center. These lesions rapidly enlarge and eventually girdle the leaf or inflorescence stalk. In moist weather the surface of the spot is covered with the brown or almost black sporulation of the fungus. Usually the affected leaf or stem falls down and dies within 3 or 4 weeks under favorable environmental conditions.

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8. Disease cycle The fungus survives from one season to other in infected plants debris as dormant mycelium. the fungus can also survive in diseased onion leaves and seed stalk debris for 12 month buried at 5 to7.5 cm depth. wherever the chlamydospores of the fungus are formed they can also serve as source of penetration , invasion takes place either through stomata or directly through the cuticle , to form an intercellular mycelium, which in turn forms conidiospores and conidia. Conidia produced on the primary infection lesions serve as the source of secondary inoculum.

9. Favourable condition: The fungus requires rain or persistent dews for reproduction and penetration. The optimum temperature for disease development is 21 – 30 degree C and relative humidity above 90%.

10. Various cultural practices like use of healthy seed/planting materials, crop rotation with non-related crops, collection and destruction of infected debris, good drainage, summer ploughing ( Srivashtava et al. 1996) Use of recommended doses of fertilizers Hot water ( 50 ºC for 20 min .) soak was found to be highly effective in reducing seed borne inoculum ( Aveling et. al ., 1993 ) Use of disease resistance varieties viz . Pusa red, IIHR-56-1, hybrid PVM-7 etc. Spraying crop with Copper oxychloride , mancozeb , Metalaxyl + mancozeb , Fosetyl -al, Difenconazole etc. Management