Widely Prevalent Plant Pathogen Status – This map is based on data from the Widely Prevalent Fungi Project, a collabaration between USDA APHIS PPQ and . Twenty seven (27) isolates of Alternaria porri were isolated from diseased leaf samples collected from different onion growing regions of Bangladesh and. PDF | Effect of different culture media, pH levels and natural substrates on mycelial growth and sporulation of Alternaria porri and Stemphylium.

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Purple blotch is caused by the fungus Alternaria porri. It can infect all above-ground parts of the plant in addition alternarua the bulb. Initial symptoms appear on older leaves, usually late in the summer as spores are blown from infested debris. Older leaves and plants are more susceptible to infection. The fungus is disseminated within and among fields by splashing water and wind, and overwinters in and on infested crop debris.


The pathogen may also be seed-borne. Lesions are elongate, small, sunken and whitish with a purple center. Concentric light and dark zones later appear over part or all of alternaeia purple area.

Alternaria porri – Bugwoodwiki

These blotches may enlarge up to four inches long and become covered with black fruiting bodies spores. Leaves wilt and die. Bulbs can be infected at harvest if the pathogen enters neck wounds. Storage symptoms appear as a dark yellow to wine-red spongy rot of outer or inner scales of bulbs.

Plant high quality seed and transplants free from the purple atlernaria pathogen.

Practice a three-year or longer rotations to non-hosts such as small grains and corn. Reduce over- wintering and survival of the pathogens by eliminating culls, onion debris, and volunteers.

Alternaria porri

Avoid dense plantings of late maturing varieties. Apply adequate but not excessive nitrogen fertilizer before bulb initiation. Undercut onion roots and harvest at full maturity when intact necks top over naturally, ideally during dry weather.


Chemical controls are most effective when combined with sound cultural practices.

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Copper fungicides are registered for control of purple blotch, but are not highly effective. Contact your local extension service for the recommendations that are appropriate to your state.

Discussion View source History. Alternaria porri From Bugwoodwiki. Alternaria porri Ellis Cif.

Common Names and Diseases. Retrieved from ” http: This page was last modified Content is available for non-profit, educational use under our Prori Agreement.

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