Bacterial fruit blotch of cucurbits

Acidovorax avenae citrulli

Symptoms on fruits appear as dark olive green stain (or blotch) on the upper side of the fruit. Lesions usually become apparent shortly before fruit ripening. The epidermis of the rind can then rupture and frequently bacterial ooze is produced. On leaves, small dark brown, somewhat angular and water-soaked lesions can appear, but they are generally inconspicuous. On seedlings, water-soaked areas on the underside of cotyledons can be seen and lesions on the hypocotyl cause collapse of the emerging plants. Some seedlings may remain symptomless until fruit set.
In the USA, the disease usually occurs in relatively few fields but under favourable conditions (warm and wet weather) fruit losses of up to 90-100% have been observed in some commercial fields of watermelons. In Brazil, the disease is causing severe losses in the Nordeste (mainly Rio Grande do Norte and Ceará) on melon crops. In 2000, crop losses in Rio Grande do Norte were estimated at 40-50%, reaching 100% in some melon crops. In a survey carried out in 2001 in 18 melon fields, the disease was present in all fields with an incidence varying from 4% to 47%.

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