Bacterial leaf spot of Cucurbits
|Bacterial leaf spot of Cucurbits|
|Bacterial leaf spot on a Cucurbit leaf|
|Species:||Xanthomonas campestris pv. cucurbitae|
|Locations where bacterial leaf spot of Cucurbits is present (blue)|
|Bacterial leaf spot of Cucurbits
Bacterium cucurbitae Bryan
Bacterial leaf spot is a pathogenic disease of Cucurbits. The pathogen attacks agricultural plants of the family Cucurbitaceae (pumpkin, marrow, cucumber, and squash; water-melon and melon in a lesser degree). Under favorable conditions for the pathogen development and during period of the bacteriosis maximum development (more than 40% on the average), the amount of infected plants reaches 100% (Moldova) in some years. Yield losses may reach more than 20% in highly susceptible cultivars, and the disease severity sometimes reaches 50-60% at fruit storage.
The disease symptoms are marked on seedlings first. Small spots of brown color (slightly pressed-in, then getting a kind of ulcer) appear on cotyledons. Mass development of the disease is marked usually in the beginning of July, directly dependent on the amount of precipitation.
On adult plants, the disease is shown as necrotic spots on leaves and characteristic lesions on fruits. On leaves, the disease begins as chlorosis of light-yellow color along their margins. Later, small round necrotic spots form in chlorotic zone, where they increase in sizes, merge, and soon occupy the majority of the leaf surface, forming sites with dead brown tissue. As a rule, the necroses penetrate deeply into leaf lengthwise veins, being limited by the veins. Necrotic spots do not drop out. The described symptoms occur on leaves of any age. On fruits, the disease begins as dimness of tissue of seed chamber, as a rule, at the flower end. Initially, the fruit appears to be completely healthy. Then round oily, slightly pressed-in brown spots, frequently with chlorotic border, appear on its surface. Viscous liquid drops of an amber color are formed on the surface of these spots in damp weather. At strong lesion, the fruits are deformed, becoming covered with cracks, and then rotting.
Infection development favors high temperature (25-30°C) and relative air humidity 90% or higher. The intensity of the disease incidence increases during the vegetation period and reaches peak at the end of July -and the beginning of August.