NPIPM:Bacterial leaf streak
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Causal Organism
Bacterial leaf streak is caused by the bacteria Xanthomonas translucens pv. undulosa.
Symptoms and Signs
Bacterial leaf streak, otherwise known as BLS, primarily affects the leaves of wheat plants but can also affect the head and the glumes of infected plants. Infection starts as water soaked streaks or spots on the surface of upper leaves that is followed by a shiny glaze. At this stage, dried clumps of bacteria that will eventually develop into lesions can also be visible. Olive green translucent streaks will develop into yellow-brown streaks. Brown, dry spots begin to emerge on the surface of the leaf, usually beginning at the tip of the leaf or in the middle of the leaf. In infected plants, black chaff can be present in the head and glume. Black chaff occurs when the bacteria invade the glumes during grain fill and cause dark purple or black streaks and spots on the exterior of the glume.
Disease Impacts
Bacterial infection in the head and glumes doesn’t result in severe yield loss. Infection of leaves especially the flag leaf, however, can cause a greater decrease in yield.
Life Cycle and Epidemiology
Xanthomonas campestris pv. undulosa is primarily seedborne but can also survive in crop debris and several grass species. Spread by wind and rain, the bacteria enter the plant through wounds and stomata. Severe BLS outbreaks are most common in areas with frequent rains and high winds. Overhead irrigation has also been linked to an increase in the risk for BLS.
Management Approaches
Use of clean seed and certified seed is vital in order to prevent introduction of the bacteria into the field. There are no known chemical seed treatments that have been consistently useful in managing BLS. There are no foliar applicants that have been proven to significantly reduce symptoms. Allowing 2 years between wheat crops in a single field can decrease the amount of bacteria living in crop debris. Avoiding rotating with small grains such as barley will also decrease this risk. Insect control will help in avoiding excess wounds and open sores where bacteria could potentially penetrate. Some tolerant cultivars are available.
Other Online Resources
Detailed description of bacterial leaf streak https://en.wikipedia.org/wiki/Bacterial_leaf_streak
Wegulo S.N. "Black Chaff. <https://pdc.unl.edu/agriculturecrops/wheat/blackchaff>
