black chaff of wheat

Pathogen

Black wheat chaff is caused by the bacterium Xanthomonas campestris pathovar (pv.) translucent. It enters plants through stomata and wounds. During wet or wet weather, the bacterium reproduces rapidly and produces yellow bacterial droplets in the form of mire or viscous droplets on infected plant parts. This radiation appears light and scale-like when dry. Black chaff bacteria live in the seed. It is suspected that it lives on crop residues and soil, but this needs to be well documented. The bacterium can live on the plant as an epiphyte during the growing season without causing symptoms. If it is a short distance, it spreads by spraying water and contact with plants and insects. It is spread over long distances by contaminated seeds, the primary inoculum source.

Symptoms of Disease

Black chaff receives its name from the dark transited plants. This symptom is similar to genetic melanism (darkening of cells) and glume blotch caused by Septoria nodorum. Black chaff can be distinguished from other infections by the appearance of cream to yellow bacteria in slime or viscous drops produced in infected plant parts during wet or humid weather. Necrotic clusters and healthy cells on the awn ("barber's pole") show black chaff. A brown to purple colour may appear on the stem below the head and over the flag leaf. This disease is known as a bacterial streak or stripe on leaves. Symptoms start as small water-soaked spots or streaks that turn brown after a few days. The lesions are irregularly shaped and long and can extend the length of the leaf blade. In wheat, a lime green colour may surround the lesions. Leaf spots cause the plants to have an overall orange colour.

Good Environmental Conditions

Wet and humid climates favour black chaff. In Nebraska, black chaff occurs primarily in irrigated fields.

Administration

The most effective control strategy for black chaff is certified pathogen-free seed. In seed propagation and certification programs, plants should be raised at least ¼ mile from potential inoculum sources. These include irrigated commercial production fields and fields with wheat stubble. Controlling volunteer crops and weeds can help reduce primary inoculum. Irrigation management is important for creating an environment unfavourable to disease development and spread. Watering should be controlled to allow the crown of the plant to dry completely between waterings. Although highly resistant wheat varieties are not currently available, those known to be highly susceptible to black chaff should be avoided.