The Bacterial Leaf Streak Situation is Evolving

Knowing what we don’t know can sometimes be the first step to making significant progress. That certainly is the case with bacterial leaf streak (BLS).

BLS was recently noted as a seedborne disease of possible concern in Canada, affecting cereal crops and especially in irrigated areas. On leaves, symptoms appear as small water-soaked lesions running parallel to the leaf veins. If humidity is high, you might also see a “bacterial ooze” on the lesions, which appear as little yellow milky droplets visible to the naked eye.

Accurate visual identification of bacterial disease is difficult because it doesn’t usually occur in isolation. It often occurs with other pathogens, like tan spot. However, something unique about BLS are the dark fruiting bodies that form on the tan-brown dead tissue giving lesions a speckled/dotted appearance.

Xanthomonas translucens has been identified as the pathogen responsible for BLS and black chaff diseases of small cereal grains, by infection of leaves and glumes respectively. Pathovars of X.translucens are recognized based on their ability to induce disease symptoms on different crop hosts and wild or cultivated grasses. This is a distinctly different pathogen from X. variscola which is responsible for BLS on corn. Both Xanthomonas species prefer areas with abundant moisture, as most bacteria do.