Bacterial Leaf Streak: Rising Threat to Prairie Crops and Key Management Strategies

Bacterial Leaf Streak (BLS) is a bacterial disease of increasing concern on the Canadian prairies. BLS is caused by a bacterium known as Xanthomonas translucens, with multiple strains existing that can infect crop plants including wheat, barley, oats, triticale, and rye. The disease can infect plants at all life stages, which is why early identification is important to guide management decisions. If BLS infection occurs early in the season and environmental conditions stay conducive, there is a higher chance of BLS outbreak. Severe infection caused by BLS can lead to overall yield reductions up to 50 per cent.

Scouting for BLS can begin during in-crop herbicide application timing through to the start of crop senescence. Pay special attention to scouting after severe weather events such as strong winds, hail, heavy rain and thunderstorms. Early symptoms of BLS are necrotic lesions on the leaf tissue that appear water soaked. As the disease and growing season progress, the lesions will coalesce to form yellow and brown streaks on the leaves. These streaks reduce the photosynthetic area of the leaf, which has impacts on the growth and development of the plant and overall yield of the crop. The disease can also progress into the head of the plant and reduce the filling of kernels, reducing kernel size, and therefore impacting seed and grain quality. BLS requires moisture to survive and remains dormant until moisture is available, at which time bacterial cells are produced on the host plant. The disease also requires a living host in order to complete its lifecycle, and is most virulent at temperatures between 15-30°C. It is important to remember that even if a host crop is not being grown, many volunteer cereals and cereal weed species are hosts that can propagate and build up BLS inoculum in the field.

BLS is primarily a seed-borne disease. Currently, seed is the largest source of inoculum for BLS. In addition, the disease can also overwinter on winter cereals and survive on infected crop residues in the field. For this reason, the best way to avoid a bacterial leaf streak outbreak is to use clean seed, combined with at least two years between host crops, while also managing volunteers and other non-crop hosts. If a field has not experienced a BLS outbreak, avoiding introducing the bacterium is the best management practice. Producers are encouraged to use the cleanest seed they can source. Many seed retailers will include pathogen screening as additional information as part of the package they offer. Check with local seed retailers about testing for BLS. Alternatively, growers are encouraged to send seed samples to designated labs to test for BLS. The designated labs include: 20/20 Seed Labs- Nisku, SGS Sherwood Park and Discovery Seed Labs at Saskatoon.

If a field is suspected to have BLS, do not use harvested grain for seed. Find the cleanest seed source possible. An extended crop rotation, with greater than two years between cereals, will help reduce inoculum load as the infected crop debris decomposes. For fields under irrigation, producers can manage BLS by reducing the amount of time the canopy is wet. Recommended practices include but are not limited to: 1) irrigating in the evening when the canopy is already wet with dew; 2) allowing the canopy to dry out between irrigation events; and 3) avoiding irrigation when it is not essential.

Looking ahead, genetic resistance is expected to play an important part in BLS management. There is currently on-going research through Dr. Randy Kutcher’s lab at the University of Saskatchewan in collaboration¹ with AAFC, the University of Alberta, the Irrigation Crop Diversification Corporation and the Crop Diversification Center working on establishing BLS resistance screening in variety trials for wheat and other cereals. The group finished their second year of experiments in 2024. Preliminary results about current varieties’ BLS resistance information are expected in the near future. The group is also working on a project focused on assessing the transmission of BLS from infected seed to the subsequent seedling and the resulting disease severity and inoculum thresholds. This project will provide producers with a better understanding of the risks associated with variable disease levels of infected seed.

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¹Work done in collaboration with Dr. Lipu Wang, Dr. Constanza Fleitas, Ms. Valentina Anastasini, Dr. Sean Walkowiak, Dr. James Tambong, Dr. Michael Harding, Dr. Jie Feng, Dr. Gurcharn Brar, Dr. Gursahib Singh, and Dr. Kelly Turkington