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27
Jul
2018
Common Questions on Bacterial Panicle Blight in Rice
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

By Yeshi Wamishe, Extension Rice Pathologist

  1. Can I scout for bacterial panicle blight?

No. But monitoring your field for bacterial panicle blight would help you know if it prevailed and thus be helpful in determining seed quality for next season’s seed selection.   Seeds are the primary source of inoculum. 

  1. When is the earliest I will start seeing symptoms of bacterial panicle blight?

At grain-fill as panicles are tipping down, symptoms can easily be detected. Since the older florets are towards the tip, healthy panicles tend to tilt down from the tip.  However, blank panicles remain sticking up (Figures 1 and 2). All panicle blanking is not caused by bacterial panicle blight. There is typical basal discoloration on the glume if it is bacterial panicle blight (Figure 3). For an identification guide go to downloadable-quick-id-guide-for-panicle-blight-in-rice

  1. Why is it difficult to identify bacterial panicle blight in the field later in the season?

The color of the glumes change (Figure 5) as other fungi and bacteria grow on them. That typical symptom of reddish-brown color (Figure 3) on the bottom one-third of the rice florets gets masked. Sometimes typical discoloration on flag leaf sheath below the panicle (Figure 4) will help to identify bacterial panicle blight. The lesion on the sheath may also be masked as other microbes grow on it. 

  1. How can you tell the difference between panicle blanking from neck blast and bacterial panicle blight?

 In most cases the panicle branches/ rachis remain green if it is bacterial panicle blight and also the basal floret discoloration is not characteristic of blast infection. Neck blast forms grey to dark colored lesions on the neck joints or within the panicle which is called panicle blast. With blast, florets often are tan to white without basal glume discoloration.

  1. Is there anything I can do stop further spread of the disease after this point?

No. In panicles with severe infection, either the seeds are aborted or small in size. There is no chemistry for use in the USA that can stop damage or prevent this disease.

  1. If my field gets severe bacterial panicle blight, was there anything I could have done different?

The bacteria that are known to cause this disease are largely seed-borne. Planting good quality seed harvested from relatively clean fields would help to reduce inoculum. Variety selection is also important. There are some conventional varieties that have better resistance than others.  Jupiter or hybrids are considered moderately resistant. Early planting, adequate seeding and appropriate nitrogen fertilization rates have been proved to help lower the chance of severe bacterial panicle blight. Adequate level of potassium fertilizer is always a plus to add tolerance not only to bacterial panicle blight but also other diseases. You cannot go back and correct a past mistake, but you can always do better in the future with attention to detail.

  1. Have you seen bacterial panicle blight this year (2018)?

I have seen very little in one commercial field of CL151 and a little more in experimental plots. But nothing is overwhelming so far.

Fig. 1. Bacterial panicle blight symptom detected early at grain fill in 2018

Fig. 1. Bacterial panicle blight symptom detected early at grain fill in 2018

Fig. 2. Blank panicles with bacterial panicle blight remain sticking up while the healthy panicles fill grains and tip down. Note the color differences between the sick and healthy panicles.

Fig. 2. Blank panicles with bacterial panicle blight remain sticking up while the healthy panicles fill grains and tip down. Note the color differences between the sick and healthy panicles.

Fig. 3. Typical symptom of bacterial panicle blight if detected early enough.

Fig. 3. Typical symptom of bacterial panicle blight if detected early enough.

Fig. 4. Typical discoloration on flag leaf sheath below the panicle

Fig. 4. Typical discoloration on flag leaf sheath below the panicle

Fig. 5. Glume color changes as other microbes grow on them. Typical bacterial panicle blight basal discoloration may not be easy to detect in such a situation.

Fig. 5. Glume color changes as other microbes grow on them. Typical bacterial panicle blight basal discoloration may not be easy to detect in such a situation.


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