7 - Bacterial Leaf Streak in the Field: Identifying, Researching, and Managing the Disease

Mike Kamm Author

12/04/2020 Added

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Gabriella Martens, Master of Science Graduate Student Plant Pathology - Bacterial leaf streak, or BLS, is a bacterial disease that affects corn. BLS is relatively new in the United States and we continue to learn about the bacterium which causes BLS. In this video we cover a brief history of BLS, identifying the disease symptoms, comparing symptoms with other common diseases, current BLS research at UNL, and general management strategies.

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[00:00:04.410]Hi everyone.
[00:00:04.880]John, my name is Gabriela Martin.
[00:00:06.740]I'm a current master's student at UNL and I work with Tamra Jackson Ziems'
[00:00:11.510]research group. Today.
[00:00:12.950]I'll be talking to you about bacterial leaf streak or BLS.
[00:00:17.330]we're out here today at the South central ag lab, outside of clay center.
[00:00:22.550]So bacteria leaf streak or BLS is a bacterial disease that affects corn.
[00:00:27.770]It affects dent, corn, sweet corn, and popcorn.
[00:00:31.280]It was first confirmed in the United States in Nebraska in 2016.
[00:00:36.140]Since that initial confirmation in Nebraska,
[00:00:38.330]it's been found in 75 of the 93 Nebraska counties and has been
[00:00:43.160]confirmed in an additional eight States in the Midwest and great Plains region.
[00:00:48.320]In the past few years,
[00:00:49.310]it's also been confirmed in two of the South American countries of Brazil and
[00:00:53.840]Argentina bacteria.
[00:00:56.720]Leaf streak is caused by the bacterial pathogen.
[00:00:59.210]Xantham on a specific path of our vascular rum or XX.
[00:01:02.540]VV XEV is a residue born pathogen,
[00:01:06.620]and it overwinters in the residue after a season where the previous crop is
[00:01:11.030]infected. Since it's a residue borne disease, we usually see,
[00:01:16.700]BLS start in the lower canopy, and then we see it move up in the canopy.
[00:01:21.950]However,
[00:01:22.250]our research has not shown that BLS is a systemic disease or XV is not a
[00:01:27.240]systemic pathogen.
[00:01:28.730]So just because you have infection once in the lower canopy does not mean you're
[00:01:32.030]going to continue to see it gradually just grow, go up in the canopy.
[00:01:37.730]So it takes a wind event or a rain event to move it up. The canopy.
[00:01:41.900]So wind moving,
[00:01:43.550]rain drops and rain splash off of those lesions is what you'll see,
[00:01:46.760]carry it up into the canopy.
[00:01:50.450]cause VV bacteria can enter the plant through a variety of ways.
[00:01:54.710]like other bacterial pathogens that can affect via wounds.
[00:01:57.680]But our research has shown that that's not necessary for infection.
[00:02:01.640]So we have had infection without wounding.
[00:02:05.240]So it enters the plant in other ways as well.
[00:02:08.630]So this year has been a favorable year for BLS development,
[00:02:12.710]similar to the first years that we were seeing it in 2015 and 2016.
[00:02:17.510]So here in the plots were now you can see that the entire canopy has lesions and
[00:02:21.590]we're seeing new lesions developing even now in the upper canopy.
[00:02:25.820]So the previous two years were not nearly as favorable with weather conditions,
[00:02:29.780]but this year has been very favorable for BLS.
[00:02:33.950]Now that we're talking about symptoms,
[00:02:35.510]I'd like to switch gears and show the differences between bacterial leaf streak
[00:02:39.710]lesions and a disease that has similar symptoms, which is gray leaf spot.
[00:02:44.660]Next,
[00:02:44.960]I want to talk to you about the BLS lesions and how they are similar to another
[00:02:49.370]disease. That's caused by a fungal pathogen, which is gray leaf spot.
[00:02:54.050]So these two diseases look very similar in the field and they are easily
[00:02:57.620]misdiagnosed for each other.
[00:02:59.890]So right here I have gray leaf spot.
[00:03:05.130]And the way that you can tell this is gray leaf spot is it has smooth
[00:03:09.180]rectangular lesions in the inner vinyl spaces.
[00:03:12.780]So you see how it's a smooth rectangles, smooth sides.
[00:03:16.650]That's gray leaf spot. Now,
[00:03:18.570]when we compare that to bacterial leaf streak,
[00:03:23.160]they're also intervener lesions, but they have irregular margins.
[00:03:27.390]So they're not smooth and rectangular like gray leaf spot.
[00:03:31.230]So here we have an example of both diseases on one leaf.
[00:03:34.380]So you can tell a side-by-side of the lesion differences below here.
[00:03:38.100]We have an example of gray leaf spot with the smooth sides on the lesions in a
[00:03:42.450]rectangular lesion shape above that we have BLS where the
[00:03:47.250]margins are more irregular,
[00:03:48.510]but still long and linear in the interventional space.
[00:03:52.260]Another one of the features that we see with both of these diseases can be
[00:03:55.350]haloing with BLS.
[00:03:57.690]You'll always see a bright yellow halo behind lesions,
[00:04:02.010]but with gray leaf spot,
[00:04:03.120]you may see a more of a pale yellow halo around the lesions,
[00:04:06.480]but this varies based on hybrids.
[00:04:08.370]So not all hybrids are going to show this on gray leaf spot,
[00:04:11.670]but some will next I'd like to highlight some of the research that has been done
[00:04:16.080]at different universities on BLS and the pathogen SVB Silvina
[00:04:20.670]Arias at Iowa state university has recently published a study on seed
[00:04:25.470]transmission of X VV in her research.
[00:04:28.320]She was able to have artificially inoculated seeds planted.
[00:04:32.910]And when they grew, the leaves had BLS symptoms, however,
[00:04:37.350]she was not able to get the same effect from naturally infected
[00:04:42.000]seeds that were planted. There's still a lot of room for research in this area.
[00:04:46.230]Seed transmission is a hot topic in BLS right now,
[00:04:50.220]the grad student before me here with Tamra Jackson Ziems’ research group was Tara
[00:04:54.330]Hartman. In Tara's research.
[00:04:57.210]She screened 54 species for susceptibility bacteria
[00:05:02.130]leaf, straight to serve as an alternative host of these plants.
[00:05:06.000]She did some in the greenhouse and some out in the field and identified
[00:05:09.360]symptomatic and asymptomatic hosts.
[00:05:12.150]Three of the symptomatic hosts were big blue SIM bristly,
[00:05:15.930]Fox tail and yellow nutsedge asymptomatic.
[00:05:19.170]Hosts she identified were Downy brome, tall fescue and Western wheat grass.
[00:05:24.780]So of these symptom asymptomatic species,
[00:05:29.430]they did not show symptoms when she inoculated,
[00:05:31.980]but when she cut the leaves open,
[00:05:33.570]she was able to recover X VV bacteria from inside the leaf
[00:05:38.400]tissue. And we're diagnosing bacterial diseases under a microscope.
[00:05:43.200]When you cut a leaf open that has bacteria in it,
[00:05:45.990]it gushes out which we refer to as bacterial streaming.
[00:05:50.160]So when Tara was looking at endophytic bacteria,
[00:05:53.310]that's the bacteria that's inside the leaf tissue,
[00:05:56.790]my focuses on empathetic bacteria.
[00:05:59.420]So that's bacteria on top of the leaf surface.
[00:06:02.840]So the work that I've been doing has been in the greenhouse and in the field.
[00:06:06.680]And I have been able to recover X VV bacteria from the leaf surface of
[00:06:11.000]asymptomatic plants. So they had been inoculated,
[00:06:13.940]but they were not showing symptoms,
[00:06:15.500]but I was still able to recover the bacteria that was surviving on the leaf
[00:06:19.490]surface.
[00:06:20.900]What I'm doing now is working with a project that's sponsored by Bayer crop
[00:06:24.710]science and our research group here at UNL works on and it
[00:06:29.420]focuses on optimizing inoculation techniques to generate consistent disease
[00:06:34.070]symptoms so that we can have reliable ratings.
[00:06:37.190]This is important because this disease is still fairly new.
[00:06:41.810]So we are doing the work to get consistent disease and reliable ratings
[00:06:46.850]to help seed companies have ratings for their hybrid.
[00:06:51.260]So right now, if you opened up a seed catalog,
[00:06:54.020]you may not see a rating for BLS since the disease is new,
[00:06:58.670]we're trying to help with that. So in our experiments,
[00:07:02.270]we are testing two different inoculation methods.
[00:07:05.090]One is spraying the inoculum over the top of the Leafs and the other is
[00:07:10.010]spraying the inoculum directly into the world.
[00:07:14.030]We also had two inoculation timings. We inoculated at V nine and B12.
[00:07:19.340]And then additionally, we had multiple watering timings as a treatment as well.
[00:07:24.200]So we were keeping that leaf surface in that world wet to help aid in disease
[00:07:28.790]development.
[00:07:29.840]So the plots we're standing in right now are from that experiment.
[00:07:34.220]So you can see, we have generated bacterial leaf streak in these plots.
[00:07:39.110]And I take regular ratings out here now.
[00:07:42.380]So that is the ratings are ongoing.
[00:07:44.990]And so this study is currently ongoing as well.
[00:07:49.490]Next I'd like to talk about management. It's a question.
[00:07:52.160]We get a lot with bacteria, leaf streak, being a newer disease.
[00:07:55.550]We get a lot of questions on how can I minimize it?
[00:07:58.970]How can I manage the disease in my field, bacteria leaf streak,
[00:08:03.170]like many other residue, born diseases or pathogens that are residue born.
[00:08:07.790]We want to talk about managing the amount of [inaudible] in the field.
[00:08:11.030]So that goes to the residue,
[00:08:13.370]managing the residue and also managing alternative hosts.
[00:08:17.090]Crop rotation can be helpful to manage disease and residue,
[00:08:20.420]born diseases,
[00:08:22.940]but having alternative hosts present, like we talked about earlier,
[00:08:27.770]can maybe reduce some of the benefits that you would get from crop rotation.
[00:08:31.880]So if you have some of those common grasses that we talked about outside of your
[00:08:36.230]fields or in waterways or on terraces, that might not,
[00:08:39.410]you might not see as many benefits from crop rotation.
[00:08:42.440]If you have alternative hosts present as well,
[00:08:46.010]going back to managing the residue,
[00:08:48.740]tillage is also a way that can help manage some of that residue that you have on
[00:08:52.700]the ground surface. That's not compatible for everybody's operation,
[00:08:57.180]but if reduced tillage is something that works for you,
[00:09:00.060]it's another way that you could attempt to manage the residue in the inoculum in
[00:09:04.860]your field.
[00:09:06.240]The best recommendation that we can make is to work with your seeds rep and
[00:09:10.680]place the best product in your field for your operation.
[00:09:14.460]So even though the disease is new, it has been around for a few years. Now,
[00:09:19.590]some hybrids show to be more susceptible and some just handle it better.
[00:09:24.630]And your seed rep has been working with those hybrids.
[00:09:26.850]So there'll be more familiar with that and can help you make an educated
[00:09:30.090]decision until we start to get ratings in the seed catalogs.
[00:09:35.610]So I want to thank you for tuning in with me today to listen to me,
[00:09:38.790]talk about bacterial leaf streak.
[00:09:40.890]If you have anything in your field that you need help identifying,
[00:09:43.650]you can send in a sample to the UNL plant in pest diagnostic clinic.
[00:09:48.510]And if you have any other further questions,
[00:09:50.190]you can reach out to Nebraska Extension and we'll be happy to help. Thank you.

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7 - Bacterial Leaf Streak in the Field: Identifying, Researching, and Managing the Disease

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