Have You Ever Wondered How We Culture and Isolate for Oak Wilt?

This week the students at the U of I Plant Clinic learned how to culture and isolate the fungal pathogen, Ceratocystis fagacearum, that causes oak wilt in oak trees.

When someone suspects that their oak tree is dying from oak wilt, they can send a sample to the U of I Plant Clinic. We usually suggest that they sample from areas of the trees that are showing symptoms typical of oak wilt as well as wood that may show streaking or darkening of vascular tissue (see pictures below). We would like the sample to consist of several 1 to 2 foot long branches with at least the diameter the size of a thumb. 

Some oak leaves showing a symptoms of oak wilt.

Dark streaking of the wood caused by the oak wilt fungal pathogen.

Here students at the U of I Plant Clinic:
1.  Take notes on the condition of the oak sample.
2.  Label agar plates with sample number, date, type of agar, and OW (Oak Wilt)
3.  The bark is peeled back from the end of the branch, so that the wood is exposed under a sterile hood.
4.  They flame their knife and notch the wood into tiny wood chips, which remain attached to the branch.
5.  Then, they flame their tweezers and pick off wood chips.
6.  These wood chips are placed, very quickly, (to avoid any unwanted contamination) into PDA -Potato Dextrose Agar, plates under a sterile hood.

The agar plates are stored on a shelf in our lab, with their paperwork.  They are kept there for up to 7 to 10 days to allow time for the fungal isolates to grow.

If we were successful at isolation of the oak wilt fungus, the above pictures show what it would look like growing in our PDA culture plates.

Lastly, we take clear tape and place it on top of the fungus to "catch spores".  This clear tape is placed onto a microscope slide with a drop of water on it.  If the oak tree is infected with oak wilt (oak wilt positive), we will see the chains of spores that is seen in the picture above.  If none of these spores can be found, the oak sample will be considered "oak wilt negative". (Picture above taken by Travis Cleveland)

For more information on oak wilt, you can refer to: http://ipm.illinois.edu/diseases/rpds/618.pdf

Everyone is Talking about Corn that has Turned White......

There have been several reports of corn turning white in different parts of Illinois. 

One of those reports from Southern Illinois (not yet confirmed at the U of I Plant Clinic)  refers to the possibility of Holcus spot in corn.  Holcus spot is caused by a bacterial pathogen and can be easily confused with paraquat (herbicide) injury.  Holcus spot is difficult to diagnose because the bacteria may not be readily found within the lesion.  Holcus spot has a wide host range and can infect foxtail millet, pearl millet, Sudan grass, broom corn, Johnson grass, wheat, and sorghum.  This disease is not a major problem in corn, but it is not commonly found.  For additional information, you can go to:   http://cropdisease.cropsci.illinois.edu/corn/holcusspot.html

These are pictures of suspect Holcus spot or paraquat injury from another sample that was previously submitted to the U of I Plant Clinic:

Now, the next issue that is causing "quite the buzz" among agronomists and consultants is the issue of corn turning white in the field.  I was lucky enough to find a case of this and I did take pictures.  I am not sure what may be causing this and I am unable to investigate further on this particular case, as I do not have any information on what chemicals (herbicide or insecticide) that have been applied to or near this corn field.  This picture was taken in a field south of I-72.  There does not seem to be a pattern.  As you can see in the pictures below, these plants were found in areas of the field that had been waterlogged.

 

Dr. Aaron Hager,

Associate Professor of Weed Science, has had a few reports of this, but is not sure there has been anything consistent in each instance.  Some wonder about herbicide injury (which is possible), although there have been reports of this occurring in fields where no herbicide as yet been applied.  He suspects the weather/wet soils might also be contributing to this.

You are always welcome to submit a sample to the U of I Plant Clinic, where we and Dr. Hager will fully examine the white, corn plants.  We will also need a very extensive history of the field, which includes all chemicals applied to the field.

So, You Want to Grow Grapes..........

I have recently had some grape questions. Luckily, Dr. Elizabeth Wahle, Horticulture Specialist has some advice, for those wanting to start growing grapes. 

"All grapes have numerous disease and insect problems and there should be a commitment to a spray program. If you plan on managing the pruning and pest management for good fruit quality, then grapes would be an attractive addition to any home.  If not, it can turn ugly fast!"  

http://ohioline.osu.edu/b919/index.html (Midwest Grape Production Guide)

 Here are a few grape diseases that affect fruit quality:

Powdery Mildew of Grape (Picture by NC Jones)

Grape Black Rot and Anthracnose

Just wanted to let you know about the great, commercial and home grape production as well as other fruit resources available, thanks to Dr. Elizabeth Wahle, Horticulture Specialist, located out of Edwardsville, IL.  These links are taken directly from her website.  They are as follows:

COMMERCIAL GRAPE GROWERS

Commercial Grape Nurseries

Commercial Vinyard Suppliers

All you need to know to grow grapes!
Midwest Grape Production Guide

HOME FRUIT PRODUCTION

Growing Fruit for Home Use

Midwest Home Fruit Production Guide


Other U of I Extension information on Grapes:
http://urbanext.illinois.edu/hortanswers/plantdetail.cfm?PlantID=284&PlantTypeID=7


Do you want to take grapes or other fruits to the market?
http://web.extension.illinois.edu/edwardsvillecenter/foodcrophort2801.html

PLANT: CSI (How Plant Problem Investigation Works at the U of I Plant Clinic)

When I first started, I have a couple of tough, plant samples that I was working on.  Now, my definition of a "tough, plant problem" can mean one of following:
A.  It's not a disease (I am a plant pathologist) Suzanne Bissonnette is a plant pathologist too; however she plays the role of an entomologist on TV! Ha ha!
B.  The plant is exhibiting symptoms that could be attributed to a variety of problems (we just have to rule of some of these problems out).
C.  The plant has a variety of problems that is contributing to the symptoms that are exhibited.
D.  I don't know what the "heck" is going on!

I was helping to consult with Richard Hentschel, Extension Educator Horticulture, on a difficult plant issue (that could be an entirely different blog in itself), and in the flurry of emails back and forth between myself and his client, he mentioned that this whole process of plant diagnosis was much like, "Plant CSI".  I liked that analogy and Richard, you inspired me to write this blog : )

Plant Crime Scence Evidence: Dead or yellowing plant parts/not normal plant symptoms <invision yellow crime scence tape placed around the plant sample>

Unfortunately, we are unable to come to the "plant scene", but alot of times, we want you to send us pictures of the "plant scene".  Then, we recommend that you send the "Plant Crime Scene Evidence" to the lab: U of I Plant Clinic

First, we do an "initial walk-through" to get an overall feel for the injured plant scene.  Luckily, we don't have to worry about touching things!  Now, we can make some theories of diagnosis based on visual plant symptoms.

Here we don't swab or collect fingerprints, hair, or dried blood (that is why I am a plant doctor, not a medical doctor).  We look for signs of fungal diseases, nematodes, chemical injury, environmental injury, or insects.

We do try to document all of this "evidence".  And, of course, we are very careful to preserve this plant evidence in it's current form by using refridgeration or even watering (if we have an entire plant).  Sometimes, we even document the "plant crime scene" by taking pictures, sketches, but no video walk throughs are necessary.

Next, we take the plant sample to the scopes (dissecting scope and microscope) to collect potential evidence.  We don't use a swab, but we do use tweezers, as well as other tools such as pruners, knives, and razor blades.  Here are some things we may find on the plant sample in question:  fungal structures, fungal spores, bacterial oozing, nematodes, insect exoskeletons, insect frass, insect webbing, insect feeding, or even nematodes.   Depending on the plant symptoms, we could also use assays or quick strip tests involving ELISA or PCR!  Then, I guess you could say we tag, log, and package it!

If we can't find any of these things above (signs of disease or insect), now that is when it can get tricky!  It could be an environmental, nutrient, or pesticide injury situation.

In this case, we may need to rely on documents such as soil tests, water analysis, or pesticide application log.

Don't forget, once we have a plant sample in hand, we reserve the right to call or email a grower, and perform a full interrogation!  No, we don't ask them were the plant was on the night in question, but we may ask them questions such as:
When was it planted?
What pesticides have been applied?
When were the pesticides applied?
Have you had a soil test?
What fertilizer has been applied?
What was the rate of fertilzer applied?
What has the weather been like?
How long have you had this problem?
In what kind of site is this plant growing?
Was it planted correctly?
What is planted in this area before?
What is the soil type?
What is the condition of the nearby plants?
How old is the plant?
What is the pattern of the affected plants?
What is the name of the plant species?
Are you a homeowner or a commercial grower?
Just to name a few.................................................

When all of the evidence is collected and research has been done (books and internet), it goes straight to the lead detective or in our case, the head diagnostician (that's me).  If I need too, I can also consult with experts.  Now, I don't deal with experts in blood pattern spatter, trajectory determination, serology (blood and bodily fluides), but rather deal with campus specialists that can help me in more specific areas such as crop, fruit, and vegetable pathology or entomology. 

Some Plant CSI's only work in the field - these are Extension Educators or Consultants.  They help to collect the evidence and they pass it to our forensic lab - The U of I Plant Clinic!

Based on these procedures, we can hopefully, MAKE A PLANT DIAGNOSIS!