What is and how does Agrobacterium tumefaciens affect plants?

Agrobacterium causes many problems for plants

Image – Wikimedia Commons / CM

The plants, if they receive everything they need, it is very difficult for them to have problems, but sometimes something unforeseen arises: a drastic drop or rise in temperature, a branch that breaks freeing the way for microorganisms, people who prune with tools not too clean, … Anything can happen. And the bacteria known as Agrobacterium tumefaciens it will be there, waiting for the slightest opportunity to weaken them.

Although that name does not sound like anything to you, you may have seen a tree or shrub with galls or tumors on the trunk, in the area that serves as the union between the root and the stem itself. You could almost say that it is plant cancer, because of how quickly it spreads and the damage it can cause. Let’s know what symptoms it causes and how to treat it.

What is the Agrobasterium tumefaciens?

Guts on the mango trunkGalls on mango trunk

Image – Flickr / Plant

It is a non-sporulated bacteriacall now Rhizobium radiobacterwhich is distributed throughout the world. It is rod-shaped, and it is gram-negative (that is, it does not stain dark blue or violet by Gram’s stain, but rather faint pink). Its motility is high, and it has flagella that project in all directions. It uses a wide range of carbon sources.

What plants does it affect?

This is a microorganism that affects dicotswhich are those angiosperm plants that produce seeds with two or more cotyledons, flowers with calyx and corolla, a root system composed of a taproot (or main) and other secondary ones, and that also have a stem that can grow in thickness from of the vascular cambium that forms the wood.

If you are looking for examples, in reality any plant of this type can be a victim of this bacterium, but as we said at the beginning, sometimes an unforeseen event, sometimes an accident and / or sometimes a human error can make a plant that was healthy yesterday. today I have to fight against this bacteria.

In cultivation, of course the most frequent cause of infection is ourselves. And it is that if we do not disinfect the tools before and after using them, if we do not always use ‘new’ substrates (recently purchased or without having previously used them), or if we acquire diseased plants, the risk of infection only increases. For all this, trees and shrubs are the most vulnerableBoth ornamental and fruit trees, especially almond, apple, olive, pear, rose, vine, plum, poplar and quince.

What are the symptoms?

The disease begins when the bacteria enter the trunk of the plant, in the neck area. Once there, stimulates the production of auxins and cytokininswhich are hormones that under normal circumstances are responsible for the growth of the plant being, but that, when it is infected, are produced without control. Thus, we will see that tumors appear that are increasing in size, either in the neck and / or in the aerial part (branches), since it spreads rapidly.

These tumors or galls are shaped like small lumps at first, and larger later. During the growth period, which usually coincides with the spring and summer months mainly, globular and white inflammations on the plant may appear, which will gradually lignify and reach a maximum size of up to 30 centimeters.

How is it treated?

Agrobacterium in laboratoryAgrobacterium in the laboratory

Image – Wikimedia / Seb951

The most effective method consists of using strain 84which is avirulent. By inhibiting most disease-causing agrobacteria, it is the most interesting. To treat infected plants, or that are susceptible to infection, what is done is to spray them with a broth with a cell suspension of the bacteria that is not virulent.

But, as we always say, prevention is better than cure.

Prevention of Agrobacterium tumefaciens

Although we have been saying things already, there is still something else that is important, at least, to take into account if we do not want to end up with more than one diseased plant. Is the next:

Do not buy plants that are bad (as much as you love them)

I speak from my own experience. Go to a nursery and find one that you have been looking for a long time but that is not going through its best moment … it is one of those experiences that I do not wish for any plant collector or garden enthusiast. Why? Because even if it sounds like a laugh, you just stand there looking at it while you decide what to do. AND the best decision is to leave it where it isbut it is not always the one chosen.

But How do you know if a plant is sick? Well, in general you should not buy plants that show these symptoms:

  • Yellowish, brown, or blackish leaves
  • Whitish spots
  • Sad plant appearance
  • Strange tumors or ‘bumps’ somewhere (trunk, branches)
  • Has pests (aphids, mealybugs, red spider or whitefly are the most common)

Separate diseased plants from healthy ones

View of potted plants

View of potted plants

It is important to have a corner in the yard that serves as a »infirmary»that is, a place where to put the diseased plants until they recover. This place must be well ventilated but protected from strong winds and direct sun. In this way, they will be able to recover better and faster, without putting healthy ones at risk.

Use disinfected pruning tools and cover wounds with healing paste

Microorganisms can stick to tools and quickly enter plants. To avoid it, it is very important to disinfect them with pharmacy alcohol or a few drops of dishwasher. When you finish pruning, it doesn’t hurt to give them another review.

And by the way, once pruned, especially if the wounds have been large, heal them with healing paste (for sale here!). On the one hand, you will prevent bacteria from entering, and on the other, you will help the healing process.

With all this, you can prevent, perhaps not 100% but in a very high percentage, infection by Agrobacterium tumefaciens.

What is and how does Agrobacterium tumefaciens affect plants?

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