Crop damage: diagnosis or rapid screening?

11 March 2020 - Articles

The reason why a crop does not grow as expected is often unclear. When that happens, you want an accurate and fast diagnosis. The question is, do you go for a PlantDoctor analysis or a DNA Multiscan? Choosing the right type of analysis helps you get a rapid understanding of the possible cause.

If the cause of a problem is unknown or in doubt, an analysis by Eurofins Agro’s PlantDoctors is the appropriate course of action. If rapid screening of a pathogen that appears on the DNA Multiscan list is sufficient, you can opt for this analysis. A DNA Multiscan rules the presence of the pathogen you are looking for in or out. This method only screens for the pathogens on the list.

Advice tailored to situation

Our PlantDoctors stay abreast of the latest knowledge and developments in pests and diseases. This is essential in order for them to make an accurate diagnosis. At the moment, for example, the Tobamo virus ToBRFV is prevalent, causing widespread concern among tomato growers worldwide in recent months.

“As PlantDoctors, my colleague Trudie Coenen and I focus on providing a correct diagnosis and personal advice,” PlantDoctor Ester Dekkers says. “Only then the grower can apply the correct treatment and prevent the disease from spreading further.

“For a PlantDoctor analysis we like to receive the whole plant including the roots. That way we can observe the symptoms properly and target our analysis accordingly. There are a lot of pathogens that are harmful to plants: fungi, bacteria, viruses, viroids, phytoplasmas, insects and mites.”

Strategy depends on symptoms

The first step the PlantDoctors undertake is a microscopic examination. “We often have an idea of what is wrong based on the symptoms alone. But that isn’t always the case, so we sometimes have to investigate further. With fungi, this can be done, for example, by using plating techniques in which the primary pathogen is isolated from the plant material. Next, we can identify the fungus with microscopy or a DNA Multiscan. The combination of symptom and pathogen then provides the final result of the investigation.

Crop damage“If a virus is suspected, the leaf material is analyzed with an ELISA test or a specific PCR test. In the report the grower receives afterwards we state what the vector of the virus is and what action they can take.” Sometimes a particular smell coming from the material can indicate the presence of bacteria. Watery or glassy patches on leaves or stems can also be a sign of a bacterial infection.

If no pests or diseases are found, the problem may be one of plant nutrition and fertilization. This can be seen from symptoms such as discoloration in the leaves, necrotic leaves or stunted growth. However, these symptoms can also be caused by the incorrect use of chemicals such as growth inhibitors or crop protection products.

Suspicion confirmed quickly

If you only want a quick screening for the presence of a particular pathogen, check whether it is on the DNA Multiscan list and select the appropriate package. We can only screen for the fungi and bacteria included in this overview. [You can find the list here.] This will enable you to definitively determine the presence of the pathogen you are looking for. Make sure that the package you choose is appropriate for the crop and fits the pathogen you expect to encounter. You can apply for different crop-specific packages (e.g. for strawberry, tomato, sweet pepper, woody crops, etc.).

A sample for PlantDoctor

When samples are submitted for a PlantDoctor analysis, the PlantDoctors also like to receive as full a description as possible of the symptoms and the growing circumstances. Dekkers: “State this on the PlantDoctor form and send the form in together with your sample. To enable us to make a correct diagnosis, we like to see symptoms at an early stage. If possible, send in the whole plant. The roots and crown are often the most important parts of a sample. If you suspect an insect pest, pack the samples so that the insects can’t escape.”