Early detection and tracing virus point of entry

‘It is important to be prepared and understand the virus infection  so as to effectively mitigate it’s spread or prevent potential outbreak’

Harmen Hummelen; Field Quality Lead

The tomato brown rugose fruit virus (ToBRFV) is now so widely distributed that it is very likely to eventually reach all global production locations. As some people say, it is not a question of ‘if,’ but ‘when’. As a grower, it is therefore important to be prepared and ready to understand the virus infection or manage its spread or potential outbreak.

ToBRFV infection that are not managed properly can have a big impact on plant quality and yield. You will certainly remember the first time you see virus symptoms on your plants. Hopefully you will detect the virus very soon after infection, and this article presents some tips and suggestions for early detection.

Recognizing in the greenhouse
Early infection is not easy to recognize, partly because most people have not personally seen the disease before. There are some general guidelines to aid early detection and recognition of ToBRFV, and a good scout who can ‘read’ the plants is the most valuable tool.

A good scout or grower is most likely to see those plants which are not ‘normal’ for the particular variety or that time of the year (for example those having a slightly different color or shape). Those symptoms may not be directly linked to ToBRFV because the symptoms can often look like fertilizer deficiency or other stress factors.

For instance, one of the symptoms can be that the plant is a little shorter, without a clear reason. Those plants, or their neighbors, may have fruits which are not ripening in the normal way. Some fruits, particularly at the top of a truss, are later ripening or the ripening is more uneven, perhaps with a little more blotchiness. Maybe the top of the plant is a little bit paler in green color? These are all symptoms that can be caused by many factors, but which can also indicate ToBRFV.

One problem is that in some cases, the virus causes no plant symptoms and only shows on the fruits. This seems to occur especially in older crops, where hardly any symptoms are seen, but the virus is present. This increases the risk of a missed infection going on to the next crop cycle.

It is therefore very important that if something does not look or feel normal, to start thinking about the possibilities and check again more carefully. The final step to determine whether ToBRFV is present is to carry out a diagnostic test.

Tomato brown rugose fruit virus | Cornell Vegetables: Tomato brown rugose fruit virus | Cornell Vegetables

A good and easy method to test the presence of ToBRFV is sampling the calyx of the fruit

Leonie Hogendonk; Market Development Protected Lead

Testing
A laboratory test or a quick test can demonstrate indication of infection. In both cases, we need to make sure to collect several plant parts, for instance,  the calyx and active growing shoots in a single sample because virus may not be present in all parts of the plant. In case the first sample does not confirm the visual diagnosis do not hesitate to generate another sample from a second plant or combine multiple plants in one sample. https://research.wur.nl/en/publications/detection-of-tomato-brown-rugose-fruit-virus-is-influenced-by-inf

Drain water diagnosis is also a good way to find an infection early. Growers in Belgium have tested this water using laboratory analysis, and in some cases a virus infection can be detected up to 10 weeks before visual symptoms are seen.

Be careful with testing at the beginning of the season after a previous infection because it is possible that dead virus RNA from last season may be detected. However, if cases of the virus increase, then it is clear there is living virus increasing in the plants.

Detection of the virus should be narrowed down to a certain block or section of the greenhouse, and

such early detection allows you to take extra measures and therefore reduce the spread of the virus in the greenhouse or nursery.