Protection methods

• During cultivation

There is no method that can effectively control Ralstonia solanacearum once it has manifested itself in a tomato plot.

The measures hygiene must be taken quickly: the affected plots will be worked last and equipment, farming equipment and shoes disinfected workers. Avoid causing root injuries. We advise you to refer to sheet 24 on bacterial canker where they are described more precisely.

We can also strongly advise d '' eliminate and destroy the root systems and stems of plants at the end of cultivation. This measure will prevent many bacteria present in these organs from being maintained in the soil.

• Next crop

In countries and regions where this bacteriosis is a major threat to tomato cultivation, the control of this disease requires the combined and often preventive implementation of several complementary protection methods.

The nurseries will be set up in plots that have not grown sensitive crops. If you have the slightest doubt, we advise you to disinfect the soil (steam, chloropicrin ) or the substrate, especially if its origin is doubtful. Your best bet will be to produce seedlings above ground, with a healthy substrate. If you buy seedlings, you will need to check that they have been produced under conditions that avoid any risk of contamination.

Preferably, disease-free plots are used . It will also be advisable to implement crop rotations taking this bacteriosis into account. The management of the plots should be a concern for each producer who wants to preserve his soils and delay as much as possible the appearance and development of one, or even several soil-borne diseases. This measure is not easily applicable in the case of Ralstonia solanacearum , given its large number of potential hosts. The longer the rotation, the more it will lower the soil inoculum rate. It will be even more effective if it involves plants that are not very sensitive, or even resistant to bacterial wilt. Fescue, cotton, soybeans, grasses, corn, rice, etc. seem to fall under this type of behavior. For example, 4 years of sugar cane, 2 years of meadow Digitaria , sorghum as a green manure, cut several times on site for 5 to 6 months, allow the soil to be more or less sanitized. Likewise, the addition of high doses of urea, sludge from sewage treatment plants, probably any organic amendment, contributes to reducing the rate of inoculum in the soil.

Soil disinfection does not seem to be very effective. In Brazil, solarization soil (you can consult the sheet Pyrenochaeta lycopersici fact ) associated with the contribution of organic residues ( biofumigation ) has been tested: this association would make it possible to reduce the level of bacterial population in the soil and therefore the severity of damage. However, contradictory results have been obtained in India, where solarization is believed to be the cause of an increase in the soil bacterial population. In addition, the incidence of bacterial wilt would be proportional to the duration of implementation of this method of disinfection.

Let us point out for information that certain essential oils of plants (of thyme with thymol, of Cymbopogon martini ) used as biofumigants would have made it possible to effectively reduce the levels of populations of R. solanacearum in the ground. A comparable effect would have been obtained with an amendment containing silicon.

The various agro-cultural interventions will ensure maximum comfort to the plants. It will be advisable to promote as much as possible a good drainage of the plots and of 'avoid excess moisture soil . Water quality will be monitored: watercourses may be contaminated, which does not appear to be the case with borehole water. A balanced manure, without excess nitrogen, will be applied. Weeds will be destroyed.

The use of resistant varieties is certainly the most effective, economical and environmentally friendly solution to controlling bacterial wilt. Unfortunately, the challenge is particularly difficult because the resistance properties demonstrated are often quantitative and strongly influenced by the environment, the nature of the soil, its temperature, its pH and its humidity.

Two types of resistance can be distinguished in tomatoes: a resistance from the line Hawaii 7996 , and another obtained by the University of North Carolina, the AVRDC and the INRA Antilles -Guyana. The first, which turns out to be the most effective, is dominant and more easily inherited. The second is also polygenic (5 genes estimated) and partially effective. The latter must therefore be supported by other agrocultural measures and practices. Different selection work has made it possible to obtain several resistant varieties or lines of tomato, more or less well adapted to tropical conditions: Venus , Saturne , Caribbean , L 3? ?, King Kong

It should be noted that resistance to bacterial wilt in tomatoes seems to be associated with the production by plants of small fruits.

In addition, several resistant rootstocks are used to control this bacteriosis: lines and cultivated varieties ( Hawaii 7996 , Kewalo , Venus , CRA66 , Cranita 2.5.7 ) or selected for this use ( LS-89 , BF Okitsu 101 , PFN 1 ), various Solanum ( S. aethiopicum Iizuka , S. torvum, S. straminifolium ), eggplant lines with comparable behavior towards R. solanacearum . However, bacterial wilt damage has been observed in Japan on some of these rootstocks.

Various bacteria that stimulate plant growth or interact directly with R. solanacearum are said to reduce the attack levels of bacterial wilt: several rhizobacteria ( Pseudomonas fluorescens, Bacillus pumilus, B. subtilis, Chryseobacterium sp., Streptomyces sp., Paenibacillus polymyxa, Brevibacillus, Brevibacillus brevis ).
Another bacteria, Burkholderia sp. W3 , would be responsible for the suppression of bacterial wilt observed for more than ten years in Japan on tomato crops produced in soilless on pumice stone.

Premunition tests with a strain of R. solanacearum hypovirulent , obtained by mutagenesis in China, have shown a significant reduction in bacterial wilt in tomato.

Few products appear to be effective against this bacteria. Acibenzolar-S-methyl natural defenses activator would reduce the severity of the disease; the level of protection obtained would nevertheless fluctuate depending on the degree of natural resistance of the tomato variety and the bacterial inoculum pressure. Chitosan has also reportedly been tested with "some success".


* Chemical control : As the number of pesticides available for a given use is constantly changing, we advise you to always confirm your choice by consulting the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.