Biology, epidemiology

• Conservation, sources d'inoculum
  

Fusarium oxysporum f. sp. radicis-lycopersic i is able to stay in the debris soil thanks to plant harboring mycelium, micro- and macroconidia, and thick-walled, thick-walled chlamydospores (Figure 1). It is also found in the dust present in shelters. F. oxysporum f. sp. radicis-lycopersici has saprophytic life skills that allow it to colonize and survive on various organic compounds, and to survive in above-ground crops, even in the presence of resistant varieties.

The east of susceptible if développer sur de nombreuses automation owned des familles botaniques différentes, sans qu'elles expriment toujours des symptomes: poivron, aubergine, bean, peas, haricot, melon, betterave, yet. Several weeds would harbor it without symptoms: Chenopodium album, Solanum nigrum, Panicum fasciculatum, Trifolium repens, T. pratense, Schinus terebinthifolius, Mollugo verticillata, Gnaphalium sp., Stellaria media, Spergulum arvense, Rumex crispus, Plant, Rumex crispus, , Scoparia sp., Capsella bursa-pastoris, Polygonum convulvulus As an example, this fungus would multiply on a weed that is very present in Israel in tomato : plots Tamaris nilotica . It is found both on the roots and on the inflorescences of this plant. Its conservation is thus ensured in the soil. Contaminated seeds are said to be the cause of its spread in a plot.

It is very present in shelters, especially in irrigation, drainage and nutrient solution recycling systems. Water storage ponds are often contaminated. Water is a significant source of inoculum, as is the nutrient solution subsequently. It has been shown that the fungus can survive for more than 52 weeks in a nutrient solution stored at room temperature.

F. oxysporum f. sp. radicis-lycopersici can infect tomato seeds . For example, from plants with infected stems and fruits, seed infestation rates of the order of 0.01 to 0.1% have been observed. It has been shown that the fungus can persist for more than 12 weeks on stored seeds. Disinfecting the seeds with bleach also does not seem to be completely effective in ridding them of this fungus.

• Penetration and invasion

After germination of its chlamydospores , this Fusarium penetrates into the roots of the tomato through natural wounds (point of emission of secondary roots) or accidental , at the end of the roots . Direct penetration into epidermal cells would be possible. Recent work has shown that the mycelium of the fungus can come into contact with the root scalp, become entangled with it and eventually attach to the rootlets. The preferential site of colonization of the root surface seems to be located at the level of the furrows present at the junction of the cells of the epidermis. The fungus invades the tissues and eventually colonizes the entire root system.
 

• Sporulation and dissemination

This fungus produces numerous micro- and macroconidia , even chlamydospores on and in colonized tissues, whether they are root or located on the stem. Its dissemination can take place through shoes and agricultural equipment soiled by contaminated soil and plant debris (agricultural machinery, boxes, stakes etc.). Soil dust containing various spores is easily disseminated by air currents , as well as by splashing water .

It should be noted that airborne contaminations are possible through micro- and macroconidia which are transported by air currents. These spores can deposit either on aerial vegetation or on the soil or substrate of soilless crops. The wounds seem to favor contamination leaf .

Note that it has been shown that the fungus could spread over a radius of 4 m around an inoculum plant, by root contact from plants to plants in particular.

The dissemination of F. oxysporum f. sp. radicis-lycopersici is also provided by irrigation water , the nutrient solution which may have been contaminated during storage in the bins, or when it is recycled from contaminated substrates. Indeed, this fungus spreads rapidly in soil-less cropping systems, especially in recycled solution. It is found, at the end of a week after an artificial inoculation, both in the drainage and recycling systems of the nutrient solution.

Infected plants without symptoms, polluted stakes, contribute to its spread. Remember that this fungus was introduced in France via contaminated substrates and that some composts could be soiled. It could be spread by infected seeds.

Certain insects belonging to the genus Bradysia could play a role vector and promote the spread of this fungus. The soil flies would also ensure the dissemination of Forl. They would also influence its parasitism thanks to the wounds they cause on the roots.

• Conditions favorable to its development

F. oxysporum f. sp. radicis-lycopersici seems to prefer rather low temperatures. Its thermal optimum would be between 18 and 20 ° C and its most severe attacks would take place at temperatures between 10 and 20 ° C.

Inoculations on tomato seedlings revealed that this Fusarium wilt could be influenced by certain micro- and macroelements. The severity of the disease would be increased for example in the presence of ammoniacal nitrogen, but also of NaH ₂ PO ₄ , of MnSO ₄ , of ZnSO ₄ 7H ₂ O and would be reduced with Ca (NO ₃ ) ₂ 4H ₂ O, CuSO ₄ H ₂ O In addition, this root fusarium appears particularly severe in acidic soils, or saturated with water. Excessive salinities would increase its incidence and the severity of its symptoms.

In Israel, the use of salt water has been shown to increase the severity of the disease. The same would apply in the presence of small amounts of CaCO ₃ .

Note that F. oxysporum f. sp. radicis-lycopersici very rapidly colonizes or recolonizes recently disinfected soils and substrates. In addition, plants that have undergone water or thermal stress are more sensitive.