• Conservation, sources d'inoculum
  

Fusarium oxysporum f. sp. lycopersic i is able to survive in in the plant debris soil, up to 80 cm deep, for more than ten years, thanks to its chlamydospores with thick and resistant walls (figure 1). It is endowed with aptitudes for saprophytic life which allow it to colonize and survive on various organic compounds. Other plants are likely to harbor it, in particular several other species of Lycopersicon .

• Penetration and invasion

After germination of its chlamydospores, this Fusarium enters the plant either through injuries natural , such as those present at the point of emission of secondary roots, or through various injuries. Once in place, its mycelium travels between the cells of the cortex and reaches the xylem vessels and invades them. As in the case of verticillium wilt, plants can respond to this vascular invasion by forming gum or tyloses which prevent its progression, but which also contribute to wilting the plants.
 

• Sporulation and dissemination

This fungus produces chlamydospores , microconidia , and even macroconidia (figure 1), in vessels and on colonized and altered tissues. It can be disseminated over greater distances through contaminated seeds and plants, by substrates, water, by tillage machinery moving from one plot to another and whose tires are loaded with soil particles. and plant debris. Soil dust containing chlamydospores is easily disseminated by air currents as well as by splashing water.

• Conditions favorable to its development

F. oxysporum f. sp. lycopersici preferring rather high temperatures, it occurs during hot periods of the year, its thermal optimum is at about 28 ° C . It particularly likes sandy soils and acidic . The disease is favored by the low humidity of the soil, short days, low light intensities, plant tissues deficient in nitrogen, phosphorus and calcium. Excessive nitrogenous manures, especially ammonia-based, would have the same effects.

Root-knot nematode attacks and asphyxiating soils would sensitize tomatoes to Fusarium wilt. They would also allow the expression of this disease on resistant varieties, without dealing with a race overcoming the " gene I " . For example, an interaction between Meloidogyne incognita and F. oxysporum f. sp. lycopersici has been observed in India and Australia, where it is particularly damaging.