Verticillium dahliae Kleb.
Verticillium albo-atrum Reinke & Berthold, (1879)

Verticilliose ( Verticillium wilt)

General

• Soil fungi reported from many temperate and subtropical countries.
• Several species of Verticillium are likely to attack vegetables causing comparable symptoms.
• Very polyphagous, they affect more or less wide ranges of hosts depending on the species.
• Vegetables known to be affected: eggplant in particular, but also tomato, pepper, potato, Cucurbitaceae, artichoke, lettuce, cabbage, strawberry, rosebush, aster, chrysanthemum, tobacco, cotton, etc., various weeds (black nightshade, amaranth, etc.), etc. .
• Observed in the open field as well as under shelters.

• Sensitive botanical family (s)

• Affected production areas :

• Organs attacked

 Biology

• Conservation : poor competitors in the soil, their conservation is ensured by mycelial fragments still in place in the plant debris, but also by its microsclerotia (figure 1) which perpetuate them for more than fifteen years. Their polyphagy allows them to attack and survive on more or less wide ranges of hosts.
• Infection : Direct penetration of the mycelium into the roots, or either through various wounds, and/or attacks by root-knot nematodes and Pratylenchus spp. Invasion of the vascular system of plants which it gradually colonizes. These react by forming gum or tyloses which prevent its progression. These defense mechanisms, associated with colonization and clogging of vessels by mycelium, contribute to plant wilting.
• Sporulation : production of fragile whorled conidiophores forming ovoid conidia (figure 2).
• Dissemination : possible through potting soil, agricultural equipment soiled with contaminated soil and plant debris. Soil dust harboring microsclerotia and/or conidia is easily disseminated by air currents, as well as by splashing water and soil-borne insects.
• Favorable conditions : appreciate variable climatic conditions depending on the species and strains. Their thermal optima would be between 20 and 32°C. Short photoperiods and weak lighting sensitize plants to verticillium wilt, which would be more serious in neutral to alkaline soils. The monoculture of sensitive plants or rotations that are too short or badly chosen contribute to increasing its incidence in certain plots.

 Protection

• Use resistant varieties or rootstocks if possible.
• Carry out crop rotations , at least 4 years. Cereals do not seem to be affected by these vascular fungi. Peas, beans and cabbage could be used in rotations as they would not help maintain inoculum in the soil.
• soil disinfection : fumigant, solarization , biofungicides , etc. It should be added that the disinfected soils should not be worked too deeply before cultivation, otherwise microsclerotia will rise in the treated stratum.
• Destroy host weeds .
• Ensure a balanced manure in order to avoid obtaining young plants with too succulent tissues.
• Take care of irrigation: optimal quantity, localized supply, etc.
• Irrigate optimally during hot periods to limit wilting.
• Water plants at the hottest times of the day to reduce leaf wilt.
• Clean tools and agricultural machinery used in contaminated plots before using them in other still healthy plots. Thorough rinsing of this material with water will often suffice to remove contaminated soil.
• Eliminate diseased plant debris during and at the end of cultivation, as well as potential host weeds likely to harbor or promote the development and preservation of this fungus in the soil.
• If necessary, add a fungicide taking into account authorized uses.