Sclerotinia sclerotiorum (Lib.) de Bary

Sclerotiniose

( Sclerotinia stem and fruits rot , watery soft rot )

General

• Soil fungus widely distributed throughout the world; although rather dreaded in temperate regions, it is also observed in warmer regions but its incidence has nothing to do with that of Sclerotium rolfsii . The economic losses recorded in certain countries are sometimes very significant.
• Rather polyphagous, it is capable of infecting many vegetables belonging to various botanical families.
• Observed in the open field as well as under shelters.

• Sensitive botanical family (s)

 Biology

• Storage : has significant saprophytic potential. It can remain in the soil for 8 to 10 years thanks to its sclerotia (figures 1 and 2) which it produces on the affected organs and/or on its mycelium (figure 3) present in the plant debris left on the plots. Reported on more than 400 different plant species, cultivated or weeds, including many vegetable crops (salads, beans, cabbage, peppers, eggplant, many cucurbits, celery, peas, carrots, rutabagas, potatoes, etc.) and some number of weeds in an unnoticed way.
• Sources of inoculum : contamination occurs through the intermediary of the mycelium from sclerotia found near organs in contact with the ground. Possible aerial contamination via ascospores produced by apothecia (figure 4) ensuring its sexual reproduction. these germinate on plant tissue only in the presence of water from rain, sprinkler irrigation or dew.
• Infection : easily penetrates and invades living, injured, senescent or dead organs whether in contact with the ground or not.
• Development; sporulation : produces mycelium and sclerotia in and on tissues.
• Dissemination : via soil present on tillage tools or on plants soiled by sclerotia, and by ascospores carried by the wind and air currents.
• Favorable conditions : thermal optimum located slightly below 20°C, but capable of developing at temperatures between 4 and 30°C. Development facilitated by humid and rainy periods, by tissues having reached an advanced stage, light soils rich in humus.

   

 Protection

• Carry out crop rotations in virgin land, they are no longer very effective in contaminated soil.
• soil disinfection : steam, fumigant, solarization , biofungicides, etc.
• Well worked and drained the soil to avoid the formation of puddles conducive in particular to the formation of apothecia responsible for aerial contamination
• Work deeply in order to bury the sclerotia in depth which will be destroyed more quickly. Immersion of infested plots would reduce the number of viable sclerotia present in the soil. Orient the planting rows in the direction of the prevailing winds so that the collar of the plants and the plant cover are well ventilated.
• Control the nitrogenous manure which should be neither too strong (at the origin of very receptive succulent tissues), nor too weak (sources of chlorotic leaves constituting nutrient bases).
• Reduce the humidity of the crops and avoid the presence of free water on the plants: ventilate the shelters as much as possible, irrigate preferably during the morning and at the beginning of the afternoon — never in the evening. Prefer localized irrigation to sprinkler irrigation.
• Install a mulch to create a mechanical barrier between the soil and the plant organs, or even to trap the ascospores released from the apothecia.
• Eliminate 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.
• Take care of irrigation : optimal quantity, localized supply, etc.
• If necessary, use a biopesticide based on Coniothyrium minutans , and/or spray fungicides * taking into account authorized uses