Rhizoctonia solani

Brown and/or leaf rhizoctonia 

General

• fungus widespread soil
• Considered a parasitic fungus of the soil in temperate and Mediterranean zones, having carried on several occasions sensitive crops, particularly vegetables, it is in particular responsible for leaf attacks in very humid equatorial or tropical climates.
• Responsible for damping off seedlings in the nursery, and various symptoms in the field on the underground or aerial organs (foliar Rhizoctonia - web-blight) of vegetables.
• Several reported strains differing in their cultural characteristics, their pathogenic power, and in particular their host specificity.
• Extremely polyphagous, capable of infecting several hundred different hosts, including many vegetable crops.
• Known vegetables affected: eggplant, tomato, pepper, various salads, melon, cucumber, watermelon, zucchini, squash, bean, carrot, cabbage, celery, radish, turnip, sweet potato, etc.
• Observed in the open field as well as under shelters.

• Sensitive botanical family (s)

Biology

• Storage : persists for several years in the soil as a saprophyte in the absence of susceptible hosts, in the form of mycelium (figures 1 to 5) and pseudo-sclerotia (figures 5 and 6) present in the organic matter and plant debris. Sometimes present in certain substrates and composts.
• Sources of inoculum : contamination via mycelium already present in the soil or from sclerotia. They can also take place via basidiospores resulting from its sexual reproduction (figure 7).
• Infection : tissue penetration directly through the cuticle or through various wounds. Rapid inter- and intracellular invasion of tissues by lytic enzymes.
• Development, sporulation : formation of mycelium traveling on the tissues and on the ground, and reaching other healthy organs. Sclerotia, mixed with soil particles contaminating different materials, also contribute to its dissemination. Production of basidiospores formed on basidia present on the surface of the hymenium.
• Dissemination : by basidiospores carried by wind and air currents over fairly long distances. Transmission is also ensured by soil contaminated by mycelium and sclerotia, tillage, soiled agricultural tools and machinery, plants produced in infested nurseries.
• Favorable conditions : Appreciates both in moist and heavy soils and in lighter and drier soils, at acidic or basic pH and at temperatures between 5 and 36°C. Particularly damaging in the presence of humidity and when the temperatures are rather mild, around 23-27°C or when they are unfavorable to its hosts.

Protection

• Carry out crop rotations in virgin land, they are no longer very effective in contaminated soil.
• Use a healthy substrate and quality plants.
• soil disinfection : fumigant, solarization , biofungicides, etc.
• Avoid planting too deeply, burying the collar of the plants.
• Install mulch to create a mechanical barrier between the soil and the plant organs.
• Stake certain crops and ventilate the vegetation as much as possible.
• Take care of irrigation : optimal quantity, localized supply, etc. Avoid overhead irrigation in the presence of Leaf Rhizoctonia. Shaded plots should also be avoided.
• 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.
• If necessary, spray fungicides taking into account authorized uses