Charcoal rot disease in sesame

Charcoal rot disease is considered one of the most important and dangerous diseases affecting sesame under Egyptian soil conditions at the present time, especially in the governorates of Upper Egypt. This disease is characterized by its wide host range, as it affects the roots and bases of the stems of more than 500 plant species, and its danger increases in hot and dry areas. When plants are exposed to harsh conditions such as severe water shortage. The danger of this disease lies in the early infection of young seedling roots with the formation of the first cotyledon leaf, but the symptoms do not appear until 45-50 years after planting, as the infection appears and develops beginning with the period of flowering and fruiting, as this leads to the death of the plants and a decrease in the seed yield and the seeds it contains. There is a significant shortage of oil in quantity and quality.

Casual pathogen

This disease is caused by the fungus Macrophomina phaseolina, and this fungus has two types of reproductive structures: microsclerotia, which is the stage that causes the most infection, and the other stage is the pycnidia vessels that contain pycnidid germs, which is the stage that causes the least infection and does not form under normal conditions except under special circumstances.

The fungal species that form only stony bodies and not the vessels and pycnidid spores are called Sclerotium bataticola.

Symptoms

Symptoms of infection with the disease appear in the form of black rot of the roots and then extend to the stem, where it appears in the form of black or charcoal discoloration of the stem in the area where it connects with the soil with the root. Infection with this disease leads to easy removal of the outer shell of the root and stem, where black dots are seen underneath, which are stony bodies (sclerocetes). ) for mushrooms.

In the event that conditions are present that predispose infection, such as high temperature, severe soil dryness as a result of thirsty soil, lack or complete prevention of irrigation, and plants entering the flowering and pod formation phase, these conditions increase the virulence of the fungus and its formation of stone objects, as the infection extends to the top of the stem towards the branches, flowers, and pods, and the infection is revealed quickly. In these conditions, which leads to clear paralysis and rapid death of plants, as the infected plants turn to a charcoal color as a result of the formation of black stoney bodies characteristic of the fungus on the infected roots, stems and pods. The disease ultimately leads to the drying out of the infected plants, their easy breakage and their eventual death, and the seed and oil yield also decreases. Qualitatively, in addition to producing infected seeds that transmit the infection in the following season when planted (at a rate of 5-7 %), infected plants are also characterized by being early in maturity compared to healthy plants, as they rush to form seeds to preserve their type.

Conditions suitable for the emergence and spread of the disease

Soil dryness is considered a result of lack or prevention of irrigation (thirsty), as these conditions increase the virulence of the fungus and its formation of stone bodies, in addition to high temperature. Also, watering plants at noon, excessive nitrogen fertilization, delay in planting, and planting susceptible varieties are among the conditions that predispose to infection with this disease as well.

Resistance Disease control

1. Cultivation of resistant varieties such as the Shindawil variety (3) and the Taqah variety (2).
2. Early planting of sesame crops (mid-April to late May) reduces the infestation significantly.
3. Disposing of the remains of infected plants by burning outside the field.
4. Irrigation is regular and plants do not become thirsty for a long time, especially during the flowering period and pod formation. Also, do not stop irrigation long before harvest (preferably 7-10 days). Planting previous winter crops reduces the incidence of infection, such as planting onions, garlic, flax, and barley.
5. Cultivation of healthy seeds free of infection and taken from reliable places.
6. Treat the seeds before planting with a fungal seed disinfectant, such as Rizolex-T, at a rate of 3g/kg seed, and use gum arabic, 5% concentration, as an adhesive, at least 24-48 hours before planting.
7. Treating the seeds before planting with one of the effective and safe alternatives to pesticides to reduce and rationalize the use of pesticides, such as soaking the seeds in garlic and rhubarb extracts or one of the substances that stimulate resistance such as salicylic acid (aspirin) or indole butyric acid.
8. In the case of severe infestation or planting on land infested with the disease, the infected soil is treated with one of the recommended fungal disinfectants as a soil treatment, such as Rizolex T pesticide at a rate of 2 kg/acre or chlorothiocyb pesticide at a rate of 5 kg/acre after mixing it with an appropriate amount of soil to facilitate its distribution, then mulch or slurry is added to the lines. Under the plants, then irrigating directly, in addition to the seed treatment mentioned above

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