System for Forecasting Disease Epidemics

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Stem canker blackleg

Stem canker is one of the most wide-spread and dangerous diseases of oilseed rape in Poland and all over the world. There are two species from the genus Leptosphaeria that are the cause of this disease, namely:

  • Leptosphaeria maculans
  • Leptosphaeria biglobosa

Those fungi posses a conidial stage Phoma lingam but oilseed rape plants are predominantly infected by ascospores released in the autumn. Ascospores are produced in pseudothecia on crop residues from the previous season. After releasing from pseudothecia, ascospores may move along with the wind and infect plants a few kilometers away from the infection site. It was proved that pseudothecia with mature spores break out only when drops of rain fall on them as it allows spores to germinate on the surface of wet leaves. Pycnidiospores of Phoma lingam cause secondary infection of the same or neighboring plants. Those spores are carried short distances by rain drop splash. After penetration into the plant, the fungus colonizes leaf tissues and grows into the stem. Severity of symptoms and harmfulness of disease depend on the date of infection and the fungal growth rate in plant tissue. L. maculans is considered more harmful than L. biglobosa due to infection of the stem base which results in breaking of vascular bundles as well as necrosis of the whole plant, even at the flowering stage. L. biglobosa species is the main cause of lesions on the stem, however infection of plant tissues is superficial. The aim of protective treatment is to stop the pathogen’s growth in leaf tissue and protect the plant from fungal infection moving into the stem. As the main infection takes place in the autumn, protective treatment (fungicide sprays) should be performed in this season.