Cercospora  spp. 

Cercosporiose

General

• Mushrooms quite widespread in the world, very present in many countries on all continents. Several agents of Sigatoka affect vegetables grown in tropical areas. They cause lesions on the aerial organs of plants, mainly the leaves, even the petioles and the stem. On leaves, they show two types of behavior: some cause necrotic spots on which they fruit once the tissue has died, others sporulate mainly on the underside of the leaf blade, on tissue still living and in the form of a velvety purplish gray to black ("black leaf spots"). They produce brown conidiophores and transversely septate hyaline conidia (Figures 1 to 3).
• More or less polyphagous fungi; several can be found on vegetable species of the same botanical family. Distrust, some may come to colonize secondarily tissues damaged by a primary invader.
• Rather observed in the open field.  
• Cercospora spp. reported on eggplant : Pseudocercopsora egenula , Cercospora solenigena , C. melongenae,  C. deightonii , etc.
• Organs attacked  : leaves, stems.

•  Symptoms :
  • Initially, small circular to oval chlorotic lesions appearing mostly on old leaves (Figure 1).
  • Subsequently, the spots spread, turn brown, and gradually necrosis. A reddish-brown border surrounds them. Their diameter varies from 4 mm to 1 cm (Figures 2 to 5).
  • The center of the spots becomes more or less clear and sometimes presents discreet concentric patterns. A yellow halo is visible.
  • Comparable, but elongated lesions are sometimes visible on the petioles and the stem.
  • Degraded fabrics dry, split and eventually fall off; the blade is thus partially screened (figures 3 and 4).
  • Heavily affected leaves turn yellow, wilt, and may drop.

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• Signs  : presence of black mycelial stromas, and fruiting bodies dotting the lesions and sometimes giving them a slightly light gray tint. These fruiting bodies consist of clustered brownish conidiophores, bearing septate and slightly arching hyaline conidia.
• Possible confusion : bacteriosis

Biology

• Conservation : on plant debris thanks to their mycelium, their spores and the mycelial stromas that they form and whose viability is several months. They are perennialized in the environment of cultures probably on various cultivated or wild plant species: beware of certain weeds belonging to the same botanical families as sensitive cultivated plants. Some are perennial on seeds ( C. capsici )
• Infection : germination of spores on the surface of polluted plant organs, and penetration of the germ tubes into the tissues through the stomata. Then the mycelium invades the tissues.
• Sporulation : production on damaged lesions of partitioned brown conidiophores, bearing more or less elongated and partitioned hyaline conidia depending on the species.
• Dissemination : by spores by the wind over long distances (rather Pseudocercospora ), by splashing water (rather Cercospora ) following rains and irrigation by sprinkling, by workers and agricultural tools.
• Favorable conditions : humidity especially influences the epidemics of Sigatoka disease on vegetables. Contamination often takes place following wet periods, thanks to rains and sprinkler irrigation.

Protection

• There are differences in varietal sensitivities. Choose to grow the less susceptible varieties.
• Disinfect the seeds if necessary ( C. capsici ).
• Use healthy plants.
• Establish crop rotations that do not involve sensitive crops, for 2 or 3 years.
• Destroy spontaneous plant species in or near the crop that may harbor these fungi.
• Ensure good drainage to cultivated plots.
• Avoid excessive planting densities in order to promote aeration of the foliage.
• Avoid sprinkler irrigation, prefer drip irrigation. If they are essential, carry them out in the morning so that the vegetation dries up quickly during the day.
• Under shelters, ventilate as much as possible.
• Do not allow workers to work while the vegetation is wet.
• Leave the crop and destroy affected plants and especially diseased fruits. Eliminate plant residues at the end of the crop. Deep plowing can bury remaining debris, this measure should be combined with crop rotation.
• If necessary, spray fungicides taking into account the authorized uses.