Alternaria alternata

Black rot



  • Globally distributed saprophytic and opportunistic fungus (syn. Alternaria tenuis ).
  • Belongs to the superficial flora of many plant species, and in particular to that of the eggplant.
  • Very present in the environment of crops, settles more easily on the fruits as they ripen.
  • This damage is reported on the fruits and seeds of nightshades in many countries spread over all continents. It mainly affects field crops.
  • Also originally as other Alternaria of leaf spots in some countries such as Pakistan, Egypt, etc.
  • Its attacks on fruits are not rare, especially at the end of cultivation.
  • Organs attacked  : fruits especially.
  • Symptoms :
    • Rots on eggplant fruits, the affected tissues take on a dark tint, more or less collapse and become covered with a dark green to black mold.
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  • Possible confusion  :
  • Signs : dense velvety, dark green to black, consisting of the mycelium, conidiophores and numerous conidia of A. alternata in chains.


This Alternaria often lives as a saprophyte on eggplant and in its environment, becoming an opportunistic pathogen when the physiological state of the fruits is modified (presence of wounds, advanced maturity, etc.).

  • Conservation : on the surface of the seeds, in the soil and on plant debris, thanks to its melanized mycelium, its conidia and its chlamydospores. Able to maintain itself on many alternate hosts.
  • Infection : after germination of the conidia, the mycelium mainly colonizes the tissues through various injuries such as damage related to insects or pathogenic fungi, physiological micro-bursts, bird pecks or sun burns . Subsequently, it quickly invades them and lesions begin to be visible 2 to 3 days after the first contaminations.
  • Sporulation : produced on colonized tissues of numerous and short conidiophores surmounted by multicellular club-shaped conidia, forming long chains.
  • Dissemination : wind, but also rain, sprinkler irrigation ensures the dispersal of the spores. Seeds, workers, especially through their tools, also contribute.
  • Conditions favoring its development : favored by high humidity and temperatures between 18 ° C and 30 ° C. It can develop at temperatures between 2 ° C and 32 ° C, its thermal optimum being between 25 and 29 ° C. Dews, low continuous precipitation (5 mm) or sprinkler irrigation are sufficient for its extension. Fruits that have lost their integrity (wounds, damage linked to a primary colonizer) and / or have reached a more or less advanced stage of maturity are particularly vulnerable.


  • This phytosanitary problem does not normally require the implementation of special protection methods.
  • Use healthy seeds. If in doubt, uncoated seeds can be treated with hot water, with a fungicide.
  • Disinfect equipment used for training.
  • Do not plant in hydromorphic soils.
  • Choose a planting density ensuring good aeration of the vegetation, good wiping after rains or sprinkling irrigations.
  • Avoid any stress to the plants, and ensure them a balanced manure, in particular in nitrogen.
  • Mulch the soil to form a mechanical barrier reducing contamination
  • Prefer drip irrigation rather than sprinkling.
  • Improve the ventilation of the vegetation as much as possible in order to reduce its humidity.
  • Control the development of other pests of eggplant, in particular those causing damage to fruits and thus promoting parasitism of this opportunistic fungus.
  • Harvest before the fruits have advanced maturity.
  • Eliminate plant debris fairly quickly, especially rotten fruit during and at the end of cultivation. They will have to be destroyed or buried deep.
Last change : 10/12/21
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