Alternaria alternata

Black rot

General

• 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.

Biology  

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.

Protection

• 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.