Alternaria  spp.

Eggplant alternariosis

General

• Several species of Alternaria are reported on eggplant in the world , causing leaf spots and / or lesions and even fruit rot mainly in the open field: Alternaria solani, A. tomatophila (now named A. linariae ), A melongenae, A. alternata, A. tenuissima , etc. 
  • A. solani *, A. tomatophila and A. melongenae are generally considered to be parasitic and rather specific to a plant or even a family of plants;
  • A. alternata, A. crassa, and A. tenuissima are rather  saprophytic or even opportunistic.
• Disease manifesting itself gradually in France on the foliage of eggplant; attacks on fruits caused by A. alternata are not uncommon.
• Organs attacked  : mostly leaves and fruits.
• Symptoms :
  
  • Dark green to light brown leaf spots, quickly turning brown. They are more or less rounded, sometimes angular when delimited by the ribs. They show concentric patterns giving them the appearance of a target. A more or less discreet yellow halo surround them.
  • Affected tissues split and necrotize and fall, the leaves at term becoming more or less sifted.
  • Circular and brown spots affecting the fruits and extending more or less depending on climatic conditions.
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• Possible confusion  : Sigatoka.
• Signs : discreet brownish down consisting of short conidiophores surmounted by long conidia multicellular club-shaped (for the species Alternaria solani, A. tomatophila, and A. melongenae) .

*TO. solani , reported for several decades on Solanaceae, has long been described as affecting tomato, eggplant and potato; this name should be reconsidered on tomato to the detriment of Alternaria tomatophila which would be a different species.

Biology  

• Conservation : for several years on the surface of nightshade seeds, especially in the soil and on plant debris, thanks to their melanized mycelium, conidia and chlamydospores. They would persist from season to season on other nightshades * such as potatoes, eggplant, peppers, black morels ( Solanum nigrum ), S. carolinense , S. pseudocapsicum, and on so .
• Infection : after germination, these fungi enter the tissues directly through the cuticle, through the stomata or various wounds. Quickly invade the tissues, and lesions begin to be visible 2 to 3 days after the first contaminations.
• Sporulation : produced on colonized tissues, numerous and short conidiophores surmounted by long multicellular conidia.
• Dissemination : the wind, but also the rain and the irrigation by sprinkling ensure the dispersion 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. Dews, low continuous precipitation (5 mm) or sprinkler irrigation are sufficient for their extension. Plants that are stressed, poorly smoked or heavily loaded with fruit would be more sensitive.

* It may be appropriate to reconsider potential hosts which may not be the same for A. tomatophila , A. solani, and A. melongenae. It is indeed possible that these two species have somewhat different host spectra.

Protection*

• Carry out fairly long crop rotations, of the order of 3 to 4 years.
• Do not plant a crop near already affected eggplant plots, or other sensitive crops such as potatoes, tomatoes, peppers, etc.
• Eliminate weeds that can serve as intermediate hosts.
• Use healthy seeds. If in doubt, uncoated seeds can be treated with hot water, with a fungicide.
• Disinfect equipment used for training.
• Control the quality of the plants.
• 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.
• Eliminate plant debris fairly quickly, during cultivation following the various cultivation operations, and at the end of cultivation after uprooting the plants. They will have to be destroyed or buried deep.
• If necessary, spray fungicides taking into account the authorized uses. Applications will be made every 7 to 10 days, on dry plants, and should be repeated following heavy rains exceeding 20 mm.
• Hybrid eggplant varieties resistant to Ralstonia solanacearum and Alternaria solani appear to be available in China.

* The observation of symptoms of alternaria in France does not normally require the implementation of chemical protection. Indeed, this disease does not seem to have the same epidemic potential in eggplant as in tomato. Also, we advise you to implement the other proposed protection methods and to monitor the progression of the disease.