Eggplant alternariosis

Eggplant alternariosis

General

• Several species of Alternaria are reported on eggplant in the world , causing leaf spots and / or lesions or even fruit rot mainly in the open field: Alternaria solani, A. tomatophila (now named A. linariae ), A melongenae, A. alternata, A. tenuissima , etc. Some of these species are generally considered parasitic and rather specific to a plant or even a family of plants, others are rather saprophytic or even opportunistic such as A. alternata, A. crassa and A. tenuissima . A. solani , reported for several decades on nightshade, has long been described as affecting tomatoes, eggplant, potatoes, this name should be reconsidered on tomatoes at the expense of Alternaria tomatophila which would be a different species.
• Disease does not manifest itself little by little in France on the foliage of eggplant; fruit attacks by A. alternata are not uncommon.
• Organs attacked  : mainly leaves and fruits.

• Symptoms :
  
  • Dark green to light brown leaf spots, quickly turning brown (Figure 1). They are more or less rounded, sometimes angular when they are delimited by the ribs (figure 2). They show concentric patterns giving them the appearance of a target (figure 3). A more or less discreet yellow halo surrounds them.
  • The affected tissues merge into necrosis and fall off, the leaves eventually becoming more or less riddled.
  • Circular and brown spots affecting the fruits and extending more or less depending on the climatic conditions.

• Possible confusion  : Sigatoka,
• Signs : discrete brownish down consisting of short conidiophores surmounted by long conidia club-shaped multicellular Alternaria solani, A. tomatophila, and A. melongenae .

Biology  

• They are preserved 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.
• Other nightshades * such as potatoes, aubergines, peppers, blackberries ( Solanum nigrum ), S. carolinense , S. pseudocapsicum, etc.
• After germination, these fungi penetrate the tissues directly through the cuticle, through the stomata or various wounds.
• Rapidly invade the tissues, and lesions begin to be visible 2 to 3 days after the first infections.
• Sporulate on colonized tissues as short conidiophores surmounted by long multicellular conidia.
• The wind, but also the rain, the sprinkler irrigation ensures the dissemination of the spores. Seeds, workers, especially via their tools, also contribute to this.
• Favored by high hygrometry and temperatures between 18°C ​​and 30°C. Dews, low continuous rainfall (5 mm) or sprinkler irrigation are sufficient for their extension. Plants that are stressed, badly smoked or heavily loaded with fruit are more susceptible.

* It may be appropriate to reconsider the potential hosts which are not necessarily 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 crop rotations , of the order of 3 to 4 years.
• Do not set up a crop near already affected eggplant plots, or other sensitive crops such as potato, eggplant, pepper, etc.
• Eliminate weeds that can serve as intermediate hosts
• Use healthy seeds . If in doubt, uncoated seeds can be treated with hot water and a fungicide.
• Disinfect the equipment used for trellising.
• Check the quality of the seedlings.
• Do not plant in hydromorphic soils.
• Choose a planting density ensuring good ventilation of the vegetation, good drying after rains or sprinkler irrigation.
• Avoid any stress to the plants, and provide them with a balanced manure , particularly in terms of nitrogen.
• Mulch the soil to form a mechanical barrier to reduce contamination
• Prefer irrigation drip
• fairly quickly plant debris , 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 authorized uses ( e-phy ). The applications will be carried out every 7 to 10 days, on dry plants, and must be renewed following significant rains exceeding 20 mm.
• Hybrid eggplant varieties resistant to Ralstonia solanacearum and Alternaria solani appear to be available in China.

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