Alternaria linaria EG Simmons

Alternariose (early blight)  

General

• Disease found on all continents, wherever this solanaceae is cultivated, in tropical, subtropical and temperate production zones.
• A. solani , reported for several decades on Solanaceae, has long been described as affecting tomato, eggplant, potato, this designation should be reconsidered on tomato to the detriment of Alternaria tomatophila which would be a different species.
• Fungus rather specific to the aerial organs of tomato.
• Mainly observed in the open field.

Sensitive botanical family (s)

 Affected production areas :

  Organs attacked :

Symptoms and signs

• Symptoms :
  • Damping off, and more or less extensive black alterations on the stem near the collar or higher up. After girdling the stem, the lesions can cause plants to dry up and die quite quickly.
  • Leaf spots initially dark green, rapidly becoming brown to black (Figures 1 to 5). They are more or less rounded, sometimes angular when they are delimited by the ribs. They show discrete concentric patterns giving them the appearance of a target (figure 6). A more or less bright yellow halo surrounds them. They end up necrosing.
  • Fairly comparable lesions on stems, petioles and peduncles. They have a blackish tint and are often more elongated (figures 6 and 7).
  • Concave alterations on fruits, well delimited, appear near the peduncular scar and the sepals. The surface of weathered fruit areas wrinkles and sometimes shows concentric patterns (Figures 8-10).

• >>> More symptoms

• Signs : discreet brownish down made up of short conidiophores (figure 13) surmounted by long conidia club-shaped multicellular
• Possible confusion : corynesporiosis

Biology

• Preservation : maintained for several years on the surface of tomato seeds, in the soil and on plant debris, thanks to its melanized mycelium, conidia and chlamydospores. It lasts from season to season on other nightshades * such as potatoes, aubergines, peppers, blackberries ( Solanum nigrum ), S. carolinense , S. pseudocapsicum .
• Infection : After germination of the spores, this fungus penetrates the tissues directly through the cuticle, through the stomata or various wounds. Rapidly invades the tissues, and lesions begin to be visible 2 to 3 days after the first infections.
• Sporulation : form on the colonized tissues of short conidiophores surmounted by long multicellular conidia (figures 12 to 15).
• Dissemination : the wind, but also the rain, sprinkler irrigation ensures the dissemination of the spores. Seeds, workers, especially via their tools, also contribute to this.
• . Favorable conditions : high hygrometry and temperatures between 18°C ​​and 30°C Dews, low continuous rainfall (5 mm) or sprinkler irrigation are sufficient for its extension. Plants that are stressed, badly smoked or heavily loaded with fruit are more susceptible.

* It may be appropriate to reconsider the potential hosts of A. tomatophila which are not necessarily those of A. solani . 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 tomato plots already affected, or other sensitive crops such as potatoes, eggplant, 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 all stress to the plants, and provide them with a balanced manure, especially 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. The applications will be carried.