Stemphylium  spp.  

Stemphyliosis of Solanaceae

General

• Mushrooms differently distributed in the world; particularly serious disease in humid tropical and subtropical production zones, very present in the French overseas departments and territories.
• Fungi very specific to the aerial organs of Solanaceae, mainly foliar.
• Several species responsible for identical symptoms in Solanaceae: S. solani GF Weber, (1930) (figures 1 and 2), S. lycopersici (Enjoji) W. Yamam., (1960) (syn. S floridanum CI Hannon & GF Weber , (1955) (figures 3 to 5); S. botryosum f. Sp. Lycopersici Rotem, Y. Cohen & I. Wahl, (1966) (anamorph Pleospora herbarum (Pers.) Rabenh., (1854); S. vesicarium (Wallr.) EG Simmons, (1969) (syn. Pleospora allii (Rabenh.) (Figures 6 to 8). Ces. & De Not., (1863); S. botryosum Sacc., (1886). S. solani and S. floridanum would be more subservient to tropical regions, while S. botryosum f. sp. lycopersici and S. vesicarium would be found preferentially in more northern areas.
• Disease rather observed in the open field, sometimes under shelter.

• Organs attacked  : leaves, stems.

• Symptoms :
  • Initially, small, circular to elongated chlorotic lesions (Figure 1).
  • Subsequently, the spots spread, turn brown, and gradually necrosis. A reddish-brown border surrounds them. Their diameter can be greater than 1 cm.
  • The center of the spots becomes lighter gradually taking a gray to whitish tint (Figures 2 and 3), and sometimes presents concentric patterns giving them a so-called "frog eye" appearance. A yellow halo is sometimes visible.
  • Comparable, but elongated lesions are sometimes visible on the petioles and the stem.
  • Degraded fabrics dry, split and eventually fall off; the blade is thus partially screened (figure 4).
  • Heavily affected leaves turn yellow, wilt, and may drop.

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• Signs  : The fruiting bodies of the fungus dot the lesions, sometimes giving them a slightly light gray tint.
• Possible confusion : rare

Biology

• Conservation : easy from one season to another on and in the soil, on various plant debris (leaflets, stems, senescent floral pieces ??) of Solanaceae  and many alternative hosts, cultivated or not. S. solani and, to a lesser degree, S. floridanum are able to attack several cultivated (eggplant, pepper ??) or wild ( Solanum carolinense, S. lycocarpum nightshades ??) . Note that S. solani affecting strains cotton are aggressive on tomato, potato, and blue lupine in Brazil. S. floridanum is described on Allium, safflower, gladiolus and chrysanthemum. S. vesicarium and S. botryosum f. sp. lycopersici can also rely on their perithecia (from their sexual reproduction) to preserve themselves from season to season, as their ascospores can provide primary contamination.
• Infection : penetrate their hosts directly through the cuticle or through various wounds. Rapid invasion of tissues thanks to their mycelium, spots being already visible 5 days after the first contaminations.
• Sporulation : form conidiophores and conidia visible on the underside of the leaf blade.
• Dissemination : by conidia especially by wind, air currents, but also by splashing water following rains or irrigation by sprinkling. Remember that plants can transmit the disease if infections occur in the nursery.
• Favorable conditions : favored by humid climatic conditions, in particular the presence of water on plants (rain, dew, sprinkling, condensation in greenhouses) and by high temperatures. Their thermal optima are between 23 and 27 ° C, depending on the species.

Protection

• Use resistant varieties if possible.
• Establish healthy plants: check their quality.
• Avoid planting crops near other susceptible crops (tomato or pepper or eggplant).
• Eliminate weeds that can serve as intermediate hosts.
• Ensure good drainage to cultivated plots.
• Avoid excessive planting densities in order to promote aeration of the foliage.
• Remove leaves from the lower parts of plants in order to eliminate the first affected leaves and improve aeration of the plant cover.
• Avoid sprinkler irrigation, prefer drip irrigation. If they are essential, carry them out in the morning so that the vegetation dries up quickly during the day.
• Under shelters, ventilate as much as possible.
• Do not allow workers to work while the vegetation is wet.
• Eliminate plant residues 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.
• If necessary, spray fungicides taking into account the authorized uses (e-phy).