Colletotrichum  and Gloeosporium  spp.

Anthracnosis  

General

• Several anthracnose agents are known on vegetables, and in particular on those produced in tropical to equatorial zones. In these areas, Colletotrichum spp. encountered appear to have wider host ranges.
• Fungi quite widely distributed in the world, reported in many countries on all continents.
• More or less polyphagous, several species can be found on vegetables from the same botanical family. Distrust, some may come to colonize secondarily tissues damaged by a primary invader.
• Responsible for spots on affected organs, often well demarcated, and sometimes surrounded by veins on leaves; more elongated on the stems and fruits. Certain species are capable of attacking the roots producing microsclerotia on the latter (figures 9 to 11), in particular Colletotrichum coccodes which causes root rots under shelters in metropolitan France, on tomato and eggplant rootstocks, and on chili peppers.
• Rather observed in open fields in tropical areas.
• Flat and superficial conceptacles form on the injured tissues, rather characteristic acervuli (figures 1 to 5) producing very numerous spores in mucilaginous masses (figures 6 and 7). In many species black silks (or setae) are observed within these structures (figure 8). * Eggplant, pepper, tomato
• Organs attacked : leaves, fruits, stem.
• Symptoms :
  • Small, irregular chlorotic lesions rapidly becoming necrotic on leaves. A yellow halo rather marked the belt (figures 1 to 5). Anthracnose does not appear to have a strong effect on eggplant foliage.
  • Elongated and brownish lesions on stems
  • Moist circular spots spreading, gradually browning and blackening on fruits as they ripen (Figures 6 and 7). The spots are slightly concave and can coalesce, and cause rotting of large areas of the fruit (Figure 7), or even degrade them entirely. Damage to the seeds which take on a rusty tint.
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• Signs  : presence on the lesions of flat and superficial conceptacles, microsclerotia and acervuli, sometimes distributed in concentric circles (figure 8). Acervuli producing very numerous spores in mucilaginous masses of pinkish to salmon couleyr. In many species of Colletotrichum, black bristles (or setae) are observed within these structures.
• Possible confusion :
•  Colletotrichum spp. signales sur aubergine : C. gloeosporioides f. sp. melongenae, C. acute, C. truncatum

Biology

• Conservation : maintains itself in the soil, in particular on plant debris, or on various organic substrates. The stromatic masses (microsclerotia) that they form on the fruits represent a certain form of conservation. Some are also maintained on seeds ( C. lagenarium, species complexes associated with peppers and chilli peppers) which become contaminated during their extraction from infected fruits, and probably on various cultivated or wild plant species.
• Infection : spores germinating on the surface of polluted plant organs, and direct penetration of tissues. Subsequently, mainly intracellular mycelium invades the tissues.
• Sporulation : fairly rapid production of acervuli on lesions present on the various affected organs.
• Dissemination : the spores *** gathered in the form of a mucus are dispersed by water and splashing water, by the wind carrying fine water droplets, by workers and agricultural tools, and by some insects. Contaminated seeds also contribute to the spread of this disease.
• Favorable conditions : humidity especially influences anthracnose epidemics on vegetables. Contamination often takes place following wet periods, thanks to rains and sprinkler irrigation.

*** For simplicity, spores Colletotrichum  can be either oval to oblong, straight ( C. glosporioides , C. coccodes , C. orbiculare ); either arched, sickle-shaped, pointed at the ends ( C. capsici ).

Protection

• Do not use seeds contaminated .
• Species from the same botanical family do not seem to have the same sensitivity to anthracnose agents. Some varieties of cucumber are resistant to Goleosporium orbiculare .
• Establish crop rotations not involving sensitive crops, of at least 2 to 3 years.
• Destroy spontaneous plant species in or near the crop that may harbor these fungi.
• Ensure good drainage to cultivated plots.
• Avoid irrigation sprinkler , 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.
• Avoid wounds on fruits linked to the actions of other pests or to the pickers.
• Leave the crop and destroy affected plants and especially diseased fruits. Eliminate plant residues at the end of the crop. Deep plowing can bury remaining debris, this measure should be combined with crop rotation.
• If necessary, spray fungicides taking into account the authorized uses.