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.
• Mushrooms quite widely distributed in the world, reported in many countries on all continents.
• More or less polyphagous, several species can be found on vegetables of the same botanical family. Distrust, some can colonize 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 stem and fruit. Some species are capable of attacking the roots producing microsclerotia on the latter (figures 9 to 11), in particular Colletotrichum coccodes which causes root rot under shelters in mainland France, on tomato and eggplant rootstocks, and on peppers.
• Rather observed in the open field in tropical zones.
• Flat and superficial conceptacles form on the damaged tissues, rather characteristic acervuli (figures 1 to 5) producing very many spores in mucilaginous masses (figures 6 and 7). In many species black bristles (or setae) are observed within these structures (Figure 8).

• Sensitive botanical family (s)

* eggplant, pepper, tomato

** calabash, pumpkin, cucumber, squash, spaghetti squash, zucchini, christophine, pumpkin, bitter gourd or cucumber, melon, watermelon, squash, pumpkin, several species of Luffa , etc.

Biology

• Conservation : remains in the ground, in particular on plant debris, or on various organic substrates. The stromatic masses (microsclerotia) that they form on the fruits, represent a definite form of preservation. Some are also maintained on seeds ( C. lagenarium, complexes of species associated with capsicum and pepper) 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 tissue penetration. Then, mainly intracellular mycelium invades the tissues.
• Sporulation : fairly rapid production of acervuli on the lesions present on the various affected organs.
• Dissemination : spores*** grouped together in the form of mucus are dispersed by water and splashing water, by the wind carrying the 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 above all influences anthracnose epidemics on vegetables. Contamination often occurs following wet periods, thanks to rainfall and sprinkler irrigation.

*** For simplicity, 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 of the same botanical family do not seem to have the same sensitivity to anthracnose agents. Some cucumber varieties are resistant to Goleosporium orbiculare .
• Establish crop rotations that do not involve sensitive crops, for at least 2 to 3 years.
• Destroy in the crop or nearby any spontaneous plant species that may harbor these fungi.
• Ensure good drainage of cultivated plots.
• Avoid irrigation , prefer drip irrigation. If they are essential, carry them out in the morning so that the vegetation drains quickly during the day.
• Under cover, ventilate as much as possible.
• Do not allow workers to work while vegetation is wet.
• Avoid wounds on fruits linked to the actions of other pests or pickers.
• Get out of the crop and destroy the affected plants and especially the diseased fruits. Eliminate plant residues at the end of cultivation. Deep plowing can help bury the remaining debris, this measure must be combined with crop rotation.
• If necessary, spray fungicides taking into account authorized uses.