Anthracnose

Introduction

Anthracnose are diseases of the foliage, stems, or fruits that typically appear as dark-coloured spots or sunken lesions with a slightly raised rim. Some cause twig or branch dieback. In fruit infections, anthracnose often has a prolonged latent stage. In some fruit crops, the spots are raised and have corky surfaces. Anthracnose diseases of fruit often result in fruit drop and fruit rot. Anthracnoses are caused by fungi that produce conidia within black fungal fruiting bodies called acervuli. Colletotrichum species are responsible for most anthracnose diseases. They are found in nature mostly in their conidial stage (asexual) and can overseason as mycelium (fungal threads) or conidia (spores) in foliage, stems, twigs and infected crop debris.

Colletotrichum diseases are the most common anthracnoses and are very similar, if not identical, to the diseases caused by Glomerella. The latter is probably the sexual stage of most or all species of Colletotrichum (Gloeosporium). Anthracnose diseases, particularly those caused by Colletotrichum (Gloeosporium) or Glomerella fungi, are very common and destructive on numerous crops and ornamental plants. Although severe everywhere, anthracnose diseases cause their most significant losses in the tropics and subtropics. The diseases are favoured by wet, humid, warm conditions. They are spread by infected seed, rain splash and moist wind.
 

Damage

Anthracnose diseases, particularly those caused by Colletotrichum (Gloeosporium) or Glomerella fungi, are very common and destructive on numerous crop and ornamental plants. Although severe everywhere, anthracnose diseases cause their most significant losses in the tropics and subtropics. Pre- and post-harvest losses of many high-value crops are substantial in the tropics due to of various diseases caused by C. gloeosporioides. 

Flower infection on mangoes (blossom blight) can destroy flowers and young fruit and cause complete crop failure. Fruit infection may cause premature fruit drop, but major fruit losses occur during ripening when quiescent (dormant) infections break out and cause spreading black lesions. Anthracnose of other fruits also causes major post-harvest losses. Heavy infections cause rapid rotting, and even light infections which cause mainly cosmetic damage will shorten fruit storage life. Because of variability between seasons and locations, overall figures for losses are difficult to give, but it is clear that in many mango-growing areas losses of up to 50% of the crop to the various stages of the disease would not be uncommon.

Of the foliage diseases caused by C. gloeosporioides, yam anthracnose can be one of the most economically damaging and may prevent significant growth of tubers if the disease strikes early.

Anthracnose infected vegetables (e.g. beans, brinjals, peas, pepper and cucurbits) and fruits (e.g. avocado, mangoes and bananas) are not acceptable for export market.

Host range

C. gloeosporioides is a fungus which causes anthracnose, it is by far the most predominant a major Colletotrichum pathogen on a wide range of cultivated crops, particularly tropical perennial crops (Waller, 1992). However, because it is also a commonsaprophyte and secondary invader of damaged tissue, it has been implicated as a pathogen more often than is justified after closer investigation. Disease is favoured by wet/humid, warm conditions. It is spread by infected seed, rain splash and moist wind. 

Symptoms

Anthracnose (Colletotrichum gloeosporioides) on avocado fruit. This fungal disease is primarily a post-harvest problem when fruit is at maturity stage.

© A. A. Seif, icipe

Anthracnose diseases attack all plant parts at any growth stage. The symptoms are most visible on leaves and ripe fruits. At first, anthracnose generally appears on leaves as small and irregular yellow, brown, dark-brown or black spots. The spots can expand and merge to cover the whole affected area. The colour of the infected part darkens as it ages. The disease can also produce cankers on stems. Infected fruit has small, water-soaked, sunken, circular spots that may increase in size up to 1 cm in diameter. As it ages, the center of an older spot becomes blackish and emits gelatinous pink spore masses. 

Affected plant stages 

Flowering stage, fruiting stage, post-harvest, seedling stage, and vegetative growing stage.

Affected plant parts 

Leaves, stems, fruits/pods, and inflorescence.

The lifecycle of anthracnose diseases involves essentially production of spores on susceptible hosts, dispersal of spores, penetration of host tissue, initiation of an infection process within the cells, development of lesions, formation of bristly spores and dispersal usually by water-splash, air currents, insects or other forms of contact.

The anthracnose pathogen reaches its most serious dimension at high moisture and warm temperature. For example C. gloeosporioides has an optimum of 25-29°C but it will also survive at temperatures as low as 4°C. Spore germination, dispersal and infection require relative humidities near 100%. However, in drier situations disease expression can occur when latent infections are activated through aging or tissue damage. 

The anthracnose diseases are primarily transmitted through seed, but also through infected plant parts. Rain splash will also disperse spores within crop canopy. The pathogen persists on and in seed, crop residues, and weed hosts.

Major species of anthracnose fungi affecting crops in Africa:

• Anthracnose of avocado (Glomerella cingulata)
• Anthracnose of cotton (C. gossypii)
• Anthracnose of cucurbits (C. lagenarium)
• Anthracnose of grapes Sphaceloma (Elsinoe) ampelina
• Anthracnose of lime (Gloeosporium limitticola)
• Anthracnose of spinach (C. spinacicola)
• Anthracnose of tomato (C. coccodes, C. phomoides)
• Banana anthracnose (C. musae)
• Bean anthracnose (C. lindemuthianum (Glomeralla cingulata))
• Cereal anthracnose (C. graminicola)
• Coffee anthracnose (C. coffeanum)
• Common scab of citrus Sphaceloma (Elsinoe) fawcettii)
• Mango anthracnose (C. gloeosporioides)
• Onion smudge (C. circinans)
• Pea anthracnose (C. pisi)
• Pepper anthracnose (C. capsici)
• Red rot of sugarcane Glomerella tucumanensis (C. falcatum)
• Watermelon anthracnose (C. lagenarium)

Pest and disease Management

Pest and disease Management: General illustration of the concept of Infonet-biovision

This illustration shows the methods promoted on infonet-biovision. The methods shown at the top have a long-term effect, while methods shown at the bottom have a short-term effect. In organic farming systems, methods with a long-term effect are the basis of crop production and should be of preference. On the other hand methods with a short-term effect should be used in emergencies only. On infonet we do not promote synthetic pesticides. 

Further below you find concrete preventive and curative methods against Anthracnose.

Field sanitation

Hot water seed treatment

Copper

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