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Mango Anthracnose and Colletotrichum
Mango, Mangifera indica; is one of the world’s most important fruits and admired for its delicious taste and high nutritional value. Mango originated in the Indo-Burma region and has been cultivated for at least 4000 years in the Indian subcontinent. In Sri Lanka, mango has been grown in many parts of the country as a home garden tree in every house. Present extent of mango cultivation has about 12160 Ha. Predominantly, it’s grown in Kurunegala, Anuradhapura, Hambanthota, Puttalam, Monaragala, Jaffna etc.

Mango belongs to the family Anacardiaceae. Mango cultivars in Sri Lanka include Ambalavi, Malvana, Karathacolomban, Rata, Willard. Alampur Baneshan, Alphonso, Bombay, Brahm Kai Meu, Keitt are some mango varieties cultivated around the world.

Anthracnose caused by Colletotrichum sp. is a major pre/post-harvest disease which seriously constrains the production, marketing and export of mango and may be of a quarantine concern. Colletotrichum gleosporoides was considered the major pathogen causing anthracnose and to a lesser extent Colletotrichum acutatum.

Fruit spoilage caused by anthracnose ranges from a slight loss in the quality resulting in reduced sales to total spoilage of the fruits. Anthracnose fungus can infect almost all aerial parts of the mango tree causing blossom blight, leaf spot/blight and fruit rot.

Inoculation takes place at the initial stages of fruit development. The observable external symptom often only becomes apparent after ripening, by which it is usually equated with the edibility of the fruit. As the fruits ripen, symptoms appear as one or more dark spreading lesions. Decay is initially fairly superficial with some lesions becoming sunken in ripened fruits. Moisture extradition may occur and pink coloured spore masses can develop in the centre of the lesions. Uncolonized flesh is comparatively free of off-odours or tainting. Anthracnose stem end lesions can be confused with stem end rot lesions. Small dark lesions can also develop on young fruits particularly in wet conditions, around insect damage or when factors favour fruitlet shedding. On maturation of the fruit before harvest, tear stain pattern infections, consisting of numerous small limited lesions can develop with symptoms radiating from around the stem end or at contact points between fruit or leaves and fruit. Tear stain lesions often remain discrete as fruit ripens.

Disease susceptibility varies for different mango cultivars. Cultivars such as Willard, Ambalavi are more susceptible when compared with cultivars like Karathacolomban which is considered to be resistant for anthracnose. Antimicrobials present in the fruit peel are a major factor influencing the disease development and disease susceptibility. As the fruits ripen, the antimicrobial content in the fruit peels decrease facilitating the disease development.

Control of anthracnose disease requires periodic spraying with the fungicides in orchards and efficient post-harvest treatment. The degree of disease spread varies depending on the susceptibility of the host plant and environmental conditions. Fungicides used include benzimidazole, chloronitrile etc.

Identification of the pathogen to species level is important in disease management. Traditional methods of identification were based on morphological characteristics including shape and size of spores, appresoria formation, growth rate and sensitivity of benzaimidazole fungicides. Colletotrichum gleosporoides and Colletotrichum acutatum are defined as species complexes comprising of many species. Colletotrichum gleosporoides complex includes C. asianum, C. cordylinicola, C. fructicola, C. gloeosporioides, C. horii, C. kahawae subsp. kahawae, C. musae, C. nupharicola, C. psidii, C. siamense, C. theobromicola, C. tropicale. Colletotrichum acutatum complex comprises of C. simmondsii, C. fioriniae (formerly C. acutatum f. sp. fioriniae), C. lupine etc.

Earlier it was considered that conidia produced by Colletotrichum gleosporoides are cylindrical with rounded ends & conidia produced by Colletotrichum acutatum are fusiform. Growth rate of Colletotrichum gleosporoides was considered to be higher when compared with Colletotrichum acutatum. Colletotrichum acutatum was found to be relatively resistant to Benzaimidazole compared with Colletotrichum gleosporoides. These methods are not accurate enough to identify the pathogen. Colletotrichum sp. has more complex genetic and morphological characteristics which does not directly correspond to the species. Molecular methods can be used to identify the Colletotrichum sp. accurately. Species specific primers have been developed for amplification of DNA of these two species; Cg Int primers for Colletotrichum gleosporoides and Ca Int primers for Colletotrichum acutatum. With combining traditional methods with molecular methods, wide understanding about this pathogen can be obtained which can be used in disease management.
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Are all the species of Colletotrichum you have mentioned here already found in Sri Lanka?
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