Mango
Introduction:
Mango, a stone fruit that is safe to eat, is derived from the tropical tree Mangifera indica. It is believed to have originated in the region encompassing northwestern Myanmar, northeastern India, and Bangladesh. M. indica has been grown in South and Southeast Asia since ancient times, resulting in two types of modern mango cultivars: the "Indian type" and the "Southeast Asian type". The majority of other species in the Mangifera genus that produce edible fruits are also referred to as "mangoes" and are found in the Malesian ecoregion.
There are several hundred cultivars of mango worldwide, and the fruit varies in size, shape, sweetness, skin color, and flesh color, which can be pale yellow, gold, green, or orange, depending on the cultivar. Mango is the national fruit of India, Pakistan, and the Philippines, while the mango tree is the national tree of Bangladesh.
Mango Anthracnose
Causal Organism:
Colletotrichum gloeosporioides
Hosts:
The fungus that causes anthracnose in mango can also infect several other crops, including avocado, capsicum, coffee, eggplant, papaya, tomato, and yam. Different strains of the fungus can infect various crops and weeds.
Symptoms:
- Anthracnose is a disease that affects various parts of the mango tree, including leaves, twigs, petioles, flower clusters (panicles), and fruits.
- Symptoms of anthracnose on leaves appear as small, angular, brown to black spots that can expand and cause extensive dead areas.
- During dry weather, the lesions may fall off the leaves. On panicles, the first signs of the disease are small black or dark-brown spots that can coalesce, enlarge, and kill the flowers before the fruits are produced, leading to a significant reduction in yield.
- Petioles, twigs, and stems can also be affected, and they show the typical black, enlarging lesions found on fruits, leaves, and flowers.
- Ripe fruits that are afflicted by anthracnose develop sunken, prominent, dark brown to black decay spots before or after harvesting. The fruits may fall from the trees prematurely.
- Anthracnose can cause extensive fruit rotting as the spots on the fruit coalesce and penetrate deep into it.
- Infections in green fruits mostly remain latent and unnoticeable until ripening. Thus, fruits that seem healthy at harvest can quickly develop significant anthracnose symptoms when they ripen.
- A second type of symptom on fruits is the "tear stain," where linear necrotic regions on the fruit, which may or may not be associated with superficial cracking of the epidermis, resulting in an "alligator skin" effect, and deep cracks in the epidermis that extend into the pulp.
- On stems and fruits, lesions can produce conspicuous pinkish-orange spore masses in wet conditions.
- Anthracnose infections are favored by warm, humid weather conditions in the field. Post-harvest, warm and humid temperatures promote the development of anthracnose.
Disease Cycle:
The pathogen responsible for anthracnose in mango is disseminated passively by splashing rain or irrigation water through its spores (conidia). These spores land on infection sites, such as leaves, panicles, or branch terminals, where they germinate and penetrate immature fruits and young tissues by ramifying through the tissues. In mature fruits, infections penetrate the cuticle but remain dormant until the onset of fruit ripening.
Affected organs develop rapidly expanding, sunken, black lesions and symptomatic tissue produces sticky masses of conidia during moist conditions, especially rainy or humid weather. The fungus can undergo multiple disease cycles, multiplying during the season. It survives between seasons on infected and defoliated branch terminals and mature leaves.
Management
Cultural control:
To reduce humidity and prevent the onset of anthracnose in mango trees, it is crucial to prune them and ensure that there is free airflow throughout the tree canopy. It is recommended to keep the trees below 4 meters in height to facilitate easy management and harvesting. Infected twigs should be removed and burned, and fallen leaves should be disposed of in the same manner.
Resistant Varieties:
The Indo-Chinese and Philippine mango varieties are believed to possess some resistance to anthracnose, and their potential to resist the fungus should be evaluated in Pacific island nations. These varieties are known for their excellent flavor and low-fiber flesh.
Chemical control:
Impacts:
- Wet weather exacerbates the damage caused by the Stigmina fungus.
- The fungus causes black spots on the leaves, which can expand to form large black areas.
- In addition to the aesthetic damage, wet weather can cause early leaf fall due to the fungus.
- The damage caused by Stigmina is primarily to the leaves of the plant and does not affect fruit or shoots.
- Plant diseases have a significant impact on global food production and contribute to shortages of both food and fruit.
- Ghana's tree and horticultural crops are particularly vulnerable to diseases, which have been well documented.
- Mango production in Ghana is an important economic crop, but it is threatened by multiple diseases due to the crop's susceptibility to fungal pathogens.
- Mango's high water-nutrient content makes it a perfect medium for fungal pathogen development, leading to a high susceptibility to diseases.
- Anthracnose disease, caused by Colletotrichum gloeosporioides Penz. & Sacc, is a major limitation to mango production, with reported yield losses of up to 30% in the Yilo Kobo District of Ghana.
- The impact of anthracnose disease on mango production is not limited to Ghana, as it has been reported to cause yield losses of 39% in India and render 60% of harvested avocado fruits unmarketable in Kenya.
- Finding effective ways to prevent and control plant diseases, including anthracnose disease, is critical for sustainable food production and economic development in affected regions.
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