Photo 1. Reddish-brown and black streaks of black Sigatoka, Mycosphaerella fijiensis, on the upper surface of a leaf, with some developing white or tan centres where the spores are produced. Note that the spots have bright yellow haloes, or margins.
Photo 2. Long streaks with bright yellow margins typical of infection by black Sigatoka, Mycosphaerella fijiensis. Note the blighted areas at the leaf tip and margins where the spots have joined together to cause the blight.
Photo 3. Typical decay of a leaf infected with black Sigatoka, Mycosphaerella fijiensis, showing the brown streaks, some with white centres, and the edges of the leaf decaying before other parts where the streaks have joined together.
Diagram. Life cycle of black Sigatoka, Mycosphaerella fijiensis. Note that there are two types of spores, but it is the sexual stage that produces the ascopsores that are considered the most important in disease development. The spores are discharged from the top surface of the leaves and spread by wind.
Black Sigatoka, black leaf streak
Mycosphaerella fijiensis. This the name of the sexual state; the asexual name is Paracercospora fijiensis.
Worldwide. Asia, Africa, North, South and Central America, the Caribbena, Oceania. It is recorded from Australia (Torres Strait region), Cook Islands, Fiji, French Polynesia, GuamAmerican Samoa,, Marshall Islands, Federated States of Micronesia, New Caledonia, Niue, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, Vanuatu, and Wallis and Futuna.
The fungus infects bananas and plantains, Musa species.
Red-brown or black streaks appear on the underneath of the third or forth youngest leaf. These form spots, 20-30 mm long, with grey or light brown centres and dark brown or black margins, best seen on the upper surface (Photo 1). The spots join together, often with yellow areas between. The infected areas invariably form bands several centimetres wide on either side of the midrib. In severe infections, spots do not occur, but large areas of the leaf turn black and die. Generally, the streaks are more common at the tips and edges of the leaves (Photos 2&3).
The disease is spread by the movement of infected plant material, or by spores produced within dead or dying leaves. Spores are released from the upper leaf surface and are spread in wind and/or rain to nearby leaves or far away plantations.
Young fully expanded leaves on mother plants and suckers are the most susceptible to infection. As the leaves mature, they become resistant. The spores germinate and the germ tubes enter through natural openings in the leaf. The fungus grows within the leaf, killing plant cells, before returning to the surface to produce more spores. There are two types of spores: ascospores and conidia (see diagram); the ascospores are the more important. Different strains of the fungus (plus and minus) come together to form the sexual ascospore stage (see Diagram). Spores are produced in the dead, grey areas on the upper leaf surface. They are released during rains or during times of high humidity. They land on the underside of the emerging leaves, and the cycle begins again.
There is also evidence to suggest that the disease can be spread by contaminated fruit shipments.
Black Sigatoka is a devastating leaf disease of bananas around the world. Infected leaves die early, reducing fruit yield, and causing premature ripening of bunches.
The effect of the disease is a loss of leaves: leaves die early. Instead of lasting 200 days they last only 50 days. This reduces yield by 35-50%, depending on severity of the infection and on the variety. Cavendish varieties are particularly susceptible and these are grown for sale worldwide. About 30% of the production costs in commercial plantations are spent on fungicides to control this disease.
The weight of the bunch and the ripening of the fruit are affected by the number of leaves on the plant: if there are too few at flowering then bunch weight is low; if less than five leaves at harvest, the fruits ripen early. Ideally, 10 leaves are needed for large bunches.
On leaves, look for a rapid development of red-brown and yellow streaks, drying from the margins back to the mid-rib, and early death of leaves.
Cultural methods of control are very important; the strategy is to reduce the humidity in the plantation, reducing the time that the leaves are wet and the spores can germinate and infect.
Collect infected leaves from the mother plant left after harvest of the fruit, take them out of the plantation and burn them.
Many plantains in Pacific island countries are either tolerant or resistant to black Sigatoka. There are also other plantains elsewhere, e.g., Mysore, Saba and Pisang Awak. Additionally, Yangambi Km5, a dessert banana from West Africa, also has black Sigatoka resistance. However, if farmers want to grow varieties with Cavendish qualities for household use or the market, then they should ask their departments of agriculture for new varieties from the Honduran Foundation of Agricultural Research breeding scheme: varieties FHIA-1, FHIA-2, FHIA-3, FHIA 17, FHIA 18, FHIA 23 and FHIA 25. These are dessert or dessert/cooking bananas with resistance to black Sigatoka. Consult the Secretariat of the Pacific Community (CePaCT lab) for supplies.
Fungicides are only recommended for commercial plantations; examples are:
(i) Protectant fungicides (these stay on the surface of plants) -
Mancozeb can be used together with oil or an oil/water emulsion; chlorothalonil is used in water.
(ii) Systemic fungicides (these move inside the plants) -
It is important to rotate the fungicides in the different groups to prevent the build-up of resistant strains of the fungus. No more than two applications of the same systemic fungicide should be made before changing to another group. In drier times, mancozeb can be used alone. Note, it is important to add a sticker to any of the fungicides.
AUTHORS Helen Tsatsia & Grahame Jackson
Phot 1 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia. Diagram APSnet Education Center. Back Sigatoka of bananas and plantains, American Phytopathological Society. (http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/BlackSigatoka.aspx).
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production , implemented by the University of Queensland and the Secretariat of the Pacific Community.
This fact sheet is a part of the app Pacific Pests and Pathogens
The mobile application is available from the Google Play Store and Apple iTunes.