Mycosphaerella musicola
Encyclopedia
Mycosphaerella musicola is a fungal
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 plant pathogen, which is the causal agent of Yellow Sigatoka leaf spot
Leaf spot
Leaf spots are round blemishes found on the leaves of many species of plants, mostly caused by parasitic fungi or bacteria.A typical spot is "zonal", meaning it has a definite edge and often has a darker border. When lots of spots are present, they can grow together and become a blight or a blotch...

 disease on banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....

 plants.

Characteristics

Sigatoka leaf spot disease (SD) is a disease of bananas and is caused by the ascomycetous
Ascomycota
The Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...

 fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

, Mycosphaerella musicola. This pathogen can be distinguished morphologically from Mycosphaerella fijiensis
Black sigatoka
Black Sigatoka is a leaf spot disease of banana plants caused by ascomycete fungusMycosphaerella fijiensis . Plants with leaves damaged by the disease may have up to 50% lower yield of fruit...

, which causes black leaf streak disease (BLSD), by the characteristics of the conidia
Conidium
Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...

 and conidiophore
Conidium
Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...

. The anamorph
Teleomorph, anamorph and holomorph
The terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota.*Teleomorph: the sexual reproductive stage , typically a fruiting body....

 of M. musicola, Pseudocercospora musae
Pseudocercospora
Pseudocercospora is a genus of ascomycete fungi. An anamorphic version of the genus Mycosphaerella, Pseudocercospora species are plant pathogens. The widely distributed genus has been estimated to contain over 1100 species, concentrated predominantly in tropical regions. Pseudocercospora was...

, lacks the thickened cell walls that are present at the base of the conidia of Paracercospora fijien, the anamorph of M. fijiensis, and are shorter and less wavy. The conidiophores of P. musae are bottle-shaped and much smaller than the elongated conidiophores of P. fijiensis which are often bent and bear conspicuous conidial scars. The two species can also be differentiated by molecular methods.

Distribution

Mycosphaerella musicola was first reported from Java in 1902 and by 1962 was found in most banana growing regions of the world. Although it is spread over short distances by conidia and ascospores, over long distances it is the movement of infected germplasm such as diseased leaves and suckers that is likely to be responsible. In the Pacific islands and in lowland areas of South America and Africa, symptoms of SD are now rarely seen and BLSD has largely supplanted it. SD is more adapted to cooler regions and often predominates at altitudes over 1200 metres while BLSD is rarely seen at such elevations.

Life cycle

When spores of M. musicola are deposited on a susceptible banana leaf they germinate within three hours if there is a film of water present or if the humidity is very high. The optimal temperature for germination of the conidia is between 25-29ºC and for the ascospores, 25-26ºC. The germ tube grows epiphytically
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

 over the epidermis for about five days before penetrating the leaf via a stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...

. Once inside the leaf the invasive hypha forms a vesicle and fine hyphae grow through the mesophyll layers into an air chamber. More hyphae then grow into the palisade tissue and continue on into other air chambers, eventually emerging through stomata in the streak that has developed. Further epiphytic growth occurs before the re-entry of the hypha into the leaf through another stoma repeats the process.

Both conidia and ascospore
Ascospore
An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes ....

s are important for dispersal of M. musicola with the ascospores being involved in the movement of the pathogen over longer distances than the conidia. The deposition of ascospores by wind currents is generally near the tips of the leaves resulting in a distinctive pattern of infection on the leaf extremities. When conidia are the source of the inoculum
Inoculation
Inoculation is the placement of something that will grow or reproduce, and is most commonly used in respect of the introduction of a serum, vaccine, or antigenic substance into the body of a human or animal, especially to produce or boost immunity to a specific disease...

 and these are dislodged by rain, a distinctive line of streaks is produced as water trickles down the leaf blade.

Symptoms

It is not always easy to differentiate between the symptoms of SD and BLSD. The first sign of disease in SD is the appearance of small yellow streaks on the upper side of leaves while in BLSD small, dark brown streaks appear on the lower surface of leaves. These streaks enlarge and coalesce forming necrotic lesions with light gray centres and yellow perimeters. Large areas of leaf can be damaged causing a lowering of photosynthetic
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 ability, a reduction in crop yield and premature ripening of the fruit. BLSD is the more serious of the diseases as the symptoms emerge on younger leaves and it affects many cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...

s that have developed resistance
Plant disease resistance
Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of fuel, land, water and other inputs. There are numerous examples of devastating plant disease impacts , as well as recurrent severe plant disease issues...

 to SD, including the plantain
Plantain
Plantain is the common name for herbaceous plants of the genus Musa. The fruit they produce is generally used for cooking, in contrast to the soft, sweet banana...

subgroup.

External links

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