''Mycosphaerella musicola'' (or ''Pseudocercospora musae'',) is a

fungal A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as one of the tradit ...

plant pathogen, which is the causal agent of Yellow Sigatoka

leaf spot A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions ...

disease on

banana A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large treelike herbaceous flowering plants in the genus '' Musa''. In some countries, cooking bananas are called plantains, distinguishing the ...

plants.

Characteristics

Sigatoka leaf spot disease (SD) is a disease of bananas and is caused by the ascomycetous

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

, ''Mycosphaerella musicola''. This pathogen can be distinguished morphologically from ''

Mycosphaerella fijiensis Black sigatoka is a leaf-spot disease of banana plants caused by the ascomycete fungus ''Mycosphaerella fijiensis'' (Morelet), also known as black leaf streak. It was discovered in 1963 and named for its similarities with yellow Sigatoka, which ...

'', which causes black leaf streak disease (BLSD), by the characteristics of the

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

and

conidiophore A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word f ...

. The

anamorph In mycology, 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 (morph), typically a fruiting body. *Anamorph: an ase ...

of ''M. musicola'' is ''Pseudocercospora musae'' which 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.INIBAP

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 (including Brazil,) 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 25-29 °C and for the ascospores, 25-26 °C. The germ tube grows epiphytically over the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

for about five days before penetrating the leaf via a

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

.Meredith DS (1970) 'Banana leaf spot disease (Sigatoka) caused by ''Mycosphaerella musicola'' Leach.' (Commonwealth Mycological Institute, Kew, Surrey, England) Once inside the leaf the invasive hypha forms a vesicle and fine hyphae grow through the

mesophyll A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, f ...

layers into an air chamber. More hyphae then grow into the

palisade A palisade, sometimes called a stakewall or a paling, is typically a row of closely placed, high vertical standing tree trunks or wooden or iron stakes used as a fence for enclosure or as a defensive wall. Palisades can form a stockade. Etymo ...

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.PaDIL
/ref> Both conidia and

ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

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.Stover RH (1971) Leaf spot of bananas caused by Mycosphaerella musicola: Role of conidia in epidemiology. Phytopathology 60, 856-860. 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 In biology, inoculum (: inocula) refers to the source material used for inoculation. ''Inoculum'' may refer to: * In medicine, material that is the source of the inoculation in a vaccine * In microbiology, propagules: cells, tissue, or viruses that ...

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 ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

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 A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s that have developed resistance to SD, including the plantain subgroup.

References

External links

Index Fungorum

USDA ARS Fungal Database

Sigatoka Leaf Spot Diseases

Sigatoka Disease of Banana
{{Taxonbar, from=Q6947206 musicola Fungal plant pathogens and diseases Banana diseases Fungi described in 1902 Leaf diseases Fungus species