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Pathogens & Hosts

Twenty Mycosphaerella species have been reported to occur in Hawaii (Raabe, et al., 1981). The following is a list of the reported pathogens from this genus (Mycosphaerella) and the hosts they infect. The list is organized by the scientific name of the pathogen species (CAPITAL LETTERS), followed by the symptom or disease a given pathogen causes on the listed hosts.

Taxonomy

KINGDOM: Mycetae (fungi)

DIVISION: Eumycota

SUBDIVISION: Ascomycotina (The sac fungi)

CLASS: Loculoascomycetes

ORDER: Dothideales

Biology

The three spore(-like) structures are spermatia (produced in spermogonia), ascospores (produced in perithecia), and conida of the Cercospora-type (produced in sporodochia) (Agrios, 1988).

Perithecia are subepidermal (Streets, 1979). They are formed when sexual hyphae are fertilized by compatible spermatia (Agrios, 1988). The ascospores are hylaline, ellipsoidal, and 2-celled (Streets, 1979). They are packaged in groups of eight in structutres known as asci.

Since other biological characteristics vary from species to species, for more detailed information, consult the specific Mycosphaerella sp. summary of interest. However, many of the species listed have not been studied in great detail. A good summary for detailed biological information can be found in the [Mycosphaerella musicola] summary; the pathogen that causes yellow Sigatoka of banana (Persley, 1993).

Characteristics

The number of different species in the genus Mycosphaerella have been reported to range from 500 (Streets, 1982) to 1,000 (Alexopoulos and Mims, 1979). It is the largest genus in the Dothideaceae with the majority of species being saprobic. There are, however, many species that are economically important plant pathogens. Mycosphaerella occurs on the leaves and stems of several hundred different host plants (Tomilin, 1979; Corlett, 1991). Most species are saprobic (Agrios, 1988). However, many have been described as pathogenic to cultivated and ornamental plants and forest trees (Corlett, 1991). The genus is complex; primarily because of the large number of species. This is especially a problem since many of the species were originally described in the genus Sphaerella (now considered a synonym of Mycosphaerella).

Disease Types

Mycosphaerella spp. have been described to cause the following types of diseases: brown leafspot, ringspot, gummy stem blight, leafspot, ascochyta blight, stem-end rot, leaf splitting disease, yellow and black Sigatoka, and black leaf streak.

The disease can spread to healthy hosts either as conidia or as ascospores. Once in contact with compatible host tissue, the spores can germinate and penetrate the plant through the leaf stomata. Fungal fruiting bodies (spermagonia, sporodochia) then form. Conida produced from sporodochia is released and disseminated; this enables the condia to infect another host plant. Also, the spermatia can fertilize compatible sexual hyphae to form the perithecia where ascpores are produced. Like the conidia, these ascospores can then be released and disseminated to begin the infection process again (Agrios, 1988).

Management

In general, Mycosphaerella diseases are managed with a combination of measures. These include: quarantine, sanitation by removing infected tissue, and by year-round fungicidal spray applications (Agrios, 1988).

For more specific control programs and approaches, please see the species summaries.

References

Agrios, G.N. 1988. Plant Pathology, 3rd edition. Academic Press, Inc: San Diego. 803 pp.

Corlett, M. 1991. An Annotated List of the Published Names in Mycosphaerella andSphaerella (Mycologia Memoir No. 18). J. Cramer: Berlin. 328 pp.

Farr, , D.F., G.F. Bills, G.P. Chamuris, and A.Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. APS PRESS: St. Paul, Minnesota. 1252 pp.

Raabe, Robert D., Ibra L. Conners, and Albert P. Martinez. 1981. Checklist of Plant Diseases in Hawaii. Hawaii Institute of Agriculture and Human Resources, College of Tropical Agriculture and Human Resources, University of Hawaii (Information Text Series 022).

Streets, R.B. 1982. The Diagnosis of Plant Diseases: a field and laboratory manual emphasizing the most practical methods for rapid identification. The University of Arizona Press: Tucson, Arizona.

Tomilin, B.A. 1979. Opredelitel'gribov roda Mycosphaerella Johans. 319 pp.

JUNE 1994

1-MYCOSP

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