Classification

Classification is the placing of an individual in categories. This not only aids in determining whether it is identical or similar to an already known fungus but also in understanding its evolutionary affiliation. Naming and classification go hand in hand. The modern trend is to classify fungi based on genealogy. Some interpretations of relationships based on their evolutionary sequence conflict with the classification schemes that were developed based on morphological characters. A genus is a group of closely related species, for example, Puccinia coronata, P. graminis and P. sorghi. A family is a group of related genera, an order is a group of related families, a class is a group of related orders and a phylum is a group of several classes descending from a common lineage. However, no stable definition of these categories has yet been adopted for fungi. In particular, there is no uniformity in the name endings of the higher categories. The phylum or subdivision name ends in mycotina, the class in -mycetes; the order in -ales, and the family name in -aceae. The classification adopted here is chiefly as given in Burnett (2003). For the black wheat stem rust fungus, its classification and the nomenclature is as given below:

Kingdom/division: Eumycota

Phylum/subdivision: Basidiomycotina

Class: Urediniomycetes

Order: Uredinales

Family: Pucciniaceae

Genus: Puccinia

Species: graminis

Forma specialis (f.sp): P. graminis f.sp tritici Race: P. graminis f.sp tritici race 56

The infraspecies rank of forma speciales designates a variant of the species parasitizing a particular host. A race is a category used in pathogenic fungi that is subordinate to forma and is similar in form but distinguishable on the basis of pathogenic reaction on varieties of a plant. When first used, the full name of the fungus should be given to avoid confusion. For example, the abbreviated binomial P. graminis could also mean Polymyxa graminis.

A BROAD CLASSIFICATION OF FUNGI Kingdom Eumycota

"True" fungi. Predominantly haploid; cell walls with chitin, p-(1,3)-glucans or mannans.

Phylum Chytridiomycotina

Mostly marine forms, single-celled with rhizoids; asexual reproduction by motile zoospores; sexual reproduction unknown.

Phylum Zygomycotina

The hyphae are usually non-septate; sexual reproduction by morphologically undifferentiated gametangia. Gametangial fusion results in reproductive structure called a zygospore that presumably germinates by means of a sporangium containing uninucleate spores (Figure A1). Example: Mucor, Rhizopus.

Phylum Glomeromycotina

Here are placed the mycorrhizal fungi that form symbiotic relationships with plants. Asexual reproduction is by means of chlamydospores. Example: Glomus, Acauleospora, Gigaspora, Scutellospora.

Asexual Reproduction Rhizoids

Figure A1 Zygomycotina. (a) Rhizopus stolonifer, stolons, rhizoids, young and ripe sporangia. From Von Arx, J.A. (1981), The Genera of Fungi Sporulating in Pure Culture. J. Cramer. With permission from Koeltz Scientific Books. (b). Zygospore formation in heterothallic Mucor hiemalis by fusion of gametangia. From Ingold, C.T. and Hudson, H.J. (1993). With kind permission of Kluwer Academic Publishers.

Figure A1 Zygomycotina. (a) Rhizopus stolonifer, stolons, rhizoids, young and ripe sporangia. From Von Arx, J.A. (1981), The Genera of Fungi Sporulating in Pure Culture. J. Cramer. With permission from Koeltz Scientific Books. (b). Zygospore formation in heterothallic Mucor hiemalis by fusion of gametangia. From Ingold, C.T. and Hudson, H.J. (1993). With kind permission of Kluwer Academic Publishers.

Mature ascus

Swelling ascus

Mature ascus

Swelling ascus

Life Cycle Mucor Hiemalis

Empty ascus

Empty ascus

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