''Septobasidium'' is a fungal genus within the family Septobasidiaceae. Approximately 175 described species are associated with this genus.
''Septobasidium'' species are known to be entomopathogens.
Description
''Septobasidium'' spp. are characterized by their presence on the underside of branches and leaves of deciduous trees, shrubs and in a
symbiotic association with scale insects (
Coccoidea
Scale insects are small insects of the Order (biology), order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient g ...
),
such as the Latania Scale Insect, ''
Hemiberlesia lataniae
''Hemiberlesia lataniae'', the latania or palm scale, is a species of armored scale insect in the family Diaspididae. It was first described by the French entomologist Victor Antoine Signoret in 1869 using ''Latania lontaroides'', a species of pal ...
''.
Fruiting bodies
The sporocarp (also known as fruiting body, fruit body or fruitbody) of fungi is a multicellular structure on which spore-producing structures, such as basidia or asci, are borne. The fruitbody is part of the sexual phase of a fungal life cyc ...
form a crust (
resupinate
Resupination is derived from the Latin word ''resupinus'', meaning "bent back
with the face upward" or "on the back". "Resupination" is the noun form of the adjective "resupine" which means "being upside-down, supine or facing upward".
The word " ...
) and range in color and size, from small patches (1 mm in diameter) to 2 meters wide. Species of this genus are often distinguished based on the thickness of the fruiting body. Some species form elaborate chambers and tunnels that house
scale insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
s with top and bottom layers while others form a very thin
hypha
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one or ...
l network. Microscopic characteristics, such as the number of
basidiospore
A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are pro ...
s produced on a
basidia
A basidium () is a microscopic sporangium (a spore-producing structure) found on the hymenophore of fruiting bodies of basidiomycete fungi which are also called tertiary mycelium, developed from secondary mycelium. Tertiary mycelium is highly-c ...
, presence of pillars supporting the top layer (if applicable), number of cells in a basidia, and shape of
haustoria
In botany and mycology, a haustorium (plural haustoria) is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates t ...
(infectious cells) that form within the scale insects are used to distinguish species.
''Septobasidium'' is unique in that it is one of a few genera within the family Septobasidaceae that exists in symbiotic relationships with scale insects ranging from obligately
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
to
mutualistic.
This type of fungus is fairly unique for having a mutualistic relationship with scale insect hosts, rather than killing them. Although it weakens the insects it parasitizes, it does not kill them and it benefits the population as a whole, helping provide protection from
parasitoid
In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
wasps by forming a mycelial mat that helps conceal the insects. The fungus benefits from the relationship, as it is nourished by the waste products the insects produce.
Symbiotic association with insects
Couch proposed in 1938 that the symbiotic relationship between ''Septobasidium'' and scale insects was mutualistic.
He suggested that at a population level, scale insects benefit from certain species of ''Septobasidium'' that provide protection from predators, and prevent desiccation. Couch also remarked that some scale insects remain uninfected while others are infected and rendered sterile.
Some ''Septobasidium'' species provide no discernable shelter and parasitize all scale insects associated with the fruiting body. This suggests that the symbiotic relationships within this genus are complex, and merit further investigation.
Additionally, no clear benefit has been demonstrated for scale insects associated with the fungus compared to free-living scale insects.
The scale insect itself is a parasite of the host tree or shrub, resulting in a tri-partite symbiosis between the fungus, insect, and tree. The fungus itself does not parasitize the tree tissue and the scale insects do not need the fungus to survive.
During the spring months,
basidia
A basidium () is a microscopic sporangium (a spore-producing structure) found on the hymenophore of fruiting bodies of basidiomycete fungi which are also called tertiary mycelium, developed from secondary mycelium. Tertiary mycelium is highly-c ...
gives rise to sexual spores known as
basidiospore
A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are pro ...
s that are capable of infecting a first
instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
scale insect walking across the surface of the fruiting body.
The infected insect will either 1) settle with other scale insects within the same fruiting body it was infected by, 2) travel to another fruiting body and settle, or 3) move to an un-infected plant tissue and settle, forming a new colony of the fruiting body. Scale insects are mobile during the first instar after hatching, which co-occurs in the spring when basidiospores are released.
Scale insects begin to feed on plant sap and settle into one location, eventually molting and shedding legs. Hyphae emerge from natural openings of infected insects and form a
mycelial
Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...
mat above the infected and non-infected insects.
The lifecycle completes itself when hyphae gives rise to new basidiospores on the surface of the mycelial mat during spring rain events, and infects the next generation of scale insects.
See also
*
Velvet blight
Velvet blight is a disease that affects the stems, branches, leaves, fruits or trunks of plants and trees. This disease is primarily caused by three fungal species from the genus ''Septobasidium'': '' S. bogoriense'', '' S. pilosum'' and '' S. t ...
*
Scale insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
References
External links
Index Fungorum*
{{Taxonbar, from=Q9198734
Teliomycotina
Fungal plant pathogens and diseases