Short Notes of Forest Protection
is a large genus of filamentous fungi
widely distributed in soil and in association with plants. Most species are harmless saprobes
and are relatively abundant members of the soil microbial community.
Some species produce mycotoxins
in cereal crops that can affect human and animal health if they enter the food chain. The main toxins produced by these Fusarium species are fumonisins
The genus includes a number of economically important plant pathogenic
commonly infects barley if there is rain late in the season. The genome of this wheat and maize pathogen has been sequenced. Fusarium graminearum can also cause root rot and seedling blight.
A conk is a fibrous but sometimes fleshy fruiting body of a wood-rotting fungus that has a definite form and structure.
A conk usually indicates rot close to or in excess of the percentage of gross volume allowing in a merchantable log of any class
In veneer logs, the conk along with the accompanying rot is a grading defect, even though a scale deduction is made. The rot results in the loss of some veneer and lowers the grade of some of the veneer produced.
In factory logs
, the conk and the associated rot constitute a grading defect. Even if a scaling deduction is taken from the gross log volume, the yield of cuttings from outside the heart center is less than the normal yield. Because stain and insect attack often combine with the rot, a portion of cuttings actually recovered is of lower quality than usual.
In construction logs, the conk is a degrader, for it is evidence of rot in the interior of the log. This excludes the log from this class.
In standing trees, the presence of conks makes it more difficult to determine tree quality. The fungi producing the conks of the fungi’s fruiting bodies grow by attacking and breaking down the tissues of another plant-in this case, the wood elements of the tree. A tree with conks contains masses of rotten wood or is hollow where the rotten wood has disintegrated. The extent of rotton wood or hollow can be estimated by sounding the tree with an ax, using a standard increment borer, or using a Shigometer.
A stem canker is a relatively localized necrotic lesion, primarily of bark and cambium; likewise, it can be any localized area of dead bark, commonly bordered by callus tissue. Most cankers are caused by fungi that infect wounds; but those resulting from frost, sunscald, or other causes also provide entry for decay fungi. The presence of conks indicates excessive heart rot.
Interior rot or exterior rot is associated with nearly all cankers. Such rot commonly extends downward and upward from the cankered area for varying distances. In the few instances where there is no rot, bark pockets, insect damage (from wood borers), or stain is usually present-either singly or in any combination. They also may be found with either form of rot. In good bucking practice, a canker and any massive rot is not included in the log.
In standing trees, cankers constitute the largest group of stem deformations. The decay associated with cankers in most cases extends from 3 to 8 feet (.9 to 2.4 m) up and down the bole from the canker, depending on the causal fungus. The diameter of the decay can be estimated by taking an increment boring, with a Shigometer, or by sounding a tree with an ax.
BIOLOGICAL PEST CONTROL:
Biological Control is defined as the reduction of pest populations
by natural enemies and typically involves an active human role. Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids
, and pathogens
. Biological control agents of plant diseases
are most often referred to as antagonists. Biological control agents of weeds include herbivores
and plant pathogens. Predators, such as lady beetles
, are mainly free-living species that consume a large number of prey
during their lifetime. Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Most have a very narrow host range. Many species of wasps and some flies are parasitoids. Pathogens are disease-causing organisms including bacteria
, and viruses
. They kill or debilitate their host and are relatively specific to certain insect groups. There are three basic types of biological control strategies; conservation, classical biological control, and augmentation.
(Greek for fungus roots coined by Frank, 1885; typically seen in the plural forms mycorrhizae or mycorrhizas) is a symbiotic
(occasionally weakly pathogenic
) association between a fungus
and the roots of a plant
. In a mycorrhizal association, the fungus may colonize the roots of a host plant, either intracellularly or extracellularly. It is an important part of soil life
association provides the fungus with relatively constant and direct access to mono- or dimeric carbohydrates
, such as glucose
produced by the plant in photosynthesis
. The carbohydrates are translocated from their source location (usually leaves) to the root tissues and then to the fungal partners. In return, the plant gains the use of the mycelium
‘s very large surface area to absorb water and mineral nutrients from the soil, thus improving the mineral absorption capabilities of the plant roots. Plant roots alone may be incapable of taking up phosphate ions
that are immobilized, for example, in soils with a basic pH
. The mycelium
of the mycorrhizal fungus can however access these phosphorus sources, and make them available to the plants they colonize.
The mechanisms of increased absorption are both physical and chemical. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and can explore a greater volume of soil, providing a larger surface area for absorption. Also, the cell membrane chemistry of fungi is different from that of plants. Mycorrhizae are especially beneficial for the plant partner in nutrient-poor soils.
Mycorrhizal plants are often more resistant to diseases, such as those caused by microbial soil-borne pathogens
, and are also more resistant to the effects of drought. These effects are perhaps due to the improved water and mineral uptake in mycorrhizal plants
Mycorrhizae form a mutualistic
relationship with the roots of most plant species (and while only a small proportion of all species has been examined, 95% of these plant families are predominantly mycorrhizal).
Mycorrhizae are present in 92% of plant families (80% of species) and indeed the most prevalent symbiotic association found in all the plant kingdom.
Types of mycorrhiza
Mycorrhizas are commonly divided into ectomycorrhizas and endomycorrhizas. The two groups are differentiated by the fact that the hyphae of ectomycorrhizal fungi do not penetrate individual cells
within the root, while the hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane
Endomycorrhiza are mycorrhizas whose hyphae enter into the plant cells, producing structures that are balloon-like (vesicles). The fungal hyphae
do not in fact penetrate the protoplast
(i.e. the interior of the cell), but invaginate the cell membrane
Ectomycorrhizas, or EcM, are typically formed between the roots of around 10% of plant families, mostly woody plants including the birch
, and rose
families and fungi belonging to the Basidiomycota
, and Zygomycota
. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a hartig net
of hyphae surrounding the plant cells within the root cortex
. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients can be shown to move between different plants through the fungal network (sometimes called the wood wide web). Carbon has been shown to move from birch
trees into fir
trees thereby promoting succession
The ectomycorrhizal fungus Laccaria bicolor
has been found to lure and kill springtails
to obtain nitrogen, some of which may then be transferred to the mycorrhizal host plant.
is a genus
of parasitic fungi that live on trees and woody shrubs. It includes about 10 species
formerly lumped together as A. mellea.
Armillaria is long-lived and form some of the largest living organisms
in the world. The largest single organism (of the species Armillaria ostoyae
) covers more than 3.4 square miles (8.9 km²) and is thousands of years old.
As a forest pathogen, Armillaria can be very destructive. It is responsible for the “white rot” root disease of forests. Its high destructiveness comes from the fact that, unlike most parasites, it doesn’t need to moderate its growth in order to avoid killing its host, since it will continue to thrive on the dead material.
Honey fungus as a plant disease (white rot root disease):
Honey fungus spreads both from living trees, dead and live roots
and stumps by means of reddish-brown to black root-like rhizomorphs
(‘bootlaces’) at the rate of around 1 m a year, although infection by root contact is also possible. Infection by spores is rare. Rhizomorphs grow relatively close to the soil
surface (in the top 20 cm) and invade new roots, or the root collar (where the roots meet the stem) of woody plants. An infected tree will die once the fungus has girdled it, or when extensive root death has occurred. This can happen rapidly, or may take several years. Infected plants will deteriorate, although may exhibit prolific flower
production shortly before death.
Initial symptoms of honey fungus infection include the dying back of leafy branches or failure of leaves to appear in spring. Black bootlace-like strands appear under the bark
and around the tree, and fruiting bodies grow in clusters from the infected plant in autumn and die back after the first frost. However these signs do not necessarily mean that the pathogenic (disease causing) strains of honey fungus are a cause of plant decline or death, so other identification methods are advised before a diagnosis is made. The presence of thin sheets of cream coloured mycelium
, giving off a strong smell of mushrooms
, beneath the bark at the base of the trunk or stem, sometimes extending upwards, or a gum or resin exuding from cracks in the bark of conifers
, indicates that honey fungus is a likely cause of problems.
are linear aggregations of parallel-oriented hyphae
. The mature cords are composed of wide, empty vessel hyphae
surrounded by narrower sheathing hyphae
. Cords may look similar to plant roots
, and also frequently have similar functions; hence they are also called rhizomorphs
Mycelial cords are capable of conducting nutrients over long distances. For instance, they can transfer nutrients to a developing fruiting body, or enable wood-rotting fungi to grow through soil from an established food base in search of new food sources. For parasitic fungi, they can help spread infection by growing from established clusters to uninfected parts. The cords of some wood-rotting fungi (like Serpula lacrymans
) may be capable of penetrating masonry
The mechanism of the cord formation is not yet precisely understood. Mathematical models
suggest that some fields or gradients
of signalling chemicals, parallel to the cord axis, may be involved.
is fungal genus within the Ascomycota that causes leaf and catkin curl diseases and witch’s brooms
of certain flowering plants. One of the more commonly observed species causes peach leaf curl
. Taphrina typically grow as yeasts during one phase of their life-cycles, and then infect plant tissues in which typical hyphae are formed, and ultimately they form a naked layer of asci
on the deformed, often brightly pigmented surfaces of their hosts. No discrete fruit body is formed outside of the gall
-like or blister-like tissues of the hosts. Phylogenetically, Taphrina is a member of a basal group within the Ascomycota, and type genus for the subphylum Taphrinomycotina
, the class Taphrinomycetes
, and order Taphrinales
- Taphrina alni (BERK. & BROOME) GJAERUM,
- Taphrina betulina ROSTR.,
- Taphrina bullata (BERKELEY) TULASNE,
- Taphrina caerulescens (DESMAZ. & MONT.) TUL.,
- Taphrina deformans (BERK.) TUL.,
- Taphrina johansonii SADEBECK,
- Taphrina maculans BUTLER,
- Taphrina piri,
- Taphrina populina (FR. ex FR.) FR.,
- Taphrina pruni TUL.,
- Taphrina sadebeckii JOHANS.,
- Taphrina tosquinetii (WESTEND.) MAGNUS,
- Taphrina ulmi (FUCKEL) JOHANS.,
- Taphrina wiesneri (RATHAY) MIX
A Witch’s broom
is a disease or deformity in a woody plant
, typically a tree
, where the natural structure of the plant is changed. A dense mass of shoots
grows from a single point, with the resulting structure resembling a broom
or a bird’s nest
One example of this would be cytokinin
, a phytohormone
, interfering with an auxin-regulated bud. Usually auxin
would keep the secondary, tertiary, and so on apexes from growing too much, but cytokinin releases them from this control, causing these apexes to grow into witch’s brooms.
Witch’s broom growths last for many years and can be caused by many different types of organisms, such as fungi
. Human activity is sometimes behind the introduction of these organisms; for example when a person prunes a tree improperly, leaving the tree susceptible to disease.
Witch’s brooms occasionally result in desirable changes. Some cultivars of trees, such as Picea orientalis
‘Tom Thumb Gold’, were discovered as witch’s brooms. If twigs of witches’ brooms are grafted onto normal rootstocks, freak trees result, showing that the attacking organism has changed the inherited growth pattern of the twigs.
The word ‘mistletoe’ is of uncertain etymology; it may be related to German
Mist, for dung and Tang for branch, since mistletoe can be spread in the feces
of birds moving from tree to tree. However, Old English
mistel was also used for basil
A study of mistletoe in junipers
concluded that more juniper berries sprout in stands where mistletoe is present, as the mistletoe attracts berry-eating birds which also eat juniper berries. Such interactions lead to dramatic influences on diversity, as areas with greater mistletoe densities support higher diversities of animals. Thus, rather than being a pest, mistletoe can have a positive effect on biodiversity
, providing high quality food and habitat for a broad range of animals in forests and woodlands worldwide.
Mistletoe was often considered a pest that kills trees and devalues natural habitats, but was recently recognized as an ecological keystone species
, an organism that has a disproportionately pervasive influence over its community. A broad array of animals depend on mistletoe for food, consuming the leaves and young shoots, transferring pollen
between plants, and dispersing the sticky seeds. The dense evergreen witches’ brooms
formed by the dwarf mistletoes
species) of western North America also make excellent locations for roosting and nesting of the Northern Spotted Owls
and the Marbled Murrelets
In Australia the Diamond Firetails
and Painted Honeyeaters
are recorded as nesting in different mistletoes. This behavior is probably far more widespread than currently recognized; more than 240 species of birds that nest in foliage in Australia have been recorded nesting in mistletoe, representing more than 75% of the resident avifauna
The fruiting bodies
appear in the form of pseudothecia. They are solitary and embedded into the host plant tissue. A pseudothecium has small dark hairs around its opening, and contains pseudoparaphyses along with asci
. The asci contain eight haploid ascospores
. The haploid chromosome
number of V. inaequalis is seven.
The infection cycle begins in the springtime, when suitable temperatures and moisture promote the release of V. inaequalis ascospores
rise into the air and land on the surface of a susceptible tree, where they germinate and form a germ tube
that can directly penetrate the plant’s waxy cuticle
. A fungal mycelium
forms between the cuticle and underlying epidermal
tissue, developing asexually
, that germinate on fresh areas of the host tree, which in turn produce another generation of conidial spores. This cycle of secondary infections
continues throughout the summer, until the leaves and fruit fall from the tree at the onset of winter. V. inaequalis overwinters mostly as immature pseudothecia, where sexual reproduction
takes place, producing a new generation of ascospores that are released the following spring. Scab lesions located on the woody tissues may also overwinter in place, but will not undergo a sexual reproduction cycle; these lesions can still produce infective conidial spores in the spring.
An ascus (plural asci) is the sexual spore-bearing cell produced in ascomycete fungi. On average, asci normally contain 8 ascospores, produced by a meiotic cell division followed, in most species, by a mitotic cell division. However, asci in some genera or species can number 1 (e.g. Monosporascus cannonballus), 2, 4, or multiples of four. In a few cases, the ascospores can bud off conidia that may fill the asci (e.g. Tympanis) with hundreds of conidia, or the ascospores may fragment, e.g. some Cordyceps, also filling the asci with smaller cells. Ascospores are nonmotile, usually single celled, but not infrequently may be septate, and in some cases septate in multiple planes. Mitotic divisions within the developing spores populate each resulting cell in septate ascospores with nuclei.
Asci normally release their spores by bursting at the tip, but they may also digest themselves passively releasing the ascospores either in a liquid or as a dry powder. Typically, actively discharging asci have a specially differentiated tip, either a pore or an operculum. In some hymenium forming genera, when one ascus bursts, it can trigger the bursting of many other asci in the ascocarp resulting in a massive discharge visible as a cloud of spores – the phenomenon called “puffing”. This is an example of positive feedback
. A faint hissing sound can also be heard for species of Peziza
and other cup fungi
It is a mixture of copper sulphate
and hydrated lime
used as a fungicide
. It is used mainly to control garden, vineyard, nursery and farm infestations of fungi
, primarily downy mildew
which can result from infections of Plasmopara viticola
. It was invented in the Bordeaux region of France, where it is known locally as Bouillie Bordelaise. This fungicide has been used for over a century and is still used, although the copper can leach
out and pollute streams.
Vines of American origin brought to Europe as botanical specimen resulted in several outbreaks of vine diseases
in the 19th century, as the Vitis vinifera
vines of the classicial European wine regions lacked resistance against certain pests carried by these specimen. This did not only include the Great French Wine Blight
caused by the aphid Phylloxera vastatrix
, but also mildew
and other diseases caused by fungi.
After the downy mildew
had struck, botany professor Pierre-Marie-Alexis Millardet
of the University of Bordeaux
was studying the disease in vineyards of the Bordeaux region
. Millardet then noted that vines closes to the roads did not show mildew, while all other vines were affected. After inquiries, he found out that those vines had been sprayed with a mixture of copper sulfate and lime to deter bypassers from eating of the grapes, since this treatment was both visible and bitter-tasting. This led Millardet to conduct trials with this treatment. The trials primarily took place in the vineyards of Château Dauzac
, where he was assisted by Ernest David, Dauzac’s technical director. Millardet published his findings in 1885, and recommended the mixture to combat downy mildew.
In France, the use of Bordeaux mixture has also been known as the Millardet-David treatment.
Mode of action
Bordeaux mixture achieves its effect by means of the copper ions
(Cu2+) of the mixture. These ions affect enzymes
in the fungal spores
in such a way as to prevent germination
. This means that Bordeaux mixture must be used pre-emptively, before the fungal disease has struck.
Bordeaux mixture can be prepared using differing proportions of the components. In preparing Bordeaux mixture, the copper sulphate and the lime is dissolved separately in water and then mixed together. Calcium oxide
(burnt lime) and calcium hydroxide
(hydrated lime) gives the same end result since an excess of water is used in the preparation.
The conventional method of describing the mixture’s composition is to give the weight of copper sulphate, the weight of hydrated lime and the volume of water in that order. The percentage of the weight of copper sulphate to the weight of water employed determines the concentration of the mixture. Thus a 1% Bordeaux mixture, which is the normal, would have the formula 1:1:100, with the first “1” representing 1 kg copper sulphate, the second representing 1 kg hydrated lime, and the 100 representing 100 litres (100 kg) water. As copper sulphate contains 25% copper, the copper content of a 1% Bordeaux mixture would be 0.25% copper. The quantity of lime used can be lower than that of the copper sulphate. 1 kg copper sulphate actually requires only 0.225 kg of chemically pure hydrated lime to precipitate all the copper. Good proprietary brands of hydrated lime are now freely available but, as even these deteriorate on storage (by absorbing carbon dioxide
from the air), a ratio of less than 2:1 is seldomly used, which corresponds to a 1:0.5:100 mixture.
Schematic of a typical basidiocarp, showing fruiting body, hymenium
), is the sporocarp
of a basidiomycete
, the multi-cellular
structure on which the spore
is borne. Basidiocarps are characteristic of the hymenomycetes
do not produce such structures. As with other sporocarps, epigeous (above-ground) basidiocarps that are visible to the naked eye (especially those with a more or less agaricoid
morphology) are commonly referred to as mushrooms
, while hypogeous (underground) basidiocarps are usually called false truffles
All basidiocarps serve as the structure on which the hymenium is produced. Basidia
are found on the surface of the hymenium, and the basidia ultimately produce spores. In its simplest form, a basidiocarp consists of an undifferentiated fruiting structure with a hymenium on the surface; such a structure is characteristic of many simple jelly
and club fungi. In more complex basidiocarps, there is differentiation into a stipe
, a pileus
, and/or various types of hymenophores
Basidiocarps are classified into various types of growth forms based on the degree of differentiation into a stipe, pileus, and hymenophore, as well as the type of hymenophore, if present.
, like others in the family Pythiaceae, are usually characterized by their production of coenocytic hyphae
, hyphae without septations
rot is a common crop disease caused by a genus of organisms called “Pythium”. These are commonly called water moulds
. Pythium damping off
is a very common problem in fields and greenhouses, where the organism kills newly emerged seedlings (Jarvis, 1992). This disease complex usually involves other pathogens such as Phytophthora
. Pythium wilt is caused by zoospore infection of older plants leading to biotrophic infections that become necrotrophic in response to colonization/reinfection pressures or environmental stress (Jarvis, 1992; Owen-Going, 2005; Owen-Going et al., 2009), leading to minor or severe wilting caused by impeded root functioning (Jarvis, 1992; Bagnall, 2007).
It has been noted that in field crops, damage by Pythium spp. is often limited to the area affected, as the motile zoospores require ample surface water to travel long distances. Additionally, the capillaries formed by soil particles act as a natural filter and effectively trap many zoospores. However, in hydroponic systems
, where extensive monocultures
of plants are maintained in plant nutrient solution (containing nitrogen, potassium, phosphate, and micronutrients) that is continuously recirculated
to the crop, Pythium spp. cause extensive and devastating root rot and is often difficult to prevent or control (Jarvis, 1992; Owen-Going, 2002; Owen-Going et al., 2003; Bagnall, 2007). The root rot affects entire operations (tens of thousands of plants, in many instances) within two to four days due to the inherent nature of hydroponic systems where roots are nakedly exposed to the water medium, in which the zoospores can move freely (Owen-Going, 2002; Owen-Going et al., 2003; Bagnall, 2007).
A type of connection found within a single hyphal strand of a Basidiomycete fungus
. It ensures that two adjacent hyphal cells (divided by septa
) each have 2 different nuclei
from mating with hyphae
of another sexual type. It is used in the “nuclear shuffle” similar to that found in croziers
during sexual reproduction.
is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia
, but less severe. It is technically NOT the opposite of hyperplasia
(too many cells). Hypoplasia is a congenital condition, while hyperplasia generally refers to excessive cell growth later in life. (Atrophy, the wasting away of already existing cells, is technically the direct opposite of both hyperplasia and hypertrophy.)
The name is derived from the Greek: hypo, meaning low, and plasis, which refers to molding or forming. The adjective form is hypoplastic.
are chemical compounds
or biological organisms used to kill or inhibit fungi
or fungal spores. Fungi can cause serious damage in agriculture
, resulting in critical losses of yield
, quality and profit
. Fungicides are used both in agriculture and to fight fungal infections
in animals. Chemicals used to control oomycetes
, which are not fungi, are also referred to as fungicides as oomycetes use the same mechanisms as fungi to infect plants.
Fungicides can either be contact or systemic. A contact fungicide kills fungi by direct contact; a systemic fungicide has to be absorbed by the affected organism.
Most fungicides that can be bought retail are sold in a liquid form. The most common active ingredient is sulfur
, present at 0.08% in weaker concentrates, and as high as 0.5% for more potent fungicides. Fungicides in powdered form are usually around 90% sulfur and are very toxic. Other active ingredients in fungicides include neem oil
oil, jojoba oil
, and the bacterium Bacillus subtilis
have been found on food for human consumption, mostly from post-harvest treatments. Some fungicides are dangerous to human health
, such as vinclozolin
, which has now been removed from use.
Plants and other organisms have chemical defenses that give them an advantage against microorganisms such as fungi. Some of these compounds can be used as fungicides:
Whole live or dead organisms that are efficient at killing or inhibiting fungi can sometimes be used as fungicides:
- The bacterium Bacillus subtilis
- Kelp (powdered dried kelp is fed to cattle to protect them from fungi in grass)
The smuts are fungi, mostly Ustilaginomycetes (of the class Teliomycetae, subphylum Basidiomycota), that cause plant disease.
Smuts affect grasses, notably including cereal crops such as maize. They initially attack the plant’s reproductive system, forming galls which darken and burst, releasing fungal spores which infect other plants nearby.
A smut infestation is controlled by removing and destroying the infected plants. In agriculture, this process is known as destruction of the initial inoculum.
Sugarcane smut or culmicolous smut is caused by the fungus Ustilago scitaminea. The smut ‘whip’ is a curved black structure which emerges from the leaf whorl. Sugarcane smut causes significant losses to the economic value of a sugarcane crop. Sugarcane smut has recently been found in the eastern seaboard areas of Australia, one of the world’s highest-yielding sugar areas.
Corn smut (Ustilago maydis), which infects maize, is a delicacy in Mexico, where it was historically enjoyed by the Aztecs, and Brazil. It enlarges the ear of corn and fills it with sooty spores.
Cercospora is a genus of ascomycete fungi. Several species of this genus cause plant diseases, mostly forms of leaf spot. It is a relatively well-studied genus of fungi but there are countless species not yet described, and there is still much to learn about. The most well-known species are:
is a genus
of fungi that is distinguished by a pileate basidiocarp, di- to trimitic hyphal systems, smooth non-dextrinoid spores
, and a hymenium
usually without true hymenial cystidia.
An organism which feeds on dead plant or animal material. Most saprophytes are fungi or bacteria. They are important in nutrient cycles as they bring about decay and liberate nutrients for plant growth. OR;
Saprophyte, any plant that depends on dead plant or animal tissue for a source of nutrition and metabolic energy, e.g., most fungi (molds) and a few flowering plants, such as Indian pipe and some orchids. Most saprophytes do not produce chlorophyll and therefore do not photosynthesize; they are thus dependent on the food energy they absorb from the decaying tissues, which they help to break down.
are a Division/Phylum
of the kingdom Fungi
, and subkingdom Dikarya
, whose members are commonly known as the Sac Fungi
. They are the largest phylum of Fungi, with over 30,000 species. Characteristically, when reproducing sexually, they produce nonmotile spores
in a distinctive type of microscopic cell
called an “ascus
” (from Greek
: (askos), meaning “sac” or “wineskin”). These spores are called ascospores
. However, some members of the Ascomycota do not reproduce sexually and do not form asci or ascospores. These members are assigned to Ascomycota based upon morphological
similarities to ascus-bearing taxa, and in particular by phylogenetic
comparisons of DNA
MYCORRHIZAL FUNGI AND ENDOPHYTES:
Members of the Ascomycota make two particularly important types of relationship with plants: as mycorrhizal
fungi and as endophytes
. The former make symbiotic
associations with the root systems of the plants, which for some trees, especially conifers, can be of vital importance, enabling the uptake of mineral salts from the soil. The fungal partner is in a much better position to absorb minerals due to its finely divided mycelium, whilst the plant provides it with metabolic energy in the form of photosynthetic
products. Cases are even known where mycorrhizal fungi can transport nutrients from one plant to another, stabilizing the recipient. It is likely that mycorrhizal associations enabled the conquest of the land by plants – in any case the earliest known fossils of land plants have mycorrhizae.
on the other hand live inside plants, especially in the stem and leaves, but generally do not damage their hosts. The exact nature of the relationship between endophytic fungus and host is not yet well understood, but it seems that this form of colonization can bestow a higher resistance against insects, roundworms
(nematodes), and bacteria
; also it can enable or augment the production of poisonous alkaloids
, chemicals which can affect the health of plant-eating mammals
Typically, a single ascus will contain eight ascospores. The eight spores are produced by a combination of a meiosis
division followed by a mitotic
division. The meiosis division turns the original diploid zygote
nucleus into four haploid
ones. That is, the single original cell from which the whole process begins contains two complete sets of chromosomes
. In preparation for meiosis, all the DNA
of both sets is duplicated, to make a total of four sets. The nucleus that contains the four sets divides in two stages, separating into four new nuclei – each of which has one complete set of chromosomes. Following this process, each of the four new nuclei duplicates its DNA and undergoes a division by mitosis. As a result, the ascus will contain four pairs of spores.