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Mildew
Fungal fruiting body on woody stem

Plant fungal pathogens


 

 

Introduction

Fungi is a kingdom of eukaryotic, heterotrophic organisms that live parasitically or as saprobes (derive their nutrition from the dead remains of other organisms), including mushrooms, yeasts, smuts, molds, etc. Fungi reproduce either sexually or asexually, and have life cycles that range from simple to complex.

The primary phyla dealt with in plant pathology are Chytridiomycota (chytrids), Zygomycota, Ascomycota (sac fungi or ascomycetes), and Basidiomycota (basidiomycetes).

Usually fungal infections cause necrosis, distortion and other abnormalities in plant tissue. Most distinctive signs of fungal infections is appearance of hyphae, mycelia, fruiting bodies and spores.

 

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Basidiomycota

A phylum of fungi that produce their sexual spores (basidiospores) on the outside of the basidium. It includes forms commonly known as mushrooms, boletes, puffballs, earthstars, stinkhorns, bird's-nest fungi, jelly fungi, bracket or shelf fungi, and rust and smut fungi.

cellular organisms - Eukaryota - Opisthokonta - Fungi - Dikarya - Basidiomycota -

Organism Disease Transmission Management
Pucciniomycotina - Pucciniomycetes - Pucciniales - Phakopsoraceae - Phakopsora - Phakopsora pachyrhizi
Common name: Soybean Asian rust
An obligate parasite of soybean; originated in Asia-Australia; was first reported in the 1990s in Hawaii and, since 2001, it has been found in South America and in 2004 in continental USA. Infects leaf tissue of a broad range (at least 31 species in 17 genera) of leguminous plants. At the beginning, small, tan-coloured lesions, restricted by leaf veins, can be observed on infected leaves. Lesions enlarge and, 5–8 days after initial infection, rust pustules (uredia, syn. uredinia) become visible. The uredia open with a round ostiole through which uredospores are released. The pathogen is able to defoliate soybean fields within a few days and may lead to complete crop failure. Invasive species kudzu serve as a reservoir of the overwintering pathogen. Pustules formed on the leaves of infected plants produce spores which can be disseminated by wind over very long distances. Not known to be spread by seed. Under conditions of warm temperatures and high humidity, new infections can arise every 9-10 days. At present, can be controlled by use of several fungicides and breeding for resistance. Resistant cultivars generally develop reddish-brown lesions with little or no sporulation. None of the soybean cultivars in present commercial production is resistant to all P. pachyhrizi isolates.
Pucciniomycotina - Pucciniomycetes - Pucciniales - Pucciniaceae - Puccinia - Puccinia triticina
Common name: wheat leaf rust
The fungus is an obligate parasite capable of producing infectious urediniospores as long as infected leaf tissue remains alive. Characterized by the uredinial stage. Orange to brown uredinia scattered on both leaf surfaces produce infectious urediniospores. Cuases the most common rust disease of wheat. Symptoms are often seen in the autumn on early-sown crops as individual orange to brown pustules usually seen on leaves. When leaves begin to senesce, a 'green island' develops around individual pustules. Towards the end of the season dark teliospores are sometimes produced. Yield losses are usually the result of decreased numbers of kernels per head and lower kernel weights. Urediniospores can be wind-disseminated and infect host plants hundreds of kilometres from their source plant, which can result in wheat leaf rust epidemics on a continental scale. In warm climates, leaf rust infections that over-summer on volunteer wheat can serve as resevoirs of inoculum for the autumn-planted winter wheat. Destruction of volunteers will help to prevent carry-over of the disease. Fungicides and planting resistant cultivars are most common control measures.
Ustilaginomycotina - Ustilaginomycetes - Ustilaginales - Ustilaginaceae - Ustilago - Ustilago tritici
Common name: loose smut
Smuts are characterized by large numbers of dark, thick-walled and dust-like teliospores. The word "smut" originates from from a Germanic word for dirt. Cuases most common and detructive smut disease in barley. The smutted heads usually emerge a day or two earlier than healthy heads. The medium- to dark-brown, powdery spore masses are enclosed within a fragile, silvery gray membrane that soon ruptures releasing the pale yellow-brown spores which are lighter in color on one side. By harvest, an erect and naked spike is all that remains of the head. Seed-borne: fungus survives between crop cycles as dormant mycelium in the embryo and endosperm of diseased seed. Indirect systemic infection is possible via stigma to embryo by pollen tube. Cannot be controlled by cleaning seed surfaces. Hot water or heat with adequate temperature can kill the fungus and not the plant. Further possibilities to control it are the application of systemic fungicides, cultivar resistance, and cultural practices. Sow certified, smut-free barley seed of resistant varieties are recommended.
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Ascomycota

cellular organisms - Eukaryota - Opisthokonta - Fungi - Dikarya - Ascomycota -

Organism Disease Transmission Management
saccharomyceta - Pezizomycotina - leotiomyceta - sordariomyceta - Sordariomycetes - Hypocreomycetidae - Hypocreales - Nectriaceae - Gibberella - Gibberella moniliformis
Synonym: Fusarium moniliforme
Anamorph: Fusarium verticillioides
Giberella is a genus containing teleomorphs from mitisporic fungal order Hypocreales. The genus includes several pathogens of grains and cereals. It is also the source of plant growth regulators such as gibberellin and gibberellic acid. An example of facultative endophyte, which can exist in the biotrophic endophytic assocoation with maize as well as saprophytically. Causes ear and stalk rot primarily in maize. The most conspicuous and common symptoms are the bakanae tillers or seedlings - an abnormal elongation of seedlings that are thin and yelowish green. In mature crops, infected plants may have a few tall, lank tillers with pale flag leaves; leaves dry up one after another from below and eventually die. If the plant survives, panicles are empty. Transmitted vertically and horizontally to the next generation of plants via clonal infection of seeds and plant debris. Horizontal infection is the manner by which this fungus is spread contagiously from the outside of the plant. The endophytic phase is transmitted vertically (from seed to seedling). Currently, there is no effective measures to control the disease. Endophytic stage is hard to control by fungicides. Seeds remain the reservoir from which infection takes place in each generation of plants. A biocontrol using endophytic Bacillus subtilis has been developed that shows promise for reducing mycotoxin accumulation during the endophytic phase. In addition, an isolate of a species of the fungus Trichoderma shows promise in the postharvest control of the growth and toxin accumulation on corn in storage.
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Chytridiomycota

cellular organisms - Eukaryota - Opisthokonta - Fungi - Chytridiomycota -

Organism Disease Transmission Management
Pucciniomycotina - Chytridiomycetes - Chytridiales - Synchytriaceae - Synchytrium - Synchytrium endobioticum
Like some other Chytridiales, develops no mycelium. The fungus produces a thick walled structure known as a winter sporangium. It is 25-75 µm in diameter and contains 200-300 spores. Sporangia are clustered into thin-walled soruses. The motile life stage, zoospore is about 0.5 µm in diameter and has one posterior flagellum. Causes the potato wart disease or black scab. Small greenish warts may form in the position of the aerial buds at the stem bases. The fungus affects tubers and stolons, but not the roots. Early infection results in distorted and spongy tubers. In older tubers, only the eyes are infected; they develop into characteristic, warty, cauliflower-like protuberances which gradually darken, rot and disintegrate. May render whole crop unmarketable. Added to the federal bioterrorism list for agricultural plant pathogens. Winter sporangia can remain viable for up to 20-30 years. Has a very limited capacity for natural spread and usually is introduced by infected potato tubers or by soil from land on which potato wart has occurred in the past. The fungus is also readily transmitted to new areas by machinery and implements used in potato cultivation, on footwear and manure from animals that have fed on infested tubers. Wart resistance remains an important element to be considered in potato breeding programs, especially in central and eastern Europe, and new screening methods have recently been described. Phytosanitary measures include stock certification, not growing any kind of plants with roots (including bulbs and tubers) for export in fields where fungus has occurred.
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Plant fungal pathogens at Metapathogen

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