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Virology-Bacteriology, and mitosporic fungi
Transcript of Virology-Bacteriology, and mitosporic fungi
Virology and phytoplasmas
What is a virus?
Infectious nucleoproteid, consists of coat proteine (CP) and nucleoacid (RNA (ribonucleic acid) or DNA (dezoxiribonucleic acid))
ssRNA, dsRNA, ssDNA and dsDNA (single and double stranded)
Main function of the CP: protection
Function of nucleic acids: to encode the genetic informations
Virion: CP+nucleicacid in resting state (dormancy)
Vegetative virus: the nucleic acid during the replication
size: nanometer (1nm=1*10, so viruses are visible by EM
viruses can live only in a living plant, or vector (e.g. Aphids)
most of them have a lot of host plants (polyphagous)
the infected plants are incurable! prevention is very important
virus names: English (not Latin)
Host+symptom+virus (Plum pox virus)
By vectors (animals, fungi, parasite plants)
Grafting, plant soup, seeds, pollen, vegetative propagation
Plant diseases caused by viruses
Prunus necrotic ringspot
Pathogen: Prunus necrotic ringspot virus (PNRSV)
Host plants: P.avium, cerasus, domestica, persica, persica cv. nectarina, cerasifera, padus, spinosa, serotina etc.
Symptoms: Symptoms depend on the stage of the disease.
1. Shock (acute) symptoms
The shock stage occurs immediately after infection.
Ringspots occur on upper surface of leaves in spring.
Later areas of symptomatic leaves become necrotic and necrotic tissues fall out from the leaf, leaving irregular shot-holes as diagnostic evidence of the virus.
Symptoms fade or fail to appear in leaves formed later in the season.
2. Chronic symptoms
The chronic stage occurs later, in the second or third year after infection.
Leaves of infected tree have narrow, unsymmetrical lamina with irregular leaf edge serration.
The main vein of the leaf often branched, and sometimes has two tips.
Little leaf-like formations (enations) appear on the main and secondary veins on lower surface of the leaves.
Transmission: Movement of virus in the orchard occurs through transmission by pollen. PNRSV can be transmitted by pollen to the seed and to the pollinated plant, by grafting, by mechanical inoculation and by seed.
Pathogen: Plum pox virus (Potyvirus) syn. Sharka virus
PPV is the most important viral pathogen of Prunus trees in Europe. It infects not only plum, but other stone fruit species such as sweet and sour cherries, peach, nectarine, apricot, myrobalan and blackthorn.
The discovery of infection of blackthorn may be epidemiologically important because this woody host may provide a perennial source of PPV in the nature. The pathogen has a world-wide distribution. It causes serious symptoms and yield losses on stone fruit trees and on ornamental Prunus species.
Types of fruit symptoms differ according to plum cvs.
Fruit symptoms in the case of cvs. which have small-sized fruit (for example plum cv. Besztercei): The first early fruit symptoms are irregular blue and shallow depressions on the skin. As fruits ripen, deep irregular grooves, rings, and lines appear on their surface, and the tissues beneath become necrotic and brownish-red. The fruit flesh is fibrous and gummy. Infected fruits are not tasty, become useless, and drop prematurely (about 3 to 4 weeks before ripening).
Fruit symptoms in the case of cvs. which have large-sized fruit (for example gage or plum cv. Stanley): Only blotches can be observed on the fruit skin, which are not depressed to the fruit flesh. The fruit flesh is healthy and infected fruits do not drop prematurely. Some hosts have symptomless fruits that are considered tolerant.
PPV can be transmitted by aphids in a non-persistent manner, by mechanical inoculation, and by grafting.
Pathogen: Tulip breaking virus (potyvirus)
Tulip breaking was the first virus disease ever recorded. It was described in 1576. The plants with beautifully variegated petals were referred to as Rembrandt tulips because they were the favorite subject in many paintings by the Dutch Masters. The plants were rare and highly sought. TBV is widely known as a former source of influence on the price of tulip bulbs and flowers during the period of so-called "Tulip mania" in the 17th century's Netherland.
The natural host range of TBV includes Tulipa and Lilium spp.
Luckily, tulip breeders were able to develop virus free plants with similar breaking features as early as 1750. In modern times, most tulips sold with "broken" petals are the result of breeding, not the virus infection.
Symptoms: Infected plants are beautiful but unfortunately the virus also has detrimental effects on host plants. TBV causes symptoms on both flowers (colour-breaking) and leaves (chlorosis). Colour-breaking of flowers appears as bars, stripes, streaks, featherings or flames of different colours on the petals. The symptoms are variable, which depends on the flower variety and age at the time of infection. Infected plants also indicate mottling or chlorosis of foliage and are reduced in size and vigour. There is also a reduction in bulbil and offset production.
TBV is transmitted by aphids in a non-persistent manner, by mechanical inoculation and grafting.
Phytoplasmas are unicellular
Transmitted by insects (vectors)
Phytoplasmas require a vector to be transmitted from plant to plant, no mechanical transmission, but also transmitted by vegetative propagation.
The vector is normally a sap sucking insect, such as leaf hoppers.
In these insects the phytoplasma is also able to replicate.
Phytoplasmas are the pathogens of important plants, causing a wide variety of symptoms range from mild yellowing to the death of infected plants.
They are most prevalent in tropical and sub-tropical regions of the world.
Instead of cell walls they have a triple membrane.
Size 100-1000 nm, DNA is free in the cytoplasm.
The concentration of the phytoplasmas in the infected plants is uneaven.
Disease caused by phytoplasma
Pathogen: Stolbur phytoplasma
Host plants: tomato, potato, paprika, pepper, capsicum, tobacco, weeds (e.g.: Cirsium arvense, Convulvulus arvensis)
Polyphagous (have lot hostplants)
Symptoms on tomato:
unshapen, small and narrow leaves
violet or purple coloring on the lower surface of the leaves
(cold weather also could cause this)
abnormally big sepals and missing petals
Prevention, protection against vectors.
PLANT DISEASES CAUSED BY FUNGI
DISEASES CAUSED BY OOMYCOTA
DISEASES CAUSED BY ASCOMYCOTA
Ascomycota with exoascus
Peach leaf curl
Pathogen: Taphrina deformans
Ascomycota with chasmothecia (powdery mildews)
Ascomycota with perithecia
•Teleomorph: the sexual reproductive stage (morph), typically a fruiting body.
•Anamorph: an asexual reproductive stage (morph), often mould-like.
•Holomorph: the whole fungus, including anamorphs and teleomorph.
Venturia inequalis (teleomorph stage)
Spilocaea pomi (anamorph stage)
Ascomycota with apothecia
Monilinia fructigena (teleomorph stage)
Monilia fructigena (anamorph stage)
DISEASES CAUSED BY BASIDIOMICOTA
"autoecious" requires a single host to complete its life cycle.
"heteroecious" needs two different plant hosts
complete life cycle
incomplite life cycle
0., I./ III., IV.
DISEASES CAUSED BY MITOSPORIC FUNGI
Diseases caused by mitosporic fungi with pycnidia
Anamorph stages of Ascomycota fungi, or
no sexual stage is currently known
Diseases caused by mitosporic fungi with acervuli
Diseases caused by mitosporic fungi with conidiophores
Ascochyta blight of pea, Pathogens:
Ascochyta pisi (anamorph stage)
A. pinodes (anamorph stage)
A. pinodella (anamorph stage)
Ascochyta blight of pea can be caused by three anamorphic pycnidial fungi species Ascochyta pisi, A. pinodes, and A. pinodella, for which no sexual stages are currently known. A. pisi is the most frequent. These three fungi can be distinguished according to the localization of the pycnidia in the spots appear most common on pods after infection, but these fungi can infect also stems and leaves of pea.
Pale brown, 3-5 mm or larger, round lesions develop on pods in which the pycnidia can be seen as small, black spots. In the case of Ascochyta pisi and A. pinodes the spots have define, dark brown margins and whitish centres, while in the case of the infection of A. pinodella the spots have no margins. Pycnidia either form ring patterns at the centre (A. pisi), or at the edge of the lesions (A. pinodes), or are randomly formed (A. pinodella) in the lesion.
Oval spots are appear on the stem.
Septoria blight of celery, Pathogen:
Septoria apii (anamorph stage)
S. apii-graveolentis (anamorph stage)
Septoria blight of celery can be caused by two anamorphic pycnidial fungi species Septoria apii and S. apii-graveolentis, for which no sexual stages are currently known. Septoria apii cause the large-spot type, while Septoria apii-graveolentis the small-spot type of Septoria blight. Only the leaves are affected.
Pale brown, 1-3 mm in diameter or larger lesions develop on the leaves. The shape of these spots is variable. Within or sometimes outside the lesions osciole of pycnidia can be seen as tiny black spots.
Septoria leaf spot of tomato
Pathogen: Septoria lycopersici (anamorph stage)
Septoria leaf spot of tomato is caused by a pycnidial fungus Septoria lycopersici. The leaves are mainly infected, but the agent rarely affects the fruit too.
Brown, 1-2 mm in diameter large, round lesions develop on the leaves. The spots have define, dark brown margins and whitish centres, in which pycnidia develop. Symptoms usually firstly appear on older leaves.
Pathogen: Colletotrichum lindemuthianum (anamorph stage)
Bean anthracnose is caused by an acervulal fungus Colletotrichum lindemuthianum, for which no sexual stage is currently known. Leaves, pods and seeds are affected.
The pathogen causes spots on infected plant parts, but the most conspicuous symptoms on leaves are dark brick-red to black partial or complete vein necrosis, which can be seen on the lower surface of the leafs.
The most striking symptoms develop on the pods. Small, reddish brown to black blemishes and distinct circular, reddish brown lesions appear on pods. Mature lesions are surrounded by a circular, reddish brown to black border with a greyish black interior, in which acervuli are developed. During most periods, the acervuli may exude pink masses of spores. Severely infected pods get smaller, and the seeds they carry are usually infected. Infected seeds have brown to black blemishes and sunken lesions.
Black spot of brassicas, Pathogen:
Alternaria brassicae (anamorph stage)
Alternaria brassicicola (anamorph stage)
Black spot of brassicas can be caused by two anamorphic fungi species Alternaria brassicae and Alternaria brassicicola, for which no sexual stages are currently known. Leaves are most common affected.
The main symptom of this disease is leaf spot.
On leaves, small, dark spots measuring 1-2 mm in diameter develop first and later enlarge into circular, brown spots that are visible from both side of the leaves. These can enlarge to 5-25 mm in diameter and usually contain concentric rings. If the conditions are favourable, dark conidiophores appear on the spots. Old leaf spots become papery in texture and may tear. Spots are most frequent on older leaves.
Early blight of tomato
Pathogen: Alternaria solani (anamorph stage)
Early blight of tomato is caused by the fungus Alternaria solani, for which no sexual stage is currently known. Leaves, stems and fruits of tomatoes are affected. The pathogen also infects potato and other Solanaceae plants.
On the leaves, brown circular spots appear which are often surrounded by a yellow area. Leaf spots have characteristic dark concentric rings. Leaf spots usually appear on the oldest leaves first and progress up the plant. As the disease progresses, the fungus may infect the stems and fruits.
The spots on the stems are oval.
The spots on the fruit look similar to those on the leaves. Symptoms on fruits appear as dark brown, sunken spots with concentric rings. These are the conidiophores.
Leaf mould of tomato
Pathogen: Cladosporium fulvum (anamorph stage)
Leaf mould of tomato is caused by the fungus Cladosporium fulvum, for which no sexual stage is currently known. Leaves and fruits are affected, but C. fulvum is mainly a foliar pathogen of tomatoes grown in the greenhouse, and sometimes of field-grown tomatoes in areas of high humidity.
Symptoms appear first as yellowish green spots on the upper surface of the older leaves. Later the spots enlarge and coalesce (unite), turn brown to black, spread to the remaining younger leaves, and may cause defoliation. On the lower surface of the leaves yellowish brown conidiophores appear.
Shot-hole disease of stone fruits
Pathogen: Stigmina carpophila (anamorph stage)
Shot-hole disease of stone fruits is caused by the fungus Stigmina carpophila, for which no sexual stage is currently known. Leaves, twigs and fruits of stone fruit trees are affected.
In spring, small, about 1 mm large in diameter, red dots occur on the leaves, then the dots expand into larger round lesions with a necrotic brownish centre and purple red margins. The central necrotic area drops out, resulting a hole.
The twig lesions have clear-cut brown margins and a necrotic centre which does not drop... Early autumn lignification of infected twigs is hindered and the lesions will grow into cankers.
The fruits are covered by large quantities of red spots, which are often corky. In the case of almond the fruits often covered by a gummy exudate. Even if they reach an adult stage the fruits are damaged.
Mechanical transmission - pruning
Biological basis of plant pathology
Symptoms on Plum:
Symptoms on other plants:
BASES OF PLANT PATHOLOGY
Plant Pathology - The study of plant diseases
Plant Disease - Any physiological or morphological change in a plant that results in abnormal appearance or development
Pathogen - An organism that causes disease
Symptom - Abnormal appearance of a plant
Sign - Appearance of the actual pathogen (fruiting bodies, spores, hyphae), viruses have no sign
Plant – host relationship
Monophagous (single host pest)
Oligophagous (host plants within one family)
Polyphagous (lot of hosts)
Biotrophic pathogen (Biotrophic fungal pathogens colonize living plant tissue and obtain nutrients from living host cells.)
Necrotrophic pathogen (Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells.)
Saprophyte (Saprophytic fungi feed on dead plant and animal remains. Many are extremely beneficial, breaking down this organic material into humus, minerals and nutrients that can be utilised by plants.)
What is needed for a Plant diseases?
All together in one time
Epidemic: outbreak of a certain disease
Pandemic: is an epidemic of infectious disease that has spread through plant populations across a large region; for instance multiple continents, or even worldwide.
- Viruses, viroids, phytoplasmas
Abiotic (not transmissible)
- Environmental (temperature, moisture, drought, light, wind, hail, soil pH)
- Cultural (mechanical damage, planting problems)
- Chemical (fertilizers, herbicides, pests)
- Physiological Disorders (abnormal growth due to genetic and/or environmental interactions