Pathogens Flashcards
Fungi, bacteria, and viruses are the most common pathogen groups causing disease in plants.
Other groups include viroids and phytoplasmas.
These may be further from abiotic factors.
The Disease Triangle
Three components must be presents in order for a disease to have success, if any of them are absent then the disease shall not develop.
The components include:
1. Pathogen (Presence, virulence, abundance, etc.)
2.Host (Presence and degree of susceptibility)
3.Environment (Conditions favoring disease)
Fungi
Most fugi are saprophytes and feed on decaying material, helping to break down dead organic matter and build up soil fertility. Certain fungi live on both dead and living plants, while still others require living host plants to grow and reproduce (obligates).
Fungi-Identification
Types of damage include leaf spots; blight on leaves, branches, twigs, and flowers,; cankers; root rot; seedling damping off’stem rots’ soft and dry rots’ scab of fruit, leavess, or tubers.
Symptoms of a disease refer to changes in the appearance of the infected plant, such as the necrotic, sunken, ulcerlike lesions of an anthracnose infection.
The signs of a disease, on the other hand, are structures that the pathogen may produce on the surface of the host, such as mycelia, sclerotia, sporophores, fruiting bodies, and spores.
Fungi a living host to grow and reproduce; these are called obligate parasites and include many of the major plant pathogen species, such as rust, downy mildew, and powdery mildews.
Are mostly microscopic, made up of of tiny
tubulars filaments called hyphae, and when tips grow together are referred to as mycelium. Reproductive structure acre referred to a s spores and may produced on specialized hyphae or fruiting bodies.
Sp0res and spore0bearing structures are the most significant charcteristics for identification. Size, shape, color, arrangement of spores and the fruiting bodies can be used to help determine the species of the fungus’ these chacteristics are most often used in taxonomic keys by professionals.
Field identification of diseases symptoms cause by fungi can often help determine the spec species responsible for the damage.
Life-Cycle and Regrowth
Fungi that are known to have a sexual cycle are called imperfect fungi.
Fungi have evolved a number of mechanisms to survive when conditions are unfavorable.
Infected plant debris, bud scales or bark cankers in trees, shrubs, or soil can provide overwintering habitat for the mycelia.
Dispersal and Movement
Most fung cannot move long distances without the assistance of people, insects, animals, or environmental factors suh as wind or rai. A few fungi are able to move from one host to anohter through the growth of rhizomorphs in the soils. Most fungal spores disseminate in air and water currents and can be carried over long distances.
Dispersal and Movement
Most fung cannot move long distances without the assistance of people, insects, animals, or environmental factors suh as wind or rai. A few fungi are able to move from one host to anohter through the growth of rhizomorphs in the soils. Most fungal spores disseminate in air and water currents and can be carried over long distances.
Insects can also spread fungal pathogens, for example the glassy winged sharp-shooter transmits disease.
People can also disemminate fungi from nursery stockes, or infected seeds.
Bacteria-Identification
Prokaryotes and can infect almost every kind of plant and
Facultative parasite.
With a flagella.
Bacteria are very small, typicallunde .002mm, or about one twelve-thousandths of an inch, long. They can be rod shaped, spherical, ellipsoidal, spiral, sliphook shaped, or filamentouous
Common sympoms include cankers, galls, wilts, slow growth, disorted fruirts, rots, discoloration of plant parts, slow ripening, distorted leaves, brooming, and leaf sports.
Life Cycle an d GRowth Requirements
Each bacterial cell is an individual organism.Reproduction occurs through an asezual process known as binary fission.
Bacteria enter plants through natural opening and wounds. Pmce inside t, some bacteria move alon the sap stream.Bacteria often develop between the cplant cells inuring and ultimtaely penetrating into them.
Successful Characteristics
Survive mostly within plant hst as parasite on seeds, or in plant debries in soil. ThThey do no produce overwintering spores as fung, however are capable of overwintering saprophytically in plant debris.
Dispersal and Movememnt
Can spshed around iof flow in in moist ienvironment. The surcvive in organic debris in the soil and can be dispered by any practive that involve moving soil from one place to another, such as cultivatio.
Frequently carried on infected seeds, uttiings, or transplants. Osects and animals aoften aid in spreading bacteria. For insstance Xyllela fastiidiosa, the bacterium causes Pierces’ disease of grap and oleander is transmitted through sharp shooter.s
Virus-Identification
Mosaic patterns, ar mottling of healthy and discoloerd tissue on leaves, are a common viuz symptoms. Some viruses roll or crinkly leaves.
Is an obligate parsite of submicroscopic size that is composed of genetic material and is surrounded by a layer of of protein. Viruses multiply only in living cells’ htey are amonthe smallest and simplest of plant pathogens. Viruses cause disease by disrupting normal metablolic and physioulogical processes in plan cells.
Viral diseases produce a variety f injury symptoms on plants. Common field symptoms associated with plant viruses include growth reductions, color changes, malformations and necrosis of tissue’ severe stunting and a reduction in yield may be evident.
Life Cycle Requirements.
All virue are parasitic on cells and require a host vell for survival and reproduction. A nucleic avid is released from the viru particle when the viruz infects the host’ the host cell is then directed to form more virue. They do not divide, nor do they produce any reproductive structures. Thaye are usually elongate, bacilluslike, or spherical.
Entering through wounds made by insects or nematode vectors, mechanical injury, or from an infected p0llen grain. The first viru particles may appear about 10 hours after inoculation.
Viruzes cannot survive in dead plant debris or outside living plant tissue. Alternate host such as perennial plants, weeds, or volunteer, crop plants provide overwintering sites for many viruzes and are often suitable hostz for virusez vectors as well.
Dispersal and Movement
Viruzes can enter plants only through wounds. they are dispersed mechanically foro plant to plant through vegetative prpagation, P, EED AND POLLEN OR BY VECTOR.
Vector of one or more plant irue inlcude aphids, leafhoppers, whiteflies, beetles, thrips, mites, nematodes, fungi and dodders.
Viroids are low0molecular-weight nucleic av0ids that can infect plant cells, replicate themselves, and cause disease. Viroids lack a protein coat and contain only RNA.
Viroids can only survive within a host and are spread by implements, propagation tools, pruning tools vegetative propagation, and sometimes with seeds.
Example: Potato Spindle tuber, citrus exocortis, etc.
Phytoplasmas
Are the smallest cells know to multiply independently of other living cells, and they can survive for extended periods outside plant cells. They contain cellular-like structure without a true cell wall and may assume a wide variety of shapes and sizes.
