Biological Sciences
Plant Pathogen
A plant pathogen is a microorganism or infectious agent that causes diseases in plants. These pathogens can include fungi, bacteria, viruses, nematodes, and other organisms that can negatively impact the health and productivity of plants. Understanding plant pathogens is crucial for developing strategies to manage and control plant diseases in agriculture and natural ecosystems.
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10 Key excerpts on "Plant Pathogen"
eBook - ePub- Anne Marte Tronsmo, David B Collinge, Annika Djurle, Lisa Munk, Jonathan Yuen, Arne Tronsmo(Authors)
- 2020(Publication Date)
- CAB International(Publisher)
Chapter 3 starts with a presentation of the different lifestyle strategies exhibited by interactions between pathogens and microorganisms in their interaction with plants, ranging from the beneficial to the harmful. The next section describes a generalized disease cycle and the chain of events that lead to development of a disease. Knowing the different processes in the disease cycle and the cycle as a whole is, in essence, the prerequisite for understanding the development of diseases in time and space, as well as their management. The variation in the biological processes used by different pathogens employing different lifestyle strategies in the disease cycle illustrates the breadth and complexity in the science of plant pathology.
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1 What is a Plant Disease?Anne Marte Tronsmo, Lisa Munk, Annika Djurle, Jonathan Yuen and David B. CollingeIntroductionPlant diseases limit potential crop production and are responsible for considerable losses in agriculture, horticulture and forestry. Plant diseases are caused by infectious agents: Plant Pathogens. What we observe as a disease is the outcome of the interaction between the host plant, the pathogen and the environment. The concept is described as the disease triangle. This chapter gives an introduction to these factors and their interactions that may or may not result in a plant disease. The host plants, the pathogens and the environment (including all non-pathogenic organisms) in a distinct geographical unit constitute a phytobiome.Deviations from normal growth of a plant may be caused by an infectious agent, such as a microorganism, virus, viroid or a nematode. The deviation may also be a disorder caused by abiotic stress factors (non-infectious factors). A short definition of a plant disease is ‘abnormal functioning of a plant due to a pathogen’, and plant pathology (or phytopathology) is the study of disease in plants. Etymologically, pathology originates from the Greek words ‘pathos’, meaning suffering, and ‘logia
eBook - PDF- Khushboo Chaudhary, Pankaj Kumar Saraswat, Aniruddh Kumar Pareek(Authors)
- 2023(Publication Date)
- Delve Publishing(Publisher)
We depend on plants for our survival. But plants can catch diseases, just like we do. Any organism like fungi, bacteria, viruses, etc causing plant disease is referred to as Plant Pathogens. Plant Pathogens cause disease in plants and cause losses in the quality and quantity of food and other necessary items. The losses may be light or very severe, sometimes destroying all the plants and causing starvation, hunger, and famines (e.g. Irish potato famine), whereas in some cases they result in the extinction of entire species of plants. Plant diseases have been considered as tenacious barriers to the rapid progress of economic and life stability (NCBI). Thus it is very important to find out which pathogen is causing plant disease. Identifying the pathogen will help us to stop it from spreading. Plant Pathogens affect the plant in many like: by utilizing host cell contents for its growth and nutrition and thereby weakening the host due to loss of nutrients, by interfering with the various metabolic physiological process of the plant which may lead to the killing of Basics of Plant Sciences 14 the host plants completely”. A plant pathologist uses standard diagnostic tests in the lab and in the field to help in identifying the pathogen causing a plant disease. Identifying the Cause of Disease The symptoms of disease in infected plants can help us to diagnose which pathogen is responsible for the disease. However, different pathogens can cause similar symptoms. It’s usually necessary to do further diagnostic tests to accurately identify the pathogen causing the disease. The traditional method of identifying a plant disease is by visual examination. Many a time this is possible only after major damage has already been done to the crop. In such cases there will be limited treatment is available or disease management is of no use.
eBook - ePub- Richard P. Oliver, Janna L Beckerman(Authors)
- 2022(Publication Date)
- CAB International(Publisher)
2
Plant Pathology and Plant Pathogens
Key Points
•What is a disease? •A diverse range of organisms causes diseases of plants.•Two types of pathogens dominate, the Oomycota and the Fungi; these are the targets of the great majority of fungicides.•Fungi are more related to animals and oomycetes are more related to plants than either is to the other. This is reflected in the different fungicides that control each group. •Pathogens are divided into biotrophs and necrotrophs and an intermediate class, hemibiotrophs. •Effectors are pathogen molecules that interact with plants and contribute to the disease phenotype. •Biotrophs and necrotrophs have different types of effectors and induce different plant responses.Introduction
Fungicides work by inhibiting the infection processes used by pathogens to cause disease or by enhancing the defensive capabilities of the plant. A very large range of organisms causes disease on plants but first we must define ‘disease’. We can operationally define disease as the ability of a pathogen to reduce the yield and/or the quality of a crop while growing and reproducing on the host plant. Pathogens are defined as organisms that cause disease. They are distinguished from saprobes and symbionts. Saprobes (previously saprophytes) are species that live off dead material and are ecologically limited to that role. Symbionts are organisms that grow on or in the plant and that are beneficial to its growth. This group includes the mycorrhizae, fungi that form close associations with roots and benefit the plant by making phosphate more available, and the rhizobia, bacteria which supply nitrogen to leguminous plants. We are also becoming much more aware of the vast complexity and abundance of microorganisms that associate with plants without causing substantial impacts. The microbiome of the plant, as this group is known, has only recently been studied in detail (Berendsen et al
- Lakshman, H C(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Plant Pathogens are very similar to those that cause disease in humans and animals. Pathogens may infect all types of plant tissues to include leaves, shoots, stems, crowns, roots, tubers, fruit, seeds, and vascular tissue and can cause a wide variety of disease types ranging from root rots and rusts to cankers, blights, and wilts. The Disease Cycle of Infected Plants The development of visual disease symptoms on a plant requires that the pathogen must (a) come into contact with a susceptible host (referred to as inoculation); (b) gain entrance or penetrate the host through either a wound, a natural opening (stomates, lenticels, hydathodes) or via direct penetration of the host; (c) establish itself within the host; (d) grow and reproduce within or on the host; and ultimately, (e) be able to spread to other susceptible plants (referred to as dissemination). Successful pathogens must also be able to survive prolonged periods of unfavorable environmental conditions in the absence of a susceptible plant host. Collectively, these steps are referred to as the disease cycle. If this cycle is disrupted, either naturally or via the concerted efforts of a grower, the disease will be less intense or fail to This ebook is exclusively for this university only. Cannot be resold/distributed. develop. In general, there are five methods used to manage plant diseases. These include use of genetically resistant plants, cultural practices, chemical application, beneficial micro-organisms to suppress or counter the activity of the pathogen (known as biological control), and the use of quarantines and other regulatory practices. Viruses Matthew (1981) defined a virus as “a set of one or more nucleic acid template molecules, normally encased in a protective coat, or coats of protein or lipoprotein, which is able to organize its own replication within suitable host cells.
eBook - PDF- Nwosu, Obasai(Authors)
- 2018(Publication Date)
- Agri Horti Press(Publisher)
It is the more important, therefore, to connote This ebook is exclusively for this university only. Cannot be resold/distributed. 6 Essentials of Plant Pathology whether the term is being used to apply to the disease or to the causal organism. In the case of diseases in which parasitic organisms are a part of the causal complex the diseased plant is commonly referred to as the host. While usage has made this the most widely used term, objection has been raised that it does not imply the actual relation which ordinarily exists between the plant and the pathogen. The term suspect is a newer word coined to apply to the plant which is subject to a given disease brought about by a given causal complex. The above terminology does not always strictly apply in the case of virus diseases. While the inanimate nature of viruses is not accepted in all quarters and practically nothing is known about their mode of increase or reproduction, they have above all in common with pathogenic microorganisms the property of being transmitted from plant to plant to become a part of the causal complex. While several schemes of nomenclature for plant viruses have been proposed, none has been fully accepted as yet. Therefore in current literature the student will find a great diversity among authors in method of reference to a given virus. They are not universal referred to as pathogens, and their disease-producing property is not commonly referred to as pathogenicity, largely because of the doubt that they are living entities. One system known as the Holmes system sets up a scheme of genera and species whereby each described virus is given a binomial. While this system has many admirable features, it is nonconformist in that it uses system set up for living organisms to classify what may well be nonliving organic compounds, which cannot be defined on the bases used in the binomial system for living organisms.
eBook - ePub- Dhia Bouktila, Yosra Habachi(Authors)
- 2021(Publication Date)
- Bentham Science Publishers(Publisher)
These studies are crucial for understanding the mechanistic basis of why a certain pathogen causes disease in one host plant and not in another and also why a certain pathogen race causes disease in one host plant cultivar and not in another. Answering these intriguing questions is a valuable key toward the improvement of methods for controlling plant diseases, especially breeding for cultivar resistance. 1. DEFINITION OF A PLANT DISEASE A plant disease can be defined as a succession of invisible and visible responses of the cells and tissues of a plant, following the attack of a microorganism or the modification of an environmental factor, which causes disruption of the form, function or integrity of the plant. These responses can induce a partial alteration or even the death of the plant or of some of its parts. In the case of parasitic diseases, it is noteworthy that the term disease will exclude plant injuries caused by insects: A plant is diseased when it is continuously affected by a biotic factor, which causes a disorder in its normal structure or activities, showing some outward signs and/or symptoms of disease. The word continuously excludes such things as insect injury. Disease is a term usually reserved for those problems caused by parasites: fungi, bacteria, viruses, mycoplasma, nematodes and parasitic higher (seed) plants. 2. CLASSIFICATION OF PLANT DISEASES Plant diseases are caused by agents that are both infectious (fungi, bacteria, viruses and nematodes) and non-infectious (mineral deficiency, sunburn, etc.). Infectious diseases of plants are caused by living organisms that attack and feed on the plant they infect. The parasitic organism that causes the disease is called a pathogen, and the plant invaded by the pathogen and used as a nutrient source is designated as a host. A supportive environment is of crucial importance for the development of the disease
eBook - PDF- Nicholas, Alex(Authors)
- 2018(Publication Date)
- Agri Horti Press(Publisher)
The study of plant diseases is called plant pathology. Pathology is derived from the two Greek words pathos (suffering, disease) and logos (discourse, study). Plant pathology thus means a study of plant diseases. Disease Development and Transmission Pathogenesis and Saprogenesis Pathogenesis is the stage of disease in which the pathogen is in intimate association with living host tissue. Three fairly distinct stages are involved: 1. Inoculation : transfer of the pathogen to the infection court, or area in which invasion of the plant occurs (the infection court may be the unbroken plant surface, a variety of wounds, or natural openings— e.g., stomates [microscopic pores in leaf surfaces], hydathodes [stomatelike openings that secrete water], or lenticels [small openings in tree bark]) 2. Incubation : the period of time between the arrival of the pathogen in the infection court and the appearance of symptoms 3. Infection : the appearance of disease symptoms accompanied by the establishment and spread of the pathogen. One of the important characteristics of pathogenic organisms, in terms of their ability to infect, is virulence. Many different properties of a pathogen contribute to its ability to spread through and to destroy the tissue. Among these virulence factors are toxins that kill cells, enzymes that destroy cell walls, extracellular polysaccharides that block the passage of fluid through the plant system, and substances that interfere with normal cell growth. Not all pathogenic species are equal in virulence—that is, they do not produce the same amounts of the substances that contribute to the invasion and destruction of plant tissue. Also, not all virulence factors are operative in a particular disease. For example, toxins that kill cells are important in necrotic diseases, and enzymes that destroy cell walls play a significant role in soft rot diseases. This ebook is exclusively for this university only. Cannot be resold/distributed.
eBook - PDF- Shahid, Ahamad(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Chapter 20 Biological Control of Plant Pathogens Amit Kumar Jain 1 , Om Prakash Singh 2 and D. Prasad 3 1 Department of Botany, Janta Vedic College, Baraut (Baghpat), UP 2 Division of Plant Pathology and 3 Division of Nematology Indian Agricultural Research Institute, New Delhi – 110 012 Since the time immemorial, when man started cultivation, he had a little knowledge of plant diseases and adopted control measure time to time, which included cultural practices and use for organic and inorganic chemicals. In recent years, biological control alarmed the scientists to seek an alternative methods, which do not cause pollution and non phototoxic. Biological control methods involve disease control by some biological agents (living micro-or macro-organisms), other than disease causing organisms (the pests) and damaged plants (the host). Biological control is defined as any condition under which or practice where by, survival or activity of a pathogen is reduced through the agency of any other living organisms except man himself with the result that there is reduction in incidence of disease caused by the pathogen. Pathogen causes many diseases on different parts of the plants. An antagonist is an organism which has inhibitory relationships with other organisms. The aim of biological control is the reduction of disease by ( i ) reduction of inoculum of the pathogen through disease survival between crops, ( ii ) reduction of infection of the host by the pathogen and ( iii ) reduction of severity of attack by the pathogen. The Inoculum and Inoculum Potential Inoculum is a portion of infectious material of an individual pathogen that can cause disease when in contact with host. The inoculum potential of a This ebook is exclusively for this university only. Cannot be resold/distributed. fungus as the energy of growth of a fungus available for colonization of a substrate to the colonized.
eBook - PDF- John R. Ruberson(Author)
- 1999(Publication Date)
- CRC Press(Publisher)
Second, the plant must be at the appropriate growth stage, such as seed, seedling, or blooming stages, with immature or mature leaves or fruit, or the plant must be in a senescent stage; pathogens often specialize in Plant Pathogenic Organisms 279 attacking one or more of these organs at the appropriate stage of their devel-opment. Contact of the pathogen with plant parts that it cannot attack, or at a time when susceptible parts such as flowers, leaves, or fruit are absent or too young or too senescent for infection, will not result in disease. Similarly, the pathogen that comes in contact with the plant must, of course, be pathogenic to that kind of plant, but it must also be of a race that can attack the particular plant variety by overcoming its specific genetic resistance. Fur-thermore, the pathogen must arrive at the host plant as, or soon change to, its pathogenic state. For example, fungal pathogens must arrive as active myce-lium, or as spores that will soon germinate to produce mycelium, bacteria must be out of their dormancy, nematodes must arrive as infective juveniles or adults, and so on. Even if all of the above conditions are satisfied, however, little or no dis-ease may be initiated and develop unless certain environmental conditions of temperature and, often, moisture are also satisfied. Plants and their pathogens are active and grow and multiply only within certain ranges of temperatures with minimum, optimum, and maximum temperatures for each of them. Most patho-gens are most active, multiply faster, and cause the most severe disease when the temperature is at or near the optimum for growth of the pathogen, which is also usually close to the optimum of the susceptible host stage. In many cases, however, pathogens invade their hosts and cause more severe disease at tem-peratures which are less than optimum for the pathogen as long as the same temperatures are, comparatively, even less favorable for the development of the host plant's defenses.
eBook - PDF- George Agrios(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
In Plant Pathology (J. G. Horsfall and A. E. D i m o n d, eds.), Vol. I, pp. 349-390. A c a d e m ic Press, N ew York. C H A P T E R 6 How Plants Defend Themselves Against Pathogens E A CH P L A NT species is a f f e c t ed by approximatel y one hundred or more different kinds of pathogens, i n c l u d i ng fungi, bacteria, viruses, parasiti c higher plants, and nematodes. Frequently, a s i n g le p l a nt is attacked by hundreds, thousands , a n d, in the leafspot diseases of l a r ge trees, probably by hundreds of thousands or millions of individuals of a s i n g le kind of pathogen. Yet, although such plants m ay suffer d a m-a ge to a l e s s er or g r e a t er extent, many survive all these attacks a n d, not u n c o m m o n l y, manage to grow well and to produce appreciable yields. That plants become diseased can be readily ascertained by a more or less careful examination of one or a few plants anywhere. A l m o st every p l a nt seems to h a ve at l e a st a few i n f e c t i o ns on its foliage, s o me more p e r h a ps on its s t e ms and fruit a n d, possibly , on its roots. Why d o e s n 't a pathogen, once it has established an i n f e c t i o n, continue to invade and d e s t r oy a host p l a nt entirely A few kinds of pathogens, of course, can, and they do j u st that. B u t, of the thousands of species of p l a nt pathogens, only a b o ut a hundred attack each p l a nt species, and of these all but a few c a u se i n f e c t i o ns that are very localized in area. 105
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