The susceptibility and disease severity of a plant is determined by several factors including environmental conditions, rootstock, vector activity, and the type of pathogen (Weintraub and Jones 2010, Guerra and Steenwerth 2012, Andrade et al. 2013).
What factors affect the severity of plant disease?
Simply, plant disease will not occur if there is no viable pathogen, or no susceptible host plant, or the environmental conditions are not favorable. The severity of disease depends on the favorable level of each factor. How susceptible is the plant? How virulent is the pathogen?
What is the pathogenesis of plant disease?
This occurs when the pathogen invades the plant tissue and establishes a parasitic relationship between itself and the plant. Viruses, bacteria, and phytoplasmas are not able to actively penetrate or enter plant host tissues.
What are the different types of plant diseases?
Plant diseases can be broadly classified according to the nature of their primary causal agent, either infectious or noninfectious. Infectious plant diseases are caused by a pathogenic organism such as a fungus, bacterium, mycoplasma, virus, viroid, nematode, or parasitic flowering plant. An infectious agent is capable of reproducing within ...
What factors affect disease incidence and severity?
Environmental conditions: There are numerous variables in the environment that influence disease incidence and severity including temperature, sunlight, moisture, relative humidity, and time of year. Pathogens are typically restricted to an area based on the conditions of the macroclimate.
What is plant disease?
What is the study of plant diseases called?
Why are noninfectious causal agents not transmissible?
What is the appearance of disease symptoms accompanied by the establishment and spread of the pathogen?
What is the term for the part of the life cycle of a pathogen?
Do all pathogenic species have the same virulence?
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What are the factors that causes plant diseases?
Important environmental factors that may affect development of plant diseases and determine whether they become epiphytotic include temperature, relative humidity, soil moisture, soil pH, soil type, and soil fertility.
What are the three types of plant diseases?
For now, we'll look at diseases caused by the three main pathogenic microbes: fungus, bacteria and virus.
What are the 3 factors needed in order for a plant disease to occur?
Plant diseases– their occurrence and severity– result from the impact of three factors: the host plant, the pathogen, and the environmental conditions. This is represented with the disease triangle.
What are the three major factors involved in the development of plant diseases?
Three major factors contribute to the development of a plant disease: a susceptible host, a virulent pathogen, and a favorable environment. A plant disease results when these three factors occur simultaneously (Figure 1).
SIGNS, SYMPTOMS AND EFFECTS OF PLANT DISEASES PLANT DISEASES CAUSES OF ...
1 SIGNS, SYMPTOMS AND EFFECTS OF PLANT DISEASES PLANT DISEASES A plant disease is any abnormal condition that alters the appearance or function of a plant. CAUSES OF PLANT DISEASES Plant diseases are caused by both infectious (fungi, bacteria, viruses and
What is plant disease?
In general, a plant becomes diseased when it is continuously disturbed by some causal agent that results in an abnormal physiological process that disrupts the plant’s normal structure, growth, function, or other activities . This interference with one or more of a plant’s essential physiological or biochemical systems ...
What is the study of plant diseases called?
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.
Why are noninfectious causal agents not transmissible?
Because noninfectious causal agents are not organisms capable of reproducing within a host, they are not transmissible. In nature, plants may be affected by more than one disease-causing agent at a time. A plant that must contend with a nutrient deficiency or an imbalance between soil moisture and oxygen is often more susceptible ...
What is the appearance of disease symptoms accompanied by the establishment and spread of the pathogen?
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.
What is the term for the part of the life cycle of a pathogen?
Many pathogens, especially among the bacteria and fungi, spend part of their life cycle as pathogens and the remainder as saprotrophs. Saprogenesis is the part of the pathogen’s life cycle when it is not in vital association with living host tissue and either continues to grow in dead host tissue or becomes dormant.
Do all pathogenic species have the same virulence?
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.
What are the factors that determine disease development?
Over the years, pathologists have come to learn that disease development in a plant population is determined primarily by the interactions among three major factors. These factors are: 1 The Susceptible Host 2 A Virulent Pathogen 3 A Favourable Condition
What are the factors that affect the severity of a disease?
These variables include environmental condition, genetic diversity, biology and life cycle of the host plant and pathogen etc.
How do pathogens form parasitic relationships between host and pathogen?
After invading the host tissue the pathogens form parasitic relationships between the host plant and pathogen by absorbing nutrients from the host tissue and cause infection in the affected area of the plant body . This is the stage where the symptoms of a disease are visible.
What are the variables that affect the incidence and severity of disease?
There are many variables in the environment that affect the incident and severity of disease such as temperature, moisture, rainfall, sunlight, seasons etc. Generally, a pathogen remains restricted in a certain area based on the micro-climate.
How do pathogens and host affect the occurrence of a disease?
Likewise, a host may only be affected by a disease in a particular stage of the life cycle .
How does a disease cycle occur?
There are several stages of a disease cycle through which a disease eventually develops in the host plant.
What happens if the host is less susceptible?
So conceptually, this triangle dictates that if either the host is less susceptible, the pathogen is less virulent or the environment is less favorable, the disease will either occur at a reduced level or it will not occur at all.
What are the factors that influence disease incidence?
Environmental conditions: There are numerous variables in the environment that influence disease incidence and severity including temperature, sunlight, moisture, relative humidity, and time of year.
What are plant pathogens?
They are called plant pathogens when they infect plants. For the purposes of discussing plant pathology, only plant disease pathogens will be discussed. Pathogens can spread from plant to plant and may infect all types of plant tissue including leaves, shoots, stems, crowns, roots, tubers, fruit, seeds and vascular tissues (Figure 62). Figure 62.
What pathogens follow the red arrows?
Polycyclic pathogens follow the red arrows for the majority of the season and the black arrows at the end of the season. In order for a disease to develop, a pathogen must be present and successfully invade plant host tissues and cells.
What is a susceptible host plant?
a susceptible host plant. a virulent pathogen. a favorable environment. When these three components are present at the same time, a disease (shaded region) will occur if a susceptible host plant is in intimate association with a virulent plant pathogen under favorable environmental conditions.
What are the components of a plant system?
Three components are absolutely necessary in order for a disease to occur in any plant system. The three components are: 1 a susceptible host plant 2 a virulent pathogen 3 a favorable environment
What are the different types of pathogens?
Types of Plant Pathogens. Plant pathogens are very similar to those that cause disease in humans and animals. Fungi, fungal-like organisms, bacteria, phytoplasmas, viruses, viroids, nematodes and parasitic higher plants are all plant pathogens.
What are some examples of abiotic diseases?
Examples of abiotic diseases include nutritional deficiencies, soil compaction, salt injury, ice, ...
What happens if one of the three factors is missing?
If any one of the three factors is missing, the triangle is not complete, no disease will occur. Simply, plant disease will not occur if there is no viable pathogen, or no susceptible host plant, or the environmental conditions are not favorable. The severity of disease depends on the favorable level of each factor.
What is the disease triangle?
The Disease Triangle: Fundamental Concept for Disease Management. Plant diseases– their occurrence and severity– result from the impact of three factors: the host plant, the pathogen, and the environmental conditions. This is represented with the disease triangle. If any one of the three factors is missing, the triangle is not complete, ...
Why do humans factor into the disease triangle?
Humans factor into the disease triangle because the influence of human activity on disease is pervasive in agriculture and , perhaps to a lesser degree, in lower input systems such as forestry and range management .
What happens to the pyramid if the pathogen is incapable of infecting its host without a vector?
However, if the pathogen is incapable of infecting its host without a vector, the pyramid fails to show adequately the intermediary nature of the vector in the pathogen-plant relationship by drawing a direct connection and circumventing the vector.
What is the disease triangle?
Used in this sense, the disease triangle illustrates the continuum of host reaction from complete susceptibility to immunity.
Is the disease triangle an educational paradigm?
The disease triangle will almost certainly be an educational paradigm in the discipline of plant pathology for many years to come. One hopes the discussion here will enhance the educational value of the triangle and its variants.
What is forecasting system?
Forecasting systems are based on assumptions about the pathogen's interactions with the host and environment, the disease triangle. The objective is to accurately predict when the three factors – host, environment, and pathogen – all interact in such a fashion that disease can occur and cause economic losses.
What is a good disease forecasting system?
Good disease forecasting systems must be reliable, simple, cost-effective and applicable to many diseases. As such they are normally only designed for diseases that are irregular enough to warrant a prediction system, rather than diseases that occur every year for which regular treatment should be employed.
Why is disease forecasting important?
Future developments. In the future, disease forecasting systems may become more useful as computing power increases and the amount of data that is available to plant pathologists to construct models increases. Good forecasting systems also may become increasingly important with climate change.
How do environmental conditions affect the presence of pathogens?
Environmental conditions may determine the presence of the pathogen in a particular season through their effects on processes such as overwintering. Environmental conditions also affect the ability of the pathogen to cause disease, e.g. a minimum leaf wetness duration is required for grey leaf spot of corn to occur.
What is the plant disease triangle?
The plant disease triangle represents the factors necessary for disease to occur. Plant disease forecasting is a management system used to predict the occurrence or change in severity of plant diseases. At the field scale, these systems are used by growers to make economic decisions about disease treatments for control.
What is the factor that controls whether a disease develops or not?
In most cases the host can be suitably defined as resistant or susceptible, and the presence of the pathogen may often be reasonably ascertained based on previous cropping history or perhaps survey data. The environment is usually the factor that controls whether disease develops or not.
What is plant disease?
In general, a plant becomes diseased when it is continuously disturbed by some causal agent that results in an abnormal physiological process that disrupts the plant’s normal structure, growth, function, or other activities . This interference with one or more of a plant’s essential physiological or biochemical systems ...
What is the study of plant diseases called?
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.
Why are noninfectious causal agents not transmissible?
Because noninfectious causal agents are not organisms capable of reproducing within a host, they are not transmissible. In nature, plants may be affected by more than one disease-causing agent at a time. A plant that must contend with a nutrient deficiency or an imbalance between soil moisture and oxygen is often more susceptible ...
What is the appearance of disease symptoms accompanied by the establishment and spread of the pathogen?
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.
What is the term for the part of the life cycle of a pathogen?
Many pathogens, especially among the bacteria and fungi, spend part of their life cycle as pathogens and the remainder as saprotrophs. Saprogenesis is the part of the pathogen’s life cycle when it is not in vital association with living host tissue and either continues to grow in dead host tissue or becomes dormant.
Do all pathogenic species have the same virulence?
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.