Disease-Causing Plant Pathogens and Their Symptoms (Part-2)

Table of Contents

Introduction

Besides the predominant effects of bacteria, fungi, and viruses, and viroids, the other microbes that affect the health of the plants are nematodes, protozoans, and parasitic plants as well.

The first step to protect the plants from getting infected is to take control measures that mainly depend on identifying diseases and their causal agents. Thus, the ability to diagnose diseases is an essential skill that plant hobbyists and small and large-scale cultivators should excel at.

In the previous part of this article, the symptoms and causes of certain plants diseases caused by fungi, bacteria, and viruses have been discussed. Furthermore, their diagnostic techniques have also been mentioned.

In this article, the diseases caused by nematodes, protozoans, and parasitic plants, and their diagnosis are discussed.

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Six Most Common Disease-Causing Pathogens and Their Symptoms (in continuation to part-1)

• Nematodes

These are tiny roundworms that inhabit soil and feed on plant roots. Nematodes damage a wide range of hosts, causing economic losses to everything from turf grass to peach trees. They have a needle-like mouth, called a stylet, which punctures plant cells to obtain food.

Nematodes mainly interfere with the root uptake of water and nutrients. The symptoms of the diseases caused by nematodes include small leaves, wilting, poor growth, and off-color foliage. You may also observe stunted root system, root galls, root knots, and dark lesions on roots.

Some nematodes directly enter the leaves and cause yellowing of leaves and necrosis. Their symptoms appear only at the infected site. In the right environments, like medium temperature and high humidity, nematode infections on plants are widely distributed.

Damages caused to plants by nematodes is based on four factors, which include:

• The species of nematodes affect plants.
• The population level of nematodes.
• The specific species of infected plants.
• The growing conditions, such as moisture and nutrients.

• Protozoans

They are transmitted as zoospores and can survive in the soil for many years and they can also be a vector to transmit viruses in plants. They come in contact with plant roots and produce plasmodium that invades the roots and causes diseases. An example of plant disease-causing protozoans is Phytomonas.

• Parasitic Plants

Plants that attach to or in some other plants and derive their nutrients from the host vascular system, without benefiting them are called parasitic plants. This weakens the plants and costs them their health. A few examples of parasitic plants that attach them to the plants’ surface are dodder, mistletoe, witchweed, and broomrape.

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Prospective Solution to Protect Plant against Diseases

As earlier said, early diagnosis of the diseases is a key step in taking control over these diseases from spreading and severely affecting the plants. It also leads to an increase in the plant yield and quality of the crops. Some of the diagnostic methods of plants diseases are explained below:

By several examination approaches:

• By visually examining plants.
• By using serological methods, such as dot-blot hybridization, enzyme immunoassay, immunoblotting, electron microscopy, and immunochromatography.
• DNA-based methods like polymerase chain reaction (PCR) techniques, including multiplex PCR, real-time PCR, and nested PCR, and fluorescence in situ hybridization.
• RNA-based methods, such as the AmpliDet RNA real-time diagnostic system, the isothermal amplification of nucleic acids, and reverse-transcription PCR.

Integrated Pest Management System

Integrated pest management (IPM) addresses the long-term prevention of pests and their damage by combining various methods such as biological control, habitat manipulation, cultural practices, and resistant varieties.

It involves monitoring the field, landscape, forest, or building to identify the type of pest affecting crops, their level, and damages they cause. All this combined information helps determine and curate possible control measures, select effective management methods, and the best possible time for the implementation of the method.

For example, if the level of pest is dangerous, then mechanical and biological methods are applied (also often chemical controls). The IPM techniques increase yields by 10–30%, have a longer duration of effect, and reduce climate risks.

Seed Reserves

Seeds are a reservoir of many phytopathogens. They can have infections on the surface or inside seeds. For this reason, the examination of seeds before sowing is an essential step in cultivating plants. The solution is either to use pathogen-free seeds or to treat seeds before sowing.

To treat fungal infections in seeds, contact fungicides are used to destroy fungi on the seed surface, and translaminar fungicides that penetrate inside seeds to clear out the inside pathogens.

Besides, several other treatments to prevent pathogen infection in seeds are also developed including physical treatment (mechanical and thermal treatment, ultrasonic and ultraviolet light exposure), biological control agents, and treatment with natural compounds.

Chemical Control

Chemical control includes the methods that involve the use of pesticides, fungicides, or any chemical substances to control infectious diseases in plants. It’s generally used with other approaches to enhance its effectiveness and long-term control.

Biological control

As part of biological control, antagonist strains and antibiotic producers, bacteriophages, insects for the control of weeds, and parasitic insects for the control of insects are employed. The primary goal is to control pests by using natural enemies such as predators, parasites, pathogens, and competitors.

Other than the above-mentioned techniques plant breeding and bioengineering methods are used to engineer plants or create such varieties of plants that are resistant to viruses, bacteria, or other deadly pathogens.

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Happy Culturing!

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