Plant Disease General Characteristics

What is Plant Disease?

In general, a plant is called to be a diseased plant when it is continuously disturbed by the causal agent resulting in an abnormal physiological process that eventually disturbs the plant’s normal growth, structure and function. Plant diseases are classified according to the nature of their causal agent - infectious or non - infectious. The infectious plant disease general characteristics are caused by the pathogens such as bacteria, fungus, virus, mycoplasma, nematodes or parasites. Non - infectious plant diseases are caused by unfavourable growing conditions such as toxic substances in the soil and atmosphere, extreme temperature, disadvantageous relationships between oxygen and moisture and deficiency or excess of minerals.

Characteristics of Healthy Plants

A plant is healthy when it is completely disease-free. They grow stronger and their leaves are always firm. The parts of the plant - shoot, leaves, flowers, fruits all are well grown.

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Classification of Plant Diseases By the Causal Agent

Plant diseases are classified as per their symptoms. However, many diseases produce similar symptoms and signs but are actually caused by different pathogens. They also require different control methods. Hence, the classification of plant diseases as per their symptoms is inadequate. Another reason for this is that the causal agents may induce several symptoms which often intergrade. Instead, classification can be done on the basis of species of the plant affected. The best and most used classification method of plant diseases is based on the causal agent i.e, infectious or non - infectious. 

Non - Infectious Diseases

The non - infectious diseases of plants are generally caused by unfavourable growth conditions. They are not caused by any living organisms and can not be transmitted from one plant to another. Non - infectious diseases are very common but should be assessed carefully and should be removed immediately for the healthy growth of the plants. Examples of non - infectious disease include nutritional deficiencies, sun scorch, salt injury, soil compaction and moisture extremes.

Infectious Diseases

Plants get infected by thousands of species from a very diverse group of organisms. They can be microscopic or macroscopic. These infectious agents or pathogens are grouped as bacteria, virus and viroids, fungi, nematodes and parasites. We will learn about the general characteristics of the diseases caused by the fungi here. Infectious diseases are spread through water, wind, insects, animals and even humans. 

Fungal Diseases in Plants

Almost two-thirds of the infections of the plants are caused by fungi. These infections include leaf curls, needle casts, white & true rusts, smuts, sooty molds, mildew; root, stem, fruit, bud, leaf rots; leaf, flower and fruit spots; wilts; shoot, leaf and bud galls and many more. In its life cycle, one single plant can be attacked by many fungi. 

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General Characteristics of Fungal Infection in Plants

A fungus is a member of a large and diverse group of eukaryotic microorganisms. They have chlorophyll-less cells which have membrane-bound nuclei, mitochondria and rigid cell walls. Fungi have a plantlike vegetative body that consists of microscopic branching. They have thread-like filaments of different lengths known as hyphae, some of which extend in the air and others penetrate the substrate on which these fungi grow. These hyphae are arranged in a network which is called mycelium. It is because of this mass of mycelium that the fungal growth looks cottony. They reproduce by both sexual and asexual methods. They produce spores of various types in large quantities. 

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Signs and Symptoms of Fungal Diseases in Plants

The fungal infection can either reduce the growth of plants due to hypoplasia and atrophy or can induce excessive growth in plants due to hyperplasia and hypertrophy. The symptoms of fungal infection may include leaf spots, scab, rots, blight, anthracnose, damping-off, canker, dieback, clubroot, warts, galls and leaf curls. Sometimes, the fungi that infect the plant produce growth on the plant parts that appears as a mass of mycelium and looks like cotton. This is a sign of infection. 

FAQs (Frequently Asked Questions)

1. What is Hypertrophy in Plants?

Ans - Hypertrophy in plants is a situation in which there is excessive growth of plants due to the enlargement of individual cells. This results in the overdevelopment of the plant parts or the plant. They could also cause enlargement of the stem, roots, leaves or fruits. 

2. How are Fungal Infections in Plants Transmitted?

Ans - The fungal infections in plants are transmitted through the spores. The spores are carried and disseminated by the water, wind, soil, insects, birds or the residues of the plant itself. The fungal cells present in the dead part of the plant or in the dead plant can also transmit infections if the fungal cells come in contact with the susceptible host.

3. How Can We Control Fungal Infections?

Ans - The basic control measures for fungal infections include:

  • Using disease-free seeds

  • Propagating stock

  • Crop rotation

  • Development and use of resistant plant varieties.

  • Destruction of plants that may spread the infection.

  • Use of chemical and biological fungicides.

4. Name Some Fungal Diseases of Plants.

Ans - Some fungal diseases of plants are - the late blight of potato, black stem rust of wheat, coffee rust, corn smut, loose smut, downy mildew, apple scab, black spot of rose, brown rot, fusarium wilt of tomato, and wilts of vegetables, flowers and some trees.