Plant pathology is the study of plant diseases. These maladies could be a result of various stresses: biotic or abiotic. The biotic agents or plant pathogens infect host plants for food, shelter, and multiplication. As a result, plants get sick.
Woman checking plants for diseases. Image Credit: Chutima Chaochaiya/Shutterstock.com
Therefore, plant pathology tries to increase our knowledge about plant diseases. At the same time, plant pathology tries to develop methods and materials through which plant diseases can be avoided.
Plants can get sick too. And the sickness of plants could be of biotic (living organisms) or abiotic (non-living) nature. The biotic agents are the major limiting factor in crop plant yield. These biotic or microbial communities attack plants to steal nutrients from them. Not only do these biological entities steal nutrients from plants but also rely on them for their multiplication. Such interactions of microbial communities with crop plants lead to disease development. And the science which deals with the study of plant-microbe interactions is "plant pathology."
Plant pathology is the application of knowledge of plants and their microbes for the management of plant diseases. Diseases of crop plants put food security and safety at risk. In terms of plant pathology, "a disease is a deviation of a plant from its normal physiology due to harmful agents (microbial or environmental).
Plant Pathogens
Plant diseases are the result of constant interference of biotic and abiotic factors. The biotic factors are microbial entities or plant pathogens that invade plants to feed off the nutrients. Fungi, bacteria, viruses, phytoplasmas, fungal-like organisms (oomycetes), viroids, and nematodes are examples of phytopathogens.
Fungal pathogens constitute major plant pathogens. Almost more than 65% of plant infections are due to fungi. Fungi are multicellular and heterothallic organisms and are responsible for diseases of economic importance. For example, rust disease in wheat, blast disease in rice, and gray mold disease of berries are maladies of agricultural importance. These diseases not only affect the quality of crop yield but, also the expenditure of farmers.
Similar to fungi, Fungal-like organisms (FLO) or oomycetes are deadly pathogens of crops of economic importance. These pathogens overwinter on dead and damaged plant parts and cause tremendous losses. One such example is the famous Irish potato famine which is caused by Phytophthora infestans. This disease causes the death of one million people and the migration of two and a half million in the time period of six years.
In addition to fungi, bacteria, viruses, and phytoplasmas infect plants too. These pathogens hijack plant physiology and utilize cell organelles for their own propagation. The alterations in plant physiology led to changed phenotype. For example, interference of viruses with chloroplast of infected cells causes chlorosis (lacking chlorophyll). The other symptoms of pathogenic infections are water-soaked lesions on leaves and fruits, malformed seeds and fruits, stunted growth, and false growth of flowers. Such microbial infections of agronomic crops cause 30-40% yield losses annually.
Therefore, the study of plant diseases is of great importance. Because the proper understanding of plant-pathogen interactions is helpful for wise disease management approaches. Due to this, there would be enough food for the human population.
A fundamental concept in plant pathology is the disease triangle. The disease triangle consists of three factors—a susceptible host plant, optimum environment, and a virulent pathogen. Each side of the triangle represents a factor. And the simultaneous presence of these factors ensures disease development. So, for an infection to occur, it requires a series of events. These events are known as the disease cycle. It includes the dispersal of pathogen spores, penetration of the host, colonization of the host, reproduction, movement inside host cells, and survival of the pathogen in diseased plant parts in the absence of a host plant.
History of Plant Pathology
Ever since the human cultivated crops, most of the crop yield losses to diseases. Plant diseases caused leaves to wilt, fruits to rot, and shoots to die, thereby forcing humans to search for enough and healthy food of some kind to satisfy their hunger. This quest leads to many inventions in plant pathology to cure plant diseases. In the medieval period, Greeks believed that 'plant diseases were the manifestations of the wrath of God and, therefore, that avoidance or control of the disease depended on people doing things that would please that same superpower.'
In 1800, the potato crop was introduced in Europe from South America, was a well-established crop in Ireland. It was grown over a wide area with promising yield (free from diseases or any other problem). But in the early 1840s, most of the growing season of potato in Ireland was favorable for blight pathogen (Phytophthora infestans) spore germination. And the severity of the potato blight disease leads to no potato yield, resulting in farmer's loss indirectly. This disease was responsible for the death of millions of people in Ireland with the migration of 2.5 million across England. And this disease in the history of plant pathology is known as the famous Irish potato famine.
Another example of famous famine in the history of plant pathology is the Bengal famine in 1943. The causal agent of this disease was Helminthosporium oryzae. The fungal disease severity leads to intense losses with the death of millions. The severity of these diseases posed serious concerns about food security and safety. That is why plant pathology is of prime importance in agriculture as other major subjects (soil sciences, agronomy, and plant breeding).
Sources:
- Nelson, R., 2020. International plant pathology: past and future contributions to global food security. Phytopathology, 110(2), pp.245-253.https://doi.org/10.1094/PHYTO-08-19-0300-IA
- Timmerman, A.D., Sivits, S.A., Jackson, T.A., Giesler, L.J., Adesemoye, A.O., Harveson, R.M., Wegulo, S.N. and Broderick, K.C., 2018. Understanding Fungicide Resistance. University of Nebraska-Lincoln, Extension.
- Franc, G.D., 1998. An introduction to plant pathology and plant disease management. Laramie: University of Wyoming, Cooperative Extension Service.
Further Reading