Fundamentals of Plant Pathology

Plant Pathology is defined as the study of the organisms and environmental conditions that cause diseases in plants, the mechanisms by which this occurs, the interactions between these causal agents and the plant, and the methods of managing or controlling plant disease. It also draws on knowledge from other scientific fields such as mycology, microbiology, virology, biochemistry, bio-informatics, etc. Plant diseases are caused by biotic agents like fungi, bacteria, actinomycets, Mycoplasma, viruses, nematodes, and flowering parasites or by abiotic like unfavorable environmental conditions or nutritional deficiencies. Plant diseases are known from times preceding the earliest writings. Fossil evidence indicates that plants were affected by disease 250 million years ago. Loss of crops from plant diseases may result in hunger and starvation, especially in less developed countries where access to disease-control methods is limited and annual losses of 30 to 50 percent are common for major crops. In some years, losses are much greater, producing catastrophic results for those who depend on the crop for food. Major disease outbreaks among food crops have led to famines and mass migrations throughout history. Losses from plant diseases also can have a significant economic impact, causing a reduction in income for crop producers and distributors and higher prices for consumers. Plant diseases are a normal part of nature and one of many ecological factors that help keep the hundreds of thousands of living plants and animals in balance with one another. Plant cells contain special signaling pathways that enhance their defenses against insects, animals, and pathogens. 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 or on its host and spreading from one susceptible host to another. Noninfectious plant diseases are caused by unfavorable growing conditions, including extremes of temperature, disadvantageous relationships between moisture and oxygen, toxic substances in the soil or atmosphere, and an excess or deficiency of an essential mineral. Because noninfectious causal agents are not organisms capable of reproducing within a host, they are not transmissible.