Complete Glossary and Explanations of Specialized Terms in Plant Diseases

1. Non-infectious plant diseases Caused by unsuitable growth conditions or the influence of harmful substances in the environment, without infection by other organisms, they cannot be transmitted to one another, so they are generally called non-contagious diseases. 2. Infectious plant diseases As opposed to non-infectious diseases, diseases in which plants are parasitized by pathogens and which have the ability to spread; they may also be called parasitic diseases or contagious diseases. 3. Pathogen The collective term for organisms that cause plant diseases; those currently known mainly include fungi, bacteria (mycoplasma-like organisms), viruses (viroids), nematodes and parasitic seed plants. In addition, a small number of actinomycetes and algae can also infect plants, such as the scab actinomycete (Actinomyces scabies) that causes potato scab and red rust algae (Cephaleuros virescens) that cause algal leaf spot on tea trees and many other evergreen trees. Most plant diseases are caused by fungi; hyphae are the most common vegetative structures of fungi; the sexual reproductive stage can usually produce spores, which are the main primary infection sources of plant diseases. 4. Parasitism The biological characteristic whereby a parasite must obtain living substances (water, nutrients and other substances) from the cells and tissues of a living host in order to grow and develop. It can be divided into obligate parasitism and facultative parasitism. Obligate parasitism is when a parasite must parasitize a living host under natural conditions in order to grow and develop; facultative parasitism is when a parasite can both live parasitically on a living host and live saprophytically on dead matter or organic matter. The vast majority of plant pathogenic fungi and all plant pathogenic bacteria are facultative parasites. 5. Pathogenicity The characteristic whereby a pathogen infects a host plant and causes disease. 6. Disease symptoms Discoloration, necrosis, rot, wilting, malformation. Discoloration: refers to a change in the original color of a diseased plant; it is the most common and earliest-appearing type of symptom. Discoloration is usually most obvious in the early stages of viral diseases, and mainly manifests in many types, such as mosaic, yellowing and streak. Viral diseases of plants and some non-infectious diseases (especially nutrient deficiency symptoms) often show discoloration symptoms. Necrosis: local or extensive death of diseased tissue. Commonly seen forms include: leaf spot, blight spot, leaf blight, twig blight, canker, damping-off, shot hole, and so on. Rot: diseased tissue is acted upon by various enzymes and toxins of the pathogen, pectin and cell walls are decomposed, cells are destroyed, and the original tissue structure and external form disintegrate. It can mainly be divided into dry rot and wet rot (soft rot). Wilting: the vascular bundle tissue of the root or stem of diseased tissue becomes necrotic and loses its transport function, especially when the vessel system is severely damaged, so that water from the roots cannot be transported upward, causing the aboveground branches and leaves to wilt. Malformation: abnormal growth shown by local plant tissue under the stimulation of hormone-like substances from the pathogen, generally manifesting as hyperplasia, hypertrophy and hypoplasia. 7. Infection cycle of disease The process from the onset of disease in the previous growing season to the continuation of disease in the next growing season. It consists of several parts, including primary infection by the pathogen, re-infection, overwintering (or oversummering) and transmission. Primary infection: the initial infection caused by pathogens that have overwintered or oversummered after the plant begins to grow is called primary infection. Re-infection Plants that have been subjected to primary infection can again produce spores or other propagules, which after transmission cause re-infection; most plant diseases may undergo multiple infections in one season. 8. Transmission of pathogens The process by which pathogen inoculum spreads outward from the infection source. Most pathogens can be transmitted by means of airflow, water flow, vectors (insects, mites, fungi), soil and human activity. 9. Degree of disease occurrence This includes incidence rate and severity. Incidence rate generally refers to the percentage of diseased fields, plants or organs, while severity refers to the degree of damage to plants or organs in a field. 10. Plant disease control Using the principles of systems control theory, selecting the optimal disease management methods, and keeping the occurrence of plant diseases below the economic damage level. At present, for disease management, the main approach adopted is prevention first, integrated control, and advocacy of ecological management. The main means that can be adopted to control the occurrence and spread of diseases include plant quarantine (regulatory control), agricultural control, disease-resistant breeding, chemical control and biological control. (Kuaixue Shiqing)