Plant pathology

Plant pathologyorphytopathologyis the scientific study ofplant diseasescaused bypathogens(infectious organisms) and environmental conditions (physiological factors).^[1]Plant pathology involves the study of pathogen identification, diseaseetiology, disease cycles, economic impact,plant disease epidemiology,plant disease resistance, how plant diseases affect humans and animals,pathosystemgenetics, and management of plant diseases.

Plant pathogens, organisms that cause infectiousplant diseases, includefungi,oomycetes,bacteria,viruses,viroids,virus-like organisms,phytoplasmas,protozoa,nematodesandparasitic plants.^[2]In most plantpathosystems,virulencedepends onhydrolasesand enzymes that degrade thecell wall. The vast majority of these act onpectins(for example,pectinesterase,pectate lyase, andpectinases). For microbes, the cell wallpolysaccharidesare both a food source and a barrier to be overcome. Many pathogens grow opportunistically when the host breaks down its own cell walls, most often duringfruit ripening.^[3]Unlike human and animal pathology, plant pathology usually focuses on a single causal organism; however, some plant diseases have been shown to be interactions between multiple pathogens.^[4]

To colonize a plant, pathogens have specificpathogenicity factors, of five main types: uses of cell wall–degrading enzymes,toxins, effector proteins,phytohormones, andexopolysaccharides.

• Cell wall-degrading enzymes: These are used to break down the plantcell wallin order to release the nutrients inside and include esterases, glycosyl hydrolases, lyases and oxidoreductases.^[5]
• Toxins: These can be non-host-specific, which damage all plants, or host-specific, which cause damage only on a host plant.
• Effector proteins: These can be secreted by pathogens such as bacteria, fungi, and oomycetes^[6][7]into the extracellular environment or directly into the host cell, often via theType three secretion system. Some effectors are known to suppress host defense processes. This can include reducing the plant's internal signaling mechanisms or reduction of phytochemicals production.^[8]
• Phytohormonesare chemicals used by plants for signaling; pathogens can produce these to modify plant growth to their own advantage.
• Exopolysaccharidesare mostly small chains of sugars that help pathogens to adhere to a plant's surface, enabling them to begin the process of infection.

Some abiotic disorders can be confused with pathogen-induced disorders. Abiotic causes include natural processes such asdrought,frost,snowandhail;floodingand poor drainage;nutrient deficiency; deposition of mineral salts such assodium chlorideandgypsum;windburnand breakage by storms; andwildfires.^[9]

Epidemiology is the study of factors affecting the outbreak and spread of infectious diseases.^[10]

A disease triangle describes the basic factors required for plant diseases. These are the host plant, the pathogen, and the environment. Any one of these can be modified to control a disease.^[11]

Plant disease resistance is the ability of a plant to prevent and terminate infections from plant pathogens. Structures that help plants prevent pathogens from entering are the cuticular layer, cell walls, and stomata guard cells. Once pathogens have overcome these barriers, plant receptors initiate signaling pathways to create molecules to compete against the foreign molecules. These pathways are influenced and triggered by genes within the host plant and can manipulated by genetic breeding to create resistant varieties.^[12]

Ancient methods of leaf examination and breaking open plant material by hand are now augmented by newer technologies. These includemolecular pathologyassays such aspolymerase chain reaction(PCR),RT-PCRandloop-mediated isothermal amplification(LAMP).^[13]Although PCR can detect multiple molecular targets in a single solution there are limits.^[13]Bertolini et al. 2001, Ito et al. 2002, and Ragozzino et al. 2004 developed PCR methods for multiplexing six or seven plant pathogen molecular products and Persson et al. 2005 for multiplexing four with RT-PCR.^[13]More extensivemolecular diagnosisrequiresPCR arrays.^[13]The primary detection method used worldwide isenzyme linked immunosorbent assay.^[14]

Crop rotationis a traditional and sometimes effective means of preventing a parasitic population from becoming well-established. For example, protection against infection byAgrobacterium tumefaciens, which causes gall diseases in many plants, by dipping cuttings in suspensions ofAgrobacterium radiobacterbefore inserting them in the ground to take root.^[15]

Plant pathology has developed from antiquity, starting withTheophrastusin the ancient era, but scientific study began in theEarly Modernperiod with the invention of themicroscope, and developed in the 19th century.^[16]

• George Washington Carver
• Anton de Bary
• Erwin Frink Smith
• Agnes Robertson Arber