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Plant pathology is the scientific study of diseases in plants caused by pathogens and environmental conditions. Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
Texas root rot is a disease that is fairly common in Mexico and the southwestern United States resulting in sudden wilt and death of affected plants, usually during the warmer months. It is caused by a soil-borne fungus named Phymatotrichopsis omnivora that attacks the roots of susceptible plants. It was first discovered in 1888 by Pammel and later named by Duggar in 1916.
The cereal grain wheat is subject to numerous wheat diseases, including bacterial, viral and fungal diseases, as well as parasitic infestations.
Take-all is a plant disease affecting the roots of grass and cereal plants in temperate climates caused by the fungus Gaeumannomyces tritici. All varieties of wheat and barley are susceptible. It is an important disease in winter wheat in Western Europe particularly, and is favoured by conditions of intensive production and monoculture.
Rhizoctonia solani is a species of fungus in the order Cantharellales. Basidiocarps are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name Rhizoctonia solani is currently applied to a complex of related species that await further research. In its wide sense, Rhizoctonia solani is a facultative plant pathogen with a wide host range and worldwide distribution. It causes various plant diseases such as root rot, damping off, and wire stem. It can also form mycorrhizal associations with orchids.
Powdery scab is a disease of potato tubers. It is caused by the cercozoan Spongospora subterranea f. sp. subterranea and is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. These can eventually rupture within the tuber periderm. The powdery pustules contain resting spores that release anisokont zoospores to infect the root hairs of potatoes or tomatoes. Powdery scab is a cosmetic defect on tubers, which can result in the rejection of these potatoes. Potatoes which have been infected can be peeled to remove the infected skin and the remaining inside of the potato can be cooked and eaten.
Thielaviopsis basicola is the plant-pathogen fungus responsible for black root rot disease. This particular disease has a large host range, affecting woody ornamentals, herbaceous ornamentals, agronomic crops, and even vegetable crops. Examples of susceptible hosts include petunia, pansy, poinsettia, tobacco, cotton, carrot, lettuce, tomato, and others. Symptoms of this disease resemble nutrient deficiency but are truly a result of the decaying root systems of plants. Common symptoms include chlorotic lower foliage, yellowing of plant, stunting or wilting, and black lesions along the roots. The lesions along the roots may appear red at first, getting darker and turning black as the disease progresses. Black root lesions that begin in the middle of a root can also spread further along the roots in either direction. Due to the nature of the pathogen, the disease can easily be identified by the black lesions along the roots, especially when compared to healthy roots. The black lesions that appear along the roots are a result of the formation of chlamydospores, resting spores of the fungus that contribute to its pathogenicity. The chlamydospores are a dark brown-black color and cause the "discoloration" of the roots when they are produced in large amounts.
Soil-borne wheat mosaic virus is a rod-shaped plant pathogen that can cause severe stunting and mosaic in susceptible wheat, barley and rye cultivars. The disease has often been misdiagnosed as a nutritional problem, but this has actually allowed in part for the fortuitous visual selection by breeding programs of resistant genotypes. Soil-borne wheat mosaic virus is part of the genus Furovirus. Members of this genus are characterized by rigid rod-shaped particles and positive sense RNA genomes consisting of two molecules that are packaged into separate particles that code for either replication, mobility, structure or defense against the host. The virus is spread by a fungal-like protist, Polymyxa graminis, whose asexual secondary and sexual primary cycles help the virus spread. The disease produces secondary symptoms from the root cell infection. The disease is a serious contributor to loss in crop yield.
The laimosphere is the microbiologically enriched zone of soil that surrounds below-ground portions of plant stems; the laimosphere is analogous to the rhizosphere and spermosphere. The combining form laim- from laimos denotes a connecting organ (neck) while -sphere indicates a zone of influence. Topographically, the laimosphere includes the soil around any portion of subterranean plant organs other than roots where exuded nutrients stimulate microbial activities. Subterranean plant organs with a laimosphere include hypocotyls, epicotyls, stems, stolons, corms, bulbs, and leaves. Propagules of soil-borne plant pathogens, whose germination is stimulated by a plant exudates in the laimosphere, can initiate hypocotyl and stem rots leading to "damping-off". Pathogens commonly found to cause such diseases are species of Fusarium, Phoma, Phytophthora, Pythium, Rhizoctonia and Sclerotinia.
Fusarium oxysporum f. sp. cubensePronunciation (help·info) is a fungal plant pathogen that causes Panama disease of banana, also known as fusarium wilt of banana. The fungi and the related disease are responsible for widespread pressure on banana growing regions, destroying the economic viability of several commercially important banana varieties.
Harold Henry Flor known as H. H. Flor (1900–1991) was a plant pathologist famous for proposing the gene for gene hypothesis of plant-pathogen genetic interaction whilst working on rust of flax.
Beet vascular necrosis and rot is a soft rot disease caused by the bacterium Pectobacterium carotovorum subsp. betavasculorum, which has also been known as Pectobacterium betavasculorum and Erwinia carotovora subsp. betavasculorum. It was classified in the genus Erwinia until genetic evidence suggested that it belongs to its own group; however, the name Erwinia is still in use. As such, the disease is sometimes called Erwinia rot today. It is a very destructive disease that has been reported across the United States as well as in Egypt. Symptoms include wilting and black streaks on the leaves and petioles. It is usually not fatal to the plant, but in severe cases the beets will become hollowed and unmarketable. The bacteria is a generalist species which rots beets and other plants by secreting digestive enzymes that break down the cell wall and parenchyma tissues. The bacteria thrive in warm and wet conditions, but cannot survive long in fallow soil. However, it is able to persist for long periods of time in the rhizosphere of weeds and non-host crops. While it is difficult to eradicate, there are cultural practices that can be used to control the spread of the disease, such as avoiding injury to the plants and reducing or eliminating application of nitrogen fertilizer.
Collar rot is a symptomatically described disease that is usually caused by any one of various fungal and oomycete plant pathogens. It is present where the pathogen causes a lesion localized at or about the collet between the stem and the root. The lesions develop around the stem eventually forming a "collar". Observationally, collar rot grades into "basal stem rot", and with some pathogens is the first phase of "basal stem rot" often followed by "root rot". Collar rot is most often observed in seedings grown in infected soil. The pathogens that cause collar rot may be species or genera specific. But generalist pathogens such as Athelia rolfsii are known to attack over 200 different species. While bacteria caused collar rot is not common, trees infected with Fire blight may develop collar rot. Non-parasitic collar rot may be caused by winter damage.
Stephen Wilhelm was a professor of plant pathology, known for his success in controlling Verticillium wilt. His research on plant hybridization and soil fumigation contributed to revolutionary developments in the strawberry and raspberry industries.
Ernest Robert Sears was an American geneticist, botanist, pioneer of plant genetics, and leading expert on wheat cytogenetics. Sears and Sir Ralph Riley (1924–1999) are perhaps the two most important founders of chromosome engineering in plant breeding.
Kenneth Frank Baker was an American phytopathologist. In his early career he held a number of positions with the United States Forest Service and United States Department of Agriculture. Following a three-year period in Hawaii researching pineapple pathogens, he accepted a position at the University of California, Los Angeles, where he remained for twenty-one years. He was elected as a fellow of the American Association for the Advancement of Science in 1950 and as a fellow of the American Phytopathological Society in 1969. Additionally, he served as the editor of the Annual Review of Phytopathology for five years.
Robert Kent Webster is an American phytopathologist who specialized in pathogens affecting rice during his career at the University of California, Davis. He was the editor of the Annual Review of Phytopathology from 1995–2003.
Stephen Denis Garrett was a British plant pathologist and mycologist who did pioneering work on soil-borne pathogens, root pathology and soil ecology. He was the first to apply ecological concepts to interactions in the soil. Much of his research used as a model system the fungus Gaeumannomyces graminis, which causes the important cereal disease take-all. He also studied Armillaria root rot of trees, among other plant diseases.
Clarence James Hickman was a British-Canadian mycologist. He is noteworthy for his discovery in 1940 that the oomycete species Phytophthora fragariae is the cause of the disease red stele in strawberry plants.
John Colhoun was a British mycologist, phytopathologist, and professor of cryptogamic botany. For a one-year term from 1963 to 1964 he was the president of the British Mycological Society.
References
- 1 2 3 4 5 "R. James Cook". Washington State University. Retrieved 1 December 2020.
- ↑ Minnesota Department of Health (1937), Birth Index, 1935-2000
- 1 2 "Cook Will Occupy Chair Named in His Honor". Washington State University. Retrieved 1 December 2020.
- ↑ "Preface". Annual Review of Phytopathology. 23. 1985. doi:10.1146/annurev.py.23.060804.100001.
- 1 2 "Kenneth F. Baker and R. James Cook Student Travel Award". American Phytopathological Society. Retrieved 1 December 2020.
- ↑ "R. James Cook". John Simon Guggenheim Memorial Foundation. Retrieved 1 December 2020.
- ↑ "R. James Cook". Plant Health International. Retrieved 1 December 2020.
