Phytophthora infestans is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight. Early blight, caused by Alternaria solani, is also often called "potato blight". Late blight was a major culprit in the 1840s European, the 1845–1852 Irish, and the 1846 Highland potato famines. The organism can also infect some other members of the Solanaceae. The pathogen is favored by moist, cool environments: sporulation is optimal at 12–18 °C (54–64 °F) in water-saturated or nearly saturated environments, and zoospore production is favored at temperatures below 15 °C (59 °F). Lesion growth rates are typically optimal at a slightly warmer temperature range of 20 to 24 °C.
Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".
Erwinia is a genus of Enterobacterales bacteria containing mostly plant pathogenic species which was named for the famous plant pathologist, Erwin Frink Smith. It contains Gram-negative bacteria related to Escherichia coli, Shigella, Salmonella, and Yersinia. They are primarily rod-shaped bacteria.
Verticillium is a genus of fungi in the division Ascomycota, and are an anamorphic form of the family Plectosphaerellaceae. The genus used to include diverse groups comprising saprobes and parasites of higher plants, insects, nematodes, mollusc eggs, and other fungi, thus the genus used to have a wide-ranging group of taxa characterised by simple but ill-defined characters. The genus, currently thought to contain 51 species, may be broadly divided into three ecologically based groups - mycopathogens, entomopathogens, and plant pathogens and related saprotrophs. However, the genus has undergone recent revision into which most entomopathogenic and mycopathogenic isolates fall into a new group called Lecanicillium.
Dickeya dadantii is a gram-negative bacillus that belongs to the family Pectobacteriaceae. It was formerly known as Erwinia chrysanthemi but was reassigned as Dickeya dadantii in 2005. Members of this family are facultative anaerobes, able to ferment sugars to lactic acid, have nitrate reductase, but lack oxidases. Even though many clinical pathogens are part of the order Enterobacterales, most members of this family are plant pathogens. D. dadantii is a motile, nonsporing, straight rod-shaped cell with rounded ends, much like the other members of the genus, Dickeya. Cells range in size from 0.8 to 3.2 μm by 0.5 to 0.8 μm and are surrounded by numerous flagella (peritrichous).
Leptosphaeria maculans is a fungal pathogen of the phylum Ascomycota that is the causal agent of blackleg disease on Brassica crops. Its genome has been sequenced, and L. maculans is a well-studied model phytopathogenic fungus. Symptoms of blackleg generally include basal stem cankers, small grey lesions on leaves, and root rot. The major yield loss is due to stem canker. The fungus is dispersed by the wind as ascospores or rain splash in the case of the conidia. L. maculans grows best in wet conditions and a temperature range of 5–20 degrees Celsius. Rotation of crops, removal of stubble, application of fungicide, and crop resistance are all used to manage blackleg. The fungus is an important pathogen of Brassica napus (canola) crops.
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.
Pseudomonas cichorii is a Gram-negative soil bacterium that is pathogenic to plants. It has a wide host range, and can have an important economical impact on lettuce, celery and chrysanthemum crops. P. cichorii was first isolated on endives, from which it derives its name. It produces 6-aminopenicillanic acid. Based on 16S rRNA analysis, P. cichorii has been placed in the P. syringae group.
Tobacco rattle virus (TRV) is a pathogenic plant virus. Over 400 species of plants from 50 families are susceptible to infection.
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), is considered the most important and most destructive disease of crucifers, infecting all cultivated varieties of brassicas worldwide. This disease was first described by botanist and entomologist Harrison Garman in Lexington, Kentucky, US in 1889. Since then, it has been found in nearly every country in which vegetable brassicas are commercially cultivated.
Bacterial soft rots are caused by several types of bacteria, but most commonly by species of gram-negative bacteria, Erwinia, Pectobacterium, and Pseudomonas. It is a destructive disease of fruits, vegetables, and ornamentals found worldwide, and affects genera from nearly all the plant families. The bacteria mainly attack the fleshy storage organs of their hosts, but they also affect succulent buds, stems, and petiole tissues. With the aid of special enzymes, the plant is turned into a liquidy mush in order for the bacteria to consume the plant cell's nutrients. Disease spread can be caused by simple physical interaction between infected and healthy tissues during storage or transit. The disease can also be spread by insects. Control of the disease is not always very effective, but sanitary practices in production, storing, and processing are something that can be done in order to slow the spread of the disease and protect yields.
Streptomyces scabiei is a streptomycete bacterium species found in soils around the world. Unlike most of the 500 or so Streptomyces species it is a plant pathogen causing corky lesions to form on tuber and root crops as well as decreasing the growth of seedlings. Along with other closely related species it causes the potato disease common scab, which is an economically important disease in many potato growing areas. It was first described in 1892, being classified as a fungus, before being renamed in 1914 and again in 1948. Several other species of Streptomyces cause similar diseases to S. scabiei but other, more closely related species, do not.
Dickeya solani is a bacterium that causes blackleg and soft rot in potato crops. Its symptoms are often indistinguishable from those caused by Pectobacterium but is more virulent, causing disease from lower levels of inoculum and spreading through the plant more effectively.
Pectobacterium is a bacterial genus of the family Pectobacteriaceae; it used to be a member of the genus Erwinia, which was split into three genera: Erwinia, Pectobacterium, and Brenneria.
Pectobacterium atrosepticum is a species of bacterium. It is a plant pathogen causing blackleg of potato. Its type strain is CFBP 1526T. Its genome has been sequenced.
Pectobacterium wasabiae is a plant pathogenic bacterium that was first reported to cause disease on wasabi plants. A closely related species, yet to be formally named, also causes disease on potato. Unlike most Pectobacterium, P. wasabiae strains lack a type III secretion system. Its type strain is CFBP 3304T(=LMG 8404T =NCPPB 3701T =ICMP 9121T).
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.
Blackleg is a plant disease of potato caused by pectolytic bacteria that can result in stunting, wilting, chlorosis of leaves, necrosis of several tissues, a decline in yield, and at times the death of the potato plant. The term "blackleg" originates from the typical blackening and decay of the lower stem portion, or "leg", of the plant.
Hemibiotrophs are the spectrum of plant pathogens, including bacteria, oomycete and a group of plant pathogenic fungi that keep its host alive while establishing itself within the host tissue, taking up the nutrients with brief biotrophic-like phase. It then, in later stages of infection switches to a necrotrophic life-style, where it rampantly kills the host cells, deriving its nutrients from the dead tissues.
Amy Olymbia Charkowski is an American plant pathologist and Professor of Plant Pathology at Colorado State University. She was elected Fellow of the American Association for the Advancement of Science in 2020.
