Phialophora gregata
| Phialophora gregata | |
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| Species: | P. gregata
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| Binomial name | |
| Phialophora gregata (Allington & D.W. Chamb.) W. Gams, (1971)
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Cadophora gregata | |
Phialophora gregata is an ascomycete fungus that is a plant pathogen that causes the disease commonly known as "brown stem rot of soybean." The fungus exists infects as two strains.[1] P. gregata does not produce survival structures, but has the ability to overwinter as mycelium in decaying soybean residue.[1]
Two strains of the fungus exist; genotype A causes both foliar and stem symptoms, while genotype B causes only stem symptoms.[1] Common leaf symptoms are browning, chlorosis, and necrosis[1] Foliar symptoms which are often seen with genotype A are chlorosis, defoliation, and wilting.[1][2]
There are many ways to manage Phialophora gregata. The most effective form of management is disease resistance,[1] but crop rotation, tiliage, SCN management, and changing the pH of the soil can also be effective [1][3]
Symptoms and Signs
Phialophora gregata’s infection of a soybean plant is accompanied by browning of the plant’s vascular and pith tissues.[1] The plant often exhibits chlorosis and necrosis, as well as leaf browning.[1] Wilting and defoliation are also known to occur.[1] Signs of infection often go unnoticed until reproductive stages of a plant’s life cycle. They can be diagnosed earlier on by opening the stem and visualizing the pathogen. One can visualize signs by cutting open the stem in early stages of infection,[1] but symptoms do not become apparent until after the soybean pod formation.[4]
Depending on which strain infects the plant, genotype A or genotype B, the effect is more or less potent. Genotype A causes browning of stems as well as foliar symptoms such as interveinal chlorosis, defoliation and wilting.[1][2] Symptomatic leaves have a shriveled appearance, but remain attached to the stem.[2] These foliar symptoms can often be confused by those caused by the pathogen "Fusarium virguliforme," which causes Sudden Death Syndrome in soybean.[2][4] Genotype B causes only browning of stems.[2]
Secondary symptoms of brown stem rot are stunting, premature death, decrease in seed number, reduced pod set, and decrease in seed size.[2]
Environment
As the disease is soilborne, it is not uncommon to find clusters of diseased plants together.[2] The pathogen proliferates in stem tissues when soil has high moisture content and air temperatures from 70-80 degrees Fahrenheit.[2] Rainy seasons promote brown stem rot.[2] When soil is untilled, the disease is more likely to persist in soil.[2] The incidence of brown stem rot is highest at soil pH ~6.3.[5]
External links
References
- ^ a b c d e f g h i j k l Grau, C. "Brown Stemrot of Soybeans." <http://fyi.uwex.edu/fieldcroppathology/files/2010/11/bsr_063.pdf>
- ^ a b c d e f g h i j Robertson, A. & Tabor, G. “Soybean Brown Stem Rot.” Iowa State University. <http://www.extension.iastate.edu/Publications/PMR1004.pdf.>2012.
- ^ Robertson, A.E. and Nutter, F.W. Iowa Soybean Disease Survey. www.soybeandiseasesurvey.info
- ^ a b Monsanto. "Brown Stem Rot and Sudden Death Syndrome in Soybean." Lewis Hybrids. Lewis Hybrids, 2010. Web. <http://www.lewishybrids.com/files/File/Agronomic%20Spotlight%20-%20Brown_Stem_Rot_Sudden_Death_Soy.pdf?PHPSESSID=0c6bc72c5c097a7e80e53605fd2effce>
- ^ Pedersen, Palle. “Brown Stem Rot.” <http://extension.agron.iastate.edu/soybean/diseases_bsr.html> 2006.