Phytophthora sojae
Phytophthora sojae | |
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Scientific classification ![]() | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Stramenopiles |
Phylum: | Oomycota |
Order: | Peronosporales |
Family: | Peronosporaceae |
Genus: | Phytophthora |
Species: | P. sojae
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Binomial name | |
Phytophthora sojae Kaufm. & Gerd., 1958
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Phytophthora sojae is an
Phytophthora sojae is a
The natural chemical farinomalein (a metabolite from entomopathogenic fungus Paecilomyces farinosus[3]) has shown potent and selective inhibition (0.15-5 μg/disk) against eight isolates of plant pathogenic Phytophthora sojae.[2] These results suggest that farinomalein might be useful as a candidate pesticide for the treatment of Phytophthora stem rot in soybean.[2]
Phytophthora sojae is so similar to .
Hosts and symptoms
Phytophthora sojae infects soybean plants (Glycine max) and many members of the genus Lupinus.[4] They have the ability to infect soybeans at any point during its development process, including during seed development.
They cause seed decay and
It also causes root and stem rot and the severity of the infection depends on how susceptible or tolerant the plant is to pathogens. In a highly-tolerant soybean plant, the root rot will simply cause the plant to be stunted and slightly
Foliar blight is also a symptom of Phytophthora sojae, especially when the plant has recently experienced heavy rain. The soybean plant has an age-related resistance in which the older leaves are not susceptible to foliar blight.[7]
Soybean fields infected with Phytophthora sojae can be easily spotted by looking for stunted soybean plants or looking for empty patches where the soybean seed had been planted.
Microscopic identification of an oospore that measure around 40 micrometers in diameter from a soybean plant sample is a definite sign of Phytophthora sojae. Oospores, in general, measure around 20-45 micrometers in diameter and have very thick cellulose cell walls for overwintering.[7]
Disease cycle
Phytophthora sojae overwinters in plant debris and soil as oospores. Oospores are made after the male
Once zoospores have made contact with the host root, they encyst on the surface, break down the plant cell wall with
Phytophthora sojae is considered to be a monocyclic pathogen and has one effective infection in its cycle. This is because the oospores don't germinate together at the same time; rather they each have their own distinct favorable condition in which they'll initiate their germination.[7]
Environment
Phytophthora sojae favor fields that are poorly drained or highly-susceptible to flooding. Solving it only by creating optimal drainage does not restrict the pathogen because the field may be subject to continuous heavy rain which induces flooding.[9] Similar to other Phytophthora, warm soil, intermittent rain (including the rain splashes that results from rain), and windy weather are favorable conditions for development and the spread of the disease respectively. The optimum temperature for its disease development is above 60 °F (16 °C).[7]
Management
Host resistance is the primary method of control for Phytophthora sojae. There are three types of resistance: R gene mediated resistance, root resistance, and partial resistance.[10] Currently there are 14 Rps genes, meaning 14 different single-resistance genes, which have been identified for R-gene mediated resistance and mapped in the soybean genome.[11] Effectively, the most damage that the oomycete can induce is a lesion. Root resistance is inherited and is generally expressed in the roots.[12] In this case, the stem of a germinating seedling is most susceptible. Once the first leaves begin to emerge, the partial resistance of the plant is expressed.[13] Colonization is reduced and lesions are smaller in comparison. This management prevents the zoospores from germinating in the root tip and therefore unable to produce hyphae, which it needs to survive.
Phytophthora sojae can also be controlled using fungicides. For example, Metalaxyl, a fungicide that is specifically used for oomycetes, is used for treating soybean seeds. It's used to prevent seed decay and pre-emergence damping off. This fungicide has been observed to be more effective on highly-tolerant soybean plants. Metalaxyl is most effective when applied to the soil as it allows the plant to take it up through the roots and elongate the control period in comparison to a seed application.[14] Metalaxyl prevents the spores of Phytophthora sojae from entering the soybean plant tissues. As with all fungicides, Metalaxyl is effective for prevention only and should be applied before the disease has established itself inside the tissues of the soybean plant.[14] Replanting must be done once severe pre-emergence damping off is observed.
Improving field drainage and soil tillage are cultural practices that can help minimize the effect of Phytophthora sojae. Improving soil tillage can help eliminate oospores from the soil. Oospores are very sturdy and can remain stagnant in the soil for a long time and therefore crop rotation alone is not effective.[7] Proper field drainage prevents flooding and therefore inhibit zoospore movement towards the host.
Importance
Phytophthora root and stem rot of soybean was first observed in the United States in Indiana in 1948 and its causal agent, Phytophthora sojae, first identified in 1958.[15] In the 1970s, soybean plants only had one single-resistance gene, meaning they were more susceptible to an infection.[9] Eventually plants with this gene were killed by new races of Phytophthora sojae. As a result, several states suffered significant yield losses particularly in the state of Ohio, which lost 300,000 acres of soybean plants in a year. Soon thereafter, a variety of new disease prevention methods were implemented and as a result this disease is currently one of the well-managed and well-known soybean diseases in the USA.[1]
Origin
Recently there's been evidence that soybean plants from South Korea and China had a diversity of resistance that is much higher in these countries compared to other soybean-cultivating nations.[6] This indicates that soybean plants have been around in these areas longer and thus had more time to develop resistance against a variety of diseases including Phytophthora sojae.
References
- ^ a b c Schmitthenner, A.F. 1985. Problems and progress in control of Phytophthora root rot of soybean. Plant Disease 69:362-368.
- ^ a b c Sastia Prama Putri, Hiroshi Kinoshita, Masayasu Kato and Takuya Nihira. Antimicrobial and antioomycete activities of the novel antibiotic farinomalein. Poster Presentation 2P-2124, Annual Conference, The Society for Bioscience and Bioengineering, Japan, 28 October 2010.
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- ^ http://nt.ars-grin.gov/fungaldatabases/new_allView.cfm?whichone=FungusHost&thisName=Phytophthora%20sojae&organismtype=Fungus&fromAllCount=yes[permanent dead link]
- ^ a b Jee, H., W. Kim, and W. Cho. 1998. Occurrence of Phytophthora root rot on soybean (Glycine max) and identification of the causal fungus. Crop Protection 40:16-22.
- ^ a b Erwin, D.C. and O.K. Ribeiro. 1996. Phytophthora Diseases Worldwide. APS Press, St. Paul MN.
- ^ a b c d e f Agrios, George N. 2005. Plant Pathology. 5th ed. Elsevier Academic Press, Burlington, MA.
- ^ Morris, P.F., and E.W.B. Ward. 1992. Chemoattraction of zoospores of the soybean pathogen, Phytophthora sojae, by isoflavones. Physiological and Molecular Plant Pathology 40:17-22
- ^ a b Schmitthenner, A.F. 1988. Phytophthora rot of soybean. Pages 71-80 in: Soybean Diseases of the North Central Region, T.D. Wyllie and D.H. Scott, eds. APS Press, St. Paul, MN.
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- ^ Qutob, D., P.T. Hraber, B.W. Sobral, and M. Gijzen. 2000. Comparative analysis of expressed sequences in Phytophthora sojae. Plant Physiology 123: 243-254.
- ^ Walker, A. K., and Schmitthenner, A. F. 1984. Heritability of tolerance to Phytophthora rot in soybeans. Crop Sci. 24:490-491.
- ^ Grau, C.R., A.E. Dorrance, J. Bond, and J.S. Russin. 2004. Fungal Diseases. Pages 679-763 in: Soybeans: Improvement, Production, and Uses, 3rd ed. Agronomy Monograph no. 16. H.R. Boerma and J.E. Specht, eds.
- ^ a b Anderson, T. R., and Buzzell, R. I. 1982. Efficacy of metalaxyl in controlling Phytophthora root and stalk rot of soybean cultivars differing in field tolerance. Plant Dis. 66:1144-1145
- ^ Kaufmann, M.J., and J.W. Gerdemann 1958. Root and stem rot soybean caused by Phytophthora sojae n. sp. Phytopathology 48:201-208.