''Phytophthora sojae'' is an

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

and a soil-borne

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

that causes stem and

root rot Root rot is a condition in which anoxic conditions in the soil or potting media around the roots of a plant cause them to rot. This occurs due to excessive standing water around the roots. It is found in both indoor and outdoor plants, although ...

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...

. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. ''Phytophthora sojae'' also produces

oospore An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes. They are believed to have evolved either through the fusion of two species or the chemically-induced stimulation of mycelia, ...

s that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery. ''Phytophthora sojae'' is a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

organism with a

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

size of 95 Mbp (Millions of base pairs). The natural chemical

farinomalein Farinomalein is a natural maleimide with formula C10H13NO4 - was first isolated from the entomopathogenic fungus '' Isaria farinosa'' (''Paecilomyces farinosus'') - source H599 (Japan). Farinomalein has shown potent and selective inhibition (0.15 ...

(a metabolite from

entomopathogenic fungus An entomopathogenic fungus is a fungus that can kill or seriously disable insects. Typical life cycle These fungi usually attach to the external body surface of insects in the form of microscopic spores (usually asexual, mitosporic spores also ...

'' Paecilomyces farinosus''Sastia P. Putri, Hiroshi Kinoshita, Fumio Ihara, Yasuhiro Igarashi and Takuya Nihira. ''Farinomalein, a Maleimide-Bearing Compound from the Entomopathogenic Fungus ''Paecilomyces farinosus. J. Nat. Prod., 2009, 72 (8), pp 1544-1546 ) has shown potent and selective inhibition (0.15-5 μg/disk) against eight isolates of plant pathogenic ''Phytophthora sojae''.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. These results suggest that farinomalein might be useful as a candidate

pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...

for the treatment of ''Phytophthora'' stem rot in soybean. ''Phytophthora sojae'' is so similar to ''

Phytophthora megasperma ''Phytophthora megasperma'' is a species of water mould in the family Peronosporaceae. It is well known as a plant pathogen with many hosts. It often causes a plant disease called root rot.Phytophthora medicaginis'' were respectively known as ''Phytophthora megasperma'' f. sp. ''glycines'' and ''Phytophthora megasperma'' f. sp. ''medicaginis''. Recent discoveries about their molecular structure, however, proved that they were indeed unambiguous

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

Hosts and symptoms

''Phytophthora sojae'' infects soybean plants ''(Glycine max)'' and many members of the genus ''

Lupinus ''Lupinus'', commonly known as lupin, lupine, or regionally bluebonnet etc., is a genus of plants in the legume family Fabaceae. The genus includes over 199 species, with centers of diversity in North and South America. Smaller centers occur ...

''. They have the ability to infect soybeans at any point during its development process, including during seed development. They cause seed decay and pre- and

postemergence Pesticide application refers to the practical way in which pesticides (including herbicides, fungicides, insecticides, or nematode control agents) are delivered to their ''biological targets'' (''e.g.'' pest organism, crop or other plant). Publ ...

damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. Symptoms There ar ...

when the soil is flooded after planting. Seedling roots may appear to have light brown soft rot as soon as the seedlings begin to sprout from the soil. 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

chlorotic In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

instead of killing the plant. In contrast, infection of a low-tolerant soybean plant will most likely lead to the death of the plant. Infection initiates in the roots and then progresses several

nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

up the stem, turning the root and the stem brown and the leaves yellow.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. As the pathogen progresses, the entire plant transforms into an orange-brown color. The wilted leaves bend towards the plant and remain attached as it succumbs to death.Erwin, D.C. and O.K. Ribeiro. 1996. Phytophthora Diseases Worldwide. APS Press, St. Paul MN. 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. 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.Agrios, George N. 2005. Plant Pathology. 5th ed. Elsevier Academic Press, Burlington, MA.

Disease cycle

''Phytophthora sojae'' overwinters in plant debris and soil as oospores. Oospores are made after the male

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

antheridium An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...

, and female gamete, oogonium, undergo fertilization and then sexual recombination (

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

). They possess thick

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

s with

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

that enables them to survive harsh conditions in the soil without germinating for several years. They begin to germinate once the environmental condition is favorable during spring (see § Environment) and produce

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...

. They can either germinate directly or indirectly. In direct germination, sporangia directly penetrate the host cells at the plant's root tips (if it's within reach). Indirect germination involves sporangia releasing

s (if the root is at a farther distance from the sporangia) which

encyst A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist or rarely an invertebrate animal, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of ...

on the host plant cells and germinate. Zoospores are

biflagellate A flagellate is a cell or organism with one or more whip-like appendages called flagellum, flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes ...

asexual motile spores. They are dispersed by water flow in the soil and are able to inoculate the roots of plants or seeds. Chemicals such as

daidzein Daidzein (7-hydroxy-3-(4-hydroxyphenyl)-4H-chromen-4-one) is a naturally occurring compound found exclusively in soybeans and other legumes and structurally belongs to a class of compounds known as isoflavones. Daidzein and other isoflavones ar ...

s and

genistein Genistein (C15H10O5) is a naturally occurring compound that structurally belongs to a class of compounds known as isoflavones. It is described as an angiogenesis inhibitor and a phytoestrogen. It was first isolated in 1899 from the dyer's bro ...

are released at the tip of the plant roots which attract the liberated zoospores. Once zoospores have made contact with the host root, they encyst on the surface, break down the plant cell wall with

proteolytic Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, ...

enzymes and begin to germinate. Their

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e will begin to grow through the intercellular space of the plant cells. After establishing its haustoria for nutrients, more oospores will begin to form in the cortical cells of the root. The host plant will begin to exhibit secondary symptoms such as stem canker, wilting, and chlorosis as ''Phytophthora sojae'' continue to reproduce. This continuous reproduction renders the plant dead at the end of the season. The oospores are then left to overwinter in the dead plant's debris and the soil. The cycle is repeated once again in the spring when environmental conditions are favorable (see § Environment). The disease is mostly localized where zoospores initially infected the host plant. ''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.

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.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. 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 .

Management

Host resistance is the primary method of control for ''Phytophthora sojae''. There are three types of resistance:

R gene Resistance genes (R-Genes) are genes in plant genomes that convey plant disease resistance against pathogens by producing R proteins. The main class of R-genes consist of a nucleotide binding domain (NB) and a leucine rich repeat (LRR) dom ...

mediated resistance, root resistance, and partial resistance. 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

. Effectively, the most damage that the oomycete can induce is a lesion. Root resistance is inherited and is generally expressed in the roots. 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. 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

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

s. For example,

Metalaxyl Metalaxyl is an acylalanine fungicide with systemic function. Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control ''Pythium'' in a number of vegetable crops, and ''Phytophthora'' in peas. 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.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 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. Replanting must be done once severe pre-emergence damping off is observed. Improving field drainage and soil

tillage Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shoveling, picking, mattock work, hoein ...

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 Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...

alone is not effective. 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 The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...

in 1948 and its causal agent, ''Phytophthora sojae'', first identified in 1958.Kaufmann, M.J., and J.W. Gerdemann 1958. Root and stem rot soybean caused by ''Phytophthora sojae'' n. sp. Phytopathology 48:201-208. In the 1970s, soybean plants only had one single-resistance gene, meaning they were more susceptible to an infection. 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 Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

, 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.Schmitthenner, A.F. 1985. Problems and progress in control of Phytophthora root rot of soybean. Plant Disease 69:362-368.

Origin

Recently there's been evidence that soybean plants from

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...

and

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

had a diversity of resistance that is much higher in these countries compared to other soybean-cultivating nations. 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

{{DEFAULTSORT:Phytophthora Sojae sojae Water mould plant pathogens and diseases Soybean diseases