Phakopsora pachyrhizi

Phakopsora pachyrhizi is a plant pathogen. It causes Asian soybean rust.

Phakopsora pachyrhizi
Scientific classification
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Pucciniomycetes
Order:	Pucciniales
Family:	Phakopsoraceae
Genus:	Phakopsora
Species:	P. pachyrhizi
Binomial name
Phakopsora pachyrhizi Syd. & P. Syd., (1914)
Contour map showing numbers of NADP sites testing positive for P. pachyrhizi in the center and east of US in 2006
Synonyms
Malupa sojae Malupa vignae Phakopsora sojae Phakopsora vignae Physopella pachyrhizi Uredo sojae Uredo vignae Uromyces sojae

Hosts

Phakopsora pachyrhizi is an obligate biotrophic pathogen that causes Asian soybean rust. Phakopsora pachyrhizi is able to affect up to 31 different plant species that belong to 17 different genera under natural conditions. Experiments in laboratories were able to use Phakopsora pachyrhizi to infect 60 more plant species.[1][2] The main hosts are Glycine max (soybean), Glycine soja (wild soybean), and Pachyrhizus erosus (Jicama).

Scientific name	Common name
Alysicarpus glumaceus	Alyce clover
Alysicarpus nummularifolius
Alysicarpus rugosus	Alyce clover
Alysicarpus vaginalis	Alyce clover
Cajanus cajan*	Cajan, pigeon pea
Calopogonium mucunoides
Canavalia gladiate	Swordbean
Centrosema pubescens	Butterfly pea
Clitoria termatea	Kordofan pea, butterfly pea, Asian pigeon wings
Coronilia varia	Crownvetch
Crotalaria anagyroides	Rattlebox
Crotalaria saltiana	Rattlebox
Crotaria spectabilis
Delonix regia	Poinciana or royal Poinciana
Desmodium triflorum	Three-flower beggarweed
Erythrina subumbrans	Dadap
Erythrina variegate	Indian coral tree
Glycine canescens	Soybean relative
Glycine clandestine	Soybean relative
Glycine clandestine	Soybean relative
Glycine falcadata	Soybean relative
Glycine max*	Soybean
Glycine soja
Glycine tabacina	Soybean relative
Kennedia prostrata
Kennedia rubicunda
Lablab purpureus	Lablab, hyacinth bean
Lespedeza bicolor	Lespedeza
Lespedeza striata	Lespedeza
Lespedeza stipulaceae	Lespedeza
Lotus spp.	Trefoil
Lotus Americana
Lupinus *	Lupines
Lupinus albus	White lupine
Lupinus angustifolius	Narrow-leaved lupine
Lupinus hirsutus	Blue lupine
Lupinus luteus	Yellow lupine
M. speciosus
Macroptilium atropurpurem	Siratro, purple bean siratro
Macrotyloma axilare
Medicago arborea	Medic
Medicago lupulina	Black medic
Melilotus officinalis	Yellow sweet clover
Mucuna	Velvetbean
Mucuna cochinchinesis	Velvetbean relative
Neonotonia (glycine) wrightii	Glycine
Pachyrhizus ahipa *	Yam bean
Pachyrhizus erosus *	Yam bean, Jicama, chop suey bean
Phaseolus lunatus *	Buttler bean, lima bean
Phaseolus vulgaris *	Kidney bean, green bean
Pisum sativum	Peas (green)
Psophocarpus tetragonolobus	Winged bean or Goa
Pueraria lobate*	Kudzu
Puerarua montana var. Lobata*	Kudzu
Puerarua phaseoloides	Tropical kudzu
Rhynchosia minima
Senna obtusifolia	Sickpod
Senna occidentalis	Coffee senna
Sesbania exaltada	Colorado River hemp, hemp sesbania, coffeebean
Sesbania macrocarpa	Peatree or Colorado River hemp
Sesbania vescaria
Trifolium repens	White clover
Trifolium incarnatum	Crimson clover
Trigonella foenum-graicum	Fenugreek
Trigonella foenum-gracecum	Fenugreek
Vicia angustifolia	Narrow-leaf vetch
Vicia dasycarpa	Wooly-pod vetch
Vicia faba	Broadbean or fava bean
Vicia narbonensis	Broad-leaved vetch
Vicia villosa ssp. Varia	Woolypod vetch
Vigna mungo	Urd or black gram
Vigna radiate*	Mung bean
Vigna unguiculata*	Cowpea, black-eye pea, yearlong bean
Voandzeia subterranea	Bambara groundnut

*Preferred hosts. Other hosts were minor or determined experimentally under artificial conditions.

[3]

Symptoms

The disease forms tan to dark-brown or reddish-brown lesions with one to many prominent, globe-like orifices.[4] Urediniospores form from these pores.[5] At initial stages, small yellow spots are formed on the surface of the leaf. These spots may be better observed using assistance of a light source. As the disease progresses, lesions start to form on the leaves, stems, pod, and petioles. Lesions are initially small, turning from gray to tan or brown as they increase in size and the disease gets more severe. Soon volcano-shaped marks are noticed in the lesions.[6]

Disease cycle

Phakopsora pachyrhizi is a fungus which has a spore moved by wind, called urediniospore. These spores are quite different from others as they don’t need an open stomata or natural openings in the leaves. Urediniospores are able to penetrate the leaf. Pustules are visible after 10 days and they can produce spores for three weeks.[7] The disease reaches its climax when the crop begins flowering. The cycle of the pathogen continues until the crop is defoliated or until the environment becomes unfavorable to the pathogen.[8]

The Asian soybean rust is a polycyclic disease: within the disease cycle, the asexual urediniospores keep infecting the same plant. Teliospores (sexual spores) are the survival spores that overwinter in the soil. Basidiospores are the spores that are able to contaminate an alternative host. The urediniospores need a minimum of six hours to infect leaves at a favorable temperature (between 15-24°C).[9]

Environment

The favorable conditions for the disease to progress are related to temperature, humidity, and wind. The appropriate temperature for the pathogen to be active is 12 to 29°C (more efficient between 18-26.5°C). The humidity must be high, about 90% or more, for more than 12 hours. A significant amount of wind is also important for the pathogen to move from one plant to the other.[6][9] Currently, in the United States, infected plants can be found in Florida, Georgia, Louisiana, and Texas.[2]

Risk factors

Uredospores are wind-blown and are produced abundantly on the infected tissue of soybeans or other legume hosts.[4]

Management

The disease is often controlled using the fungicides oxycarboxin, triforine, and triclopyr.[4]

Phakospsora pachyrhizi is a pathogen that acts quickly in contaminating the host. The plant can be severely contaminated in as short a period as 10 days. This makes it difficult to control the disease, as it does not just spread quickly, but its progression is also fast. That is why it is important to implement control techniques as soon as possible.

Genetic resistance

The disease may be controlled by using genetic resistance, but this has not exhibited great results and has not been durable[6] because the soybean genome almost entirely lacks potential genes for ASR resistance.[Kawashima et al 2016 1]​ A gene from Cajanus cajan has shown promise when transferred to soybean.[Kawashima et al 2016 2]​[Kawashima et al 2016 3]​ This method could be expanded to a wide array of genes in the entire family;[Kawashima et al 2016 4]​[Kawashima et al 2016 5]​ as with native genes these are best deployed in combination due to P. pachyrhizi's ability to rapidly overcome resistance.[Kawashima et al 2016 6]​

Chemical control

A second form of management that can work is using fungicides, but this is only efficient at early stages of the disease. The disease spreads fast and it is complicated to control after certain stages, so it is important to act with care around contaminated plants, as the spores can be attached to clothing and other materials and infect other plants.[2]

References

1. Goellner, Katharina; Loehrer, Marco; Langenbach, Caspar; Conrath, Uwe; Koch, Eckhard; Schaffrath, Ulrich (March 2010). "Phakopsora pachyrhizi, the causal agent of Asian soybean rust". Molecular Plant Pathology. 11 (2): 169–177. doi:10.1111/j.1364-3703.2009.00589.x. ISSN 1364-3703. PMC 6640291. PMID 20447267.
2. "details". www.tsusinvasives.org. Retrieved 2017-12-07.
3. Coker, Hurst, Kirkpatrick, Rupe, Tingle, Trent, Cliff, Kim, Terry, John, Chris, Mark. "Asian Soybean Rust" (PDF).CS1 maint: multiple names: authors list (link)
4. Shanmugasundaram, S.; Yeh, C.C.; Hartman, G.L.; Talekar, N.S. (1991). Vegetable Soybean Research Needs for Production and Quality Improvement (PDF). Taipei: Asian Vegetable Research and Development Center. pp. 86–87. ISBN 9789290580478. Retrieved 6 February 2016.
5. Sinclair, James Burton; Backman, P. A. (1989). Compendium of Soybean Diseases (3rd ed.). St Paul, MN: APS Press. ISBN 9780890540930.
6. Network, University of Nebraska-Lincoln | Web Developer (2015-09-18). "Asian Soybean Rust". CropWatch. Retrieved 2017-12-07.
7. "Phakopsora pachyrhizi - Bugwoodwiki". wiki.bugwood.org. Retrieved 2017-12-07.
8. "soybean rust, Phakopsora pachyrhizi N/A Uredinales: Phakopsoraceae". www.invasive.org. Retrieved 2017-12-07.
9. "Phakopsora pachyrhizi (soyabean rust)". www.cabi.org. Retrieved 2017-12-07.

• Kawashima, Cintia G; Guimarães, Gustavo Augusto; Nogueira, Sônia Regina; MacLean, Dan; Cook, Doug R; Steuernagel, Burkhard; Baek, Jongmin; Bouyioukos, Costas; Melo, Bernardo do V A; Tristão, Gustavo; de Oliveira, Jamile Camargos; Rauscher, Gilda; Mittal, Shipra; Panichelli, Lisa; Bacot, Karen; Johnson, Ebony; Iyer, Geeta; Tabor, Girma; Wulff, Brande B H; Ward, Eric; Rairdan, Gregory J; Broglie, Karen E; Wu, Gusui; van Esse, H Peter; Jones, Jonathan D G; Brommonschenkel, Sérgio H (2016-04-25). "A pigeonpea gene confers resistance to Asian soybean rust in soybean". Nature Biotechnology. Springer Science and Business Media LLC. 34 (6): 661–665. doi:10.1038/nbt.3554. ISSN 1087-0156.

1. p. 664, "Previous work did not identify novel soybean germplasm that displayed immunity to ASR and identified only 33 accessions with moderate RB type resistance, and thus revealed that the number of ASR resistance genes in soybean germplasm is limited^[16]. Resistance genes that provide immunity to ASR are a valuable resource."
2. p. 664, "In conclusion, we have identified and cloned a gene from C. cajan that confers resistance to P. pachyrhizi when expressed in soybean."
3. p. 664, "Thus, the significance of this work is the demonstration that it is possible to effectively transfer a dominant resistance gene from a related legume into soybean."
4. p. 664, "The Fabaceae (Leguminosae) is a large and diverse plant family, with around 700 genera and 20,000 species^[29]. Our results suggest that this tremendous natural resource can be used to identify additional resistance genes against ASR that are absent from the soybean gene pool."
5. p. 664, "These legume resistance genes could be used to develop durable and environmentally sustainable ASR control strategies."
6. p. 664, "Finally, although we have not been able to identify P. pachyrhizi isolates that can overcome CcRpp1, P. pachyrhizi has demonstrated that it can rapidly overcome resistance genes that are deployed individually. With 30 million hectares of soybean under cultivation in Brazil, it would be prudent to only deploy CcRpp1 in soybean together with additional resistance genes that have different specificity or different mechanism of ASR resistance, to increase the durability of these resources^[30]."

External links

• USDA ARS Fungal Database