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Fusarium crown rot of wheat
Crown Rot of Wheat is caused by the fungal pathogen ''Fusarium pseudograminearum''. ''F. pseudograminearum'' is a member of the fungal phylum Ascomycota and is also known as ''Gibberella coronicola'' (teleomorph). It is a monoecious fungus, meaning it does not require another host other than wheat to complete its life cycle. Although ''F. pseudograminearum'' can produce both anamorphic and teleomorphic states, the teleomorph is usually not present for crown rot of wheat.〔Backhouse, D; Abubaker, AA; Burgess, LW; Dennis, JI; Hollaway; Wildermuth, GB; Wallwork, H; Henry, FJ, (2004) Survey of Fusarium Species Associated with Crown Rot of Wheat and Barley in Eastern Australia, Australian Plant Pathology Society, Vol 33, pp255–261.〕 This ''Fusarium'' species has, until recently, been considered to be the same as the species known as ''Fusarium graminearum'' (head blight of wheat) due to many similar characteristics. One of the only differences between the two species is that ''F. pseudograminearum'' lacks its sexual stage on the wheat host.〔Stephens, AE; Gardiner, DM; White, RG; Munn, AL; Manners, JM, (2008) Phases of Infection and Gene Expression of Fusarium graminearum During Crown Rot Disease of Wheat, Molecular Plant-Microbe Interactions, Vol 21, No. 12, pp1571–1581. 10. Wallwork, H; Butt, M; Cheong, JPE; Williams, KJ, (2004) Resistance to Crown Rot in Wheat Identified Through an Improved Method for Screening Adult Plants, Australian Plant Pathology Society, Vol 33, pp1–7〕
An important characteristic in terms of infection that also distinguishes ''F. pseudgraminearum'' from ''F. graminearum'' is that ''F. pseudograminearum'' rarely infects the head of the wheat plant, only the crown, whereas ''F. graminearum'' can infect the entire wheat host.〔Agnieszka M. Mudge, Ruth Dill-Macky, et al, (2006) A role for the mycotoxin deoxynivalenol in stem colonisation during crown rot disease of wheat caused by Fusarium graminearum and Fusarium pseudograminearum, Physiological and Molecular Plant Pathology, Volume 69, Issues 1–3, July–September, Pages 73–85, ISSN 0885-5765, 〕 Other than these differences, the signs and symptoms of both fungal pathogens are very similar, showing necrosis of the stem base and crown. ''F. pseudograminearum'' also produces mycotoxins once colonization of the wheat has been fully established, which are responsible for the majority of the symptoms produced.〔 Crown Rot of Wheat is an important plant disease that needs to be well managed due to its detrimental effects that it can have on entire fields of wheat. The infection of ''F. pseudograminearum'' can develop during stressful water deficits in fields and can spread quickly to other wheat plants, whose symptoms will ultimately lead to plant death.〔
==Hosts and symptoms==
''F. pseudograminearum'' has a limited host range, only infecting species of wheat and barley. ''F. pseudograminearum'' can infect seedlings, but can also infect the crowns of mature wheat hosts. Crown rot of wheat produces asexual structures called conidiospores, which are produced in sporodochium structures inside the stem of the infected host. As the conidiospores germinate and invade the xylem and pith of the stem, both the stem and crown develop a red-brown or white discoloration.〔Desmond, Olivia,Edgar, Cameraon et al, (2006) Methyl jasmonate induced gene expression in wheat delays symptom development by the crown rot pathogen Fusarium pseudograminearum, Physiological and Molecular Plant Pathology, Volume 67, Issues 3–5, September 2005 – October 2006, Pages 171–179, ISSN 0885-5765, 〕 The primary infection of the host’s xylem is thought to occur at the crown or lower sheath of the stem from stubble containing a spore and mycelial inoculum.〔 The infection of the xylem leaves the tissue water-soaked and with a pink or salmon color. As the infection proliferates the crown then becomes punky and is ultimately dysfunctional.〔Chakraborty, S; Liu, CJ; Mitter, V; Scott, JB; Akinsanmi, OA; Ali, S; Dill-Macky, R; Nicol, J; Backhouse, D; Simpfendorfer, S, (2006) Pathogen Population Structure and Epidemiology are Keys to Wheat Crown Rot and Fusarium Head Blight Management, Australian Plant Pathology Society, Vol 35, pp643–655〕
Due to the vast infection throughout the host, the plant's growth is stunted and will show incomplete grain fill. As well as infecting the xylem and pith of the host, ''F. pseudograminearum'' produces mycotoxins once it has fully been established. Mycotoxins are toxins produced by fungi that are harmful to animals and human if consumed. ''F. pseudograminearum'' produces the trichothecene mycotoxin deoxynivalenol, or DON, which spreads throughout the plant stem and builds up in the tissue. The production of DON can produce the formation of whiteheads, which are heads of grain that died prematurely. It is known that ''F. pseudograminearum'' does not infect the heads of the wheat, but the formation of the "whiteheads" is a secondary symptom of the buildup of the mycotoxin DON.〔 The transport dysfunction occurring in the xylem and the buildup of DON will ultimately lead to death of the infected wheat plants.〔Nyvall, RF. Field Crop Diseases. 3rd ed. Ames, Iowa: Iowa State University Press, 1999〕
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