Fusarium crown rot caused by Fusarium pseudograminearum in cereal crops: recent progress and future prospects.

Diseases caused by Fusarium pathogens inflict major yield and quality losses on many economically important plant species worldwide, including cereals. Fusarium crown rot (FCR), caused by Fusarium pseudograminearum, is a cereal disease that occurs in many arid and semi-arid cropping regions of the world. In recent years, this disease has become more prevalent, in part as a result of the adoption of moisture-preserving cultural practices, such as minimum tillage and stubble retention. In this pathogen profile, we present a brief overview of recent research efforts that have not only advanced our understanding of the interactions between F. pseudograminearum and cereal hosts, but have also provided new disease management options. For instance, significant progress has been made in the genetic characterization of pathogen populations, the development of new tools for disease prediction, and the identification and pyramiding of loci that confer quantitative resistance to FCR in wheat and barley. In addition, transcriptome analyses have revealed new insights into the processes involved in host defence. Significant progress has also been made in understanding the mechanistic details of the F. pseudograminearum infection process. The sequencing and comparative analyses of the F. pseudograminearum genome have revealed novel virulence factors, possibly acquired through horizontal gene transfer. In addition, a conserved pathogen gene cluster involved in the degradation of wheat defence compounds has been identified, and a role for the trichothecene toxin deoxynivalenol (DON) in pathogen virulence has been reported. Overall, a better understanding of cereal host-F. pseudograminearum interactions will lead to the development of new control options for this increasingly important disease problem. Taxonomy: Fusarium pseudograminearum O'Donnell & Aoki; Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. Disease symptoms: Fusarium crown rot caused by F. pseudograminearum is also known as crown rot, foot rot and root rot. Infected seedlings can die before or after emergence. If infected seedlings survive, typical disease symptoms are browning of the coleoptile, subcrown internode, lower leaf sheaths and adjacent stems and nodal tissues; this browning can become evident within a few weeks after planting or throughout plant development. Infected plants may develop white heads with no or shrivelled grains. Disease symptoms are exacerbated under water limitation. Identification and detection: Fusarium pseudograminearum macroconidia usually contain three to five septa (22-60.5 × 2.5-5.5 μm). On potato dextrose agar (PDA), aerial mycelia appear floccose and reddish white, with red or reddish-brown reverse pigmentation. Diagnostic polymerase chain reaction (PCR) tests based on the amplification of the gene encoding translation elongation factor-1a (TEF-1a) have been developed for molecular identification. Host range: All major winter cereals can be colonized by F. pseudograminearum. However, the main impact of this pathogen is on bread (Triticum aestivum L.) and durum (Triticum turgidum L. spp. durum (Dest.)) wheat and barley (Hordeum vulgare L.). Oats (Avena sativa L.) can be infected, but show little or no disease symptoms. In addition, the pathogen has been isolated from various other grass genera, such as Phalaris, Agropyron and Bromus, which may occur as common weeds. Useful websites: https://nt.ars-grin.gov/fungaldatabases/; http://plantpath.psu. edu/facilities/fusarium-research-center; https://nt.ars-grin.gov/fungaldatabases/; http://www.speciesfungorum. org/Names/Names.asp.