Cocksfoot mottle virus
(Cocksfoot mottle virus)

Cocksfoot mottle virus (CfMV) is distributed in the Eastern and Western hemispheres. Invasiveness through introduction outside of Europe is probable.

Major hosts of CfMV, orchardgrass (Dactyllis glomerata) and Italian ryegrass (Lolium multiflorum), are both widespread in most regions of the world (Holm et al., 1997), thus new introductions of CfMV through new introductions of the host is unlikely. The cereal leaf beetle (Oulema melanopus), however, has a reported distribution currently restricted to North America, Canada, Europe, and reported in India, Pakistan and Iran (Bailey et al., 1991; Kher et al., 2011; Philips et al., 2011). It was not reported in New Zealand, where evidence suggests that the virus has spread by means of mechanical inoculation by machinery (Campbell and Guy, 2001). Thus, the risk of introduction of CfMV into new areas follows the risk of introduction of cereal leaf beetle with virus or of the virus alone into new regions. Cereal leaf beetle has received a medium rating of risk of introduction to new areas in California from the US APHIS risk assessment programme, in part because the vector mates after overwintering and only produces one generation per year (Kher et al., 2011; Philips et al., 2011; Leathers, 2015). Canada assigned cereal leaf beetle a low risk of introduction into new areas within Canada due to the beetle’s inability to withstand harsh winters or hot summers (CFIA, 2008). Cereal leaf beetle is not expected to expand its range into areas with warmer climates or harsh winters and therefore expansion of the range of CfMV is unlikely as well. Suggested pathways of spread of cereal leaf beetle include through transportation of grain, forage seed, straw, hay, grass sod, plant litter, used harvest equipment, and cut or balled Christmas trees (CFIA, 2008; Leathers, 2015).

CfMV has primarily been reported as a pathogen affecting orchardgrass (Dactylis glomerata), but natural infections have been reported on wheat (Serjeant, 1967). The experimental host range of CfMV includes orchardgrass (D. glomerata), wheat (Triticum aestivum), oats (Avena sativa), barley (Hordeum vulgare), rye (Secale cereale), Agrostis puchella [A. tenerrima], Anthoxanthum puelii [A. aristatum], Bromus secalinus, Lagurus ovatus, Lamarckia aurea, Phalaris minor, P. paradoxa, Phleum arenarium and P. paniculatum (Serjeant, 1967; Catherall et al., 1977). Plants identified as non-hosts include rice (Oryza sativa), maize (Zea mays) and the grasses Agropyron repens [Elymus repens], Alopecurus pratensis, Anthoxanthum odoratum, Apera spica-venti, Brachypodium pinnatum, Bromus arvensis, B. mollis [B. hordeaceus], Cynosurus cristatus, Festuca arundinacea, Holcus lanatus, Lolium perenne, Poa pratensis, P. trivialis, Sorghum halepense and S. vulgare [S. bicolor], as well as other monocotyledonous species Lilium formosum [L. sargentiae], L. regale and Musa balbisiana, and dicotyledonous species Chenopodium amaranticolor [C. giganteum], C. hybridum, C. quinoa, Cucumis sativus, Datura stramonium, Nicotiana clevelandii, N. glutinosa, N. tabacum, Petunia hybrida, Phaseolus vulgaris and Vicia faba (Serjeant, 1967; Catherall et al., 1977).

No seed transmission of CfMV was observed in tests to assess it (Serjeant, 1964; Serjeant, 1967).

Incidence

Incidences up to 55% were reported for CfMV in orchardgrass (Dactylis glomerata) seed cropping fields the East Midlands of England, UK, with virus incidence observed increasing with crop age (Upstone, 1969). In New Zealand, incidences of up to 80% were measured at South Island sites, with higher incidences at mowed than unmowed sites, and an establishment and increase in infection over 3 years (Campbell and Guy, 2001). Incidences high enough to be problematic in production in the Fraser Valley, Canada, were alluded to the resistance screening report by Bittman et al. (2006). Gilmore et al. (2017) reported incidences >45% and increasing incidences of CfMV in orchardgrass in Oregon, USA from 2014-2016.

Virus symptoms including mosaic suggest the possibility of CfMV but are not sufficient to determine the pathogenic agent. CfMV can be definitively diagnosed using serological assays such as enzyme-linked immunosorbent assays (ELISA) or sequence-based amplification assays.

Cocksfoot streak virus produces symptoms very similar to Cocksfoot mottle virus and is also manually transmitted; however, Cocksfoot streak virus has filamentous particles, is transmitted by aphids (Myzus persicae and Hyalopterus humilis), and cannot be transmitted to oats, barley or wheat (Serjeant, 1964). Ryegrass mosaic virus is similar to CfMV in that it infects oats and orchardgrass; however, it does not infect wheat and is mite-transmitted (Serjeant, 1964). CfMV may be confused with Cocksfoot mild mosaic virus partially due to similar symptomology and isometric particles; however, Cocksfoot mild mosaic virus can readily be transmitted by aphids to Setaria italica (Huth, 1968). CfMV was found to be co-infected with Wheat streak mosaic virus (WSMV) in Ohio (Hodge et al., 2018), but WSMV does not infect orchardgrass.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

There are no currently recommended measures for CfMV infection prevention.

Cultural Control and Sanitary Measures

Mowing may efficiently spread CfMV even in the absence of cereal leaf beetle vectors (Catherall and Potter, 1987; Campbell and Guy, 2001) such that equipment sanitation may help reduce transmission. Host-plant resistance has been reported to decrease the impact of virus infection. Crop rotation with non-hosts may also reduce disease loads.

Host Resistance (Incl. Vaccination)

Orchardgrass resistant to CfMV has been selected for improved outcomes under infection conditions (Catherall and Potter, 1987; Rognli et al., 1995; Bittman et al., 2006). Catherall and Potter (1987) reported that some cultivars were less likely to become infected and exhibited better outcomes. Most resistance to CfMV in orchardgrass was reported to exhibit quantitative variation rather than single gene-conferred immunity to virus infection (Rognli et al., 1995). Such resistance to CfMV reported is alternatively termed ‘tolerance’ because virus replication is supported but yields are better under virus infection pressure than comparison genotypes (Rognli et al., 1995). Resistance selected by Bittman et al. (2006) improved yields up to 23% after artificial inoculation compared to non-resistant controls.

Most published data on CfMV incidence and yield impact are from previous decades and may not reflect current conditions. Field data-supported management recommendations are needed if current disease impacts warrant improved management. There is no information available regarding the optimal temperature requirements for CfMV infection and symptom development in its hosts. Further research is needed to examine the potential impact that CfMV has on wheat production in areas where it has been found, such as in Ohio, USA (Hodge et al., 2018; Hodge et al., 2020).

01/04/20 Original text by:

Brian A. Hodge, The Ohio State University, Department of Plant Pathology. 1680 Madison Ave., Wooster, Ohio, USA.

Lucy R. Stewart, United States Department of Agriculture, Agricultural Research Service. Corn, Soybean and Wheat Quality Research Unit. 023 Selby Hall, 1680 Madison Ave., Wooster, Ohio, USA.