| LETTUCE BIG VEIN|
|Prepared by R. Hayes et al.|
| Pathogen Responsible|
Mirafiori lettuce virus
| Description and Sympotoms|
Lettuce big-vein disease has been known in the U.S. since 1934 (Jagger and Chandler 1934). Symptoms include loss of chlorophyll around the vascular bundles in the leaf (often referred to as vein banding) and increased stiffness of the leaves, giving a bushy appearance and preventing proper head formation. The disease occurs in all market types of lettuce. Economic damage of commercially produced lettuce results from reduced plant size and decreased frequencies of plants possessing a marketable appearance. The disease is found worldwide and is caused by Mirafiori lettuce big-vein virus (MLBVV) (Lot et al., 2002). Isolates of MLBVV collected from four continents can be divided into two major groups (A and B) (Navarro et al., 2005a; Maccarone et al., 2010). Arizona and California MLBVV isolates are closely related to each other and to group A isolates found internationally (Hayes et al., 2006). The virus is vectored by Olpidium virulentus, a ubiquitous soil-borne fungal root parasite (Sasaya & Koganezaw, 2006; Hartwright et al., 2010; Maccarone, 2013).
| Current Management|
Big-vein is most prevalent in cool wet soils, conditions that are favorable for both the vector and virus symptom expression (Campbell & Grogan, 1963; Westerlund et al., 1978a, 1978b). Winter and spring lettuce crops should be avoided in fields with a history of severe big-vein. O. virulentus produces resting spores containing MLBVV that may survive for decades and certain weed species may act as reservoirs of MLBVV and O. virulentus. (Jones, 2004; Navarro et al., 2005b, Maccarone, 2013). Consequently crop rotation is not effective at reducing disease levels. The disease may spread through movement of infested soil or water, through infected transplants, or seed externally infested with O. virulentus resting spores carrying MLBVV (Jones, 2004; Maccarone, 2013). Proper hygiene of equipment, around productions areas, and planting materials may limit the spread of big-vein disease to new sites. Soil fumigation with methyl bromide can reduce big-vein incidence for a limited number of subsequent crops (Campbell et al., 1980). Reduced disease may be observed in transplanted crops treated with fungicide or by covering the beds with black polyethylene mulch (Campbell et al., 1980; Latham & Jones, 2004).
| Genetics of Resistance|
Incomplete resistance (IR) or partial resistance to tipburn is known in some lettuce cultivars that is expressed as a decreased rate of symptom development or lower frequencies of symptomatic plants at harvest maturity (Campbell & Grogan, 1963; Bos & Huijberts, 1990; Ryder & Robinson, 1995; Fujii et al., 2003; Latham & Jones, 2004; Hayes et al., 2006). Cultivars and progeny from experimental crosses exhibit quantitative differences for IR as well as extensive genotype x environment interaction (Ryder & Robinson, 1995). Iceberg cultivars were developed by the USDA-ARS in Salinas, CA with increased IR (Ryder and Robinson, 1991) and quantitative trait loci for IR on multiple linkage groups have been identified (Michelmore, 2010). Accessions of the wild relative L. virosa can be asymptomatic to big-vein (Bos & Huijberts, 1990; Hayes et al., 2008), though some asymptomatic accessions may accumulate high levels MLBVV (Hayes et al., 2008). Progeny from interspecific crosses between L. sativa cultivars and L. virosa accession IVT280 developed by B. Maisonneuve (INRA, France) were tested for big-vein resistance in Salinas, CA. Hybrid progeny were identified that expressed a high level of IR, but no progeny completely lacking big-vein symptoms were identified (Hayes & Ryder, 2007). However, the genes controlling IR from L. virosa appear to be independent of the genes controlling resistance in cultivated lettuce (Hayes & Ryder, 2007). Resistance to big-vein and MLBVV was reported in transgenic lettuce expressing inverted repeats of the MLBVV coat protein gene (Kawazu et al., 2009; Kawazu et al., 2010). Lettuce has genetic variation for susceptibility to Olpidium (Campbell, 1978). However, the genetic basis of this variation and its role in big-vein resistance, if any, has not been investigated. Clearly, there is potential for increasing resistance to big vein that has yet to be exploited.
| Genetic Marker Development|
Additional genetic analyses of the genetics of big vein resistance from a variety of sources are warranted. Some are underway. So far, no molecular markers for marker assisted selection of big-vein resistance have been developed and validated.
- Bos, L. and Huijberts, N. 1990. Screening for resistance to big vein disease of lettuce. Crop Protection 9:446-452.
- Campbell R.N. 1978. Lettuce virus and virus-like diseases (1977-78). Report to the California Iceberg lettuce Research Program, April 1, 1977 to March 31, 1978.
- Campbell, R.N. and Grogan, R.N. 1963. Big vein virus of lettuce and its transmission by Olpidium brassicae. Phytopathology 53: 252-259.
- Campbell, R.N., Greathead, A.S., and Westerlund, F.V. 1980. Big vein of lettuce: infection and methods of control. Phytopathology 70:741-746.
- Fujii, H., Sasaya, T., Takezaki, A., Ishikawa, K. and Fujino, M. 2003. Resistance to lettuce big-vein disease in lettuce cultivars. J. Japan Soc. Hort. Sci. 72:315-317.
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- Hayes, R. J., Wintermantel, W. M., Nicely, P. A., and Ryder, E. J. 2006. Host resistance to Mirafiori lettuce big-vein virus and Lettuce big-vein associated virus and virus sequence diversity and frequency in California. Plant Dis. 90:233-239.
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- Kawazu, Y., Fujiyama, R., Noguchi, Y., Kubota, M., Ito, H., and Fukuoka, H. 2010. Detailed characterization of Mirafiori lettuce virus-resistant transgenic lettuce. Transgenic Res. 19:211-220.
- Latham L.J. and Jones, R.A.C. 2004. Deploying partially resistant genotypes and plastic mulch on the soil surface to suppress spread of lettuce big-vein disease in lettuce. Australian Journal of Agricultural Res. 55:131-138.
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- Maccarone, L.D., Barbetti, M.J., Sivasithamparam, K., Jones, R.A.C. 2010. Comparison of the coat protein genes of Mirafiori lettuce big-vein virus isolates from Australia with those of isolates from other continents. Arch Virol 155:1519-1522.
- Maccarone, L.D. 2013. Relationships between the pathogen Olpidium virulentus and the viruses associated with lettuce big-vein disease. Plant Dis. 97:700-707.
- Michelmore, R.W. 2010. Genetic variation in lettuce. Annual Report to the California Lettuce Research Board. http://calgreens.org/control/uploads/Michelmore_Variation_report_2009-2010_final_%282%291.pdf. Accessed January 13, 2014.
- Navarro, J. A., Torok, V. A., Vetten, H. J., and Pallas, V. 2005a. Genetic variability in the coat protein genes of lettuce big-vein associated virus and Mirafiori lettuce big-vein virus. Arch. Virol. 150:681-694.
- Navarro, J. A., Botella, F., Maruhenda, A., Sastre, P., Sanchez-Pina, M. A., and Pallas, V. 2005b. Identification and partial characterisation of Lettuce big-vein associated virus and Mirafiori lettuce big-vein virus in common weeds found amongst Spanish lettuce crops and their role in lettuce big-vein disease transmission. Eur. J. Plant Pathol. 113:25-34.
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- Ryder, E. J. and Robinson, B. J. 1995. Big-vein resistance in lettuce: identifying, selecting, and testing resistant cultivars and breeding lines. J. Amer. Soc. Hort. Sci. 120, 741-746.
- Sasaya, T and Koganezaw, H. 2006. Molecular analysis and virus transmission tests place Olpidium virulentus, a vector of Mirafiori lettuce big-vein virus and tobacco stunt virus, as a distinct species rather than a strain of Olpidium brassicae. J. Gen. Plant. Pathol. 72:20-25.
- Westerlund, F.V., Campbell, R.N., and Grogan, R.G. 1978a. Effect of temperature on transmission, translocation, and persistence of the lettuce big-vein agent and big-vein symptom expression. Phytopathology 68, 921-926.
- Westerlund, F.V., Campbell, R.N., Grogan, R.G., and Duniway, J.M. 1978b. Soil factors affecting the reproduction and survival of Olpidium brassicae and its transmission of big-vein agent to lettuce. Phytopathology 68, 927-935.