Submitted to: Legume Viruses Working Group Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 1/10/2005
Publication Date: 4/30/2005
Citation: Wintermantel, W.M., Hayes, R.J., Nicely, P.A., Ryder, E.J. 2005. Mirafiori lettuce virus (MiLV) and Lettuce Big Vein Virus (LBVV) sequence diversity and frequency in California and Arizona lettuce, and analysis of big vein resistance. Joint Conference of the International Working Groups on Legume and Vegetable Viruses Proceedings. p. 44. Interpretive Summary:
Technical Abstract: Lettuce plants with varying severity of lettuce big vein disease symptoms were collected from fields throughout the Salinas Valley (CA), Yuma Valley (AZ), and adjacent lettuce producing areas. Symptom severity was determined based on a disease scale, and total nucleic acids were extracted from leaf tissue and analyzed by RT-PCR for the presence of MiLV and LBVV, and for genetic similarity to these viruses from other parts of the world. All symptomatic plants were infected with MiLV, and 83% were also co-infected with LBVV. Twenty-five percent of non-symptomatic plants were infected with MiLV and 69% were infected with LBVV. Sequence analysis of RT-PCR amplicons from each of 4 MiLV RNAs and from the LBVV coat protein region was used to determine the genetic diversity of these viruses in western lettuce growing regions and their similarity with samples from other parts of the world. Amplicons from each of the MiLV RNAs were at least 95 percent identical to one another and to sequenced isolates deposited in data bases, with RNAs 3 and 4 having the highest conservation. The LBVV amplicon shared at least 93% identity among western isolates. Growth of plants in infested soil under conditions facilitating disease induction in the greenhouse resulted in variable symptom production on susceptible and tolerant lettuce cultivars, but no symptoms on the L. virosa accession IVT 280. RT-PCR was used to confirm the presence or absence of MiLV and LBVV in symptomatic and asymptomatic plants. RT-PCR results confirmed that both susceptible and tolerant varieties accumulate virus, but that IVT 280 appears to be immune to both viruses. RT-PCR analysis for the presence of MiLV is an effective and valuable tool for germplasm improvement.