Submitted to: Eucarpia Conference on Lettuce and Leafy Vegetables
Publication Type: Abstract Only
Publication Acceptance Date: September 20, 2006
Publication Date: April 20, 2007
Citation: Hayes, R.J., Ryder, E.J., Wintermantel, W.M. 2007. Variation for Big Vein Resistance in Lactuca virosa L. and Introgression of Resistance into Cultivated Lettuce (Lactuca sativa L.). In Eucarpia Leafy Vegetables 2007 Conference Abstracts, University of Warwick, UK. pp. 16. Technical Abstract: Big vein is a damaging disease of lettuce (Lactuca sativa L.) caused by the Olpidium brassicae vectored Mirafiori Lettuce Big Vein Virus (MLBVV). Resistance to this disease is needed since no feasible cultural control methods have been identified. Partial resistance is available in cultivars such as Pavane, and is expressed as a delay in symptom expression and a reduced percentage of symptomatic plants at market maturity. Complete resistance has been identified only in Lactuca virosa accession IVT280, an incongruent wild relative of lettuce. Resistance from L. virosa IVT280 has not been introgressed into lettuce. The objectives were to 1) determine if L. virosa accessions exhibit variation for resistance, and 2) determine if resistance can be introgressed into lettuce. Greenhouse testing was used to evaluate resistance in L. virosa accessions, L. virosa – L. sativa hybrids and L. sativa cultivars. Seedlings were inoculated with root macerate of big vein symptomatic plants, transplanted to big vein infested soil, and greenhouse grown. The percentage of big vein symptomatic plants was recorded every week for 8 weeks. Seventy-nine accessions of L. virosa were tested over 3 years along with susceptible Great Lakes 65 (GL65). Great Lakes 65 ranged from 89% to 100% symptomatic plants. Variation for symptom expression was observed; 65 accessions had no symptoms, eight accessions had typical big vein symptoms, and 7 accessions had atypical symptoms (stunting and leaf crinkling). MLBVV accumulation was detected in IVT280 using a combination of RT-PCR and nucleic acid hybridization, although 83% of the plants were virus free, indicating that IVT280 appears to have a very high level of resistance. 90% of the plants in accessions with typical big vein symptoms were positive for MLBVV. Only one accession with atypical symptoms had MLBVV accumulation. The appearance of atypical symptoms does not appear to be related to the accumulation of MLBVV. Greenhouse testing was conducted on L. virosa - L. sativa hybrids from BC1F2 through the BC1F4:5 generation, IVT280, and L. sativa parents. Complete resistance as observed in IVT280 was not identified in these families, but variation for partial resistance was observed in every generation. Line 00-366-3 from the cross (IVT280 x Cocarde) x Galore, was the most resistant family in every generation, and was significantly more resistant than Cocarde and Galore. 00-366-3 and the related line 00-366-9 were used as parents to create BC2 progeny from crosses with high partial resistant cultivars, intermediate partial resistant cultivars and susceptible cultivars. Randomly selected BC2F2:3 families were greenhouse tested in an unreplicated experiment and variation for partial resistance was observed. Families that were numerically better than both parents were selected as putative transgressive segregants. These selections were retested as BC2F3:4 families, and confirmed the existence of transgressive segregants in crosses using high, intermediate, and susceptible parents. This research suggests that L. virosa contains alleles that confer partial resistance to big vein disease when introgressed into L. sativa, and, these alleles are distinct from those present in partially resistant cultivars. Alternative breeding strategies should be pursued to introgress complete resistance from L. virosa.