Introgression of Big Vein Tolerance from Lactuca virosa L. into Cultivated Lettuce (Lactuca sativa L.)

Big vein (BV) disease of lettuce is caused by soil borne fungal vectored viruses, and reduces marketability through head deformation. Tolerant cultivars reduce BV frequency, but no resistant cultivars exist. L. virosa L. is highly resistance. The objectives were to 1) determine if L. virosa P.I.s exhibit variation for resistance, and 2) determine if resistance is transferable to lettuce. Seedlings were inoculated with root macerate of BV infected plants, transplanted to BV infested soil, and greenhouse grown for 3 months. Twelve plants in each of 1,2, or 3 reps of Great Lakes 65 (GL65-susceptible), Pavane (Pav-tolerant), L. virosa (11 accessions), and BC1 F2 through F5 families of lettuce cultivars x L. virosa accession IVT280 were tested. The percentage of BV afflicted plants was recorded. In hybrid families, BV free plants from tolerant families were selected and advanced. No BV was found in L. virosa. Variation for tolerance was observed in BC1 F2 and F3 families; 33% had greater tolerance than Pav (17% afflicted). Additional tests identified 11 BC1 F3 families (14%) with greater tolerance than Pav (42% afflicted). Subsequent BC1 F4 and F5 generations however, were more susceptible than Pav. Lactuca virosa is highly resistant, but resistance did not transfer to hybrid progeny. Variation for tolerance was observed in BC1 F2 and F3 families, but later generations were susceptible. Interactions or linkage of genes for developmental processes and BV resistance may hinder introgression. Introgression will continue using congruity backcrossing and a greater diversity of L. virosa.