Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 7, 2006
Publication Date: February 20, 2007
Citation: Hayes, R.J., Ryder, E.J. 2007. Introgression of novel alleles for partial resistance to big vein disease from lactuca virosa into cultivated lettuce. HortScience 42(1):35-39. Technical Abstract: Big vein is an economically damaging disease of lettuce (Lactuca sativa L.) caused by Mirafiori Lettuce Big Vein, which is vectored by the soil borne fungus Olpidium brassicae. Resistance to this disease is needed since no feasible cultural control methods have been identified. Partial resistance is available within cultivated lettuce, and is expressed as a reduced percentage of symptomatic plants. Complete resistance has been identified only in accessions of Lactuca virosa, a wild relative of lettuce. Resistance from L. virosa has not been introgressed into lettuce. The objective of this research was to determine if big vein resistance from L. virosa can be introgressed into lettuce. Backcross (BC) 1 hybrids between L. virosa and L. sativa cultivars were greenhouse tested for big vein resistance for 4 generations by infecting hybrid seedlings with O. brassicae zoospores collected from big vein symptomatic plants. Plots were evaluated for the percentage of symptomatic plants, and asymptomatic plants from resistant families were retained in every generation. Selected plants from resistant BC1 families were used as parents to create BC2F2 and BC2F2:3 populations for resistance testing. Complete resistance was observed in one BC1F3 family, however, high susceptibility was observed in the subsequent BC1F4 or BC2F2 generations. Variation for partial resistance was observed in all BC1 generations evaluated. One BC1 family was selected for high levels of partial resistance and used to create BC2 progeny by crossing to resistant and susceptible L. sativa parents. Transgressive segregants were identified among these BC2F2:3 families. This research demonstrates that Lactuca virosa contains alleles that confer partial resistance to big vein when introgressed in a L. sativa background, and, these alleles are distinct from those present in cultivated lettuce. Complete resistance to big vein may not have been recovered due to linkage between resistance alleles and alleles causing incongruity. Alternative breeding strategies should be pursued to introgress complete resistance from L. virosa into cultivated lettuce.