Developing lettuce with improved quality for processed salads.

Authors: Hayes, Ryan; TRUCO, MARIA - University Of California; MCHALE, LEAH - The Ohio State University; MICHELMORE, RICHARD - University Of California; ANTONISE, RUDIE - Keygene Nv; HAND, PAUL - Harper Adams University College; Simko, Ivan

Submitted to: Eucarpia Conference on Lettuce and Leafy Vegetables
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2011
Publication Date: 8/24/2011
Citation: Hayes, R.J., Truco, M.J., Mchale, L.K., Michelmore, R.W., Antonise, R., Hand, P., Simko, I. 2011. Developing lettuce with improved quality for processed salads. Eucarpia Conference on Lettuce and Leafy Vegetables. August 24, 2011, Lille, France.

Interpretive Summary:

Technical Abstract: Lettuce is increasingly consumed as minimally processed salads. Cultivars grown for this market may require breeding for improved shelf-life and resistance to physiological defects such as tipburn (TB). Tipburn is a calcium deficiency related defect causing necrosis on the leaf margins, typically on the inner leaves where the damage is not easily observed until processing. Low heritability and correlations between plant morphology and tipburn incidence may impede resistance breeding efforts but make tipburn resistance an excellent candidate for marker-assisted selection. Three recombinant inbred line (RIL) populations (Salinas x (Valmaine x Salinas 88)=SV, Salinas 88 x La Brillante=SLa, and Saladin x Iceberg=SI), their parents and the check iceberg type cultivar Calicel were evaluated for TB incidence, head weight, core height, head closure, and head firmness in two replicated Yuma, AZ field experiments. Planting dates were in mid-December and evaluated in early April when high day-time temperatures (27-32°C) may promote tipburn. Tipburn incidence was high in all experiments, occurring in 85% of Calicel heads and 38% of Salinas 88 heads. The variation for TB incidence among RILs was significant (P<0.01). Broad-sense heritability estimates for TB on a per-plot basis were low for all populations (SI = 0.14, SV and SLa = 0.23), indicating that phenotypic selection for reduced tipburn incidence is relatively ineffective. Significant and positive genetic correlations with TB incidence were found with head closure in SV (0.84) and SLa (0.66), core height in SV (0.66), and head weight (0.86) and head maturity (0.67) in SI. The results indicate that specific morphological characters can condition low tipburn incidence and the relationships between tipburn incidence and plant morphology can be population dependent. These associations may hamper successful breeding of new tipburn resistant cultivars. Decay of cut leaf pieces is the limiting shelf-life factor for salad packaged in modified atmospheres. In three spring, summer, or winter replicated field experiments located in Salinas, CA and Yuma, AZ, the SLa population and parents were grown, harvested, processed into salad and packaged into modified atmosphere bags using the method of Hayes and Liu, 2008, J. Am. Soc. Hort. Sci., 133:228–233. Up to nine bags of salad were made for each RIL in each experiment. Each bag was assessed weekly for percent decayed pieces until all bags reached 100% decay. The variation among RILs was significant, and La Brillante had faster decay than Salinas 88 in all experiments. The mean percent decay data was used to detect quantitative trait loci (QTL) on a genetic linkage map comprised of single nucleotide polymorphisms and amplified fragment length polymorphisms. A significant (P<0.01) QTL on linkage group four (LG4) was detected in all field experiments, explaining 27% to 69% of the total phenotypic variation depending on the experiment. Significant (P<0.01) QTL with smaller effects (R2 <25%) were detected on LG9 in all experiments and LG1 in the Yuma, AZ experiment only. In this population, decay of salad-cut lettuce is a simply inherited trait with limited genotype x environment interaction and suitable for development of molecular markers for use in marker-assisted selection.