University of California

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Breeding lettuce for fresh-cut processing

Ryan J. Hayes (United States Department of Agriculture, Agricultural Research Service, Crop Improvement and Protection Unit, 1636 E. Alisal St, Salinas, CA 93905)

Ivan Simko (United States Department of Agriculture, Agricultural Research Service, Crop Improvement and Protection Unit, 1636 E. Alisal St, Salinas, CA 93905)

Lettuce is increasingly consumed in fresh-cut packaged salads. New cultivars specifically bred for this use can enhance production and processing efficiency and extend shelf life. Cultivars with novel head architectures and leaf traits are being released by private and public breeding programs with the goal of increasing consumer appeal, increasing yield, or decreasing waste. Cultivars grown for processing require elevated resistance to tipburn (TB) and improved shelf life. Multiple field experiments with three lettuce populations determined that tipburn incidence has low heritability, large genotype x environmental interactions, and significant genetic correlations with head morphology. Several morphological traits that promote low TB are undesirable for fresh-cut processing. Improved TB resistance is needed most in romaine cultivars. Romaine lines with enhanced TB resistance have been selected from iceberg x romaine crosses, though further improvements are needed. Accessions with genes conferring resistance to viral, fungal, and bacterial diseases have exceptionally rapid decay as fresh-cut salad, which has prevented adoption of these resistances by the lettuce industry. The genetics of rapid decay was investigated in two recombinant inbred line populations of lettuce grown in six field experiments. A large effect quantitative trait locus (QTL) was mapped to chromosome 4 and had limited QTL x environment interactions. Breeding lines combining disease resistance and slow decay have been released and molecular markers for use in marker-assisted selection for slow decay are under development. The biology of shelf life is poorly understood. Cloning the gene controlling this QTL may improve our understanding of fresh-cut lettuce decay.

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