January 6, 2016

Fresh-cut lettuce breeders focus on decay

As a specialty market, fresh-cut produce demands specific attributes of the varieties of raw fruits and vegetables that supply it. Lettuce is the mainstay of fresh-cut, and breeders and researchers are diving deep into coming up with new varieties that have the mixture of desired attributes.

At the recent International Fresh-cut Symposium at the University of California, Davis, Ryan Hayes, research geneticist with the USDA-ARS Crop Improvement and Protection Unit in Salinas, California, described the latest developments, including research conducted with colleague Ivan Simko.

New cultivars aimed at satisfying consumer demand are being bred and released by both private and public breeding programs. Attributes breeders are seeking include:

  • Better production and processing efficiency
  • Extended shelf life
  • Elevated resistance to tipburn
  • Reduced browning and pinking
  • Higher yield
  • Decreased waste
  • Novel head architecture and leaf traits

Breeders desire certain physical qualities of lettuce because they lead to improved production and processing, Hayes said. These qualities include plant density, leaf color and core length. Lettuce is also bred to diminish the kinds of internal defects that are not visible until processing.

Tipburn is a concern for romaine and iceberg varieties. Improved tipburn resistance is highly desired in most romaine cultivars. Iceberg and romaine crosses have produced romaine lines with enhanced resistance, but further improvements are desired, Hayes said.

Progress has been made by incorporating genetic resistance, but the result has been a mixed blessing. Genes that provide resistance to viral, fungal and bacterial diseases also contribute to rapid decay in fresh-cut salads.

Hayes and Simko led research to explore the genetics of rapid decay in fresh-cut lettuce by studying two recombinant inbred line populations grown in six field experiments. They used a technique known as quantitative trait loci (QTL) mapping, which identifies a gene or genes controlling a specific trait. They found one particular chromosome group that shows sufficient promise to make it a target for marker-assisted selection against decay.

“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,” Hayes and Simko wrote in their project abstract.

Future improvements to postharvest quality of fresh-cut lettuce seem likely, Hayes said. There are factors complicating research, such as the diversity of modified atmosphere packaging systems. Marker based breeding schemes need to be generated for use in early generations.

Lee Dean, editorial director

 





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