Crops & Livestock | Farm

Scientific Research Helps Improve Romaine Lettuce

Credit: Pixabay/ Hundankbar

USDA scientists have identified five Romaine lettuce varieties that both brown less quickly after fresh-cut processing and are slower to deteriorate postharvest.

They also are determining the genetic basis for deterioration. The researchers have identified the location of genes associated with postharvest deterioration of fresh-cut lettuce and are in the process of identifying genes associated with browning – two economically important traits.

This will speed up the development of new Romaine varieties with better shelf life because now lettuce breeders will be able to check that offspring carry these genes without needing to grow out and destructively test for browning and deterioration resistance.


Lettuces are the most popular, commercially produced, leafy vegetables in the world. They had a farmgate value of more than $2.5 billion in the United States in 2017, making it one of top 10 most valuable crops for the country. But fresh-cut lettuce is a highly perishable product.

“Now having these molecular markers means that slow deterioration and eventually less browning can be more easily integrated into lettuce breeding, traits that are important economic considerations,” says research geneticist Ivan Simko with the agency’s Agricultural Research Service Crop Improvement and Protection Research Unit in Salinas, California. Simko led the study.

The researchers found the chromosome region that contains the genes for slow deterioration also contains four genes that code for resistance to downy mildew – one of the most-costly lettuce diseases. 

There is a strong linkage between one or more of four genes and the rate of deterioration. DNA-based markers can be used to develop new breeding lines with a slow rate of deterioration and desirable combinations of resistance genes.

Deterioration is the rupture of cells within lettuce leaves, leading to waterlogging and the lettuce turning to mush. Browning is the discoloration of the edges of lettuce after cutting or tearing. Either development can spoil the leafy vegetable’s value by decreasing shelf life.

Like deterioration, there was a significant correlation between high resistance to browning and pedigree, which gives promise that lettuce breeders will be able to improve the trait and incorporate it into new varieties.

This research was published in Horticulture Research and Postharvest Biology and Technology.