Genetic Variation for Shelf-life of Salad-cut Lettuce in Modified-atmosphere Environments

Abstract

Packaged salad-cut lettuce (Lactuca sativa L.) for food service and salad mixes is an increasingly important component of the lettuce industry. The product is highly perishable; cold storage and modified-atmosphere (MA) packaging are used to extend its shelf life. Given the importance of this market, lettuce cultivars, breeding lines, and populations should be selected for increased shelf life in MA environments. The objectives of this research were to determine the genetic variation in lettuce for shelf life in low-O2 MA environments and to develop rapid evaluation methods suitable for a lettuce breeding program. Lettuce was processed from field-grown plants of 33 romaine and three crisphead cultivars over 2 years. Shelf life was evaluated after storage in MA bags and in CO2-free controlled-atmosphere (CA) chambers with gas ratios of 0.2% O2:99.8% N2, 1.0% O2:99.0% N2, or 5.0% O2:95.0% N2. Deteriorated leaf blade tissue was water soaked and wilted with a dull to dark or black color, and midrib tissue and heart leaves were water soaked with a translucent to dark brown color. Genetic variation for shelf life was detected using MA bags or CA chambers, and the results from both years and testing methods were significantly correlated. Oxygen concentration did not affect shelf life in the CA chamber experiment, which indicated that the observed symptoms in the majority of cultivars were probably not from low O2 damage or CO2 injury, although multiple mechanisms of deterioration may be involved. Selection for lettuce cultivars, breeding lines, and populations with extended shelf life is possible using MA bags or CA chamber testing methods and could facilitate a consistent release of germplasm with stable shelf life in MA environments.