Post-harvest leaf quality and shelf life continue to be of major importance in preventing crop losses and increasing profitability for the lettuce industry. This is true for several lettuce types, harvested whole, prepared as chopped or baby leaf salad mixes. Over the past ten years, we have identified a suite of pre-harvest traits that are tightly linked to long shelf-life and include the development of leaves with tightly packed small cells, low stomatal number, high contact angle and most importantly, high break strength (the ability of the leaf to withstand breaking following application of a weight). The plasticity and elasticity of lettuce leaf cell walls appears to be key in determining shelf life – defined here as the ability of the crop to withstand harvesting, washing and packaging. We have identified QTL, co-locating QTL for traits of interest and robust QTL in multiple environments for these traits. At the same time we have also quantified significant variation in wild lettuce for metabolic traits that underpin antioxidant status and this is a novel trait that has yet to be exploited.
The over-arching aim of this new research programme is to develop highly targeted molecular markers for both shelf life and leaf nutritional quality and to test these in a wide diversity population. Moving from to candidate genes to markers has now entered a new era with the availability of the lettuce genome and we will use CRISPR-Cas gene editing and other approaches as proof of concept that our candidate genes are active. We will initiate new crosses at UC Davis and introgress these traits into breeding material. At the end of this project we will have gained significant new understanding of the underpinning genes for shelf life and leaf nutrition and have developed novel markers, with proof of concept from a number of biotechnical approaches to test their robustness.