Genetic variation, genotype × environment interaction, and selection for tipburn resistance in lettuce in multi-environments

Abstract

Tipburn is a calcium related and environmentally induced physiological disorder causing economic damage in all lettuce (Lactuca sativa L.) production regions. The objectives of this research were to determine (1) the genetic variation for tipburn incidence, (2) the genotype (G) × environment (E) interaction (GE) for tipburn incidence, and (3) the efficiency of field selection for tipburn resistance. Tipburn incidence was recorded over 2 years in Salinas, CA, and Yuma, AZ, for 55 romaine, crisphead, green leaf, and red leaf type cultivars, and over 3 years in Quebec for 15 romaine cultivars. Analysis revealed that G, E, and GE affected tipburn incidence, including crossover interactions that were not repeatable over years. This indicates that cultivar/breeding line evaluations should be based on mean performance and stability over multiple environments. Among lettuce types, only crisphead had significant genetic variability for tipburn resistance, reflecting the greater breeding effort applied to this type compared romaine, green and red leaf types. Analysis of a dataset with five romaine cultivars in eight environments in California, Arizona, and Quebec for 2 years revealed that Yuma in 2006 and Saint-Blaise in 2005 were highly correlated (r = 0.923, P < 0.05), and were the most discriminating and most representative environments for tipburn evaluation. Single plant selection for tipburn resistance in three F2 romaine populations was ineffective. Further, the degree of head closure was significantly associated with tipburn incidence. Identification and selection of morphological characters associated with resistance in conjunction with direct selection against tipburn may be an effective method for genetic improvement of tipburn resistance.