Genetic composition of contemporary proprietary U.S. lettuce (Lactuca sativa L.) cultivars

Pedigree history of 146 lettuce (Lactuca sativa L.) cultivars registered in the U.S. by Plant Variety Protection and/or utility patent of the era from 2000 through 2010 facilitates determination of coefficient of parentage among these cultivars, identification of ancestral parental lines, and their genetic contribution. Principal ancestors of leaf lettuce developed in this era are the cultivars ‘Malibu’, ‘Waldmann’s Green’, and ‘Salad Bowl’ contributing 6.4, 6.1, and 3.5% of the genes, respectively. The cultivars ‘Parris Island Cos’ and ‘Tall Guzmaine’ are major ancestors of romaine lettuce, contributing 25.9 and 23.4% of the genes, respectively. Three crisphead lettuce ancestors identified are the cultivars ‘Vanguard’, ‘Salinas’, and ‘Calmar’, the former two descend from interspecific crosses of L. sativa with Lactuca virosa L. and Lactuca serriola L. Among these three, ‘Vanguard’ is the major ancestor contributing 23.8% of the genes to crisphead lettuce. The crisphead cultivar ‘Salinas’ was frequently crossed with romaine lettuce types and the romaine parental cultivar ‘Parris Island Cos’ was crossed with leaf types contributing to romaine and leaf lettuce genetic diversity, respectively. Genetic similarity was less within leaf cultivars (coefficient of parentage = 0.02) than found within romaine (0.15) and crisphead (0.13) cultivars registered in the U.S. during this era.