Wild Lactuca Species in North America

Abstract

This chapter presents a brief history of the uses of lettuce (Lactuca sativa L.) and its wild North American relatives, and reviews the agricultural importance of lettuce and challenges in its cultivation, in relation to nutritional quality, diseases, pests, and edaphic and climatic limitations. The evolution and taxonomy of the genus Lactuca are presented, with a primary focus on the wild Lactuca species of North America, their characterization, biogeography and distribution, habitat ecology, and genepools. Specific examples of phenotypic variability, genetic diversity and disease resistance of wild Lactuca taxa from both published reports and recent evaluations conducted in our laboratory are also presented. The past (and future) exploitation of wild Lactuca relatives in lettuce breeding is examined and discussed in the broader context of crop improvement. The current status of in situ and ex situ conservation of wild and weedy North American Lactuca is reviewed, along with recommendations on how these genetic resources could be better conserved and utilized.

Research Gaps and Challenges in the Conservation and Use of North American Wild Lettuce Germplasm

“…The genus Lactuca is composed of >100 species, the majority occur in Asia (51 species) and Africa (43 species), some others in Europe ( 17) (Lebeda et al, 2004b). From North America, up to 12 species have been described (Lebeda et al, 2007(Lebeda et al, , 2019; Kilian et al, 2017). Unfortunately, from a taxonomic viewpoint, the genus has not been the subject of a modern monograph (Lebeda et al, 2019).…”

“…From North America, up to 12 species have been described (Lebeda et al, 2007(Lebeda et al, , 2019; Kilian et al, 2017). Unfortunately, from a taxonomic viewpoint, the genus has not been the subject of a modern monograph (Lebeda et al, 2019). However, useful perspectives on the biosystematics and phylogeny of North American Lactuca species have recently been published ( Jones et al, 2018).…”

“…Within North America, native Lactuca species are widely distributed from Canada south to Florida and Mexico. These species are, in most cases, biennial (Lebeda et al, 2019). Lactuca species native to North America likely arose relatively recently, in the Pliocene (Kilian et al, 2017).…”

“…Additionally, three weedy, Old World species (L. saligna L., L. serriola L., and L. virosa L.) are found in North America (Lebeda et al, 2012), as well as the domesticate, cultivated lettuce (L. sativa L.) (Lebeda et al, 2007). All these species were introduced to the New World by European settlers (Lebeda et al, 2019), with the introduction of L. sativa possibly dating back to Columbus's second voyage of 1494 (Hedrick, 1972). Two additional taxa, L. terrae-novae Fern.…”

“…Cultivated lettuce is among the most important and popular leafy vegetables, used in salads in most parts of the world (Lebeda et al, 2007(Lebeda et al, , 2019. It is one of the most morphologically and genetically diverse vegetables, having distinct horticultural types (crisphead, cos [romaine], butterhead, leaf, Latin, stem [stalk], red leaf, baby lettuce, and oilseed), which differ in head shape and size, the shape, size, and texture of the leaves, stem length, and seed size (Lebeda et al 2007;Simko et al, 2014aSimko et al, , 2014b.…”