Genetic variation and phylogenies detected from isozyme markers in species of Lactuca

Altozyme variation among 31 collections of cultivated Lactuca sativa L. and wild Lactuca species was scored and used to assess genetic diversitles and phylogenies. Forty-two isozyme systems revealed 70 putative loci of which 22 showed polymorphism and 11 were shown to segregate in F₂ populations. Intra-line diversity based on 45 loci for which all 31 collections had been assayed, was low (H₉ = 0.007) as expected; inter-line diversity was markedly higher (D_st = 0.063) than that detected among natural populations of other taxa. The wild species exhibited even greater levels of diversity. The phylogenies of the cultivars and wild species as determined from the allozyme data, generally corroborated those based on morphological characters. Butterhead, crisphead, and romaine-like cultlvars formed distinct clusters. Similarly, accessions of each wild species L. serriola, L. sallgna, L. virosa, and landrace L. sativa all generally clustered as distinct entities.