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Edward J. Ryder and David C. Milligan

Six genes controlling flowering time or bolting time in Lactuca L. have been reported. Several crosses between parents differing in time to opening of first flower were made to ascertain the inheritance of additional flowering time traits in Lactuca species. The parents in the crosses were of five flowering classes: very late (VL), late (L), early (E), very early (VE), and very, very early (VVE). Segregation from a cross between C-2-1-1 (VL) (L. sativa L.) and `Vanguard 75' (L) confirmed that `Vanguard 75' flowering was controlled by the previously identified gene Ef-2ef-2. Mutant line 87-41M-7 (VVE) was crossed by D-3-22M (VE) and segregated 3VVE:1 VE, indicating a dominant allele, Ef-3, that decreased flowering time an additional 7 days. Cos-like line 796 (VE) was crossed to cultivars Salinas (VL) and Vanguard 75. Segregation indicated a gene Ef-4ef-4, with lateness dominant. PI 175735 (E) (L. serriola L.), crossed with C-2-1-1 produced an F2 population with a bimodal distribution, segregating 3 E:1 VL, indicating a single gene Ef-5ef-5. PI 236396 (E) and PI 250020 (E) were crossed to `Salinas' and `Vanguard 75'. Segregation and morphological similarity indicated the same gene in both PI lines, Ef-6ef-6, with earliness dominant.