Abstract
To discuss the sampling method for quantification of sesquiterpene lactones (SLs) in breeding of lettuce (Lactuca sativa L.) varieties with high SL concentrations, differences in SL concentrations in different leaf parts and head formation stages were investigated in three lettuce cultivars using HPLC. Significant differences in SL concentrations among the outer leaves, outer head-leaves, inner head-leaves and stem were observed. A high correlation coefficient was observed between SL concentration in the outer leaves and that in the whole head. Excision of outer leaves for sampling does not affect progeny seed production, therefore outer leaves are available as the sample for rough estimate of the SL concentration in the lettuce head. Differences in SLs concentrations were significant among three stages of head formation; beginning of heading, optimal harvesting and over-ripening. Varietal differences of SLs concentration were observed from the beginning stage of heading and a significant correlation between SL concentration at the beginning stage and that at the optimal harvesting stage was observed. This means that an earlier sampling at the beginning stage of heading is available for an estimate of SL concentration at the optimal harvesting stage.
