Intensity of radicle fluorescence as related to the resistance of seedlings of lettuce to the lettuce root aphid and carrot to the carrot fly

SUMMARY A technique is described which indicates by u.v. fluorescence the concentration of caffeoylquinic, chlorogenic and isochlorogenic acids in roots of germinating lettuce and carrot. The surface fluorescence of radicles from lettuce root aphid ( Pemphigus bursarius ) resistant seedlings was more intense than for susceptible seedlings, attributable to the higher concentration of isochlorogenic acid. In contrast, radicles of carrot seedlings resistant to carrot fly ( Psila rosae ) were less fluorescent than susceptible seedlings, corresponding to the lower concentration of chlorogenic acid in resistant seedlings. The technique is non‐destructive and has been developed to distinguish between cultivars or breeding lines potentially resistant to these insect pests.