CHLOROPHYLL FLUORESCENCE IN RELATION TO SUPERFICIAL SCALD DEVELOPMENTIN APPLE

The relationship between chlorophyll fluorescence of 'Cortland', 'Redc hief Delicious', and 'Empire' apple (Malus xdomestica Borkh,) fruit an d the development of superficial scald was studied during 120 days of refrigerated air (RA) storage at 0 degrees C and during 7 days of post storage holding at 22 degrees C, Minimal fluorescence (lo), maximal fl uorescence (Fm), photochemical efficiency (Fv/Fm, where Fv = Fm - Fo) and coefficient of photochemical fluorescence quenching (qp) were meas ured. During storage, while Fv/Fm and Fm declined in 'Cortland' and 'R edchief Delicious' fruit over time, these two measures of chlorophyll fluorescence remained stable in 'Empire' fruit. Of the three cultivars , only 'Empire' is resistant to and did not develop superficial scald. A decline in Fv/Fm preceded scald development in 'Cortland' and 'Redc hief Delicious' fruit. After 30 days of storage, qp began to decrease in fruit from all three cultivars, Prestorage diphenylamine (DPA) appl ication had no effect on Fv/Fm, Fo, and Fm and only marginally improve d maintenance of qp, but completely prevented the development of super ficial scald. Poststorage holding at 22 degrees C accelerated the rate of change in most fluorescence measurements. The decline in the Fv/Fm ratio and/or qp with storage time may be in response to senescence-re lated factors that also enhance scald susceptibility, however, Fv/Fm d oes not appear to be directly related to superficial scald susceptihil ityper se.