EFFECTS OF FLORET MATURITY, CYTOKININ AND ETHYLENE ON BROCCOLI YELLOWING AFTER HARVEST

The phytohormones ethylene and cytokinin have a central role in the po stharvest yellowing of broccoli. The relationship between ethylene syn thesis and the extent of yellowing was examined in three broccoli cult ivars ('Shogun','Green Belt' and 'Green Beauty'). In these cultivars, no consistent relationship was found between basal ethylene production and the rate of floret degreening (20 degrees C in darkness). In cult ivar 'Shogun', floret maturity stages were determined by examining the developmental stages of the pollen. Different patterns of ethylene pr oduction, ethylene sensitivity, respiratory activity and chlorophyll l oss occurred in florets of different maturities. Floret maturity is li kely to have the greatest effect on the rate of broccoli yellowing. Di pping florets (cv. 'Shogun') in 6-benzylaminopurine (6-BA) stimulated ethylene production, depressed respiration rate and delayed floret yel lowing. The effect of cytokinin on broccoli yellowing was related to c ytokinin concentration and postharvest floret age when the cytokinin w as applied. A continuous propylene treatment reduced the positive effe ct of cytokinin on broccoli colour changes.