EFFECT OF WATER STATUS ON DENDROBIUM FLOWER SPRAY POSTHARVEST LIFE

The postharvest life of Dendrobium spp. flower sprays was limited by wilting and shedding of individual flowers. Late-summer-harvested sprays had a reduced postharvest life compared to winter-harvested sprays. Cultivars differed in postharvest life in response to packing and storing for 2 days at 22C. Water loss rates of 'Princess' sprays continuously held in deionized water declined from almost-equal-to 1.25 g/day per spray 4 days after harvest to 0.35 g/day per spray 20 days later. Flower shedding occurred when the rate of water loss fell below almost-equal-to 1.0 g/day per spray. Addition of a floral preservative to the vase water slowed the decline in water loss and increased postharvest life. Sprays packed and stored for 6 days at 22C had half the postharvest life of nonpacked controls held in deionized water or of sprays packed for 2 or 4 days at 22C. Submerging sprays in water immediately after harvest did not significantly increase postharvest life; submerging the sprays after harvest, before packing, and again after unpacking reduced postharvest life. Sprays could not be held for more than 4 days at 10C without suffering chilling injury. Silver thiosulphate (2 mM) and other silver preparations had no effect on postharvest life, although silver ions did reach the top flowers of the spray; thus, ethylene may play only a minor role in spray postharvest life. The postharvest life of sprays was increased by using boiled deionized water in vase solutions and by the continuous presence of chloramphenicol. Other antimicrobial agents, such as Physan, sodium hypochlorite, and sodium dichloro-s-triazinetrione dihydrate were without effect. Microbial growth in the vase solution and at the cut stem end may have reduced water transport and induced subsequent flower wilting and shedding.