Rose (Rosa hybrida L.) flowers are subjected, after harvest, to a number of stress conditions that stimulate the production of ethylene. This hormone, even in concentrations as low as 0.06 µl/l-1, predisposes flowers to infection by Botrytis cinerea Pers. Fr. (Jarvis, 1977).
Pulsing flowers with substances such as citric acid, salicylic acid, sucrose, calcium sulfate, and silver thiosulfate (STS) is promising in reducing damage caused by B. cinerea (Nowak & Rudnick, 1990; Torre et al., 1999). The term pulsing has been used by scientists to describe a technique where flower stems are immersed in a chemical solution to carry to the tissues, through the xylem, substances that may reduce senescence and increase the vase life of the flowers.
Citric acid seems to act by reducing the pH of water and, consequently, the proliferation of bacteria, which block the xylem vessels in the cut region and interfere with the normal flux of water through the stem (Nowak & Rudnicki, 1990). There is little research on the effects of citric acid on the severity of gray mold in harvested roses or other species.
Salicylic acid has been tested for control of post harvest diseases. Gaur & Chenulu (1982) determined that salicylic acid in concentrations of 100, 500, and 1000 µl/l-1 was effective in controlling at least four pathogens of orange [Citrus sinensis (L.) Osbeck] and potato (Solanum tuberosum L.). Most of the research using salicylic acid is directed to induction of systemic acquired resistance (SAR) in hosts against the attack of pathogens (Ryals et al., 1996; De et al., 1999).
Sucrose has been used to increase the longevity of many kinds of flowers (Halevy et al., 1978a). Apparently, this sugar provides energy for fundamental cellular processes, such as maintenance of the structure and function of mitochondria and other organelles. Sucrose also helps in the regulation of the flux of water and minerals into the xylem vessels by controlling transpiration (Nowak & Rudnicki, 1990). It is important to emphasize the scarcity of research using sugars, in association or not with other substances, to control diseases.
Calcium ions in the form of sulfate (CaSO4), chlorate (CaCl2), or nitrate (CaNO3) are promising in the control of B. cinerea. Several studies have evaluated the effect of calcium, both in flowers and fruits to control diseases (Volpin & Elad, 1991; Conway et al., 1993). Since B. cinerea infects, preferably, tissues undergoing senescence (Jarvis, 1977), researchers have emphasized the utilization of calcium to increase the resistance of tissues and delay senescence, by inhibiting ethylene synthesis or action (Torre et al., 1999). This effect on ethylene production and mode of action culminates in the control of gray mold after the harvest of flowers (Elad & Evensen, 1995)
Silver thiosulfate (STS) has been often used in the pulsing of flowers (Han, 1998). This substance improves the vase life of many species of flowers, by inhibiting the action of ethylene (Serek & Reid, 1993). The STS increases the longevity and reduces abscission of flowers (Han, 1998). Many studies have utilized STS to increase flower vase life, but few have examined its ability to control B. cinerea in roses.
Considering the losses due to gray mold after harvest of roses and the potential of the afore mentioned substances in reducing these losses, a study was carried out to determine the effect of these substances on the vase life and gray mold severity in rose cv Kiss.