POSTHARVEST CONTROL OF VASE LIFE AND SENESCENCE OF ROSE FLOWERS
A number of parameters are used to characterize longevity and to define the symptoms of termination of the life span of cut rose flowers. For example, flowers are commonly reported to be no longer acceptable because of sepal yellowing or petal wilting or petal blueing or petal abscission or lack of flower bud opening, or peduncle bending. However, these symptoms may reflect different processes and mechanisms occurring concomitantly during flower senescence. Often, 'the longevity was improved', however the sepals turned yellow or petals blue or buds failed to open.
The subject of the present review is to attempt to distinguish between some of the major factors involved in the postharvest vase life of rose flowers and to examine them in some detail.
The postharvest behaviour of roses is distinguished from that of other flowers mainly by their low sensitivity to ethylene and the absence of flower bud and leaf abscission. However, both flower bud and leaf abscission may occur on exposure of flowers to elevated levels of ethylene (Zimmerman et al. 1930).
The postharvest behaviour of rose flowers is an outcome of physiological processes occurring in the leaves, stem, the flower bud, and the leafless peduncle or scape connecting the bud to the stem. Some of these processes may act independently to affect the senescence and vase life of rose flowers, but most of them are interrelated and correlated. Many of the post-harvest phenomena observed in the flower bud and in the peduncle are dependent on the water supply through the stem. Thus, a major factor in the performance of the harvested flowers is the water status of the leafy stem, which in turn is a result of water uptake through the stem base, its conductance through the stem, its loss through the leaves regulated in [art by stomatal function. It was clearly shown (Durkin and Kuc, 1966) that the reduced life span of roses can be attributed to the stem injury caused by the harvesting procedure. Flower excision results in a water loss in excess of the water uptake (Burdett, 1970; De Stigter, 1980a), leading to a decline in the stem water potential (Mayak et al., 1974). The longevity of cut roses was extended when their water loss was reduced by cooling (Farnham et al. 1978), high humidity (Kohl and Rundell, 1972), leaf removal (Carpenter and Rasmussen, 1974) or stomatal closure by the application of abscisic acid (Halevy et al. 1974; Kohl and Rundell, 1972), aluminum ions (Schnabl, 1976; Schnabl and Ziegler, 1974) or CO+2 ions (Venkatarayappa et al., 1980). Halevy et al. (1974) elegantly demonstrated the opposing effects of ABA on rose flower longevity, i.e., its positive effect in leafy flowers by reducing water loss and its negative effect in leafless flowers by promotion of petal senescence. An improvement in the water balance was achieved through an increase in water uptake and water conductivity by recutting the stem base under water (Dunkin, 1982; Rasmussen, 1979; Thompson and Staby, 1983), by water acidification (Conrado et al. 1980; Durkin, 1979b; Marousky, 1971; Zieslin and Kofranek, 1980) and by degasification of water (Durkin, 1979a).