Postharvest Biology and Technology of Cut Flowers and Potted Plants

The relatively brief postharvest life of most cut flowers and potted flowering plants can be extended by a range of technologies. Studies have shown that vase life is negatively correlated with respiration after harvest, so prompt cooling to the lowest safe storage temperature is a key to long-distance transport of these perishable crops. Forced air cooling is the method of choice for cut flowers, and vacuum cooling has been shown to be very effective for cooling potted plants. In contrast to some other horticultural crops, controlled andmodified atmospheres seem to have little effect on petal respiration, and these techniques have not proved commercially useful in the marketing of many cut flowers. Low temperatures are also important in managing the effect of other factors contributing to early senescence, including water loss, the effects of ethylene, leaf yellowing, and the growth of diseases, particularly caused byBotrytis cinerea. Ornamentals originating in the tropics and subtropics cannot be cooled below 10 C because they rapidly show the symptoms of chilling injury. Chemical strategies to improve the life of ornamentals include the application of abscisic acid to reduce water loss, particularly in potted and bedding plants, pretreatment with the volatile ethylene inhibitor 1-methylcyclopropene (1-MCP) to prevent the 1 Horticultural Reviews, Volume 40, First Edition. Edited by Jules Janick. 2012 Wiley-Blackwell. Published 2012 by John Wiley & Sons, Inc. effects of endogenous or exogenous ethylene, treatment with gibberellins or cytokinins (CKs), which often delay leaf yellowing and may increase bud opening and flower life. Thidiazuron, a nonmetabolized CK, has proven particularly effective for this purpose. A new strategy for inhibiting the growth of B. cinerea on floral tissues is to treat them with low concentrations of hypochlorite. Floral senescence is an active process with many of the hallmarks of programmed cell death. Molecular analysis has revealed a large number of candidate genes with possible roles in senescence and remobilization. Virusinduced gene silencing has been used to evaluate the potential role of some of these genes, particularly regulatory genes such as transcription factors and kinases, although none has yet been identified as a key controller. Ornamentals are particularly suited to testing transgenic strategies for extending shelf-life, and we report results of experiments using constructs where inducible promoters are used to drive genes that extend flower life. Of particular interest is the dramatic extension of longevity resulting from silencing a component of the 26S proteasome, which indicates the importance of targeted protein degradation in control of floral senescence, and could serve as a strategy for extending the life of ethylene-insensitive ephemeral flowers. Future research will undoubtedly focus on providing better germplasm by using traditional, genomic assisted, and/or molecular breeding approaches for improving the postharvest performance of ornamentals.