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KMID : 0903619980390010125
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Journal of the Korean Society for Horticultural Science
1998 Volume.39 No. 1 p.125 ~ p.128
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Plant Bioregulators in Fruit Production
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Looney, Norman E.
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Abstract
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Plant bioregulators (PBRs), frequently called plant growth regulators or PGRs, play an important role in modern fruit production. While the usage is greatest with deciduous tree and vine fruits, there are also important practices in citriculture and in the production of tropical fruits. PBRs influence cropping by synchronizing or advancing flowering, improving fruit set, $quot;thinning$quot; excessive flowers and young fruit, and by preventing preharvest fruit abscission. PBRs add value to fruit crops by improving fruit size, appearance and internal quality. They are also used to advance or delay fruit harvest by influencing fruit maturation and ripening (with important implications for managing harvest labour and targeting specific markets). PBRs have long played a role in facilitating a broad range of orchard, vineyard or nursery management practices. Examples include the use of ethephon to aid the mechanical harvest of tart cherries; using a combination of benzyladenine and gibberellins to encourage lateral branching of young apple and cherry trees; the use of rooting hormones (auxins) to propagate clonal rootstocks by cuttings; and use of cytokinins to facilitate the multiplication of fruit crops by meristem culture. Controlling shoot extension growth in fruit trees with gibberellin inhibitors continues to be an important practice in many countries. There are many good reasons for the continuing interest in these technologies, and the overall outlook for PBR usage in fruit production remains bright. However, it must be acknowledged that the development of new PBR products and practices slowed during the 1990´s. Contributing to this decline was a level of public apprehension about agricultural chemicals in general that was reflected in less government support for research on PBR chemistry and technology. Another factor was the promise of molecular genetics to achieve major gains in crop protection, quality and productivity. This field attracted funding away from PBR research and development. Finally, the agricultural chemical industry found that the escalating costs of developing and registering new products often exceeded potential returns. I contend, nonetheless, that there are important socio-political considerations and scientific advances that could result in a $quot;new age$quot; for PBR research, development and their usage in fruit production. First, the safety and suitability of PBRs for use in $quot;sustainable$quot; or $quot;integrated$quot; fruit production will be confirmed. The many instances where PBR usage can reduce or eliminate the use of more intrusive agricultural chemicals will be recognized and applauded. Second, the need for PBRs will persist. The problems presently addressed by PBR usage in fruit production will not be solved anytime soon by advances in breeding. Orchards and vineyards planted today will still be in production 20 to 50 years from now and the public´s demand for attractive, high quality fruit is unlikely to diminish in either the short or long term. It is also likely that our successes in genetic engineering, such as a fruit tree cultivar transformed to impart disease resistance, will still require a PBR treatment to maximize its value in production horticulture. Finally, new needs and opportunities for PBR chemicals will continue to appear. Plant physiologists, using the new tools of molecular biology, are making remarkable progress toward understanding the mechanisms of natural control of growth and development in fruiting plants. We can expect that this knowledge will be used to develop new chemicals and new PBR strategies that are more effective and more specifically targeted than is presently the case.
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