WSU--Tree Fruit Research & Extension CenterResearch Summaries
Return to E-mail to Don C. Elfving: delfving@wsu.edu |
Regulation of vegetative and reproductive growth in tree fruitDon C. Elfving, Horticulturist, WSUPlant growth regulators constitute an integral part of tree fruit production technology today and offer the promise of additional effective tools for improving tree fruit productivity and profitability in the future. In today's demanding economic environment, the cost of PGR materials mandates that we have the strongest possible technical base of knowledge about beneficial effects and limitations of PGR products to assure that Washington growers have the knowledge needed to effectively apply this technology in the orchard with the highest assurance of an economic benefit. We have a significant opportunity to develop new and better uses for both traditional and new PGR materials to help the Washington tree fruit growers and industry to succeed in a competitive world market environment. Many critical horticultural or physiological processes in tree fruits are influenced by plant hormones and may be affected by applications of growth regulators. Control of vegetative growth and regulation of flowering can have powerful impacts on production costs and returns. Fruit effects, such as enhancement of fruit size, effect on fruit shape, control of fruit maturity, regulation of preharvest drop, improvement of fruit color development, and management of postharvest fruit quality for extended storage represent processes potentially subject to external regulation and offer many opportunities for improved returns to the producer. The key ingredient in successfully applying these concepts to the improvement of orchard production efficiency is the research needed to understand how PGR materials can be used effectively to achieve those goals. My research program is focusing on management of vegetative growth and manipulation of fruit quality in the orchard. The program has two ultimate aims:
Management of Vegetative Growth and FloweringA new growth-regulating product, Apogee®, offers considerable promise as a tool for the control of vegetative growth in apple and pear. It may also have a stimulative effect on flowering. This material represents different chemistry than has been used for vegetative growth control in the past, yet it appears to have a similar mode of action. Trials are underway in both apple and pear to determine the potential for this material to control vigorous shoot growth and to assess its possible effects on fruit development. Past experience with vegetative growth controlling substances shows that they can have detrimental side effects on fruit growth. Initial observations with Apogee® on pear suggest that there may be effective growth control strategies that do not adversely affect fruit growth. In some apple orchards, the ability to reduce flower bud formation might be advantageous. In some blocks, especially of trees on dwarfing rootstocks, the routine overproduction of flowers, high fruit set potential and difficulties in chemical thinning have presented significant problems for growers seeking large fruit size. Gibberellic acid (GA) is a naturally occurring plant hormone known to inhibit flowering in apple. A variety of commercial GA products is available, and their possible beneficial use for regulation of flowering is unknown. Preliminary data from experiments on eastern apple cultivars suggest that field management of flowering may be possible with GA. Initial trials are underway to evaluate this concept. Enhancement of Fruit Size and Postharvest Quality1. The newly registered product ReTain® (aminoethoxyvinylglycine) functions as an inhibitor of ethylene synthesis in plant tissues. It has been used to delay ripening in apples and pears. Its use on pears has not produced consistent results. The effective delay of harvest maturity in both summer and winter pears would permit growers to more effectively schedule harvest, obtain better fruit size, and possibly have a product of better quality out of storage. Trials are underway to evaluate the potential of this material for managing pear fruit behavior and to design strategies that will permit maximum effective use of the product, especially in dense, crowded orchards where applications near harvest can damage significant quantities of fruit.
2. Cytokinin-containing products have the potential for increasing fruit size by stimulating cell division in the fruitlet. Trials are underway with the cytokinin-containing products Perlan® and Promalin® to assess their comparative effects on fruit size in Gala apple, a cultivar known to produce small fruit.
3. A preliminary screening trial has been established with a product based on a jasmonate derivative. Jasmonates are naturally occurring compounds thought to have some influence on the development of fruit maturity and quality parameters such as fruit color. This trial is intended to provide a quick look at a commercial jasmonate formulation for its possible impact on fruit quality factors.
Plant growth regulators have been and continue to be critical components in successful tree fruit production. The chemical thinning growth regulators NAA, NAD, Accel and carbaryl are widely used to control fruit set to improve fruit quality. Cytokinins, gibberellins and other plant growth regulators are used to regulate fruit shape, finish and quality. Fruit maturity can be enhanced (ethephon) or retarded (ReTain). Vegetative growth and flowering are subject to modification that can be accompanied by significant improvements in productivity. With the variety of new growth regulating materials appearing on the market today, opportunities exist to expand the number of growth regulating tools available to the commercial apple and pear growers of Washington.
|
Washington State University
Tree Fruit Research and Extension Center
1100 N. Western Ave.
Wenatchee WA 98801
phone: 509-663-8181
fax: 509-662-8714
Comments to webmaster@tfrec.wsu.edu