THE DEVELOPMENT AND USE OF PLANT BIOREGULATORS IN TREE FRUIT PRODUCTION

Abstract

The discovery of plant hormones and their ability to regulate all aspects of plant growth and development were defining moments in horticulture. Plant bioregulators (PBRs) were soon identified that could improve yield, quality and postharvest life. No where has their impact been more vividly chronicled than in tree fruit production. Tree fruit are considered high value crops and even small modifications in production efficiency, product quality or enhanced cosmetic appeal have the potential to significantly increase product value. Following the discovery of auxins, NAA was found to both to useful in counteract two of the most serious problems of apple production, biennial bearing and preharvest drop. NAA continues to be an important PBR. The discovery of gibberellins and cytokinins led to commercial uses of products in these hormone categories that include improved shape of fruit, enhanced market value by reducing blemishes, improved tree architecture that may be accomplished the by overcoming apical dominance. PBRs were later discovered that could either advance ripening or extend postharvest life, thus greatly expanding the effective period when high quality fruit could be harvested and marketed. Other areas of fruit production where PBRs are especially useful include prevention of preharvest fruit drop, control of vegetative growth, enhanced flower bud formation and control of fruit ripening. Future uses of PBR will emerge. Prohaxadione calcium, an inhibitor of gibberellin biosynthesis, not only retarded shoot growth but it can also alter plant metabolism to impart resistance to insects and diseases. The naturally occurring hormone abscisic acid is showing potential for overcoming plant stress and also enhancing early fruit drop. Recently 1-MCP, a competitive inhibitor of ethylene, has revolutionized storage of pome fruit by extending the postharvest life and improving storage quality of fruit. Recently, great progress in PBR use has come in areas of fruit thinning and retardation of preharvest drop. In these areas greater understanding of fundamental processes, the use of molecular biology techniques and continued empirical research has lead to more effective control of these important process in tree fruit production.