ISHS Acta Horticulturae 463: VIII International Symposium on Plant Bioregulation in Fruit Production
THE PLANT SURFACE: A DEFINING FACTOR IN PERFORMANCE OF PLANT BIOREGULATORS |
| Author: | Martin J. Bukovac |
| Keywords: | cuticle, cuticular penetration, spray application, droplet retention |
| Abstract:
Plant bioregulators are unique agrochemicals in that they must be absorbed by the plant tissue and transported to a reaction site before the desired response can be achieved. Most plant bioregulators are applied as aqueous sprays to a variety of plant surfaces. The total surface area and, in particular, its surface chemistry and morphology are key factors in determining the bioregulator dose that will be retained and, hence, available for penetration. Essentially, all aerial plant organs are covered with a thin cuticle or cuticular membrane (CM), a noncellular, lipoidal covering that serves as the prime barrier to penetration of foliar applied chemicals. The CM is composed of a cutin matrix of esterified long chain hydroxylated fatty acids. The outer morphological surface is usually covered with difficult-to-wet epicuticular waxes, and a well-defined layer of highly oriented cuticular waxes is found embedded in the cutin matrix. While the surface chemistry and morphology (particularly roughness) determine the wetting properties and degree of spray retention, the structure and chemistry of the CM influence transcuticular penetration. Spray additives, like surface active agents, may alter the physio-chemical properties of the spray solution, thus improving wetting, spray retention and coverage. Penetration, however, is affected mainly by the nature (e.g., polarity, charge, and solubility), concentration and formulation of the penetrant, and by temperature and humidity. Specific surfactants may also enhance penetration not only by increasing the interaction between the penetrant and CM, but also by plasticizing the waxes and/or cutin polymer. The physical nature and composition of the chemical deposit formed on the plant surface after evaporation of the aqueous phase of the spray droplets appear to have a marked effect on penetration from the apparently dry deposits. | |
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