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  • Author or Editor: M. J. Bukovac x
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The effect of CPPU [forchlorfenuron; N-(2-chloro-4-pyridinyl)-N-phenylurea] on berry development of selected seedless and seeded grape cultivars was evaluated under field conditions. A concentration response curve was initially established by spraying clusters of `Himrod' at a mean berry diameter of 5 mm with 0, 5, 10, and 15 ppm CPPU. Berry enlargement was monitored (16, 30, 44, and 59 days after treatment) during development and cluster weight, berry number/cluster, weight, firmness and °Brix were determined at harvest. Berry size was dramatically (2.3 vs. about 3.6 g/berry) increased at harvest by all concentrations of CPPU; the response being linearly related to concentration (r 2 = 0.89). Cluster weight and compactness (rated) and berry firmness were significantly increased. There was no significant effect on berry number (79 to 86/cluster). °Brix and rachis necrosis (at harvest) as well as berry abscission after 30 days of refrigerated storage were significantly reduced. Effect of time of CPPU application (0, 5, and 10 ppm) was established by treatment of clusters at mean berry diameters of 4, 5, 7, and 9 mm. Response was indexed by following berry enlargement at 14, 28, 42, and 56 (maturity) days after treatment. Maximum berry enlargement for both 5 and 10 ppm was obtained from applications at 4 to 7 mm in diameter. Relative responsiveness of seedless and seeded cultivars was compared by application of CPPU at 0, 5, 10, and 15 ppm to clusters (4–6 mm berry diameter) of seedless `Himrod', `Vanessa' and `Lakemont' and seeded `Concord' and `Niagara'. Bioresponse was determined by a time course of berry enlargement and berry and cluster weight, number of berries/cluster and rating cluster compactness at maturity. CPPU at all concentrations increased seedless berry diameter significantly from the first measurement at 14 days through 56 days after maturity. Berry and cluster weight and cluster compactness were increased in the seedless cultivars, although `Lakemont' appeared less responsive than `Himrod' and `Vanessa'. CPPU did not change (`Lakemont') or decreased (`Himrod', `Vanessa') berries/cluster. In contrast, the only effect of CPPU on the seeded cultivars was an initial increase in berry diameter 14 days after application.

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Most growth regulators and crop protection chemicals are delivered to the plant as aqueous sprays. Spray droplet:plant surface interaction is central to establishing spray and, hence, dose retention by the plant. Further, the nature of chemical deposition from spray droplets plays an important role in determining the efficiency of the active ingredient (a.i.). Using scanning electron microscopy and dispersive x-ray analysis, we investigated chemical deposit formation of selected growth regulators (e.g. ethephon, 2,4, 5-TP, TIBA) on leaf surfaces differing in wettability and surface fine-structure. The a.i. frequently deposited in the form of an annulus on droplet drying, and the degree of spreading was related to surface tension of the spray solution, and wettability, fine-structure and morphology of the leaf surface. Marked differences were observed in spreading following impaction on veins vs. interveinal areas of leaves of Prunus and Pyrus sp. The epidermis over veins was more readily wetted leading to rapid lateral diffusion along veins. Surfactants (e.g. Tween 20, Regulaid) altered the deposition pattern, expanding the annulus and increasing spreading on the leaf surface.

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Conjugation of 14C-1-naphthaleneacetic acid (NAA) was followed in leaf discs of apple, apricot, grape, orange, peach and pear. NAA was metabolized by all crops studied. Free NAA and 2 metabolites that chromatographed with naphthylacety1-β-D-glucose (NAG) and naphthylacetylaspartic acid (NAAsp) constituted 90% of the radioactivity recovered, NAG was the major metabolite (45-90%) followed by NAAsp (5-30%) and NAA (2-22%). Conjugation was most complete in orange (98%), intermediate in apple, apricot, peach and pear and least in grape (68%).

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