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M. Tagliavini and N.E. Looney

Root and shoot growth of peach seedlings was strongly suppressed when the roots were held at 8 to 10C. Shoot and root dry weights and root volume increased linearly with increasing root-zone temperature (RZT) to 22C. GA3 at 5.7 μm (2 ppm) added to the aerated full nutrient solution reversed the effect of low RZT on shoot elongation but inhibited root growth at all RZTs. Paclobutrazol (PBZ) (6.8 × 10-3μm) (2 ppb) inhibited shoot elongation at all RZTs and shoot dry weight at 16 and 22C. However, PBZ had no effect on root dry weight accumulation at any RZT. The shoot growth-promoting effect of GA3, relative to control plants, disappeared at higher RZTs, but GA3 reversed the growth-inhibiting effect of PBZ at all RZTs. PBZ increased mean root diameter at all RZTs and significantly increased root volume at 22C. These results show that growth of peach seedlings is profoundly influenced by a cool root-zone environment. The plant growth regulator effects suggest that seedling roots play an important role in whole-plant gibberellin physiology. Some possible implications for fruit production are discussed. Chemical names used: gibberellic acid (GA3); β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol(paclobutrazol,PBZ).

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M. Tagliavini, L.J. Veto, and N.E. Looney

Using area profile integration software and an image processing system, we reliably estimated total root surface area of intact each [Prunus persica (L.) Batsch.] seedlings by 1) producing high-quality monochromatic video images under preset and constant conditions; 2) determining a threshold gray intensity value that differentiates the finest roots on the image; 3) producing a binary image where all pixels with gray values above the threshold are black; 4) determining the proportion of black pixels on the 480× 512-pixel matrix; and 5) multiplying this two-dimensional root surface value by π to estimate total root surface area. Normalized intensity (an average intensity weighted according to the proportion of the binary image in each gray scale class) was calculated using software that superimposed the video image on the binary image and was used to estimate mean root diameter. Evidence of reliability and examples of the use of both estimates are provided.

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A.G. Reynolds, D.A. Wardle, C. Zurowski, and N.E. Looney

One of three levels (O, 1, 10 mg·liter-1) of the cytokinin-active substituted phenylurea compound CPPU was applied with or without 100 mg GA/liter to developing clusters of `Sovereign Coronation' and Summerland Selection 495 grapes (Vitis spp.). In a similar experiment, one of three levels (0, 1, 10 mg·liter-) of either CPPU or the related compound thidiazuron was applied to `Simone' and Summerland Selection 535. Both phenylurea chemicals tended to linearly increase cluster weight and berry weight while reducing degrees Brix, pH, and anthocyanins and increasing titratable acidity. A subsequent trial with O, 4, and 8 mg thidiazuron/liter on all four varieties yielded similar results. GA had no individual or synergistic effects. Due to the very low concentrations required, CPPU and thidiazuron show great promise as chemical tools for the increase of berry weight in seedless table grapes. Chemical names used: N-(2-chloro-4-pyridyl) -N'-phenylurea (CPPU); N1-phenyl-N'-l,2,3-thiadiazol-5-yl urea (thidiazuron);