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D. J. Garrot Jr., M. W. Kilby and R. D. Gibson

Arizona is currently experiencing an explosion in the commercial cultivation and production of table grapes. Decreasing water supplies, increasing water cost, and recent groundwater legislation are forcing Arizona growers to be more water efficient if they are to remain competitive with other markets. Research was conducted to determine the effect of water stress on vine growth and berry ripening. “Flame Seedless” table grapes (4th leaf) were subjected to increasing water stress levels based upon infrared canopy temperatures and the crop water stress index (CWSI). A lower water stress level (CWSI = 0.18 units at irrigation) promoted earlier berry sizing, increased berry weight, and increased cluster weight over drier treatments. Significantly higher growth (P= 0.01), based on pruning weights, also was attained at the lower water stress level. However, highest production (grade 1 and 2 packed boxes) was attained when irrigations were scheduled at 0.30 CWSI units. Total applied water to maintain the wet, medium, and dry treatments was 1136 mm (CWSI = 0.18), 775 mm (CWSI = 0.30), and 669 mm (CWSI = 0.33), respectively.

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Philip G. Gibson, Gregory L. Reighard, Simon W. Scott and David R. Ouellette

Delaying bloom to reduce spring frost risk and reducing labor costs by increasing orchard efficiency are important goals of peach producers. At the Musser Fruit Research Center near Clemson, S.C., `Coronet' peach trees were inoculated with Peach Latent Mosaic Viroid (PLMVd) to induce bloom delay and reduce shoot vigor. Trees were grown in a high-density, Y-trained orchard system to determine the potential benefit of reduced shoot vigor on labor efficiency in summer pruning operations. In Aug. 1997, `Ta Tao 5' buds were grafted onto the scaffolds of 2-year-old `Coronet' peach trees to transmit PLMVd. Transmission was confirmed by dot-blot on N+ nylon membranes using cRNA probes. Bloom was not delayed in the following year, Spring 1998, but bloom was delayed 7 days in Spring 1999. Yields were unaffected in 1998, but the total fruit weight produced on PLMVd-treated trees was significantly less in the 1999 harvest. Individual fruit weight, firmness, and color were improved on the treated trees. Shoot vigor was reduced on the PLMVd treated trees in the summers of 1998 and 1999, resulting in a significant reduction in pruning time and pruning weights. Light penetration was significantly increased in the treated trees when compared to the untreated controls in the summers of 1998 and 1999. Fruiting shoot length and the number of fruit per shoot was unaffected by the PLMVd presence. The trunk cross-sectional area was significantly less on the treated trees when compared to the untreated controls after each year of growth. Autumn defoliation occurred earlier on the treated trees in Fall 1998 and Fall 1999. The manipulation of peach tree growth and development was accomplished using graft transmissible agents as PLMVd induced several beneficial growth and developmental modifications in established peach trees.

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R.O.M. Mwanga, B. Odongo, G. Turyamureeba, A. Alajo, G.C. Yencho, R.W. Gibson, N.E.J.M. Smit and E.E. Carey

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R.O.M. Mwanga, B. Odongo, C. Ocitti p'Obwoya, R.W. Gibson, N.E.J.M. Smit and E.E. Carey