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Mongi Zekri

Since the environmental conditions and cultural practices are unique in southwest Florida, a study was performed to determine the horticultural adaptability and performance of `Valencia' orange trees on four commercial rootstocks grown in a high-density planting. The trees were planted in 1991 on a flatwoods soil in a commercial grove at a density of 627 trees/ha. Leaf mineral concentration, growth, and fruit production and quality were measured 4 and 7 years after planting. Compared to Florida citrus leaf standards, leaf mineral concentration values were within the optimum to the high range. Yield efficiency expressed as kilograms of solids per cubed meter of canopy and juice quality in terms of juice content, soluble solids concentration, and kilograms of solids per box increased with tree age. Tree and fruit size were the highest for Volkamer lemon (Volk) and the lowest for Cleopatra mandarin (Cleo). Fruit yield was the highest for Volk. However, yield expressed in kilograms of solids per hectare was not significantly different between Volk and `Swingle' citrumelo (Swi) due to the higher solids per box for Swi. Yield efficiency was also higher for Swi than for Volk. Juice content and soluble solids in the fruit were higher for Swi and Cleo than for the lemon rootstocks. Financial analysis showed that at high-density planting, trees on Swi were the most profitable. On noncalcareous flatwoods soil, Swi is the best suited rootstock for high-density planting.

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George M. Greene II and Alvan G. Gaus

The influence of rootstocks on the growth and productivity of `Starkspur Supreme Pagnelli Delicious' was determined in an NC-140 experiment started in 1984. The planting was supplemental to the main experiment and it contained Ottawa (Ott) 3, M.20, and Arnold Lynd (AL) 800, but did not contain Budagovsky (Bud) 490, Bud 9, Antonovka 313, or C6. Trees that apparently would not stand were given support. Data on tree size and yield were collected every year. As expected, many characteristics were strongly influenced by rootstock. Yield efficiency calculated as the total fruit weight per square cm of trunk cross-sectional area was used as a measure of production efficiency. In 1989, efficient producers of fruit (all in decreasing order) were Poland (P) 2, EMLA.26, P 16, and Michigan Apple Clone (MAC) 39. Intermediate in productivity were M.20, Cornell-Geneva (CG) 10, Pl, and AL 800. A lower efficiency group of rootstocks were EMLA.7, Ott 3, MAC 1, Seedling, M.4, P 18, and CG 24. `Golden Delicious' and `McIntosh' on EMLA.26, used as pollinizers, were ranked second and third in yield efficiency.

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Timothy Spann, Robert H. Beede, Steven A. Weinbaum, and Theodore M. DeJong

Rootstock significantly alters the pattern of shoot growth of pistachio (Pistacia vera) cv. Kerman. Trees grown on P. atlantica typically produce a single flush of spring growth, whereas trees on P. integerrima selection PGI and P. atlantica × P. integerrima selection UCB-1 can produce multiple flushes during the season. We have shown that the spring flush is entirely preformed in the dormant bud for all three rootstocks, but later flushes are neoformed, that is, nodes are initiated and extended during the same season. Shoots producing both preformed and neoformed growth have lower yield efficiency than those producing only preformed growth. Additionally, yield components of the crop from shoots with both preformed and neoformed growth was different than for shoots producing only preformed growth. However, these differences do not appear to be significant at the whole tree level. These data suggest that neoformed growth can both compete with fruit growth for available resources (lower yield efficiency) and act as an additional source (altered yield components), depending on the factor being measured. Controlling neoformed growth may potentially increase pistachio yield through a shift to the more efficient preformed shoots while at the same time lowering orchard maintenance costs by reducing required pruning. We have data to indicate that regulated deficit irrigation and new pruning techniques may be viable methods for controlling neoformed growth in pistachio without affecting yield.

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Stephen M. Southwick, James T. Yeager, Joseph Osgood, Richard Buchner, William Olson, and Maxwell Norton

Ten new marianna root-stocks [Prunus cerasifera Ehrh. × P. munsoniana Wight & Hedr.(?)] derived from open pollination of `Marianna 2616' (M series) were planted in 1987 and evaluated at four commercial orchard locations in California (Tehama, Butte, Sutter, and Merced counties) with `Improved French' prune (P. domestica L.) as the scion. These rootstocks were compared to three standard rootstocks: `Marianna 2624', myrobalan seedling (P. cerasifera Ehrh.) and `Myrobalan 29C'. Leaf potassium (K) and nitrogen (N), tree growth, fruit production and fruit quality were measured. Selection M40 in particular had high leaf N, high leaf K (equal to `Marianna 2624' and better than the myrobalan standards), higher yield efficiency per tree, fruit size, drying characteristics, and few root suckers when compared to the three standard rootstocks. M40 is being considered for patent and release by the Pomology Department at the University of California, Davis. Selection M58 had the highest yield efficiency of any tested rootstock. Several selections had characteristics that would make expanded planting worth considering.

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Esmaeil Fallahi and Brenda R. Simons

The influence of three rootstocks, various levels of soil-applied nitrogen in fall, and spring spray applications with and without minimum ground nitrogen on tree growth, productivity, leaf and fruit nutrient partitioning, and postharvest quality of fruit at harvest and after storage in `B.C. 2 Fuji' apple was studied over several seasons. Early results showed that trees on M.26 and M.9 were more precocious and had higher yield and yield efficiency. Trees on M.9 had significantly higher leaf Ca and incidence of sunburned fruit than those on other rootstocks. Trees on M.7 had larger fruit and higher leaf N, K, and Cu, but had lower fruit starch degradation pattern (SDP) and leaf Ca. Soluble solids at harvest were lower in fruit from trees on M.26 rootstock. Trees with fall nitrogen application had lower leaf N and better fruit color. Lower quantities of N application had smaller fruit but better fruit color and higher firmness at harvest. Fruit from all rootstocks did not produce ethylene for several days in the ripening chambers. After this period, fruit on M.9 rootstock produced ethylene before those from other rootstocks. Trees established with only nitrogen spray without any ground application had leaf N deficiency after they started bearing fruit. Establishment of a new `Fuji' orchard based on only nitrogen spray produced weak trees with low yield and yield efficiency, while addition of a small quantity of ground-applied N improved tree growth and fruit quality.

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D.M. Glenn and W.V. Welker

Planting sod beneath peach trees to control excessive vegetative growth was evaluated from 1987 to 1993 in three field studies. Peach trees were established and maintained in 2.5-m-wide, vegetation-free strips for 3 years, and then sod was planted beneath the trees and maintained for 5 to 7 years. Reducing the vegetation-free area beneath established peach trees to a 30- or 60-cm-wide herbicide strip reduced total pruning weight/tree and weight of canopy water shoots in many years. Fruit yield was reduced by reducing the size of the vegetation-free area in some, but not all, years; however, yield efficiency (kg yield/cm2 of trunk area) was not reduced in two studies, and in only 1 year in the third study. Planting sod beneath peach trees increased available soil water content in all years and yield efficiency based-evapotranspiration (kg yield/cm soil water use + precipitation) in some years compared to the 2.5-m herbicide strip. Reestablishing sod beneath peach trees has the potential to control vegetative growth and may be appropriate for high-density peach production systems where small, efficient trees are needed.

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Terence L. Robinson, Alan N. Lakso, and Stephen G. Carpenter

A field planting of `Empire' and `Redchief Delicious' apple trees (Malus domestics Borkh.) was established in 1978 to evaluate four planting systems: 1) slender spindle/M.9, 2) Y-trellis/M.26, 3) central leader/M.9/MM.111, and 4) central leader/M.7a. During the first 5 years, yields per hectare for `Empire' were positively correlated with tree density. In the second 5 years, the Y-trellis/M.26 trees produced the highest yields while yields of the other systems continued to be related to tree density. Cumulative yields were highest with the Y-trellis/M.26 trees. With `Delicious', the Y-trellis/M.26 yields were greatest during all 10 years despite lower tree density than the slender spindle/M.9. Yields of `Delicious' with the other three systems were a function of tree density during the 10 years. At maturity, canopy volume per tree was greatest on the central leader/M.7a trees and smallest on the slender spindle/M.9 trees; however, there were no significant differences in canopy volume per hectare between the systems despite large differences in yield. Trunk cross sectional area (TCA) per hectare was greatest with the Y-trellis/M.26 trees and smallest with the central leader/M.7 trees. Yield was highly correlated to TCA/ha. Yield efficiency with `Empire' was greatest for the slender spindle/M.9 system, followed by the Y-trellis/M.26, central leader/M.9/MM.111, respectively. With both cultivars, the central leader/M.7a system had the lowest yield efficiency. With `Delicious', there were no differences in yield efficiency for the other three systems. The greater yield of the Y-trellis/M.26 system was the result of greater TCA/ha and not greater efficiency. `Empire' fruit size was largest on the central leader/M.7a and the central leader/M.9/MM.111 trees and smallest on the slender spindle/M.9 and the Y-trellis/M.26 trees. With `Delicious', fruit size was larger with the Y-trellis/M.26 trees than the other systems. When fruit size was adjusted for crop density, there were no significant differences due to system with `Empire', but with `Delicious' the Y-trellis/M.26 trees had larger adjusted fruit size than the other systems. Crop density calculated using TCA correlated better to fruit size than did crop density calculated using annual increase in TCA, canopy volume, or land area. Fruit color and quality with `Redchief Delicious' were not influenced by system. With `Empire', average fruit color and soluble solids content were lower for the Y-trellis/M.26 and slender spindle/M.9 in some years when canopy density was allowed to become. excessive.

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T. Caruso, P. Inglese, C. Di Vaio, and L.S. Pace

Fruit thinning is the most effective tool in regulating fruit growth potential for early-ripening peach and nectarine (Prunus persica) cultivars, and the common strategy is to space fruit 25 to 30 cm (9.8 to 11.8 inches) throughout the canopy, while scarce attention to the canopy environment in which the fruit develops. It is likely that different light environments within the canopy require different thinning patterns and to test this hypothesis, an experiment was set up to evaluate various fruit thinning patterns (fruit densities) in relation to fruit location within the canopy of early-ripening `May Glo' nectarine trees trained to Y-shape. Differentiated fruit thinning resulted in higher yield efficiency due to a higher fruit number and average fruit weight. Differentiated thinning hastened fruit harvest and shortened the harvest period. Differentiated thinning reduced fruit variability within the tree in terms of size and soluble solids content, resulting in a higher crop value.

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B. Buckley, W.A. Mulkey, J.D. Griffins, K.C. Peel, T. Talbota, and W. Russell

Four southernpea cultivars were evaluated for fresh market mechanical harvest at Calhoun, Chase, and Ruston, Louisiana. The cultivars were 'Encore', 'Royal Cream', 'Queen Anne', and 'Texas Pinkeye'. In addition, 'Early Acre' and breeding lines AR87-435 and AR91-135 were also evaluated at Chase. The marketable yield from mechanical harvest ranged from 1075 kg·ha-1 for 'Royal Cream' at Calhoun and Ruston to 1855 kg·ha-1 for 'Encore' at Calhoun and Chase. Low concentrated maturity was the main factor limiting marketable yield. The percent mature pods at harvest was near 55 for most cultivars. Yield efficiency of mechanical harvest vS. hand harvest was above 75% for most cultivars. The percent trash resulting from machine harvest ranged from 6 for AR91-135 to 24 for 'Queen Anne'.

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D.C. Elfving, I. Schechter, R.A. Cline, and W.F. Pierce

Mature `Macspur McIntosh'/MM.106 trees trained to the CL tree form were converted to the PL tree form in 1987 by removal of east- and west-oriented upper scaffold limbs. Control trees were pruned to maintain the CL form. Dormant pruning in later years maintained either tree form. No summer pruning was used in this study. Canopy light levels along horizontal transects at one m above the soil and vertical transects, both through the center of the canopy, were unaffected by tree form or transect direction. Yields were significantly lower for PL trees in 1987 and 1989, while yield efficiency was reduced in PL trees in all 3 years. Fruit size, trunk cross-sectional area, and foliar macro-nutrient content were unaffected by tree form during this study. Fruit color development in both the upper and lower halves of the canopy was uninfluenced by tree form.