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Esmaeil Fallahi, D. Ross Rodney, and Zahra Mousavi

Tree growth, yield, and fruit quality of eight lemon cultivars [Citrus limon (L.) Burro. f.] on macrophylla (Alemow) (C. macrophylla Wester) rootstock were compared when grown in sandy soil in the arid climate of south-western Arizona. `Foothill Lisbon' had higher cumulative yield and titratable acids than `Monroe Lisbon', `Prior Lisbon', `Eureka', and `Villafranca', and had larger fruit than other `Lisbon' cultivars. `Prior Lisbon' produced a larger tree canopy with lower yield efficiency than all other cultivars and did not show any decline due to sieve tube necrosis 12 years after planting. Overall, `Eureka' cultivars and `Villafranca' had lower relative cumulative yields, canopy volumes, total soluble solids content, titratable acids, and seed content, but higher tree decline than `Lisbon' cultivars. Overall, `Foothill Lisbon', in spite of carrying exocortis viroid, produced good yields and fruit quality and `Prior Lisbon' had a satisfactory growth-performance.

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Shahrokh Khanizadeh, Yvon Groleau, Audrey Levasseur, Raymond Granger, Gilles L. Rousselle, and Campbell Davidson

Two hundred and nine hybrid seedlings developed by crossing Nertchinsk × M.9, Osman × Heyer 12, and Nertchinsk × M.26 were evaluated since 1970 in Agriculture and Agri-Food Canada (AAFC), Horticultural Research and Development center (HRDC), Quebec. Canada. `McIntosh' was used as the scion. Seven of these rootstocks obtained from crossing `Nertchinsk' with M.9 and M.26 were found to be winter hardy, disease resistant, dwarfing, with good yield efficiency and easier to propagate than O.3 under North Eastern Central Canada climate. O3A, a mutation of O.3 (Ottawa 3) was also added to the advanced lines and evaluated along with seven rootstocks in replicated trials compared to M.26, M.9, M.111 and O.3 in four locations during 1995–2002. These seven rootstocks (SJM15, SJM44, SJM127, SJM150, SJM167, SJM188, SJM189, along with O3A are being released for commercial evaluation.

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Christopher S. Walsh, Arthur H. Thompson, and Richard H. Zimmerman

`Gala' apples are increasing in worldwide popularity. Despite this, little information on the cultivars vigor, precocity, or interaction with size-controlling rootstock is available. In 1985, a factorial planting was set to study these variables. `Gala' and `Golden Delicious' trees were found similar in precocity. Cumulative yields were about 20 kg per tree after the fifth leaf. `McIntosh' and `Delicious' trees were less precocious. `Gala' trees were also quite vigorous. Tree size and yield efficiency data will be presented, comparing `Gala' with other cultivars budded onto M 7a, MM 111, or propagated in tissue culture as scion-rooted plants. Tree management techniques have been identified that decrease fruit size. Trees budded onto precocious rootstock, and fruited heavily on one-year wood produce small-sized fruit. This tendency is pronounced on trees fruiting in the second leaf, or on older trees damaged by late-spring freezes that reduce the proportion of crop borne on spurs.

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Ido Schechter, J.T.A. Proctor, and D.C. Elfving

Fruit and leaves were harvested from sample branches in Oct. 1987 and 1988 from `Starkspur Supreme Delicious' apple (Malus domestica Borkh.) trees on nine rootstocks (Ottawa 3, M.7 EMLA, M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC-9, MAC-24, OAR 1) planted in 1980. Harvested leaves were separated into shoot leaves and spur leaves. Based on a standardized unit (centimeter of limb circumference), rootstocks strongly influenced the number, area, dry weight, and percentage of leaves in each category in both years. Yield per centimeter of limb circumference (limb yield efficiency, LYE) varied widely among rootstocks. LYE was highly correlated with spur density and with spur leaf variables but not with shoot leaf number, dry weight, or area. Rootstock effect on spur density may partially explain their effect on yield characteristics. The rootstock OAR 1 affected some of these characteristics differently than the others.

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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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Richard P. Marini, Donald S. Sowers, and Michele Choma Marini

`Sweet Sue' peach (Prunus persica L. Batsch) trees were subjected to a factorial arrangement of treatments. At planting, trees were headed at 10 or 70 cm above the bud union and trees were trained to an open-vase or central-leader form. For the first 4 years, high-headed trees were larger than low-headed trees. After 7 years, open-vase trees had larger trunk cross-sectional area, tree spread, and canopy volume than central-leader trees. Open-vase trees had higher yield and crop value per tree, but lower yield and crop value per unit of land area or unit of canopy volume than central-leader trees. Crop density and yield efficiency were similar for all treatments.

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D.M. Glenn and W.V. Welker

Mature peach trees were grown in six different-sized vegetation-free areas (VFA) (0.36 to 13 m2) with and without stage-III drip irrigation for 6 years. As the VFA increased, so did the trunk cross-sectional area, total yield/tree, large fruit yield/tree, and pruning weight/tree. The application of supplemental irrigation increased yield of large fruit and leaf N percentage in all VFAs. Winter hardiness was not affected by either size of the VFA or irrigation. The yield efficiency of total fruit and large fruit decreased, however, with the increasing size of VFAs. The smaller VFAs resulted in smaller, more-efficient trees. Managing the size of the VFA was an effective, low-cost approach to controlling peach tree size and, when combined with irrigated, high-density production, offers a potential for increased productivity.

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Winfred P. Cowgill Jr., M.H. Maletta, W.H. Tietjen, J. Compton, D. Polk, and J.F. Goffreda

Six scab-resistant apple cultivars, Enterprise (CO-OP 30), CO-OP 36, Liberty, Freedom, Nova-Ez-Grow, and NY-754 were propagated on M.26 EMLA. Trees were planted in 1990 in a randomized complete-block design with six replications, five trees per replication. `Empire'/M.26 EMLA was the control cultivar. Tree spacing was 3 m apart in the row and 6 m between rows. Trees were individually staked and trained to a modified spindle bush. Precocity, bloom counts, tree height and width, TCA, cumulative yield efficiency, and fruit quality have been determined annually. `CO-OP 36', `Enterprise', and `Liberty' had significantly higher cumulative yields in 1993–94 than the other cultivars. The same three also had significantly superior fruit quality characteristics. `Liberty' was the most precocious of the scab-resistant cultivars, very similar to `Empire'. `Liberty' was also the weakest-growing cultivar, followed by `Empire'.

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J.G. Williamson and D.C. Coston

Several planting treatments modified vegetative and reproductive growth of young, own-rooted peach (Prums persica) trees evaluated at two levels of irrigation in a high-density orchard (5000 trees/ha). Trees planted in auger holes, narrow herbicide strips, and in fabric-lined trenches, but not those from raised beds, were smaller than control trees set in holes dug with a shovel. After two growing seasons, trees planted in the fabric-lined trenches were smaller and had more flowers per node and greater flower bud densities than trees in other planting treatments. Yield efficiency was greatest for this treatment, although fruit size was small throughout the orchard. Irrigation rates did not affect fruit yield or size. The effects of irrigation rate on vegetative growth were small compared to differences among planting treatments.

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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.