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Carlos Miranda Jiménez and J. Bernardo Royo Díaz

Spring frosts are usual in many of Spain's fruit-growing areas, so it is common to insure crops against frost damage. After a frost, crop loss must be evaluated, by comparing what crop is left with the amount that would have been obtained under normal conditions. Potential crop must be evaluated quickly through the use of measurements obtainable at the beginning of the tree's growth cycle. During the years 1998 and 1999 and in 62 commercial plots of `Golden Delicious' and `Royal Gala' apple (Malus ×domestica Borkh.), the following measurements were obtained: trunk cross-sectional area (TCA, cm2), space allocated per tree (ST, m2) trunk cross-sectional area per hectare (TCA/ha), flower density (FD, number of flower buds/cm2 TCA), flower density per land area (FA, number of flower buds/m2 land area), cluster set (CS, number of fruit clusters/number of flower clusters, percent), crop density (CD, number of fruit/cm2 TCA), fruit clusters per trunk cross-sectional area (FCT, number of fruit clusters/cm2 TCA), fruit clusters per land area (FCA, number of fruit clusters/m2 land area), fruit number per cluster (FNC), average fruit weight (FW, g), average yield per fruit cluster (CY, g), yield efficiency (YE, fruit g·cm-2 TCA), and tree yield (Y, fruit kg/tree). FCT and average CY were related to the rest of the variables through the use of multiple regression models. The models which provided the best fit were FCT = FD - TCA/ha - FD and CY= -FCA - FCT. These models were significant, consistent, and appropriate for both years. Predicted yield per land area was obtained by multiplying TCA/ha × FCT × CY. The models' predictive ability was evaluated for 64 different plots in 2001 and 2002. Statistical analysis showed the models to be valid for the forecast of potential yields in apple, so that they represent a useful tool for early crop prediction and evaluation of losses due to late frosts.

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Cheryl R. Hampson, Harvey A. Quamme, and Robert T. Brownlee

In 1993, a planting of virus-free 'Royal Gala' apple (Malu×domestica Borkh.) on 'M.9' rootstock was established at Summerland, B.C., Canada, to determine whether angled-canopy training systems could improve orchard tree performance relative to slender spindles. The trees were trained in one of five ways: slender spindle (SS), Geneva Y-trellis (GY), a modified Solen training we called 'Solen Y-trellis' (SY), or V-trellis (LDV), all at the same spacing (1.2 m × 2.8 m), giving a planting density of 2976 trees/ha. In addition, a higher density (7143 trees/ha) version of the V-trellis (HDV) was planted to gauge the performance of this system at densities approaching those of local super spindle orchards. The plots were drip-irrigated and hand-thinned. No summer pruning was done. After 8 years, differences among training systems at the same density and spacing were small and few. The two Y-shaped training systems had 11% to 14% greater cumulative yield/ha than the SS, but did not intercept significantly more light at maturity. No consistent differences occurred in fruit size or the percentage of fruit with delayed color development among the four training systems at the same density. Relative to the LDV, the HDV yielded less per tree, but far more per hectare, particularly in the first 3 years. After 8 years, the cumulative yield/ha was still 65% greater than with LDV. Yield efficiency was unaffected by tree density. Fruit size on HDV ranked lowest among the systems nearly every year, but was still commercially acceptable. The HDV intercepted more light (73%) than SS (53%). The percentage of fruit with delayed color development in HDV was not significantly different from that for LDV in most years. The trees in HDV were difficult to contain within their allotted space without summer pruning. The substantially similar performance of all the training systems (at a given density, and with minimal pruning) suggests that cost and ease of management should be the decisive factors when choosing a tree training method.

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Richard E.C. Layne and Perry Y. Jui

Ten genetically diverse peach [Prunus persica (L.) Batsch] seedling rootstocks were studied for 10 years on Fox sand using `Redhaven' as the scion. The purpose of the experiment was to assess the performance of three Harrow Research Station (Ont.) hybrid selections (H7338013, H7338016, and H7338019) and two northern China introductions (`Chui Lum Tao' and `Tzim Pee Tao') against five commercial standards, two of which were selected in Canada (`Harrow Blood' and `Siberian C') and three in the United States (`Bailey', `Halford', and `Lovell'). Rootstock performance was assessed indirectly by measuring or subjectively rating various aspects of scion performance including annual trunk cross-sectional area (TCA); final tree height, spread, and TCA; bloom and fruit set intensity; yield and yield efficiency; canker (Leucostoma spp.) severity; defoliation rate; winter injury; cold hardiness of flower buds and shoot xylem; and tree survival. Rootstock effects on the above measurements and ratings were significant in some years and not in others. Year effects were always large and significant, while rootstock × year interactions were usually small and not significant. In the combined analyses over years, the largest rootstock effects were obtained for bloom, fruit set, and defoliation ratings and for TCA measurements. Three cumulative responses, including marketable yields, yield efficiency, and tree survival, were used for comparing the five experimental rootstocks with the five commercial standards and also for ranking the 10 rootstocks with respect to each other to assess their potential commercial value as peach rootstocks. `Chui Lum Tao', H7338013, and `Bailey' had the most commercial potential for southern Ontario because they typically promoted above average cumulative yield, yield efficiency, and tree survival. `Tzim Pee Tao', `Siberian C', and `Harrow Blood' were less valuable, with low cumulative marketable yields. `Halford' and `Lovell' were the least valuable, with the lowest tree survival (17%). Performance of H7338013 exceeded that of both parents (`Bailey' and `Siberian C'), H7338019 exceeded `Siberian C' but not `Bailey', while performance of H7338016 was inferior to both parents. Wider testing of the experimental rootstocks on different soil types and climatic zones is needed.

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Ignasi Iglesias, Pere Vilardell, Joan Bonany, Elisabet Claveria, and Ramon Dolcet-Sanjuan

A new spontaneous mutation of the pear variety Dr. Jules Guyot, named `IGE 2002', was selected from a pear growing area in Catalonia. The clone was established in vitro from a 40-year-old tree, a highly recalcitrant material unable to root by cuttings. An in vitro micropropagation protocol, with an average multiplication rate of 5, a 90% rooting, and an acclimation of 79% of the plantlets, was defined. Self-rooted plants were grown in two experimental stations, covering two distinct fruit growing areas. The main agronomic characteristics of the clone `IGE 2002' were evaluated during six seasons, 1997 to 2002. Blooming and harvest period were at a similar time than `Dr. Jules Guyot'. Soluble solids concentration and acidity are also similar to `Dr. Jules Guyot'. However, at the same harvest time, a lower fruit firmness of `IGE 2002' in comparison to `Dr. Jules Guyot' indicated an advanced ripening. In addition, a finer flesh texture of `IGE 2002' than `Dr. Jules Guyot', distinguished the former from the later variety. Important differences between both plot sites were found on cumulative fruit yield, fruit size, and fruit size distribution, of `IGE2002' grown on its own roots. However, the site did not affect the fruit quality parameters. Superior fruit yields were associated with higher vigor and yield efficiency of the self-rooted variety.

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Tara Auxt Baugher, Kendall C. Elliott, and D. Michael Glenn

Three growth suppression treatments were compared during 1991 to 1993 on `Stayman' apple (Malus domestica Borkh.) trees grown in the T-trellis and the MIA trellis systems. All treatments—root pruning, K-31 fescue (Festuca arundinacea Schreb.), and K-31 fescue plus root pruning—suppressed tree growth compared to the nontreated control, but results were inconsistent between years and systems. Sod or sod plus root pruning reduced terminal shoot length in both systems in 2 out of 3 years. Root pruning decreased shoot length in the T-trellis in 1992. Sod decreased trunk cross-sectional area in the T-trellis in 1993. Treatments did not affect 3-year average yield efficiency but did appear to increase biennial bearing. Sod, with or without root pruning, decreased fruit cracking in the T-trellis 69% and 42%, respectively, in 1992, and sod plus root pruning decreased cracking in the MIA trellis 50%. Sod reduced fruit diameter in the T-trellis in 1992. Secondary effects of growth suppression treatments included increased light penetration and improved fruit color. Sod decreased leaf N and Mg and increased leaf P, K, and Cu. The Oct. 1993 stem water potential gradient from root to canopy was more negative in the sod plus root pruning treatment, and the osmotic potential of rootsucker leaves in the combination treatment was greater than in the control, indicating that sod plus root pruning alters the distribution of water within a fruit tree.

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Gennaro Fazio, Yizhen Wan, Dariusz Kviklys, Leticia Romero, Richard Adams, David Strickland, and Terence Robinson

architecture ( Fazio et al., 2009 ), dwarfing, induction of early-bearing, yield efficiency, root suckering, and formation of burr knots and spines; 2) population G935B9: 126 progeny from a cross between G.935 and B.9 apple rootstocks; 3) population MM106G65

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Jaume Lordan, Anna Wallis, Poliana Francescatto, and Terence L. Robinson

et al., 2006 ). Trunk circumference (cm) at 30 cm above graft union was measured at the end of the trial (2016) ( Reig et al., 2018 ). Trunk cross-sectional area (TCSA, cm 2 ), cumulative yield efficiency (kg·cm −2 ), and crop load (fruit number/cm 2

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T.A. Wheaton, W.S. Castle, J.D. Whitney, and D.P.H. Tucker

`Hamlin' and `Valencia' oranges [Citrus sinensis (L.) Osb.], `Murcott' tangor (C. reticulata Blanco × C. sinensis), and `Redblush' grapefruit (C. paradisi Macf.) on 15 rootstock and own-rooted cuttings were planted at a 1.5 × 3.3-m spacing providing a density of 2020 trees/ha. Growth rate, productivity, and fruit quality varied among the scion and stock combinations. Combinations of moderate vigor and precocious fruiting performed better than very vigorous or dwarfing materials. Several freezes slowed canopy development and delayed production. Most trees had filled their allocated canopy space 7 years after planting. At that age, the orange trees yielded 23 to 75 t·ha-1. Scion and stock combinations with desirable vigor and fruiting characteristics were satisfactory in this high-density planting. However, there appears to be little advantage of high tree density under Florida conditions, and moderate densities of fewer than 1000 trees/ha may be preferable.

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Richard P. Marini, John A. Barden, and Donald Sowers

Abbreviations: FW, fruit weight; TCSA, trunk cross-sectional area; YE, yield efficiency. 1 Associate Professor. 2 Professor. 3 Research Technician. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal

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P. Gordon Braun, Keith D. Fuller, Kenneth McRae, and Sherry A.E. Fillmore

10% of the apples per tree in 2006 and 2007, respectively. The average apple weight was multiplied by the average number of apples per tree to give an estimated yield. In 2007, the yield efficiency was calculated by dividing the average yield per tree