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Patricia I. Garriz, Hugo L. Alvarez, and Graciela M. Colavita

Nondestructive estimation of pear fruit weight is an important horticultural element for size prediction, particularly when repeated measurements of the same tree must be made without affecting growth. Our objective was to develop a method for determining pear fruit weight (W) using models correlating it with fruit maximum diameter (D), an easily measured dimension. A mature crop of Pyrus communis L. cv. Williams was studied at our Experimental Farm. Five trees were selected at random and fruits were sampled at weekly intervals, starting in September, 21 days after full bloom (DFB) and ending in January, 142 DFB, during three growing seasons (1991–92, 1992–93, and 1993–94). Regression equations were developed using SYSTAT procedure. Data for three years were amalgamated because analysis showed that their curves did not differ. W vs. D was best fitted to the model W = 0,8236 D2.778 R 2 = 0,98. Variability of W and D increased with fruit growth.

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Patricia I. Garriz, Hugo L. Alvarez, and Graciela M. Colavita

The objective of this work was to predict `Packham's Triumph' (Pyrus communis L.) fruit growth as a function of time using an empirical mathematical model. A mature crop was studied at the Experimental Farm of the Comahue National Univ., Rio Negro, Argentina, during the 1992–93, 1993–94, and 1994–95 growing seasons. Trees were selected at random and fruits were collected at weekly intervals. The range of sampling dates was 27 and 178 days after full bloom (DFB). Fresh fruit mass (FM) was measured using an electronic scale (n = 1169). Fruit number/trunk cross-sectional area was also determined; cultural practices were performed according to the local standard program. Equations were developed with SYSTAT procedure. Results showed that the following logistic model provided the most satifactory fit to the pooled data, as compared to the power and linear models: FM (g)= 316.081/(1+ e^5.030–0.039 DFB) R 2=0.84 P < 0.001. The accuracy of predictions was tested on an independent crop in the 1995–96 growing season. According to the values of the statistical F test, no significant differences (Pr0.05) were detected between the mean squared deviations of the observed and the estimated values, suggesting that, overall, the model works well. It can provide growers with a means of determining adequate fruit mass at harvest, considering that unless a certain minimum size is obtained, the fruit will be given a lower grade and price.

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Patricia I. Garriz, Hugo L. Alvarez, and Angel J. Alvarez

This investigation was undertaken to determine the response of pear fruit growth and quality to shade imposed during development. Whole branches of mature `Bartlett' trees on P. communis L. growing at the Experimental Farm on a sandy loam soil were covered with a 20% transmission black, neutral-density shadecloth from 43 days after full bloom (DFB) to 138 DFB, during the 1995–96 growing season. Two comparable branches on each of five uniform trees were selected for good exposure and one branch of each pair was shaded. Fruit diameters were measured at 2-weekly intervals. Pulp pressure and soluble solids concentration (SSC) were measured at harvest time on 31 Jan. Specific leaf mass (SLM) also was recorded (leaf dry mass was obtained by drying discs at 80°C). Relative fruit growth rates were initially similar between light regimes, becoming lower for the shaded fruit at the subsequent measurements. Light exposure induced a 8.76% increase in final fruit diameter (66.40 mm); this increment would appear to depend on carbohydrate availability, since highly significant differences at P ≤ 0.01 emerged in the spur SLM of the exposed and covered branches (7.68 vs. 5.79 mg·cm–2, respectively). SCC was similar for the two light environments, while flesh firmness was 8.80% higher in the shaded fruit. Our results indicate that solar radiation deprival had clearly detrimental effects on fruit growth and maturity, and they provide a basis for improving pruning and training practices in the future.

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Patricia I. Garriz*, Hugo L. Alvarez, Graciela M. Colavita, and María S. Gajdos

Flower thinning of pears has advantages over fruit thinning in that the earlier it is performed the greater the potential effect on fruit size. At the Comahue National Univ. in Argentina (lat. 38°56' 67°59'W), lime sulphur was evaluated as flower thinner on 10-year-old `AbbAbbé Fetel' (Pyrus communis L.) pear trees trained to palmette leader. Cultural practices were similar to those of commercial orchards in the High Valley. Treatments were 1) control, and 2) 7% lime sulphur, applied on 16 Sept. 2002 (30% bloom) using an orchard sprayer. Fruit diameter (FD) was recorded two weekly (n = 20 per date and treatment). At 144 days after full bloom (DAFB), or initial commercial harvest, crop load, fruit weight and the maturity indices were determined. Fruits were then graded into size categories. Growth equations were developed with SYSTAT procedure and mean separations were computed with Student's t-test. Mean FD was significantly increased by the lime sulphur sprays, starting from 115 DAFB. Logistic models best fitted the fruit growth vs. time curves. The equation was: FD = 77.87/1+e2.26-0.03DAFB (R 2 = 0.97), for the non-thinned trees. Treatment 2 increased the percentage of fruits ≥70mm by 42.16%. At 144 DAFB, thinned trees showed firmer fruits than the controls (64.4 vs. 61.7 N) and there were no statistical differences among treatments in soluble solids concentration and starch index; the values were 11.5 °Brix and 3.55, respectively, for the control fruits. Consequently, our data indicate that lime sulphur applied at 30% bloom was an effective practice to thin `Abbé Fetel' pears and to enhance fruit quality at ripening.