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Elaboration of a predictive table of apple diameter cv. Granny Smith using growing degree days

Samuel Ortega-Farías1*, Luis Flores1 y Lorenzo León1

A study was performed in three orchards of San Fernando, VI Region, Chile, in order to develop a predictive table of apple size (Malus domestica Borkh.) using a logistical equation, whose main variable was accumulated degree days (GDA). To this end, data were collected on fruit equatorial diameter and air temperature for the 1989/90 and 1992/93 seasons in three apple orchards cv. Granny Smith. Sampling was carried out from 80 GDA until harvest, selecting 5 trees in each orchard, in which 40 fruit/tree were chosen, covering all the size ranges, at a height approximately 1.0 to 2.0 meters about the soil. At harvest, the evaluated fruit was grouped according to four ranges of diameter (63-68, 69-74, 75-80, and 81-86 mm), to develop the logistic growth models as a function of GDA. The results of this study indicated that the implemented models were able to estimate apple sizes with a coefficient of determination (r2), absolute error (Ea) and standard error of estimate (SEE) ranging from 0.91 to 0.94; 5.8 and 6.7%; and 3.0 to 3.6 mm, respectively. Based on these statistical results a predictive table able to predict apple size as a function of GDA was constructed, which presented an Ea of 5% starting at 600 GDA.

Key words: logistic model, fruit size, apple growth, pome fruit

1 Universidad de Talca, Facultad de Ciencias Agrarias, Casilla 747, Talca, Chile. E-mail: sortega@pehuenche.utalca.cl

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