seasonal changes in fruit growth and development in some asian pear (pyrus serotina rehd.) genotypes under tehran

growth in plants is defined as irreversible increase in volume and size. these changes are varied depending on stage of growth and physiological activity of the fruit tree. this research was conducted to determine the duration period of fruit growth and development and to come up with a mathematical model representing the relationship between fruit diameter, volume, and fruit fresh and dry weight. two experiments were carried out using four mid- (ks13, ks14) and late season (ks8, ks12) maturing fruits of asian pear (pyrus serotina rehd.) genotypes grown in research orchard, department of horticultural sciences at tarbiat modarres university (tmu), iran. in the first experiment, 24 fruits from the middle canopy zone of trees were tagged and fruit diameter measured in time intervals up to fruit harvest. in the second experiment, 3-5 fruits were destructively harvested from each genotype. these fruits were randomly sampled at 15 day intervals from 35 days after full bloom until fruit harvest (ripening). fruit diameter, length, volume, fresh and dry weights were measured on destructively harvested fruits. results indicated that simple and complete fruit sigmoid curves were existent for all four genotypes, even though the period of each phase of fruit growth was different for the studied genotypes. slow growth phase of the curves for mid season genotypes between 120 – 180 days after full bloom (dafb)while for late season maturing fruit genotypes between 150 – 200 dafb. in addition, mathematical models were presented based on the correlation existing between fruit diameter, volume and weight. these models are important and can be used in such orchard management systems as irrigation, applying fertilizers and estimation of fruit harvest and yield.