Validation of Apple Harvest Index of Low Chilling Requirements

The aim of this work was to evaluate harvest indexes in apple trees with low winter chilling requirements. We used fruits of three apple varieties obtained from crosses made by IAPAR (Agronomic Institute of Parana Brasil): 'Eva' (Anna x Gala); 'Caricia' (Anna x Prima) and 'Princesa' (Anna X NJ 56). The experiment was conducted during 2009 and 2010 years, and the fruits were harvested at different times beginning after reaching the final size and a dominant green color. The following variables were measured: (i) starch index IA (adim.), (ii) external firmness, F (N), and (iii) total soluble solids content, TSS (%). We produced a radial IA chart in order to adapt its use for these varieties of apple. Although the IA was different for each variety in relation to time from start of harvest, it was the index that showed the lowest variability (R-2 = 0.77) and the best predictability of ripeness. Although the correlations made between the three harvest indexes were low, they were higher when we compared IA and SST for the three apple varieties. We discuss the relationship between the three indexes and the possible causes of the dispersion of the measured data.