Relationship Between Trunk Cross-Sectional Area, Harvest Index, Total Tree Dry Weight and Yield Components of ‘Starkspur Supreme Delicious’ Apple Trees

Abstract

The relationship between trunk cross-sectional area (TCSA) and total tree dry weight (DW), and between harvest index (HI) and yield efficiency (YE) of ‘Starkspur Supreme Delicious’ ( Malus domesticaBorkh.) apple trees on nine different rootstocks was examined. In general, as tree size increased, the reliability of TCSA as a predictor of total tree DW decreased. A log transformation increased the accuracy of the estimate. The relationship between YE and HI was improved when a log transformation of TCSA is used to compute the YE. A comparison of tree evaluations based on TCSA and total tree DW revealed that trees on M.27 EMLA had a greater partitioning of dry matter to flowers and fruit when actual DW was used in calculations. The larger trees on MAC.24 and M.7 EMLA rootstocks, ranked higher in YE and flower density when TCSA was used instead of DW as a basis for accounting for tree size. The rootstocks with the highest HI's, ranging from 0.46 to 0.48, were M.9, M.27 EMLA, M.9 EMLA, MAC.9, and O.3. OAR1, M.26 EMLA, M.7 EMLA, and MAC.24 were contained in a second grouping with HI's ranging from 0.33 to 0.39. M.27 EMLA had one of the lowest YE's but had a high HI. M.7 EMLA had a relatively high YE but a low HI. OAR1 had the lowest YE but not the lowest HI.