Selection of dwarfing pear rootstock clones from Pyrus betulaefolia and P. calleryana seedlings

Abstract

A rootstock trial has been established to develop dwarfing pear rootstock clones from Pyrus species. Seedlings that were raised from the open-pollinated seeds of P. betulaefolia Bunge (PB) and P. calleryana Decne (PC); and showed significant genetic dwarfing growth and good traits based on ease of clonal propagation were screened. Among those, four seedlings of PB named SPRB1, SPRB13, SPRB15, and SPRB22 (SPRB = Shinshu University Pear Rootstock P. betulaefolia clone) and six seedlings of PC named SPRC3, SPRC5, SPRC8, SPRC13, SPRC15, and SPRC20 (SPRC = Shinshu University Pear Rootstock P. calleryana clone) were selected. Clones that were generated from the selected seedlings had significantly higher rooting ability by softwood cuttings compared with the control during an 8-year test. Japanese pear 'Kosui' and European pears 'La France' and 'Conference' revealed a dwarfing growth habit when grafted onto the selected clones. All scion/stock combinations interacted significantly to affect shoot growth, trunk cross-sectional area (TCSA), and canopy spread. There was no noticeable difference in the fruit yield per tree of three cultivars grafted on PB and SPRB1, but the estimated yields per ha increased more than 20% in all cultivars on SPRB1. 'La France' trees on SPRB15 and SPRC20 began to bear early with significantly higher yields. Fruit quality characteristics of 'La France' and 'Conference' did not differ because of the influence of stock clones, however, 'Kosui'/SPRB1 had lower average fruit weight that corresponded to the lighter fruit skin color.