Pear Cultivars as Interstems — The Initial Five Years. Do They Have Anything to Offer?

Abstract

Size controlling rootstocks are available for a number of tree fruits, but are not widely available for pear. Interstems may reduce tree size, increase productivity and fruit size, and delay the onset of flowering in a number of tree fruits. The objective of this trial was to determine if the use of the pear cultivars 'd' Anjou', 'Bartlett', 'Bosc', and 'Conference' as interstems would reduce tree size, and improve fruit size and production. After the first five years of trial, 'Bartlett' or 'Cornice' trees with 'Bartlett' interstems exhibited the worst survival rates. Trees with 'Conference' interstems had 100 % survival. Trees with 'Bartlett' interstems had the smallest trunk cross sectional area (TCSA) measured at 15 cm above the lower bud union, while trees with 'Bosc' interstems had the largest TCSA. Differential measurement 5 cm above the upper bud union indicated that trees with 'Conference' interstems exhibited the greatest reduction in TCSA, while trees with 'Comice' scions were generally overgrowing the interstems. Interstemmed trees produced more lateral branches as compared to non-interstemmed trees. Trees with 'Bosc' interstems produced the greatest number of lateral branches as compared to the non interstemmed trees with one-year-old rootstocks. 'Cornice' trees were the shortest with the least canopy spread. 'Bosc' and 'd' Anjou' interstem trees had the widest tree spread. By the end of the initial five year trial, trees with either 'Bartlett' or 'Conference' interstems had the smallest canopy volume (CV). Interstem affected first but not full bloom dates. Final fruit set was not influenced by interstem. Initially, trees with 'Bosc' interstems produced the most flower clusters; however, by the end of the 5-year period, the non-interstemmed controls with 1-year-old rootstocks, and 'd' Anjou' and 'Bosc' interstem trees produced the most flower clusters. Trees with 'Bosc' interstems were the most productive over the 5-year trial. Trees with 'Conference' interstems had the greatest volume density (VD) due mainly to the fact that they had the smallest CV. VD and YE did not appear to be correlated. Although the trees in this trial were not fully mature, this 5-year study indicates that cultivars utilized as interstems may affect yields, growth habit, and crop density.