Evaluation of Potential Rootstocks to Improve Pear Tree Precocity and Productivity.

Nine single cultivar replicated trials located in six locations in the states of California, New York, and Washington in the US, Nova Scotia, Canada, and Chihuahua, Mexico were established in 2004 and 2005 as part of the “NC-140 Improving Economic and Environmental Sustainability in Tree-Fruit Production Through Changes in Rootstock Use” project. Rootstocks were grafted to ‘Bartlett’ (‘Williams’) in four locations, ‘Golden Russet Bosc’ in three locations, and ‘Concorde’ and ‘Taylors Gold Comice’ in two locations. ‘Bartlett’ tree spacing ranged from 1.5x3.0 to 2.7x4.6 m, ‘GR Bosc’ from 1.5x3.0 to 1.8x3.7 m, and ‘Concorde’ and ‘Taylors Gold Comice’ was 2.4×4.8 m. Training systems included central leader, vertical trellis and slender spindle. ‘Bartlett’ was grafted onto 708-36, BM 2000, Horner-4, Fox 11, OHxF 87, Pyrodwarf, and Pyro 2-33 in all four locations. The same rootstocks were included for ‘Golden Russet Bosc’, however, only Horner 4 and Pyrodwarf were included in all three locations; ‘Concorde’ and ‘Taylors Gold Comice’ were grafted to Pyrodwarf, OHxF 87 and OHxF 97. OHxF 69 and ‘Winter Nelis’ were each included in one ‘Bartlett’ trial and one ‘Golden Russet Bosc’ trial also included BU-3. Percent tree survival, trunk cross sectional area (TCSA), fruit yield, number of flower clusters, number of fruit, and number of root suckers was measured and percent set, yield efficiency and average fruit weight were calculated. Percent tree survival and reasons for mortality varied by location and included fire blight and poor vigor. Production data are preliminary, however several trends are notable. Generally, for ‘Bartlett’, trees on Horner-4 exhibited the largest TCSA but trees on Pyro 2-33, Pyrodwarf, and OHxF 87 performed the best overall across four locations. For ‘Golden Russet Bosc’, there was no statistical difference between Horner-4 and Pyrodwarf; while trees on Horner-4 generally had the largest TCSA in two of the three trials, OHxF 87 appears to induce better yields and yield efficiency. Cumulative yield efficiencies were equal for ‘Concorde’ and ‘Taylors Gold Comice’ on all rootstocks. There was no clear trend in number of suckers, but BM 2000 and Pyrodwarf had the most in some locations. For all rootstock cultivars, fruit weight trends were unclear due to limited data. Formal data collection and reporting will continue through 2014.