Rootstock Performance in Ontario: III. Apple Rootstock

Choosing a suitable rootstock for a new orchard has economic and orchard management consequences. As with cultivars, there are a great number of rootstocks available for apple - but many are not suitable for our climate, cultivars, or orchard systems. The Tree Fruit Research Program at the University of Guelph, Vineland and Simcoe campus, has been actively involved in rootstock research for apple, peach, nectarine, plum, and cherry production in Ontario. This long term research is to assess size controlling characteristics of a number of rootstocks from around the world. The information gathered from these experiments is extremely useful in determining the environment-genetic interactions rootstocks have on yield, precocity, tree performance, longevity, resistance to disease and winter injury, and tendency to sucker. This article will provide a brief summary of some of our most recent results from studies conducted in Simcoe on apples.

Experiment 1

Ten trees each of Royal Gala on 17 different rootstocks (V.1, M.26 EMLA, M.9 Pajam 2, M.9 RN29, M.9 EMLA, M.9 Pajam 1, O.3, M.9 NAKB T337, B.9, Mark, P.2, B.469, V.3, B.491, P.16, M.27EMLA, P.22) were planted in a silt-loam soil in 1994 at the University of Guelph Campus, Simcoe, at a spacing of 2.5 m within and 4.5 m between rows (889 trees/hectare; 360 trees/acre). Trees were trained to a slender spindle with a 2.5 m support post and were trickle irrigated. Brief results after nine years of production indicate (Figure 1):

• Eight rootstocks (P.22, M.27E, P.16, B.491, V.3, B.469, Mark and P.2) were significantly smaller, and three rootstocks (M.9 Pajam 2, M.26, V.1) were significantly larger than M.9 EMLA. Tree size (TCSA) ranged from 18-158% relative to M.9E with P.22 being the smallest and V.1 the largest.
• Total yield per tree in 2002 was significantly greater for V.1, O.3, and M.26 while significantly less for P.22, M.27, P.16, and P.2 in comparison with M.9E.
• As in other years, fruit from trees on P.22, M.27, P.16, B.491, B.469, P.2, Mark, B.9, and O.3 were significantly smaller than M.9E; part of this is attributed to fruit densities per tree associated with these rootstocks.
• Cumulative yields after 7 years of fruiting indicated that V.1, M.9 Pajam 2, O.3, and M.26E ranked as the most productive. Cumulative yields of P.2, B.469, V.3, B.491, P.16, M.27E, and P.22 have been significantly less than M.9E.
• Cumulative yields were directly related to tree vigour; the larger the tree the greater the cumulative yield.
• Suckering has been significantly greater for P.16, O.3, M.9 Pajam 1, M.9 Pajam 2, and M.9 RN29, in comparison with M.9E.

Experiment 2

Ten trees each of Royal Gala on 4 different semi-dwarf rootstocks (M.26 EMLA, G.30, V.2, and P.1) were planted in a silt-loam soil in 1994 at the Horticultural Experiment Station, Simcoe, Ontario, at a spacing of 3.0 m within and 5.0 m between rows (667 trees/hectare;269 trees/acre). Trees were trained to a slender spindle with a 2.5 m support post and were trickle irrigated. Brief results after nine years of production indicate (Figure 2):

• Trees on P.1 have been significantly larger than trees on M.26. Trees on M.26, V.2, and G.30 have been statistically similar.
• As of 2002, no significant differences in cumulative yields have established between rootstocks, although numerically, M.26 has had the highest cumulative yield.
• Average fruit size has been similar for all rootstocks.

Experiment 3

Eight trees each of Northern Spy, Jonagold (DeCoster), and Empire on eight rootstocks (V.1, V.2, V.3, V.4, V.7, M.26, M.9 T337, O.3) were planted in a silt-loam soil in 1997 at the Horticultural Experiment Station, Simcoe, Ontario, at a spacing of 3.0 m within and 4.5 m between rows (741 trees/hectare;300 trees/acre). Trees were trained to a slender spindle with a 2.5 m support post and were
trickle irrigated. Brief results after four years of production indicate (Figure 3):

• Two rootstocks (O.3 and V.3) were significantly smaller, and three rootstocks (V.1, V.4, and V.7) were significantly larger than M.26 EMLA. Tree size (TCSA) ranged from 74 to 204 % relative to M.26E with V.3 being the smallest and V.4 the largest.
• Significant interactions in performance (yield and tree size) exist between the cultivars and rootstocks.
• Trees of Northern Spy have had the lowest cumulative yield and largest tree size; Jonagold has been the most productive cultivar while Empire the weakest in vigour.
• Cumulative yields after 4 years of fruiting indicated that V.1, M.9 Pajam 2, O.3, and M.26E ranked as the most productive. Cumulative yields of P.2, B.469, V.3, B.491, P.16, M.27 E, and P.22 have been significantly less than M.9 E.
• Suckering has been significantly greater for V.4, particularly for the Northern Spy and Empire scion cultivars.

Concluding Remarks

Apple producers have a wide selection of rootstocks to choose from. The decision of rootstock selection should be based on a number of factors including growing region (hardiness zone), soil fertility, orchard system, cultivar, tree spacing, and prevalence of disease. Our results indicate that M.9 and M.26 remain very productive size-controlling stocks with many positive attributes. Their primary weakness however is their high susceptibility to fire blight and lack of cold hardiness. The Vineland series rootstocks and Bud 9, in particular, may help to address these concerns.