Tree Fruit Leader, Vol. 5(1) April 1996

B.9 and O.3: Dwarfing Rootstocks for Cold Sites

By H.A. Quamme, R.T. Brownlee and C.R. Hampson Agriculture and Agri-Food Canada, Research Centre, Summerland, BC

Malling 9 (M.9) is a widely planted dwarfing rootstock that performs well on a wide range of soils. It has been grown in British Columbia for over 35 years. The move to higher density plantings has resulted in a large increase in plantings on M.9 in the last 10 years. So far, few losses from winter injury have occurred with M.9. Winter injury losses that do take place are more common on light-textured soils and in the absence of snow cover. M.9 is rated hardier than M.7, but not as hardy as M.26. Budagovsky 9 (B.9) and Ottawa 3 (O.3) are dwarfing rootstocks that offer more cold hardiness than M.9 for cold sites. Trees on B.9 and O.3 require support, just as for trees on M.9 and other rootstocks in the same size-controlling range.

Budagovsky 9

The Budagovsky rootstock series originated from a hardy apple rootstock improvement program at the Michurinsk College of Agriculture in Russia. B.9 is similar to M.9 EMLA in size, or slightly larger (Table 1 and Fig. 1). It is reasonably precocious and has shown good yield stability over 28 sites in North America in a USDA-sponsored NC-140 rootstock trial. Few plantings have been made on B.9 thus far, but it has had good crown rot resistance in laboratory and field plot tests. Roots of B.9 survived to a lower temperature than those of M.9 in controlled freezing tests, and trees survived better in the field after whole-tree freezing (Table 1).

Ottawa 3

Clonal rootstocks of the Ottawa series were selected for hardiness at the Ottawa Experimental Farm, and tested at the Smithfield Experimental Farm, Agriculture and Agri-Food Canada, in Ontario. The size control for O.3 is between M.9 EMLA and M.26 (Table 1), and slightly larger than B.9. On light-textured soils, however, trees on O.3 may perform better than smaller trees on the more size-controlling rootstocks.

Some losses from crown rot have occurred in a few orchards in BC, but laboratory tests indicate that its resistance is similar to that of M.26. Losses have not been reported from other localities. Trees on O.3 may be subject to transplanting losses. Use fully dormant nursery stock and avoid late planting.

Trees on O.3 showed better survival in the field after whole-tree freezing than did trees on M.9, and the roots survived to a lower temperature in laboratory freeze tests (Table 1).

Table 1. Performance of B.9 and O.3 Relative to M.9 (EMLA) and M.26

Propagation and Tree Sources

Both B.9 and O.3 are more difficult to propagate than M.9. However, several nurseries in the Fraser Valley are successfully propagating these rootstocks in limited quantities. Contact your BCMAFF district horticulturist for a list of suppliers of rootstocks and trees.

The virus resistance of B.9 and O.3 is not fully known. It is advisable for orchardists to plant virus-free trees to avoid the possibility of poor tree performance caused by virus infection.

Conclusion

O.3 and B.9 are dwarfing rootstocks worthy of consideration for orchards on cold sites. They show size control and cumulative yield efficiency intermediate between that of M.9 and M.26. Both O.3 and B.9 are more cold-hardy than M.9 and appear to be moderately resistant to crown rot. O.3 trees are slightly more vigorous than trees on B.9, and may offer some advantage on light-textured soils.

At the Summerland Research Centre, we continue to evaluate dwarfing rootstocks for apple production in British Columbia. New rootstocks under evaluation that potentially possess cold hardiness and disease resistance in addition to dwarfing include Bemali, P.2, and the Vineland rootstocks V.l, V.2 and V.7.

Fig. 1. Height and spread of B.9 and O.3 compared to M.9 (EMLA) and M.26. The values are an average from six trials conducted in the Okanagan and Creston valleys.

• Return to Tree Fruit Newsletters
• Return to Tree Fruit Page