Rootstocks are used in commercial orchards to improve tree anchorage, pest tolerance and pest resistance. A rootstock should be selected based on two primary factors, 1) compatibility with the scion onto which it will be grafted and 2) climatic and environmental conditions of the planting site. For example, a less vigorous rootstock is typically planted in orchards with ideal soil conditions to control tree size and reduce pruning costs while maintaining high yield (Reil et al. 2007).
Commonly used rootstocks in California include Pyrus communis (Winter Nelis and Bartlett) seedlings and clones, Pyrus betulaefolia seedlings and other Pyrus communis hybrid clones of ‘Old Home x Farmingdale’. Quince can also be used with Comice pears, without the use of an interstem (Elkins et al. 2012). Pyrus betulaefolia has been the standard rootstock in North Coast orchards. Historically, Winter Nelis has been the standard in the Sacramento River district, but 'Old Home x Farmingdale' 87 and 97 are becoming more popular.
Winter Nelis seedlings are a cross between Winter Nelis and Bartlett. Seeds are collected from Winter Nelis trees located in Bartlett orchards. The benefits of using Winter Nelis as a rootstock include 1) trees with a consistent size and productivity 2) tolerance of multiple soil conditions (except for heavy clay), and 3) tolerance of psylla feeding without decreased fruit production. However, Winter Nelis seedlings are susceptible to fire blight and crown gall, and have vigorous growth.
Bartlett seedlings are similar to Winter Nelis seedlings because the seeds are extracted from Bartlett fruit that was cross-pollinated by another cultivar in the orchard (including Winter Nelis). Bartlett rootstocks are generally less vigorous than Winter Nelis. However, the paternal seed parent is never known and there is a substantial amount of variation among individual seedlings (Reil et al. 2007). Bartlett rootstocks are susceptible to fire blight.
P. betulaefolia is the most vigorous of all pear rootstocks. It can tolerate a wide range of soil conditions and is the most resistant to psylla feeding and pear decline when grafted to a Bartlett scion.
'Old Home x Farmingdale' clonal rootstocks are growing in popularity because they have been shown to have 60 to 70% less vigor and a higher yield than Winter Nelis. In addition, these crossed rootstocks are resistant to fire blight (Hancock and Lobos 2008). 'Old Home X Farmingdale' rootstocks are promising for high-density and shorter orchards. Clones 87 and 97 are currently used in California (Elkins et al. 2012).
Quince rootstocks are preferred for Comice pears. The quince rootstock results in a short wide fruit with a large diameter, while Winter Nelis, Bartlett and the Old Home crosses produce long narrow fruit (Reil et al. 2007). For more on quince rootstock, see Quince as a Pear Rootstock.
Breeding programs are currently focused on developing new rootstocks that will produce pears similar to Bartlett, with low vigor, tolerance to multiple soil conditions, and an improved resistance to environmental conditions and pest problems, especially fire blight (Reil et al. 2007). Large, low fiber pears with a buttery flesh and aromatic flavor are preferred (Hancock and Lobos 2008).
Bartlett is the most common scion used for commercial production in California, with approximately 70% of production (USDA 2012). Additional cultivars include Bosc, Clapp’s Favorite (Starkrimson), Sunsprite, Forelle, Comice, and Seckel (Calpear website, 2011).