Apricot Scion & Rootstock Selection

Rootstock selection

Prunus rootstocks:
Apricot can be grown successfully on rootstocks of other species within the Prunus genus, including peach, plum, and various interspecific Prunus hybrids. Specifically, apricot has been successfully grown on several rootstocks including Nemaguard, Nemared, Lovell, Marianna 2624 (plum), and Citation (hybrid) (Hartmann et al. 2011). Nemaguard (seedling peach rootstock) and Citation are the most common rootstocks used in commercial apricot production in California. Nemaguard confers vigor, good anchorage, and is resistant to root knot nematode. Mariana 2624 is occasionally used in commercial plantings in Northern California because it tolerates wet, heavy soils, although it is very susceptible to bacterial canker (Norton and Coates 2012). Citation has been used in the southern edge of California apricot production in the central valley, and is increasing in popularity (Norton and Coates 2012, C. Ledbetter pers comm). Apricot can also be grown on Myrobalan plum rootstocks, although weakness and breaking at the graft union has been reported after high winds. As a result of this problem Myrobalan rootstocks should only be used in very heavy or wet soils.

Apricot seedling rootstocks:
Apricots can be grown successfully on apricot seedling rootstock (Hartmann et al. 2011). Within California, both Royal and Blenheim apricot varieties work well as rootstocks because they are immune to the root knot nematode and are somewhat resistant to the root lesion nematode and to crown gall (C. Ledbetter pers comm). However, apricot seedlings are susceptible to both oak root fungus and Verticillium wilt, and are not commonly used in commercial plantings.

New alternative rootstocks:
Several new experimental rootstocks have been evaluated by the NC-140 rootstock trials over the past ten years, conducted by a group of North American scientists and the USDA. One goal of the NC-140 rootstock trials has been to identify new dwarfing rootstocks that limit tree height and size, without altering scion production or fruit characteristics. Ideally, the shorter, more compact trees will require less pruning and reduce labor costs by eliminating the need for ladders to harvest fruit (DeJong et al. 2010). Although they may help reduce costs and increase competitiveness, dwarfing rootstocks developed by the USDA and evaluated in NC140 trials (including HBOK32, HBOK10, HBOK50, Controller 5 and Controller 9) are not yet widely used in commercial plantings.

Scion selection

The most commonly grown cultivars within California include Patterson, Blenheim, Apache, Poppy, Earlicot, Lorna, Robada, and Helena (California Fresh Apricots 2012, C. Ledbetter pers comm). Patterson (81% of volume) and Blenheim (4% of volume) are the most popular varieties in California and are primarily produced for processing markets, with only a small percentage devoted to fresh markets (Norton and Coates 2012, California Fresh Apricots 2012). The remaining 15% of the California apricot market is primarily produced for fresh market consumption and includes Apache, Poppy, Earlicot, Lorna, Robada, and Helena cultivars. Although once popular, Castlebrite acreage has been declining steadily in favor of other cultivars (C. Ledbetter pers comm). In addition to the traditional apricot cultivars, several popular proprietary apricot-plum hybrids exist, including Pluot® and Aprium®,

Several factors should be considered when selecting an apricot cultivar, including local climate, desired market (fresh or processed), ripening date, and fruit characteristics (see Scion table). Cultivar performance varies in response to local climatic conditions. For example, Blenheim does not perform well when harvested at temperatures above 100^oF. In contrast, Tilton produces well in hot summer conditions, but requires at least 1,000 hours below 45^oF in the winter to produce fruit (Radosevich and Peterman 2008). In addition to selecting cultivars that tolerate local climatic conditions, growers also tend to plant multiple cultivars with a range of ripening dates to reduce labor demand at one time during the season and to take advantage of different niches within the fresh market (Norton and Coates 2012).

Scion table: Characteristics of the most popular apricot cultivars grown in California