ROOTSTOCK SELECTION
As mentioned at the opening of this paper, rootstock selection is the single factor in the orchard
that is virtually impossible to change without total removal of the trees.Therefore rootstocks
should be selected carefully, wisely, and conservatively.There is no need to be the first grower
to find out that a rootstock does not work in your area—leave that to someone else.

Standard Rootstocks
In California only three rootstocks are used for peaches and nectarines, Nemaguard, Nemared
and Lovell peach.Nemaguard and Nemared are preferred because of their resistance to rootknot
nematode.However, they are not as tolerant of wet soil conditions as Lovell.Therefore in
heavy soils, and where rootknot nematode is not a problem, Lovell is preferred.Lovell is also
slightly more resistant to bacterial canker than Nemaguard, but neither is immune, and other
options must be considered in areas where bacterial canker occurs.

Plums (Prunus salicia) can be grown on Nemaguard, Nemared or Lovell.They can also be
grown on plum rootstocks such as Marianna 2624 and Myrobalan 29C.As for peaches and
nectarines, Nemaguard is the preferred rootstock when it can be grown.In heavy, wet soils the
plum rootstocks Marianna 2624 and Myrobalan 29C provide much better tolerance of wet
conditions than any of the peach rootstocks.Marianna 2624 has been the preferred choice over
Myrobalan 29C for many years.This is somewhat surprising since Marianna 2624 has a
profusion of rootstock suckers that are nearly impossible to control.Myrobalan 29C has very
few if any suckers but gives a more vigorous tree than Marianna or the peach rootstocks.
Growers also feel that plum fruit size is reduced on peach rootstock, but yields are heavier and
maturity is advanced.The advanced maturity is probably a function of crop load.

Dwarfing Rootstocks
Growers would very much like to have a dwarfing rootstock option for orchard system design.
Such an option would allow for smaller, more compact trees and reduced labor costs.Current
feelings are that a semi-dwarfing rootstock would be of more value than a true dwarfing
rootstock because very high summer temperatures in California would otherwise burn fruit if
they were not sufficiently protected.

In 1982 UC pomologists began evaluating Citation, then a new semi-dwarfing rootstock from
Zaiger Genetics.Peaches, nectarines, and plums growing on Citation were compared against
standard rootstocks.Nearly all of the peaches and nectarines developed some incompatibility
symptoms after a few years and had to be removed.Similar experiences were observed in
grower plots.However, all of the plums grew well, and Citation appeared to reduce tree growth
by 10 to 25% and also advanced fruit maturity.

Based on this trial, another block was planted on Citation and Nemaguard in 1986 that compared
four plum varieties with a wide range of growth habits (Table 5).The results were the same as
the first trial.Citation reduced tree growth by about 15 to 20%, advanced fruit maturity 3 to
5 days, and increased fruit size when cropped to the same level as the trees on Nemaguard
(DeJong et al., 1991b).Only the Queen Ann/Citation combination performed poorly.Queen
Ann is a very weak growing tree, and its fruit are prone to sunburn when exposed to excessive
sunlight.The degree of dwarfism produced by Citation yielded a tree that was too weak for
California conditions.

Table 5.Yields for plum cultivars growing on Citation or Nemaguard rootstock at the Kearney
Agricultural Center; trees planted in 1986 at a 6 x 12 foot spacing (605 trees per acre) (after
DeJong et al., 1991b).
Yield (pounds/tree)
__________________________________________________
Variety/
Rootstock1988198919901991Total

Red Beaut/
Citation

9.5

37.7

55.6

14.2

117.0

Red Beaut/
Nemaguard3.333.430.77.975.3
————————————————————————————————————
Santa Rosa/
Citation28.139.312.268.7148.9

Santa Rosa/
Nemaguard16.937.211.862.5128.4
————————————————————————————————————
Queen Ann/
Citation8.324.131.216.580.1

Queen Ann/
Nemaguard5.926.341.818.092.0
————————————————————————————————————
Royal Diamond/
Citation24.844.539.133.6142.0

Royal Diamond/
Nemaguard

9.9

41.7

32.4

25.8

109.8

Since this study, many plum blocks have been planted on Citation in California.It has
performed very well in virtually every instance.Trees are smaller, harvest is earlier, and fruit
size is improved.The trees appear to be adapted to a wide range of soil types.They are
certainly more tolerant of wet soil conditions than either Nemaguard or Lovell, but appear not
quite as good as either Marianna 2624 or Myrobalan 29C.In orchard situations the lack of
appropriate vigor problem seen with Queen Ann has not been observed.Apparently the vigor
problem can be corrected with applications of additional water and nitrogen.

New Studies
In 1986 University of California pomologists planted a group of more than 80 size-controlling
rootstock selections for evaluation.By 1996, eight of these rootstocks that exhibited promise for
peach and nectarine were selected and planted in a new block for further, more intense screening.
These rootstocks produce trees with a range of 20 to 50% size control potential.By 1998, 4 of
the 8 selected rootstocks showed signs of incompatibility when used with different scion

cultivars.The remaining trees appear healthy.Further testing is required before field studies
with growers can be performed.

SUMMARY
Peaches and Nectarines
The open vase with Nemaguard rootstock, planted at a 16 x 18 foot spacing and pruned using the
minimally pruned method, is currently a very economically efficient training system for fresh-
shipping stone fruits in most areas of California.The Quad V at 9 x 16 to 18 feet is a higher
density system that works well for particular situations because of issues involving labor and tree
uniformity.These choices are made primarily because of the high cost of trees.If tree cost were
less, as it is in many other areas of the world, the Kearney V at a 6 x 16 foot spacing is probably
the simplest and most efficient system.

Plums
Currently, Citation is probably the best rootstock for fresh market plums.The degree of
dwarfism it provides seems to be ideal for California.We recommend planting trees at spacings
of 14 x 16 feet in the row and 16 feet between rows, using tie down clips to secure the branches
in the desired location and orientation, and practicing minimal pruning for the first few years.
This procedure brings trees into bearing within 5 years.

LITERATURECITED
Day, K.R. and R.S. Johnson.1997.Pruning to improve yield and quality.University of
California Kearney Tree Fruit Review.5 pages.
Day, K.R., R.S. Johnson, and T.M. DeJong.1993.Evaluation of new techniques for improving
stone fruit production, fruit quality, and storage performance: high density training trials.
California Tree Fruit Agreement Annual Research Report.7 pages.
DeJong, T., K. Day, J. Doyle, and S. Johnson. 1991a. Evaluation of training/pruning systems of
peach, plum and nectarine trees in California.Acta Hort. 322:99-106.
DeJong, T.M., K. Day, J.F. Doyle, and R.S. Johnson. 1991b. Evaluation of the physiological
efficiency of peach, nectarine and plum trees in different orchard systems.California Tree
Fruit Agreement Annual Research Report.7 pages.
DeJong, T.M., K.R. Day, J.F. Doyle and R.S. Johnson. 1994. The Kearney Agricultural Center
Perpendicular “V”(KAC-V) orchard system for peaches and nectarine.Hort Technology
4: 362-367.
Gerdts, M., H. Andris, and J. Beutel.1979. High density goes big time.Fruit Grower.pp. 9-10.