AGRICULTURAL EXTENSION SERVICE
Circular 132 May 1955
By JASPER N. JOINER
Rootstocks exert a vital influence on the production and man-
agement problems of citrus groves and their importance should
not be overlooked when planting or buying a grove. The wrong
rootstock for a given soil type or for a particular variety can
mean the difference between success and failure in a grove
The fact that some rootstocks perform better on certain soils
than others has been common knowledge for many years. Dur-
ing the infancy of the Florida citrus industry, however, the se-
lection of rootstocks was relatively simple. Generally, sour
orange rootstocks were used on low, wet soils, rough lemon on
high, sandy soils and either the trifoliate or sour orange stocks
in the colder areas.
The advent of tristeza, xyloporosis and many other virus dis-
eases has complicated the rootstock problem and brought a need
for further information. In addition to the virus problem, de-
mands for higher solids in fruit is growing, which emphasizes
a need for better rootstocks as well as varieties.
Problems connected with rootstocks are little understood, but
the influence of stocks on scions and vice versa is often more
important than the influence of environmental factors. Al-
though each of the two distinct portions of the tree retains its
individual genetic characteristics, the expression of these char-
acteristics may be modified slightly by each other. Rootstocks
influence vigor, cold resistance, fruitfulness, fruit quality, min-
eral composition of leaves and disease tolerance of the tree.
This rootstock has been the basis of the citrus industry in
the Indian River section, and on other low, hammock soils and
in the northern part of the citrus belt. It is highly resistant
to foot rot, gummosis and xyloporosis, but is one of the most
susceptible of all varieties to tristeza.
Because of its resistance to foot rot, sour orange rootstock is
well adapted to low, moist and fairly heavy soils. It is a slow
grower on light, sandy soils, however.
Of the commonly used roostocks, sour orange is second only
to the trifoliate orange in cold hardiness. Citranges are prob-
ably intermediate between sour orange and the trifoliate in
Although it produces fruit of outstanding quality, its use for
commercial plantings in the future seems unwise in view of the
tristeza problem and its potential threat to the industry. The
best choice in rootstocks to replace the sour orange for low,
heavy soils appears to be Cleopatra tangerine until a better one
Rough lemon is the most widely used rootstock in the state
today, particularly for plantings on the light, sandy soils of
the Ridge section. It is a strong grower-producing large trees
faster than most other rootstocks on light soils-and produces
heavy yields. This rootstock is not recommended for low, heavy,
wet soils, due to its disease susceptibility.
This rootstock is highly tolerant of tristeza and xyloporosis,
but is very susceptible to root and crown rot diseases. Like
all other known rootstocks, it is subject to attack by various
nematodes which plague citrus.
Although a prolific bearer, it produces fruit of poorer quality
than sour orange, sweet orange, Cleopatra or trifoliate. The
quality problem can be only partially overcome with a good fer-
tilizer program. Rough lemon cannot be recommended for
colder areas, for it is one of the least cold-resistant of all root-
When choosing between rough lemon, sweet orange and Cleo-
patra rootstocks for light sandy soils one must weigh the advan-
tages of increased yields by rough lemon against the improved
quality and somewhat smaller crops of the other two.
Sweet orange is rapidly gaining in popularity and use as a
rootstock throughout the state. It appears to be adaptable to
light, sandy soils and the well-drained, heavier soils. This stock
is second to rough lemon in production with most orange and
grapefruit varieties. Valencias are apparently much more pro-
ductive on rough lemon rootstocks.
Although susceptible to foot rot organisms, it is highly tol-
erant to tristeza and xyloporosis. Sweet orange falls between
rough lemon and sour orange in cold hardiness.
This rootstock produces fruit of excellent quality, on both
light, sandy soils and well-drained, heavier soils.
Many people feel that the Cleopatra tangerine is the most
likely to replace sour orange as a commercial rootstock. While
there is some indication that Cleopatra can fill some of the needs
left vacant by the elimination of sour orange, it is by no means
equal to sour orange under all conditions. It is adaptable to a
wide range of soils, apparently doing equally well on high, sandy
and low, moist soils.
Cleopatra is highly resistant to foot rot, xyloporosis and tris-
teza. Due to this disease resistance, it seems an excellent choice
in replacing sour orange on the low, wet soils.
This rootstock produces fruit of excellent quality and is a pre-
ferred stock for mandarin types, especially Temples and tange-
rines. It apparently comes into production more slowly than
rough lemon and with Hamlin scions produces fruit of small
size. As a rootstock for Valencias and grapefruit it is a shy
bearer, decreasing production by 1 to 11/2 boxes or more per
mature tree, as compared with rough lemon.
The cold resistance of Cleopatra is more than rough lemon
but less than sour orange and therefore it has an added dis-
advantage in northern producing areas.
Many years ago hundreds of acres of citrus on grapefruit
rootstock were planted in the state. For a while it was thought
to be an excellent stock, since it produced vigorous trees. It
soon became evident that this rootstock produced fruit of ac-
ceptable quality, but shy bearing trees with a definite tendency
to bear even fair crops only in alternate years. Because of its
shy-bearing nature it requires heavier rates of fertilization and
water to produce economical yields than trees budded on most
This rootstock is somewhat susceptible to tristeza, gummosis
and foot rot. Since it has no major advantages to offset its
many disadvantages, grapefruit rootstock is not currently
being recommended or planted.
The exceptional cold hardiness of varieties budded on trifoli-
ate makes this a desirable rootstock for home planting in the
northern and northwestern areas of the state. It appears to
have a slightly dwarfing effect with most scion varieties, which
is undesirable commercially but can be an advantage for citrus
used in landscaping small properties.
Trifoliate rootstock produces excellent quality fruit and good
production per volume of tree. Although it has not been exten-
sively tested on the light, sandy soils, it appears too lacking in
vigor on all but heavy clay soils to be a useful stock on sandy soils.
Its susceptibility to exocortis or "scaly butt" is an additional
hazard but it is the preferred stock for Satsuma oranges on the
heavy soils of northern Florida.
Under research conditions this rootstock looks promising as
a future possibility. It does appear to have a dwarfing effect
on most scions, particularly on very light soils, the exact extent
of which is unknown. Rusk citrange is resistant to exocortis
and believed to be tolerant of tristeza. It produces fruit of good
This stock has been mentioned often as a possible rootstock
to replace sour orange on the low, heavy, wet soils, since it is
reported in Brazil to be tristeza tolerant. It grows rapidly, pro-
duces fruit of acceptable quality, but is short-lived and is sub-
ject to a bark disease of unknown cause. The disease is thought
to be virus in nature and probably accounts for the observed
short life of this rootstock. It can probably be avoided by the
selection of clean budwood.
There are some 50 to 100 other citrus varieties being tested
by Experiment Station workers as possible rootstocks but to date
insufficient data are available upon which to base any recom-
mendations. To be worthy of consideration new rootstocks must
have such characteristics as vigor, adaptability to wide range
of soil conditions, production of high yields and quality, cold
resistance, and resistance to various root diseases and nematode
attack. Research in this phase of horticulture is a long-term
process and many years will be needed to answer many of the
current questions on rootstock relationships to environment rind
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