| Material Information
||A summary concerning the present status of certain burrowing nematode tolerant and resistant rootstocks
||Citrus Station mimeo series
||3 leaves : ; 28 cm.
||Ford, Harry W., 1922-
Feder, William A
Citrus Experiment Station (Lake Alfred, Fla.)
||Florida Citrus Experiment Station
||Place of Publication:
||Lake Alfred FL
||Citrus -- Rootstocks -- Florida ( lcsh )
Citrus -- Propagation -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||H.W. Ford and W.A. Feder.
||"September 18, 1962."
||"A cooperative project of the Citrus Experiment Station, Lake Alfred, and the U.S. Horticultural Station, Orlando."
||Citrus Station mimeo report ;
| Record Information
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 75959297
Citrus Station Mimeo Series 63-5
OcrT 1 ." September 18, 1962
A SUMMARY CONCERNING THE PRESENT STATUS OF CERTAIN
BURROWING NEMATODE TOLERANT AND RESISTANT ROOTSTOCKS
H. W. Ford and W. A. Feder1
The writers have received inquiries from interested growers, nursery-
men, and citrus organizations desiring to use the new nematode-tolerant
rootstock selections in their respective groves even though field trial
data are extremely limited. We continue to emphasize that the only infor-
mation established in reasonable detail is the laboratory and greenhouse
evaluation of the burrowing nematode status of these selections. The
horticultural evaluation and other information necessary to make specific
recommendations has not yet been established. Such information can only
be collected after extensive testing in field trials, which at present
are only a few years of age. ANYONE USING THESE SELECTIONS SHOULD CONSIDER
THEM AS EXPERIMENTAL AND STATEMENTS MADE HEREIN ARE SUBJECT TO CHANGE AS
ADDITIONAL DATA ARE AVAILABLE.
This report covers only those stocks that are currently in field root-
stock trials. Seven additional stocks will be field-tested in the near
"Clone X" Hybrid.--This selection was found as a rootstock in a bur-
rowing nematode-infested commercial grove in Polk County in 1954. The 15-
year-old tree, which was 16 feet in height, showed no visible deleterious
effects associated with the burrowing nematode. The scion variety was
Parson Brown and yielded 6 boxes of fruit. The unknown rootstock, which
could not be identified by leaves from root sprouts, had an extremely con-
centrated root system to a depth of 8 feet. The maximum depth of the
root system was 10 feet. No burrowing nematodes were found on the roots
over an 18-month sampling period. The roots of all adjacent trees were
heavily infested with burrowing nematodes.
Laboratory and greenhouse studies have established that this root-
stock known as "Clone X" hybrid has the unique property of reducing
burrowing nematode populations by preventing the development of nematode
eggs in the root cortex. There is no resistance to root penetration or
feeding by the nematode. Seedlings and budded plants of "Clone X" hybrid
have reduced or eliminated burrowing nematode populations from infested
soil in pots in the greenhouse over a period of 6-9 months. No burrowing
nematodes could be detected in the root systems by the methods employed
at the present time.
"Clone X" hybrid is apparently not resistant to the citrus nematode,
as indicated by the population on the parent tree at the present time.
A cooperative project of the Citrus Experiment Station, Lake Alfred, and
the U. S. Horticultural Station, Orlando.
The parentage of "Clone X" hybrid is in doubt. Since Clone X came from
a population of rough lemon seedlings and it is known that rough lemon seed-
lings are not 100 per cent nucellar, it is logical to assume that Clone X is
a rough lemon hybrid, male or pollen parent unknown. The soluble solids of
the juice from the Parson Brown scion has been 1 Brix higher than from the
same scion on rough lemon. Two-year-old cuttings of "Clone X" hybrid appear
to be more cold-tolerant than rough lemon.
Laboratory studies suggest that "Clone X" hybrid is more tolerant to
foot rot than rough lemon. It is tolerant to xyloporosis, and budded trees
inoculated with tristeza virus for 5 years in Florida have shown no sup-
pression of growth. Laboratory and greenhouse studies suggest that the
stock may grow satisfactorily in a rather wide range of soil pH.
Cuttings and seedlings of "Clone X" are vigorous in the nursery and
in the field. They appear to be tolerant to anthracnose but susceptible
Five-year-old cuttings budded with 6 different scions are all bearing
fruit in 1962. The scions are: Marsh, and Ruby Red grapefruit; Hamlin,
Parson Brown, Pineapple, and Valencia sweet orange; and Orlando tangelo,
Nothing is known concerning drought tolerance.
Rough lemon A and Rough lemon B.--Rough lemon A is a selection of
rough lemon found growing in a commercial grove in Lake Alfred in 1950.
Rough lemon B was found in a commercial grove in 1952. Rough lemon A had
been infested with the burrowing nematode for only 5 years and was removed
from its grove site in 1953. Rough lemon B is still growing in burrowing
nematode-infested soil in its original site and is now 23 years old. Both
Rough lemon A and Rough lemon B have shown similar responses in laboratory
tests. Burrowing nematode populations continue to exist in significant
numbers on the root systems and plant growth appears to be reduced up to
20 per cent due to activity of the nematode. The fruit and growth
characteristics of the seedlings of both Rough lemon A and B cannot .be
distinguished from ordinary Florida rough lemon.
The writers have tended to emphasize Rough lemon B primarily because
of the long period this stock has been growing in burrowing nematode-infested
soil. The scion is Valencia and has consistently yielded 4 times as much
fruit as adjacent trees in the grove. Yields of 8 boxes have not been un-
common. Fruit quality is the same as Valencia on rough lemon. The root
system extends to a depth of 9 to 14 feet. The variation seems to be caused
by the activity of the nematode. The maximum depth of the root system of
trees on ordinary rough lemon surrounding Rough lemon B is 4 to 5 feet.
At present it can only be assumed from observations of the parent
trees that Rough lemon P and B will grow and produce like ordinary rough
Carrizo citrange.--Carrizo citrange seedlings are somewhat tolerant
to the burrowing nematode. Growth may be reduced up to 25 per cent and
burrowing nematodes will continue to live on the roots. There is laboratory
information that variation exists in the sources of Carrizo. The California
selection may be more vigorous than the Texas or Florida selection. Carrizo,
which is a hybrid between P. trifoliata and sweet orange, is a vigorous
nursery seedling. It has not been evaluated extensively as a rootstock in
Florida. Information from California and other sources as well as the
limited information in Florida suggest that fruit quality is good, and that
it is tolerant to foot rot, tristeza, drought, cold, and the citrus nematode.'
Sanguine grosse ronde sweet orange.--The parent tree is in the USDA
citrus collection at Orlando. Sanguine grosse ronde sweet orange is tolerant-
to the burrowing nematode in laboratory tests. The seedlings and budded
plants show practically no reduction in root systems or top growth even
though nematodes are present on the root systems. At present this variety
appears to be horticulturally similar to other sweet oranges used as root-
stocks. Budded trees on this stock have been in the field in Florida for
Pineapple--156.--Pineapple--156 is a selection that appears to be
identical to ordinary Pineapple. The parent tree is in the USDA citrus
collection at Orlando. It is resistant to the burrowing nematode in
laboratory tests in that growth is not reduced and burrowing nematode popu-
lations decline to a low level. This stock will be placed in field trials
in 1963. Nothing is known concerning its use as a rootstock. For the pre-
sent we can only assume that, horticulturally, it will perform similarly to
ordinary sweet orange.
Currently, the above-mentioned stocks are being field-tested in 11
different locations in the State. These field plots were set out in the
spring of 1961 in non-infested and burrowing nematode-infested soils. The
sites include locations on the deep ridge sands, in the flatwoods areas,
and in the shallow soils along the East Coast. Horticultural evaluation
of the stocks on these sites will continue over the next 10-15 years and
will be reported on periodically by the writers.
At present, a large number of citrus nurseries have received budwood
of one or more of these candidate rootstocks through the auspices of the
Budwood Certification Program of the Division of Plant Industry of the
State of Florida. The Budwood Certification Office has a record of bud-
wood recipients. In addition, by agreement between the writers and the
Florida Citrus Nurserymen's Association, 3 nurserymen selected from a group
of volunteers, have been developing a supply of budded trees utilizing these
nematode-tolerant selections as rootstocks. These nurserymen have been
supplied with fruit and seed, seedlings and cuttings of these various root-
stocks as quickly as they have become available. It is their role to supply
trees budded on these rootstocks as soon as possible, and at a reasonable
price, to growers and organizations expressing aninterest in evaluating the
stocks in their own situations.