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Green-Seeds.com
Fruits
& Others
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CITRUS PROPAGATION & ROOTSTOCKS
BY DR. MARTIN L. PRICE
Published 1983
In response to various questions from overseas, we have tracked down
some answers that are of general interest to our readers. These have been
published in past issues of ECHO Development Notes. This technical note
reprints those in their entirety. It also adds a couple of helpful tables
that were provided by the Holm Citrus Nursery concerning characteristics
of citrus rootstock and varieties of citrus.
WHAT VARIETIES OF CITRUS WILL GROW TRUE FROM SEED?
 Jerry Larson with Double
Harvest in Haiti asked us what varieties of citrus might come true from
seed. I checked with Dr. Carl Campbell at the University of Florida Extension
research center. Carl has given me many in-depth, insightful answers to
tropical fruit questions sent by several of our readers. He said that a
great number of citrus trees would come true from seed. There is a way that
you can tell by examining a few seeds from the tree. Peel off the outer
and inner seed coat. If the seed is polyembryonic, i.e. has many embryos,
it will come true. I asked what it would look like if it were polyembryonic.
Carl said that the various embryos would be convoluted upon each other.
If it is mono-embryonic there will be one embryo with two distinct cotyledons.
Almost any sweet orange will come true from seed, as well as key limes,
grapefruit, tangerine and tangelo. Two varieties that will not come true
from seed are temple and pomelo.
What are the advantages
and disadvantages of growing citrus from seed when that is possible? One
obvious advantage is that it is much less labor intensive to simply sow
citrus seeds and eliminate the grafting step. Another advantage is that
the seedling will most likely be free from viruses that sometimes get into
the budwood that is used for grafting large numbers of trees. I asked Carl
about reports that non-grafted citrus trees live longer, up to twice as
long, as grafted trees. He said that this can be true, depending on the
number and kinds of disease organisms that may be present in the budwood.
If one uses certified disease-free budwood, and if there are no microorganisms
present that we don't even know to look for yet, then there should be no
difference in the longevity of the trees.
One advantage to grafting
is that one can combine the best traits of the above ground part of the
tree with the best adapted rootstock for the particular soils and conditions
of the area. A seedling will tend to grow upright, tending toward a single
trunk, and becoming quite thorny. A grafted tree will be more highly branched.
The seedling tree will not fruit for 6-7 years, contrasted to the 3-4 years
for a grafted tree. The earlier fruiting of the grafted tree is partly responsible
for the more highly branched form of growth. Apparently the weight of the
fruit after about 3 years bends the branches and causes new buds to begin
growing; resulting in a more highly branched tree.
But not all of the reasons
for the differences between seedling and grafted trees are known.
If you live in an area
where citrus is not a major crop but would like to introduce it, you might
consider trying some of the polyembryonic seeds. If you are more adventuresome,
in a few years also plant some accepted rootstock varieties for grafting
using budwood from the new trees you have introduced. If you prefer to start
with a Florida variety rather than a good local variety, and want only a
few seeds, we can at times provide them. If you want larger amounts, we
have located a supplier, Lawrence Reed at Holm Citrus Seed Co., who routinely
ships overseas. Seed currently sells for $30 per pound plus airfreight.
He can provide phytosanitary certificates if you so request and include
your full address and phone number. I asked about the danger of introducing
a new disease. He said this does not appear to be a problem with citrus
seed. There has never been an instance where a citrus disease has been proven
to have been introduced by seed. They are sending me a one-page guide to
help select seed for rootstock. I will send you a photocopy upon request.
If you have money on deposit with us, we will be glad to place orders for
you.
I asked Dr. Campbell
to proofread the above. He added that in some of the polyembyronic citrus,
some of the embryos are of gametic origin and therefore do not come true.
The percentage varies by species and variety.
SUGGESTIONS FOR PURCHASE OF CITRUS SEEDS
Carl Berg, a Peace Corps
volunteer in Ecuador, inquired about citrus rootstock and how best to introduce
assorted varieties of citrus into his part of the country. I phoned Mr.
Reed at Holmes Citrus Nursery for help.
There are five rootstocks
that he recommends for anyone, anywhere (though he sells 18). These five
are sour orange, ëCarrizoí citrange, ëSwingleí,
Cleopatraí mandarin and Poncirus trifoliata. If there is no danger
of freeze or frost, he would add to the list the following: Citrus macrophylla
(for extremely warm climate, but poor fruit quality), 'Rangpur' lime, 'Palestine'
lime, 'Milam' and volkameriana. We also sent Carl budwood of superior varieties
to bud onto wild citrus. These will be used to bud the new rootstock when
it is ready.
The prices per quart
range from $30 to $125, so most of ECHO's collaborators would be unable
to try more than perhaps one variety. I asked if he would be willing to
prepare an assortment in smaller packets. He agreed to the following. You
can send him $40 for an assortment of the first 5 mentioned above, all ten
mentioned above, an assortment of citrus that will come true from seed,
or any combination of these. He will arrange packet size to make the bill
come out to $40. We agreed to allow him some flexibility, as he would not
have time for precise measurements, etc. You will receive approximately
1.5 pounds of seed. I would recommend that you add about $20 for airmail
postage, as citrus seeds begin to lose viability within a couple weeks after
removal from refrigerated storage. Alternatively, you may know someone in
the States that is about to visit you. The seeds could be sent to them via
UPS. Mr. Holmes is doing this as a favor to help your work and does not
assume responsibility for delivery by international mail systems. Send your
order, mentioning the ECHO package arrangement, to Mr. Chuck Reed, Reed
Brothers' Citrus, P.O. Box 1863, Dundee, FL 33838 (Phone 813/439-1916).
I also asked about susceptibility
to Phytophthora root rot. He said that rough lemon is one of the worst rootstocks
in regions where Phytophthora is a problem. It once was the primary rootstock
in Florida, but has been totally replaced. All citrus trees are susceptible
to Phytophthora root rot to some degree. If a workman injures a root and
the organism is in the soil, it can enter and damage the tree. It can then
kill after a few months or just reduce production. Some trees in a row may
become infected and others not. Budwood is not infected.
ANSWERS TO SOME QUESTIONS ON CITRUS 
Two of our readers asked
some interesting questions about citrus. We called Larry Reed at Holm Citrus
nursery who has so often been helpful. The questions and answers are of
general interest, so I repeat them here.
Q. (From William Boykin
in Zambia). "The navels, valencias and hamlins do not have the sweet
flavors we had hoped. Is there anything we can do, or might it be the rootstock?
We budded onto cape lemon."
A. The cape lemon rootstock
is your major problem. Lemon rootstocks produce big quantities of fruit,
but the quality is always poor. Lemon rootstock is for commercial juice
production where they want to emphasize quantity. They then mix with smaller
amounts of other juices to get the right taste. An advantage of the lemon
stock is rapid growth, it being more vigorous than other stock. However,
this also results in poor taste. Climate can also cause inferior taste.
It would help if the climate were cooler. I would suggest budding onto either
Carizzo or sour orange. They may not allow sour orange into the country
because it is so susceptible to Tristeza. For example, Brazil's citrus industry
was wiped out some years ago by tristeza. But it depends a lot on how virulent
is the strain in your country. It is so good that I would take the risk
and not worry too much about tristeza. My third choice would be Cleopatra
mandarin. The disadvantage with it is foot rot. This worldwide problem is
caused when workers injure the root while cultivating. It is most susceptible
during the first 5 years. The safest thing would be to use a combination
of rootstocks. Then it will be unlikely that you will be wiped out.
If you wish to plant
some true-to-type seeds I would recommend two varieties: ridge pineapple
or what is called "old sweet seedling." By the way, any true-to-type
seedling [plant grown from seed that will give fruit like the parent tree]
is susceptible to foot rot.
Q. (From Peter van Lonkhuyzen
in Haiti). I have used budwood from some three-year-old trees that are not
bearing fruit yet. Someone told me that by using such young trees my grafted
trees will start bearing late and never will give good yields. Is this true?
A. A grafted tree will
normally start bearing some fruit within a year. The fact that the parent
trees you used were not bearing at three years suggests that they were seedlings.
If so, you will have to wait about as long as if you had planted the seed.
There is one way you
can get some quick budwood. Take budwood from a mature bearing tree and
graft onto a rootstock in your area. As soon as this has grown to produce
some branches, you can use this to bud other trees. They call this "first
generation budwood." However, the second generation of trees should
not be used for budding until they have started bearing.
Q. What rootstock should
I use that is resistant to both drought and tristeza?
A. Sour orange is drought
resistant, but if you want tristeza resistance also I would recommend Carizzo.
Of course, even that is only drought resistant to a point. True-to-type
seedlings will never tolerate drought as well as the normal rootstocks.
I might also mention that a rooted cutting from any variety of citrus will
have about half the normal life expectancy of a grafted citrus, due to susceptibility
to a range of root diseases.
Q. How is it possible
that in some places they have Washington naval trees without thorns while
somewhere else the same variety has thorns?
A. There can be some
differences in thorniness within a variety. In the one location they must
have budded from trees that did not have thorns. You will still have some
thorns of course. Alternatively, the thorny ones could be seedlings, as
they tend to have more thorns.
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Table 1. SOME REACTIONS OF ROOTSTOCKS TO DISEASES,
NEMATODES, AND COLD.
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Rootstock
Variety
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Tristeza
|
Xyloporosis
|
Exocortis
|
Footrot
|
Blight
|
Burrowing
Nematode
|
Citrus
Nematode
|
Cold
|
|
Rough
lemon
|
T
|
T
|
T
|
S
|
HS
|
S
|
S
|
S
|
|
Sour
orange
|
HS
|
T
|
T
|
T
|
S**
|
S
|
S
|
T
|
|
Cleopatra
mandarin
|
T
|
T
|
T
|
S
|
S**
|
S
|
S
|
T
|
|
Sweet
orange
|
T
|
T
|
T
|
HS
|
S**
|
S
|
S
|
T
|
|
Trifoliata
orange
|
T
|
T
|
HS
|
T
|
S
|
S
|
T
|
T
|
|
Rusk
citrange
|
T
|
T
|
S
|
S
|
S
|
S
|
S
|
S
|
|
Carrizo
citrange*
|
T
|
T
|
S
|
T
|
S
|
T
|
S
|
S
|
|
Estes
Rough lemon
|
T
|
T
|
T
|
S
|
HS
|
T
|
S
|
S
|
|
Milam
|
T
|
T
|
T
|
HS
|
S**
|
T
|
S
|
S
|
|
Ridge
Pineapple orange
|
T
|
T
|
T
|
HS
|
S**
|
T
|
S
|
T
|
|
Rangpur
lime
|
T
|
S
|
S
|
S
|
S
|
S
|
S
|
S
|
|
Sweet
lime
|
T
|
S
|
S
|
S
|
?
|
S
|
S
|
S
|
|
Citrus
macrophylla
|
HS
|
S
|
T
|
T
|
S
|
S
|
S
|
S
|
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Smooth
flat Seville
|
S
|
T
|
T
|
T
|
S
|
S
|
S
|
T
|
|
Rangpur
x Troyer
|
T
|
S
|
S
|
T
|
S
|
S
|
S
|
S
|
|
Swingle
|
T
|
T
|
T
|
T
|
?
|
S
|
T
|
T
|
|
Volkamer
lemon
|
T
|
T
|
T
|
T
|
S
|
S
|
S
|
S
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*Psorosis virus is transmitted through Carrizo citrange seed. Use seed
from tested psorosis free sources only.
**Less susceptible than all others.
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Green - Seeds Co., Ltd.
81/10B Ho Van Hue Street, Phu Nhuan District, Ward 9, Ho Chi Minh City, Vietnam
Tel: +84 (8) 847 6901 - Fax: +84 (8) 844 1392 - Email: info@green-seeds.com
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