No. 2829
Introduction
For many years sapodilla (
Manilkara
zapotilla (Jacq.) Gilly)
trees were known mainly as the source of chicle, the elastic gum which
is made from the latex of the bark and which was the main ingredient of
chewing-gum. Today manufacturers prefer synthetic ingredients, the
supply of which is more dependable, and sapodilla trees are grown in
southern Florida and many tropical areas for their fruit and as
ornamentals. The sapodilla is a highly savory fruit and lends itself to
many dessert uses.
The availability of grafted trees of superior
fruiting varieties has always been limited. One reason has been the
lack of a practical method of propagation which requires a minimum of
labor and time, and is adapted to profitable
nursery practices.
This
paper describes new methods of handling stocks and scions by which a
nurseryman can produce a large number of grafted plants quickly and
reliably.
Procedure
Germinating
the seed.
Seeds for rootstocks are obtained preferably from vigorous sapodilla
trees and if possible from large fruit which contain larger than
average seeds. Although the seed will germinate after a few months if
kept dry (1), it is desirable to use fresh seed to avoid any delay in
germination and obtain uniform seedlings. Seeds germinate readily in
flats containing either perlite or a mixture of vermiculite and peat
moss.
Germination is usually better in a shadehouse. As soon as
the first pair of leaves appears, the seedlings are watered with a weak
solution of soluble fertilizer until they are ready for transplanting,
thus providing an added boost to encourage faster growth.
Growing and
transplanting the seedling.
Seedlings with two or three pairs of leaves are transplanted to No. 10
metal cans or similar containers containing a mixture of equal parts of
sand and peat moss or sand and light muck
(Fig. 1). It is preferable
to grow the seedlings in full sun. If kept moist and fertilized with
1/2 tablespoon of 8-4-8 N-P-K (with 30%-40% of the nitrogen coming from
organic sources) every 1% months the seedlings will be ready to graft
in 8 to 12 months (Fig. 2).
Grafting.
The ideal rootstock should have 5 to 8 pairs of leaves, a stem caliper
of 1/4 to 3/8 inch, and should be growing vigorously.
In
contast to previous practice (2), scions are obtained from young
terminal shoots having approximately the same caliper as the stock, and
without any preconditioning or preparation. The stocks are
veneer-grafted by removing longitudinally a 1 1/2 inch section of
cortex or bark barely cutting into the wood. The scion is prepared to
fit this cut (Fig. 3), by cutting the cortex and wood in the same
manner. Then the scion is wrapped and completely covered with a plastic
strip which allows free gas exchange, while restricting transpiration
and dehydration (Fig. 4).
Forcing.
Thirty days after grafting, regardless of whether the scion has begun
to grow or not, the plastic is removed entirely (Fig. 5), and unless
the scion is dead, the top of the stock is cut back leaving only two
leaves.
Stocks with scions that failed to take are regrafted as
soon as possible. When the scions have grown 6 to 8 inches
(Fig. 6),
the remaining section of stock is cut off at the graft union, and the
growing new shoot is tied to a training stake (Fig. 7).
Fig. 1 to 8
show different steps in the process of grafting sapodilla trees.
Discussion
One
unpleasant feature of grafting sapodilla sapodilla trees is the
continuous flow of latex from cut surfaces, which requires the operator
to work fast and clean his knife regularly. Other wise the sticky latex
makes for a difficult and slow operation, particularly when many plants
are involved.
In the past it was customary to cut and bleed the
cortex of most of the latex before grafting (2). This was done at a
point above or below the graft site, and it was thought that this
insured a higher percent of success. Recently it has been shown that
bleeding is an unnecessary and time-consuming operation which does not
improve the success of grafting.
In addition to good
grafting technique, the following points should be kept in mind, a)
Seedlings should be uniform in size and growing vigorously. Undersized
plants should be discarded, b) There is a period of perhaps 2 to 3
months when seedlings have the right combination of stem caliper and
vigor, in which the chances of success are greatest. Before and
especially after this period the number of successful grafts declines,
c) The best time of the year for grafting sapodilla seedlings in
Florida seems to be the summer and fall months, which follow the time
when seeds are available in the spring, d) When grafting the scion
should be covered completely with plastic. This prevents dehydration of
the scion during the relatively long period of time required for
formation of callus at the graft union. Sapodilla trees grafted and
handled this way are ready for field planting in about 20 to 24 months
from the time they were started from seed (Fig. 8).
Summary
A successful method for grafting sapodilla trees is described.
1.
Sapodilla seedlings are used for rootstocks. Fresh seeds from vigorous,
large fruited trees, are germinated in flats containing either perlite
or vermiculite plus peat moss.
2. Seedlings are grown in metal
cans, or other suitable containers, in a mixture of equal parts of sand
and muck. Their growth can be hastened with careful fertilization and
moisture control.
3. When seedlings have 8 to 12 pairs of
leaves, they are veeneer-grafted with scions from young terminal
shoots. Scions are covered completely with plastic strips which are
removed after 30 days.
4.
After the scion is established, growth is hastened by cutting off the
top of the rootstock and leaving only two leaves. When the scion
reaches 6 to 8 inches in height, the remaining section of stock is cut
off at the graft union, and the scion trained with a stake. Plants are
usually ready for field planting in 20 to 24 months from the time the
seeds were planted.
