From the Florida State Horticultural Society
By Simon E. Malo, University of Florida, IFAS




A Successful Method for Propagating Sapodilla Trees
Florida Agricultural Experiment Stations Journal Series
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).


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.


picture

Figures 1 to 8 show different steps in the process of grafting sapodilla trees.

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.

 

Acknowledgment
The help of Mr. EL M. Landrum of Homestead, in providing assistance and plants for the photographs, is acknowledged.
Literature cited
1. Popenoe, Wilson. Manual of tropical and subtropical fruits. The Macmillan Company, New York. 1920.
2. Ruehle, Geo. D. The sapodilla in Florida. Circular S-34. Univ. of Fla. Agric. Exp. Sta. 1951.

Bibliography

Malo, Simon E. "A successful Method for Propagating Sapodilla Trees." fshs.org. Florida State Horticultural Society. University of Florida, IFAS, Sub-Tropical Experiment Station Homestead. 1967. Web. 1 May. 2015.

Published 1 May 2015 LR
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