Practical Methods for Hybridization in the Butiinae
Merrill Wilcox and the late Charles Raulerson
Kanapaha Botanical Gardens, 4700 SW 58th Drive, Gainesville, FL 32608, U. S. A.

Abstract Methods for collection, live preservation, storage, and use of pollen in hybridization of palms in, and related to, the Butiinae subtribe are described. Pure pollen techniques (i. e., pollination was conducted so as to prevent contamination by extraneous pollen) were developed. Virtually no laboratory equipment was used. These methods have been successfully used to produce the prized hybrid of Butia capitata x Syagrus romanzoffianum, which has the botanical name XButyagrus nabonnandii. This prized hybrid is itself virtually sterile; the protection described was therefore unnecessary in producing, by great effort, the two back-crosses. The back-cross with S. romanzoffianum is considered to be even more attractive than XButyagrus nabonnandii by those who have observed it.

The Butiinae (14) subtribe (Table 1) is a group of more than 50 species of pinnate cocoid palms of widely differing forms. The forms vary from the massive Jubaea spectabilis, having a solitary trunk (11) through clustering (e.g., Syagrus flexuosa), and non-clustering (e.g., Butia) species of moderate size, to grass-like species such as S. graminifolia and S. vagans (2, 3, 6, 14). The group varies widely in cold-hardiness; Jubaea and Butia are among the most cold-hardy of pinnate palms, while many others are tender or unevaluated. Several naturally occurring hybrids have been noted within the alliance as listed in Table 2 (1, 4, 5, 7, 8, 9, 12, 17). These naturally occurring hybrids have comprised various combinations of clustering and non-clustering parents. The majority of the species in the Butiinae whose chromosome number has been determined have n = 16 (13, 14). There is extensive research relating to pollen extraction and preservation in the cocoid genera Cocos and Elaeis (10, 15, 16). There is a widely adapted medium available for testing viability of palm pollen (13). These favorable considerations, together with the esteem held in the industry for XButyagrus nabonnandii, the hybrid between Butia and S. romanzoffianum, were strong encouragement for studies of hybridization within the Butiinae.

Butia is by far the most and convenient palm to use as a female parent at the latitudes of Gainesville and Jacksonville in Florida, U.S.A. for these studies. We quickly noted that slightly less than half of the Butia specimens keyed as B. capitata; random mixtures including other species of Butia were common.

Materials and Methods

Butia specimens were selected for ease of emasculation of their inflorescences. Very large differences in this attribute were noted. All male and the occasional perfect flowers were removed, as the latter proved to be fertile. The emasculated inflorescence was enclosed in a large, clear, plastic bag prior to the emergence of the stigmas (Fig. 1a). Pollen was collected from desired male parents (15) and dried in a refrigerator over silica gel for two to four days. The pollen was no deeper than 10 mm in the container while dried. After the pollen was extracted from the inflorescence, the latter was heated in an oven at 40ºC for one-day intervals and re-extracted (15). These batches of pollen were also dried in the same manner. After drying, the bottles of pollen were capped and stored in the freezer. These were tested in the medium described (13) except that colchicine was deleted.

Depending on the available quantity of pollen, it was applied to the stigmas either by Q-tip individually or by sprinkling the entire inflorescence. The pollen was applied shortly after the stigma emerged as in Fig. 1b, when the stigmas began to separate at their tips, through the stage depicted in Fig. 1c. The plastic bag was removed no more than a week later, as it seemed to cause precocious maturity with resultant small seed size. Where XButyagrus nabonnandii was pollinated, the virtually sterile inflorescence was not protected with a plastic bag. It is usually necessary to protect the developing infructescence with a screen-wire bag, as one gray squirrel (Sciurus carolinensis) can destroy hundreds of seed at milk stage within a few hours.

Results and Discussion

Using the very simple extraction and preservation methods described herein, it was possible to store for a year, in viable condition, pollen of Allagoptera arenaria, Syagrus X tostana, and all of the Syagrus species listed in Table 2, except S. schizophylla. The latter species and Butia and its various hybrids with Jubaea were not as amenable to the extraction procedure; nevertheless, some pollen could be extracted and preserved and crosses were made from their pollen. These pure pollen methods were successful, albeit in a rather labor intensive manner, in producing XButyagrus nabonnandii, shown in Figure 2 at Florida Community College (South Campus), Jacksonville, Florida. The late Professor Raulerson (17) pollinated an astronomical number of the virtually sterile XButyagrus nabonnandii in order to produce the back-crosses listed in Table 3. A specimen of XButyagrus nabonnandii backcrossed with S. romanzoffianum is shown with the late Professor Raulerson in Figure 3. We pollinated Butia with viable pollen from Cocos or Elaeis many times under ideal conditions without success. We pollinated Butia yatay with viable pollen from S. romanzoffianum many times under ideal conditions without success.

Figure 2. XButyagrus nabonnandii at Florida Community College (South Campus), Jacksonville, Florida.	Figure 3. XButyagrus nabonnandii backcrossed with S. romanzoffianum, shown with the late Professor Raulerson.

Specimens of XButyagrus nabonnandii produced during this work have been provided for observation at the following locations:

Florida Community College (South Campus), Jacksonville, Florida
Fairchild Tropical Garden, Miami, Florida
Golden Gate Park, San Francisco, California
Huntington Botanical Garden, San Marino, California
Kanapaha Botanical Gardens, Gainesville, Florida
Lakeside Park, Lake Merritt, Oakland, California
San Diego Zoo, San Diego, California

A single specimen of XButyagrus nabonnandii backcrossed with S. romanzoffianum has been provided to Kanapaha Botanical Gardens.

There is a widespread belief in the Florida nursery industry that the Butia X S. romanzoffianum hybrid is extremely vigorous. Our belief is that those hybrid seedlings that are a much larger population of seedlings of mediocre vigor. The average vigor of seedlings from controlled crosses has been disappointingly low. The authors feel that modern asexual propagation of selected hybrids offers considerable commercial horticultural promise because of the wide variety of plant forms available in the Syagrus alliance.

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We thank Noel Lake and John B. Taylor for their support and encouragement, Ted Waas for a specimen of XButyagrus nabonnandii backcrossed with S. romanzoffianum, and David Bell, Stanley Kiem, Don Evans, and Mary Collins of Fairchild Tropical Garden for plant materials.

Literature Cited

1. Glassman, S.F. 1967. Nomenclatural changes in the family palmae. Rhodora 65:259-261.
2. Glassman, S.F. 1967. New species in the palm genus Syagrus. Mart. Fieldiana: Botany 31:235-245.
3. Glassman, S.F. 1968. New species in the palm genus Syagrus. Mart. II. Fieldiana: Botany 31:285-299.
4. Glassman, S.F. 1968. Studies in the palm genus Syagrus. Mart. Fieldiana: Botany 31:363-397.
5. Glassman, S.F. 1968. Syagrus oleracea (Mart.) Becc. and closely related Taxa. Fieldiana: Botany 32:13-33.
6. Glassman, S.F. 1968. Studies in the palm genus Syagrus. Mart. II. Fieldiana: Botany 32:77-103.
7. Glassman, S.F. 1970. A synopsis of the palm genus Syagrus. Mart. Fieldiana: Botany 32:215-240.
8. Glassman, S.F. 1970. A new hybrid in the palm genus Syagrus. Mart. Fieldiana: Botany 32:241-257.
9. Glassman, S.F. 1971. A new palm hybrid from the Fairchild Tropical Garden. Principes 15 :79-88.
10. King, J.R. 1961. The freeze-drying of pollens. Economic Botany 15:91-98.
11. McCurrach, J.C. 1960. Palms of the world. Harper Bros., New York.
12. Raulerson, C. and W.T. Waas II. 1970. Some notes on palms growing in the Jacksonville area of Florida. Principes 14:93-96.
13. Read, R.W. 1964. Palm chromosome studies facilitated by pollen culture on a colchicine lactose medium. Stain Technology 39:99-106.
14. Uhl, N.W. and Dransfield, J. 1987. Genera Palmarum. Allen Press, Lawrence, KS.
15. Whitehead, R.A. 1963. The processing of coconut pollen. Euphytica 12:167-177.
16. Whitehead, R.A. 1965. Freeze-drying and room temperature storage of coconut pollen. Economic Botany 19:267-275.
17. Wilcox, M. 1984. Charles Raulerson, 1916-1983. Principes 28:50.
    

Table 1. Summary of the Subtribe Butiinae (14)

Table 2. Naturally-occurring hybrids in the Butiinae

* A reasonable prediction in the view of the authors.
** Unpublished observations by the authors.

Table 3. Synthetic hybrids in the Butiinae

* Unpublished observations by the authors.
** A reasonable prediction in the view of the authors.

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