VANILLA
Vanilla spp., family OrchidaceaeThree species of Vanilla are of commercial importance: V. planifolia Andrews [ V. fragrans (Salisb.) Ames], V. pompona Schiede, and V. tahitensis J. W. Moore. The first is by far the most important (Childers et al. 1959). Vanilla is cultivated for its pods which, under processing, yield vanilla extract. In 1950, world production was 3 million pounds of extract, of which Madagascar produced more than half and Mexico about a fourth. The United States is the primary consumer of vanilla extract (Childers et al. 1959).
Plant:
Vanilla is a tropical, evergreen, leafy, and somewhat fleshy vine (fig. 189) that may climb to the top of trees, 50 to 75 feet, if unchecked. It has thick, oblong, 6- to 9-inch, dark-green leaves and forms roots opposite the leaves by which it clings to the tree. It is propagated vegetatively, pruned at the tip, and trained onto a trellis. The plants are usually set 6 feet apart in the row, the rows about 9 feet apart (Kanman and Plai 1966). The fruit is a beanlike pod, 4 to 6 inches long by about one-half inch thick (fig. 190). The better pods are 5 inches or more in length. A single pod contains thousands of seeds almost microscopic in size (l/3 to 1/4 mm).
A healthy vine should produce about 100 pods per year, which mature 8 to 9 months after flowering. If too many flowers are pollinated and too many pods set, the vine may be overloaded and will die.
Just before the plant flowers, the grower usually prunes 4 to 6 inches from the vine tip; this stops linear growth and seems to benefit flowering (Childers et al. 1 959).
Irvine and Delfel (1961) dispelled the former belief that plants will not flower unless they are climbing, by showing that inflorescences were produced satisfactorily on horizontal and even descending stems. Of 10 plants studied, one ascending stem had 82 inflorescences, one 60 feet tall and still climbing had only 18, and one descending vine had 29. This proved that maintenance of plants on trellises did not necessarily cause a decrease in yield.
[gfx] FIGURE 189. - Section of vine of vanilla (Vanilla planifolia) growing on tree trunk.
FIGURE 190. - Dried vanilla beans from 4 different cultivars.Inflorescence:
The small lilylike, greenish-yellow vanilla flowers, 1 l/2 by 2 1/2 inches long (Woebse 1963), develop in axillary racemes (fig. 191). There may be as many as 100 flowers in a raceme but usually there are about 20. Usually, only one flower in a raceme opens in a day, with the entire flowering period of the raceme lasting an average of 24 days. Flowering for an average plant in Puerto Rico begins in January, reaches a peak in March, and ends in June. In the Philippines, flowering extends from March to June, with the largest percentage of the flowers appearing in April (David 1953).
The individual flower has three sepals and three petals, one of the petals being enlarged and modified to form the trumpetlike lip, and a central column comprised of the united stamen and pistil. The anther is at the apex of the column and hangs over the stigma, but a flap or rostellum separates them.
The flower opens in the morning and closes in the afternoon, never to re-open. If it is not pollinated, it will shed the next day. The optimum time for pollination is in midmorning (Childers et al. 1959).
The pollen clings together in a mass and is feebly attractive to certain bees and hummingbirds (Cobley 1956*, DeVarigny 1894). The nectar source is seldom mentioned, although hummingbirds visit flowers primarily, if not exclusively, for nectar. Many species of the family Orchidaceae are noted for their nectar secretion (Darwin 1877*). Correll (1953) stated that the flowers are visited for the "honey" secreted at the base of the lip.
[gfx] FIGURE 191. - Flowers of Vanilla pompona.
Pollination Requirements:
The vanilla flower is self-fertile, but incapable of self-pollination without the aid of an outside agency to either transfer the pollen from the anther to the stigma or to lift the flap or rostellum then press the anther against the stigma. The only time this can be accomplished is during the morning of the one day the flower is open. Unless pollination occurs, the flower drops from the vine the next day. Correll (1953) stated that insect pollinated flowers, being cross-pollinated, produce viable seed, but flowers that are hand pollinated, being self-pollinated, produce only sterile seeds.
Pollinators:
The reference occurs repeatedly in the literature that in its native Mexico the flowers of vanilla are pollinated by small bees of the genus Melipona and also by hummingbirds (Ridley 1912*). Childers and Cibes (1948) noted that this report has not been carefully checked and later Childers et al. (1959) said that there is no experimental proof that they are actually effective pollinators. Mention is made by Childers et al. (1959 p. 477), that "The first effort made toward solving the (pollination) problem was to introduce bees of the genus Melipona from Mexico, but they did not thrive. After this failure a mechanical means of pollination was tried." Then Albius, in 1841, discovered the practical method (Childers et al. 1959) of using a small splinter of wood or a grass stem to lift the rostellum or flap out of the way so that the overhanging anther can be pressed against the stigma to effect self-pollination.
Now, practically all vanilla is produced by hand pollination, which accounts for 40 percent of the total labor cost in vanilla production (Gregory et al. 1967).
No further study seems to have been made on the utilization of Melipona, or other insects, or hummingbirds. No attempt has been made to concentrate pollinating insects for this purpose. It would appear logical that if nectar is secreted, as indicated by Correll (1953), honey bee colonies could be amassed in the area when desired, and the workers could be "forced" to visit the flowers. The relative cost of a high concentration of honey bee colonies as compared to the cost of human labor, would make such exploitation of honey bees highly worthwhile investigating. The reference by DeVarigny (1894) that Cuban bees, whether indigenous or naturalized European bees, were pollinating vanilla in Cuba indicates that bees could be used satisfactorily.
Pollination Recommendations and Practices:
There are no recommendations for the use of bees, bats, birds, or other agencies. The evidence indicates, however, that saturation pollination by honey bees or certain other bees offers possibilities because vanilla in Mexico was probably pollinated by bees at one time to some extent.
LITERATURE CITED:
CHILDERS, N. E., and CIBES, H. R.
1948. VANILLA CULTURE IN PUERTO RICO. U.S. Dept. Agr. Cir. 28, 94 pp.______CIBES. H. R., and HERNANDEZ-MEDINA, E.
1959. VANILLA - THE ORCHID OF COMMERCE. In Whithner, C. L., The Orchids - A Scientific Survey, pp. 477-508. Ronald Press Co., New York.CORRELL, D. S.
1953. VANILLA. ITS BOTANY, HISTORY, CULTIVATION AND ECONOMIC IMPORTANCE. Econ. Bot. 7(4): 291-358.DAVID. P. A.
1953. POLLINATION OF VANILLA FLOWERS BY HAND. Philippine Agr. 37: 301-305.DEVARIGNY. C.
1894. FERTILIZATION OF THE VANILLA FLOWER BY BEES. Bombay Nat. Hist. Soc. 4: 555-556.GREGORY. L. E., GASKINS, M. H., and COLBERG, C.
1967. PARTHENOCARPIC POD DEVELOPMENT BY VANILLA PLANIFOLIA ANDREWS INDUCED WITH GROWTH-REGULATING CHEMICALS. Econ. Bot. 21: 351-357.IRVINE, J. E., and DELFEL, N. E.
1961. FLOWERING BEHAVIOR OF VANILLA. Nature 190(4773): 366.KANMAN, K., and PILLAI, G. G.
1966. VANILLA, A NEW VENTURE FOR KEROLA FARMERS. Indian Farm. 16(2): 4 - 7.WOEBSE, A.
1963. POLLINATING THE VANILLA FLOWER. Amer. Orchid Soc. Bul 32(12): 1009-1010.
