Chapter 9: Crop Plants and Exotic Plants

SISAL AND HENEQUEN ³⁹Agave spp., family Agavaceae
Sisal and henequen are long hard fibers used primarily in cordage (ropes, cords, and twine). They are obtained from the 2- to 4-foot-long leaves of agave plants. Sisal, the most important fiber, is obtained from A. sisalana Perr. ex. Engelm. In 1965, it accounted for 779,000 tons or 85 percent of the world supply. Henequen is obtained from A. fourcroydes Lem., and it accounts for practically all of the remaining fibers produced. Sisal is produced in Tanzania, Brazil, Angola, Madagascar, and Haiti. In 1963, almost 1.5 million acres were devoted to sisal production in Africa and more than 300,000 acres in Brazil. Henequen, which is a much weaker fiber than sisal but which has a certain market, is produced primarily in Mexico.
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³⁹ Material in this section was largely taken from Lock (1962) and Wienk (1969).

Plant:
The plant has stiff, heavy, persistent leaves, 2 to 4 feet long, 4 to 8 inches wide, and 1 to 4 inches thick that are basal or come from a short stem, 3 to 6 feet long. The flower stalk is a towering spike or panicle, 6 to 15 feet above the rosette of leaves. The plant grows slowly, attaining a height of only 6 inches 9 months after planting and 2 feet at the end of 2 years. It is about full grown at 4 years when its stem is about 8 inches in diameter and the harvesting of the lower leaves begins. An average of 185 leaves may be harvested before leaf growth ceases and the flower stalk or "pole," which resembles a giant asparagus sprout, shoots rapidly upward. From first appearance of the pole through flowering, fruiting, and death of the entire plant covers a span of about 6 months. About 100 plants per acre are maintained for maximum production of fiber.

Inflorescence:

The 11/2- to 21/2-inch, pale-green, funnel-shaped flower is made up of six narrow, united lobes. Six long stamens come from the base of the corolla and surround the ovary has three locules with two series of ovules in each, which develops into a green, fleshy capsule about 2 inches long, turning black at ripening. This capsule may have as many as 300 ovules but usually less than 100 seeds. The fertile seeds are triangular, black, and hard; the unfertilized ovules produce white, papery, nonviable seeds.

Flowering of the floret commences with the extrusion to 2 inches of the six anthers from the apex of the bud 36 to 48 hours before they release pollen and 3 to 4 days before the stigma becomes receptive. The anthers begin to dehisce early in the afternoon, and by next morning all pollen has been released. The style begins to elongate and becomes receptive, but by then the stamens have withered and hang limp. One to 2 days after fertilization, the style withers and ovarian development begins. All flowers on a branch of the panicle do not open at once; therefore, pollen from newly opened flowers can pollinate those that opened earlier. Flowering covers several weeks as it moves from the bottom to the top of the pole.

The flower produces large quantities of nectar and a rather heavy, yellow, strong-smelling pollen, both of which are highly attractive to bees. This pollen is usually completely removed from the anthers by bees before the stigma becomes receptive. The honey produced from agaves is generally of inferior quality with a strong unpleasant aroma, strong taste, and dark color.

Pollination Requirements:
Propagation of the agaves is mainly by bulbils or suckers. The grower prefers this method because it enables him to maintain pure lines. However, where seed production is desired, cross-pollination is necessary. The pollen is released within a flower before the stigma is receptive; therefore, for fertilization to occur, pollen must be transferred to other flowers with receptive stigmas. Because of the large number of ovules in the ovary, numerous pollen grains must be deposited on the relatively small stigma. The heavy pollen is not a wind-carried type, nor would gravity be likely to account for the pollination of the numerous ovules of a flower.

Pollinators:
Bees, and particularly honey bees, are the primary pollinators. For maximum seed production, the grower should consider building up the bee population in the area.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
LOCK, G. W.
1962. SISAL. 322 pp. Longmans, Green and Co., Ltd., London.

WIENK, J. F.
1969. LONG FIBER AGAVES. Pp. 1-21. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial Crop Breeding in the Tropics. H. Veenman and Zonen, N. V. Wageningen, The Netherlands.