New Crop Development

By "new crops" I mean species never previously domesticated or cultivated. Several researchers at the University of Arizona have worked on desert plants that produce unusual natural products, with the goal of developing such plants as new crops producing industrial (nonfood, nonfeed) raw materials. Such plants include: jojoba (Simmondsia chinensis) for its liquid wax; guayule (Parthenium argentatum) for its high-molecular weight natural rubber; gumweed (Grindelia camporum) for its dipterpenoid resin; bladderpod (Lesquerella fendleri) for its oil rich in hydroxy fatty acids; vernonia (Vernonia ssp.) for its oil rich in epoxy fatty acids; and samandoque or hesperaloe (Hesperaloe funifera) for its strong, fine fibers. My work has been primarily with gumweed and hesperaloe.

Why produce such new crops? Many of our agricultural problems-low prices, surplus production, soil erosion, pesticide use-are due to the low diversity of our croplands. New crops can contribute to the diversification of agriculture. In the arid and semiarid lands in particular, crops that can be grown profitably with low water applications would be of great benefit.

Gumweed (Grindelia camporum)

I worked for many years on Grindelia species, herbaceous plants in the sunflower family (Asteraceae). These species produce abundant resin on the surfaces of their flower heads, leaves, and stems. The resin is composed of grindelic acid and related labdane-type diterpene resin acids, similar to the resins from pine trees that are the basis of the "naval stores" industry. These products are used in inks, adhesives, tackifiers, sizings, and many other products.
	Grindelia camporum. Resin is most abundant in the flower heads.
My research on gumweed emphasized agronomic practices and genetic variation in resin yield and other important characters. Research & development on gumweed came to an end here when the major plant resin-producing companies (just 3 in the US) decided to base their supply strategies on imports rather than on domestic production. Rising prices or declining supplies of imported resins from pines would likely work to renew interest in the resin from gumweed, although breakthroughs in the extraction and purification of the resin are needed.
	Multicellular resin gland on the leaf surface of Grindelia camporum.

For further information, see the list of publications on gumweed.

Hesperaloe (Hesperaloe funifera)

We have been working on developing Hesperaloe funifera as a new source of high-value specialty fibers since 1987. This work was initiated in collaboration with the James River Corporation, whose specialty fibers division was seeking a domestic source of high-strength fibers to replace imported sisal pulp. Hesperaloe funifera is an acaulescent perennial with a rosette habit in the Agavaceae, native to the northern Mexico states of Coahuila, Nuevo Leon, and San Luis Potosi. The leaf contains about 30-35% fibrous raw material on a dry weight basis. The cells that make up the hard fibers of the leaf are 3-4 mm long and 1.4-1.7 microns wide-as long as fibers from softwoods but as narrow as those from grasses. These long, thin fibers produce a pulp that has exceptional strength properties.

Leaf of Hesperaloe funifera, squashed by passing through a roller mill, exposing fine, white "hard" fibers of the leaf interior.

Our work at the University of Arizona has concentrated on stand establishment, gas exchange physiology (Ph. D. study of Damian Ravetta), productivity, flowering and fruit production, water use (with John Nelson, Maricopa Agricultural Center), weed management (with William McCloskey, Plant Sciences Department), and agricultural engineering (with Robert Roth, Maricopa Agricultural Center). Hesperaloe funifera is a CAM plant; it fixes CO2 and transpires water at dusk, night, and dawn. Although it has the low photosynthetic rates characteristic of CAM plants, it also expresses the high characteristic water-use efficiency. It thus has the physiological potential to be a low-water use crop in dry environments.

Damian Ravetta working on gas exchange measurements. He found that Hesperaloe funifera is an obligate CAM plant, conserving water by closing its stomata during the day.

We have found that although Hesperaloe funifera is slow to establish itself, it is still capable of high yields. The slow initial stand establishment requires that competing weeds be controlled during the first 2-4 years. After 5 years, a yield of about 200 metric tons per hectare can be obtained. The plant regrows from the base (just like mowing a lawn), and can be reharvested every 3 years after the initial harvest at 5 years. The high yield is a consequence of its long growing season and high leaf-area index, which compensate for the low photosynthetic rate per unit leaf area.

Production cycle for Hesperaloe funifera. Plot shows stand biomass for plots at three densities; plots were harvested after 5, 8, and 11 years.

A detailed study of plants through their first 5 years of growth provides further insight into the phenology and development of the crop. The seedling develops into a rosette with a single terminal meristem. This rosette grows by production of new leaves from the central meristem until its 3rd or 4th year, when the meristem switches from a vegetative to a reproductive state. It then produces a tall inflorescence on which several thousand flowers are borne over an extended flowering period. At the same time, lateral rosettes are produced by vegetative reproduction on very short rhizomes. After fruit production ceases, the lateral rosettes expand to resume vegetative growth of the plant. After flowering, the plant is able to grow at a much more rapid rate since it is now producing leaves from 3 to 6 vegetative meristems instead of the single meristem it had prior to flowering.

Growth rates of Hesperaloe funifera plants over the first 5 years. Daily growth rates increase after plants flower in year 3.

Removal of the flower stalk after it begins to emerge has the potential of diverting resources (carbon, water, nutrients) from flower and fruit production to leaf production, either increasing yields or decreasing the time to harvest.

The University of Arizona is currently working with Arbokem, Inc., and Canadian company producing specialty pulps and papers from nonwood fibers. Arbokem has a pilot plant at Vulcan, Alberta, producing copy paper from wheat straw and recycled fibers. Other commercial uses for the fiber are being explored.
	Alfred Wong, CEO of Arbokem, contemplating the applications of Hesperaloe fibers.

Major obstacles to commercialization are development of cost-effective harvesting techniques and the need to expand acreage as markets develop. See the list of publications on hesperaloe for more information.