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Thompson, A.E. 1990. Arid-land industrial crops. p. 232-241. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

Arid-land Industrial Crops

Anson E. Thompson


  1. INTRODUCTION
  2. CURRENT PROGRAMS IN NEW ARID-LAND CROP DEVELOPMENT
    1. Guayule (Parthenium argentatum Gray, Asteraceae)
    2. Jojoba [Simmondsia chinensis (Link) Schneid., Buxaceae]
    3. Lesquerella, Bladder Pod [Lesquerella fendleri (Gray) Wats., Brassicaceae]
  3. INACTIVE PROGRAMS IN NEW ARID-LAND CROP DEVELOPMENT
    1. Buffalo Gourd [Cucurbita foetidissima HBK, Cucurbitaceae]
    2. Grindelia, Gumweed (Grindelia camporum Greene, Asteraceae)
    3. Euphorbia, Gopher Plant (Euphorbia lathyris L., Euphorbiaceae)
  4. SUMMARY AND CONCLUSIONS
  5. REFERENCES

INTRODUCTION

Agricultural production in the and Southwest, as well as in other arid and semiarid areas throughout the world, is heavily dependent upon water from irrigation. The major crop plants of the world are neither xerophytic nor well adapted to and environments, and are not productive without supplemental irrigation. The amount of water available for agriculture in the year 2000 in Arizona and other contiguous areas is projected to meet only about 50% of the needs for currently available, agriculturally productive land. It is clear that development of new crops with low water requirements is of the highest priority

Yields of irrigated, conventional crops are generally high in the and Southwest, but production costs are also high and continuing to increase (Hoffmann 1983, McLaughlin 1985). Reduced water availability and increased production costs make conventional crops less attractive economically and provide an incentive for the development and adoption of new and alternative crops. Since plant productivity in and areas is closely tied to water usage, an economically viable new crop should use significantly less water. However, developing a highly productive new crop that uses less water may be easier said than done. A commonly held misconception is that desert plants use water more efficiently than non-desert plants or conventional crops. In fact many desert plants are less efficient since many of their adaptive mechanisms that conserve water also concurrently reduce photosynthesis and dry matter production. However, most desert plants use water more efficiently when water is limited and can survive long periods of water stress. Xerophytic plants may not grow and produce much biomass during periods of extended water stress, but they have the capacity to survive and reproduce under conditions that would cause death and complete crop failure to most mesophytic plants.

A new or alternative crop for future production in and environments most likely will not be characterized as having high biomass yields (Hoffmann 1983, McLaughlin 1985). Crops produced and grown for high biomass yields for use as solid fuels or conversion to liquid fuels are more likely to be produced economically on non-arid lands. Hay, grains, most oil seeds, sugar, pulp, and fiber crops that are consumed in relatively large quantities and generate relatively low prices are also not likely to be prime candidates as new crops for and environments. In contrast, plants that produce significant yields of relatively high valued industrial feedstocks and products such as rubber, resins, gums, waxes, pharmaceuticals, biologically active materials, essential oils, and other oils with unique fatty acids are likely new crop candidates for and lands. Such products are frequently referred to as botanochemicals.

This rationale should not be construed as an argument against research and development of new arid-adapted food and feed crops, which may have high social and economic impact in less developed countries. In fact, such research and developmental activity in less developed countries on arid-adapted food crops may pay much larger dividends for the resident population than concentrating efforts on industrial crops. There is good evidence from native plant populations in and areas suggesting that high productivity of native food crops can occur, and there are substantial opportunities for improving production in unfavorable environments. For example, more than 400 native species of noncultivated food plants have been identified in the Sonoran desert of Mexico and the southwestern United States (Thompson 1985). More than 40 of these have served as major local food resources for naive inhabitants. An outstanding example is the tepary bean (Phaseolus acutifolius), which is receiving increased attention throughout the world.

Notwithstanding, the framework of reference to which the preceding statements and the focus of this paper are addressed is toward development of new and alternative industrial crops. Preferably, new crops should be essentially noncompetitive with existing crops and provide a reliable domestic supply of essential industrial feedstocks. Undoubtedly, these new industrial crops would be of greater economic significance to the United States and other technically advanced countries than to those less developed. However, under appropriate conditions, the less developed countries should be able to capitalize on the benefits of producing new industrial crops for export and as resources and stimuli for their own industrial development.

Many candidate species have been suggested for domestication and development as new crops for arid environments (Foster et al. 1983; Hinman 1984,1986; Hoffmann 1983; McLaughlin et al. 1982, 1983; Princen and Rothfus 1984; Thompson 1985). Over a period of time, a rather large number of species have been tried, with varying degrees of success. For various reasons, the probability of successful development of any specific new crop adapted to and environments is likely to be lower than the generally acknowledged low rate of adoption of new crops in temperate environments. In the past few years, only a limited number of species have received active attention. In total, only about six species including guayule, jojoba, lesquerella, buffalo gourd, grindelia, and euphorbia have received what one might characterize as "major" attention. Currently, development of only guayule, jojoba, and lesquerella is being pursued actively. For various reasons, current research activity on buffalo gourd, grindelia, and euphorbia has lagged or essentially ceased. The current status of these potential new arid-land industrial crops will be discussed in the following sections.

CURRENT PROGRAMS IN NEW ARID-LAND CROP DEVELOPMENT

Guayule (Parthenium argentatum Gray, Asteraceae)

The United States is totally dependent upon importation of natural rubber for industrial and defense purposes at an annual cost of about $1 billion. The projected annual usage of natural rubber for 1990 in the United States is estimated at 0.9 million metric tons. Natural rubber is preferred to synthetic rubber where resiliency, high elasticity, and low heat buildup are essential in various products. Guayule, one of about 2000 plant species that produce rubber, has been long-recognized as a promising source of natural rubber which is essentially identical to that from the hevea rubber tree (Hevea brasiliensis). Guayule is a small woody perennial rubber-producing shrub native to the Chihuahuan desert of north Central Mexico and southwestern Texas. Unlike hevea, where latex flows from continuous ducts, obtaining rubber from guayule involves harvest of two to three year old plant tops by clipping or by digging whole plants to include the rubber producing roots. Extraction of rubber, which accumulates in the living parenchyma cells, is accomplished by grinding the stem and root tissues and using organic solvent extraction. Guayule plants also produce significant quantities of resins, which have potential uses as byproducts, and can be obtained as part of the rubber extraction process.

Harvest of native stands and initial use of guayule as a source of natural rubber began in the late 1800s and became a major source for the United States and Mexico in the early 1900s. Native stands were rapidly depleted, and a minimal research effort to domesticate and develop guayule as a new crop started in 1907. Loss of rubber supplies from the Far East in 1942 led to the initiation of a crash guayule R & D program under the Emergency Rubber Project of the U.S. Government. After a short 3 1/2-year operational period, the development of synthetic rubber and the end of World War 11 precipitated the termination of the project, with only limited research continuing to 1959. In the late 1970s renewed R & D effort was stimulated. Limited funding was initially appropriated by the U.S. Congress under the Native Latex Commercialization Act of 1978. Subsequently, funding has come from base funds of USDA-ARS, funds authorized under the Critical Agricultural Materials Act of 1984 and from the Department of Defense. Research and developmental efforts in the United States through 1959 were well summarized by Hammond and Polhamus (1965). Thompson and Ray (1988) recently reviewed the literature on improvement of guayule by plant breeding and generics.

From a cultural standpoint, there appears to be no real constraints to full commercialization (Fangmeier et al. 1984). However, full commercial production and utilization of guayule rubber are largely dependent upon development of higher-yielding cultivars through germplasm enhancement and plant breeding. A well coordinated, cooperative guayule breeding and genetic research program involving USDA/Agriculture Research Service at Phoenix, Arizona, the University of Arizona, Tucson, and the University of California, Riverside was initiated in 1986. The primary objective is to increase rubber yield to commercially acceptable levels. Rubber yield per unit of land area is an interrelated function of rubber concentration (%) and dry matter or biomass production. Other important secondary objectives include the development of genetically-enhanced germplasm and cultivars with improved seedling and mature plant vigor, plant architecture, fast regeneration following harvest by clipping, increased cold tolerance and tolerance to diseases, pests, drought, and salinity, adaptation to dryland as well as irrigated cultural systems, and improved rubber quality and quality retention following harvest and processing.

Several germplasm collections of guayule and related Parthenium species have been made within their natural range. Most guayule germplasm consists of apomictically reproducing triploids (3n = 54) and tetraploids (4n = 72), which have received most attention in the breeding programs (Hammond and Polhamus 1965, Thompson and Ray 1988). Sexually reproducing, largely self incompatible diploids (2n = 36) of guayule are found in limited numbers in a very restricted area in Mexico. Most related species are also diploids, although a polyploid series has been found in a few species. In the past, only limited use has been made of diploid guayule material in the breeding programs. However, a recent germplasm collection of new diploids, and their use in a recurrent selection program along with use of interspecific hybridization is adding dimension to the total breeding effort. Much of the current germplasm being utilized originated from breeding material developed from two major collections made during the Emergency Rubber Project. Most of this material traces back to a small number of accessions collected in a very limited area in the Mexican state of Durango. However, a surprisingly large amount of variability for rubber and resin quantity and quality and plant growth characteristics have been shown to exist within the apomictically reproducing polyploid germplasm. The facultative apomictic system found in the polyploid material apparently serves as a mechanism for conservation and propagation of a wide array of both genic and chromosomal variation. New apomictic single plant and line selections have been made with desirable combinations of rubber concentration (%) and yield (g/plant), biomass production, and vigorous top regrowth following harvest by clipping (Thompson et al. 1988). Progeny of selected plants and lines reproduced by seeds and vegetative cuttings are currently undergoing further evaluation and reselection, and hold promise of producing cultivars with rubber concentration of 7 to 9% and rubber yields of over 1100 kg/ha/year. Under most conditions, such yields should make guayule production an economic success.

The guayule research and commercialization program is a good example of the coordinated and cooperative involvement of federal, state, and industry sectors. This multidisciplinary effort involving a full array of scientists, engineers, economists, and management specialists is developing a complete, viable system for producing guayule rubber from seed production to planting, harvesting, processing, and utilization. While good progress has been made, further gains are limited by underinvestment of resources in research and development. This is difficult to reconcile in light of the annual United States import deficit of nearly $1 billion for natural rubber. Such limited research support is most glaringly apparent in the guayule breeding and genetics program, which as with most crops is scale dependent. In total, not more than 3 Scientist-Years and less than $500,000 are annually devoted to this key program. It is clear that a higher-level, sustained research effort is needed and fully justified.

Jojoba [Simmondsia chinensis (Link) Schneid., Buxaceae]

Jojoba, an evergreen woody shrub native to the Sonoran Desert in southern Arizona, California, and Baja California in Mexico is becoming one of the first new arid-land industrial crops to reach commercialization. Seeds of jojoba contain from 40-60% of a chemically unique oil, which is more accurately characterized as a long straight-chain liquid wax of non-glyceride esters. Its chemical structure is very similar to, and can substitute readily for sperm whale oil, the importation of which has been banned in the United States since 1971. Such waxes are difficult to synthesize in commercial quantities, and are useful as chemical feedstocks for a wide array of industrial products including high pressure and other specialized lubricants, antifoaming agents, detergents, disinfectants, driers, emulsifiers, fibers, plasticizers, protective coatings, resins, and surfactants. Hydrogenation converts jojoba oil into a very useful white crystalline wax. The purity, lack of odor, and resistance to rancidity, which are useful characteristics in a base for creams and ointments, have stimulated the initial use of jojoba oil in the cosmetic industry. Good reviews of all aspects of jojoba natural history, culture, production, utilization, and current research and development activities and needs are well summarized by Gentry (1958), Hogan (1979), Hogan and Bemis (1983), Hogan et al. (1981), and the National Research Council (1985).

Jojoba is a monotypic genus with a dioecious flowering habit. The staminate and pistillate flower buds usually develop in the spring and late summer on new growth and remain dormant until warm weather in late winter or early spring. Fruit maturation in Arizona occurs about five months after pollination during the summer months of July and August. Seed size varies from about 650 to 5,500 seeds per kilogram. There is also much plant to plant variability in natural populations for a wide array of other morphological characters. The jojoba plant usually produces several branches at the base of the plant and ranges from 0.5 to 5 m in height under natural conditions. It has been estimated that some older plants may be from 150 to 200 years old.

Throughout its natural range located between 23° and 34° north latitude and between 110deg. and 118deg. west longitude, jojoba grows from sea level to 1500 meters in altitude. Temperature is one of the most critical factors to be considered in site selection for commercial production. Plants can tolerate extremely high summer temperatures. Plants that are three or more years old can usually survive winter temperatures as low as -10°C. However, developing flower buds are killed by temperatures of -5° to -7°C and results in greatly reduced seed yields. For practical purposes, commercial plantings are effectively limited to those areas where minimum temperatures are expected to be above -5°C. Some native stands have been found in areas receiving annual rainfall of only about 125 mm, but 460 to 610 mm of annual moisture is thought to be essential for commercial success of plantations. Good growth and development of plants are being attained with a third or less of the amount of water required for citrus, cotton, or other row crops under comparable conditions.

Jojoba can be grown on an array of soil types from sands to loams, but the soil must be well drained. Young plants are very sensitive to flooding. Salt buildup is a common problem in most and lands. Salt in the soil or irrigation water adversely affects seed germination and growth of young jojoba seedling plants. Older, established plants are more salt tolerant. Seedlings have been observed to vary in their tolerance to salt, which opens up the possibility of selection and breeding for increased tolerance.

Commercial plantings of jojoba have been made only within the past 10 years. By 1982, over 10,500 ha were planted in Arizona and California. Prior to this, the limited amount of jojoba oil came from hand-harvested wild stands in Arizona, California, and northern Mexico. Most of this production was utilized by the cosmetic industry, and because of the limited supply, the oil commanded a relatively high price. Currently, plantings are estimated at over 16,000 ha, many of which are coming into full production. Unfortunately the yields of many of the early plantings did not meet expectations since unselected seed gathered from open pollinated natural plant stands were used as planting stock. Sizable acreages of these early established, unproductive plantings have been abandoned. Other problems contributing to unproductivity can be related to the lack of adequate research and the development of appropriate cultural and production systems involving mechanized harvesting and handling.

The lack of development of high yielding, clonally propagated cultivars has been a serious constraint to the successful commercialization of jojoba. Presently, minimally funded, understaffed breeding and selection programs are operating at the University of Arizona, Tucson, and the University of California, Riverside. Only recently have techniques been developed to clonally propagate improved selections by rooting stem cuttings or by using tissue culture techniques. However, the dioecious nature of jojoba places additional constraints on progress. Both staminate as well as pistillate selections must be made and tested for pollination capability and generic combining ability. They must also be adequately evaluated for adaptation, yield of seed, and quantity and quality of oil before being clonally propagated in large quantifies for either seed production or for use as transplanting stock in commercial plantings.

In contrast to guayule where a strong, established industry, and market potential exists for utilization of the natural rubber produced, the jojoba industry is only beginning to develop the capabilities required for successful, large-scale commercial production, utilization, and marketing. Increased production of jojoba oil from the existing, maturing areas of production will need to find a larger and more varied market. The absorption of this increased production will most certainly reduce the price of the seed oil. To offset the downward pressure on price, production efficiency must be improved and the market expanded. The oil has been experimentally transformed into at least 50 derivatives that appear to have commercial possibilities. Jojoba certainly offers chemists and industrial researchers many new areas to explore.

If jojoba is to realize its potential and become a true success as a new arid-land industrial crop, more coordinated, multidisciplinary research and development is needed. Both agricultural as well as industrial product research are clearly needed as enunciated in the National Research Council's 1985 report Jojoba: New Crop for Arid Lands, New Material for Industry. The benefits that would accrue as a result of agricultural diversification and new product development and availability would be significant to both producers and the consuming public. These factors all argue strongly for increased research and development that is broadly supported by industry, state, and federal sectors.

Lesquerella, Bladder Pod [Lesquerella fendleri (Gray) Wats., Brassicaceae]

Vegetable oils containing hydroxy fatty acids are of industrial importance as chemical feedstocks for the production of lubricants, plastics, protective coatings, surfactants, and pharmaceuticals. The United States and other industrial nations depend completely upon imported castor oil for their total supply of hydroxy fatty acids. For various economic reasons in addition to problems associated with seed toxicity, allergenic reactions of field and processing workers, and disposal of toxic seed meal after oil extraction, castor beans are no longer commercially grown in the United States. Because of its high content of hydroxy fatty acid (ricinoleic acid), castor oil is classified as a strategic material. The annual cost of importing some 40-45 thousand metric tons of oil is usually around $40-45 million.

Recently, attention has been given to species of Lesquerella as possible new domestic sources of hydroxy fatty acids (Hinman 1984,1986; Princen and Rothfus 1984; Thompson 1985, 1988; Thompson and Dierig 1989, and Thompson et al. 1989). In the 1960s, seed oils of various species of Lesquerella were identified as good sources of three new hydroxy fatty acids by the USDA-ARS Northern Regional Research Center (NRRC) plant chemical screening program at Peoria, Illinois. Of the three, lesquerolic acid was found to be almost identical in structure to ricinoleic acid except that the carbon chain was two carbon atoms longer than that of ricinoleic acid—C20 vs. C18 (Princen and Rothfus 1984, Smith 1979). Preliminary results indicate that lesquerolic acid may serve as a direct replacement for ricinoleic acid, and potentially may be even more useful in developing new uses and products.

Lesquerella is a New World genus of over 70 species within the Brassicaceae. A germplasm collection effort was made by USDA/ARS in the 1960s (Barclay et al. 1962, Gentry and Barclay 1962). Of special interest to and lands new crop development is that 14 of the 25 species collected were native to the and Southwest. Considerable intra- as well as interspecific variability were noted among the species collected. Seed oil percentages ranged from 11 to 39% and hydroxy fatty acid contents ranged from 50 to 75%. Lesquerella seed meal composition and quality were comparable to those of other cruciferous oilseeds including rapeseed and crambe. The meals are thought to be potentially useful protein supplements for feed grains since they are relatively high in lysine. Glucosinolates were found in quantities similar to that of other cruciferous seed meals, but goitrogenic substances (thiooxazolidones) were not found to be present. Thus, potential for usage of seed meals for animal feeds greatly enhances the economic viability of lesquerella as a new crop.

Germplasm evaluation of 90 accessions of 23 Lesquerella species in Arizona clearly established Lesquerella fendleri as the prime candidate for domestication (Thompson 1985, 1988). This fully substantiated the early observations of Gentry and Barclay (1962). The natural range of L. fendleri is from southeastern Arizona to Texas and Oklahoma; the widest distribution of any of the species in the genus. Within its natural range of distribution, L. fendleri grows as a winter annual in areas with annual precipitation from 250 to 400 mm and at elevations from 600 to 1800 m. The species appear to be highly cross-pollinated, and considerable genetic variation has been observed for plant and seed yielding characteristics. Seed oil percentages of the L. fendleri germplasm have been shown to average about 25%, of which 55 to 60% is lesquerolic acid.

The germplasm evaluation efforts were sufficiently encouraging to simulate the initiation of a small USDA/ARS breeding and selection program within L. fendleri in Arizona. Preliminary agronomic experiments designed to develop appropriate cultural practices were also initiated. Seed yields have proved to be very encouraging (Thompson and Dierig 1988, Thompson et al. 1989). We obtained seed yields of over 1,400 kg/ha in the replicated, well-watered plots with a total seasonal use of 626 mm water. This is comparable to the minimum water requirements for winter wheat, and considerably less than the approximate amount of 1,000 to 1,600 mm normally utilized by cotton in Arizona. It should be emphasized that these yields were from bulk populations that had undergone only one cycle of selection. Seed yields of several half-sib family progenies from single-plant selections have exceeded 1,800 kg/ha. This indicates that a gain in yield of about 25% was realized in one generation of selection. A new cycle of selection is being initiated by intermating superior selections.

The crop production and management system for lesquerella is visualized as being very similar to that of winter wheat or other small grains in Arizona. In 1988, we successfully combine harvested our experimental area after hand harvesting the breeding and yield trial plots. Even though the combine was not equipped with fine meshed screens to handle small sized seeds, it did a fairly efficient job in harvesting the crop. We are confident that properly equipped conventional combines will be able to harvest commercial plantings.

For the past two years bulk lots of lesquerella seed have been sent to the NRRC, Peoria, Illinois. These seeds are being used for research to develop methods for oil extraction, processing and utilization. Research is being conducted to determine if lesquerella oils can be directly substituted for castor oil, and to develop new applications that may arise from the longer carbon chain length in the hydroxy fatty acid. Progress in the formulation of new specialty greases appears promising (K.D. Carlson, personal communication). Analytical research conducted at NRRC is also providing needed support to the breeding and agronomic research program in Arizona.

The seed yields we have obtained in replicated experiments over a three year period, and the increases in yield after only a minimal breeding and selection effort are most encouraging. Continued and increased plant breeding and agronomic research efforts are needed and fully justified. A new effort funded by the USDA Office of Critical Materials is providing a careful assessment of the potential of lesquerella as a new industrial oilseed crop. All aspects of the potential production, marketing, and commercialization of lesquerella will be characterized and evaluated to determine the proper course action and the amount of support needed for an effective R & D effort. It is reasonable to predict that such an effort could stimulate the development of lesquerella as a new crop for semiarid arid and environments within a reasonable time frame of six to eight years.

INACTIVE PROGRAMS IN NEW ARID-LAND CROP DEVELOPMENT

Buffalo Gourd [Cucurbita foetidissima HBK, Cucurbitaceae]

The possibility of domesticating and utilizing the buffalo gourd along with other perennial cucurbits as new sources of vegetable oils and proteins was first suggested by Dr. L.C. Curtis (1946). There was a brief flurry of interest in this regard in the late 1940s and early 1950s. The attractive potential for production of edible seed oils, seed proteins, root starches, and other byproducts in one plant under and environmental conditions stimulated a new burst of activity in the early 1970s. This research was spearheaded by the late Dr. William P. Bemis and coworkers at the University of Arizona, Tucson. The potential of the buffalo gourd as a new arid-land crop was clearly enunciated and reviewed by Bemis et al. (1978, 1979) and Hogan and Bemis (1983). Results of the various facets of about 15 years of excellent multidisciplinary research have been well summarized: composition and functionality of potential food ingredients (Scheerens and Berry 1986); agronomic research (Nelson et al. 1983, 1988); and domestication (Gathman and Bemis 1990). In spite of this sustained effort, essentially all research activity on development of the buffalo gourd as a new crop has ceased.

One must ask why such a developmental program should fail after such a good, sustained research effort was expended on a species with such potentially desirable characteristics. Essentially no oilseed or protein crop is adapted to and lands, and inhabitants of these areas regularly suffer from chronic shortages of oil and protein. The buffalo gourd seemed to be tailor made for providing these essential food components plus starch, which could also have industrial implications. In addition, three unique factors were combined in this one species: perennial plant habit; an asexual mode of reproduction in addition to normal sexual reproduction through seeds, and a method of producing hybrid seed using gynoecy, and multiple yield components consisting of seed bearing fruits for oil and protein, roots for starch production, and vines for animal fodder.

An interesting cultural system was proposed by Bemis et al. (1978) for the production of buffalo gourds that effectively exploited the unique features of the species. They proposed that production fields would be established initially by direct seeding using hybrid seed. At the end of the first year, seeds would be harvested from the developed fruits. The vine growth could possibly be used as animal fodder. Seeds would then be harvested at the end of the second year and sometime during the dormant, winter season, roots from alternative one meter swaths of the field would be dug. They reasoned that this would accomplish two purposes; the harvest of roots for starch, and a thinning of the planting to prevent overcrowding of the plants. The third season would allow continued seed harvest, and the roots in the alternate one meter swaths would be dug. Meanwhile the original swaths would be regenerated by asexual rooting of the vines. They envisioned that this procedure could continue as long as the vines remained productive.

The high expectations for the proposed cropping system was not realized. Problems associated with the perennial growth habit, primarily related to susceptibility to diseases, have been a major constraint. Losses are chiefly due to soil-borne root rot organisms and the build up of viral diseases, which greatly reduced yields in the second season and older plantings. Another major factor was low seed yields, which fell well below the projected yields of 2,000 kg/ha (Nelson et al. 1988). Yields of two-year-old plantings were higher than for the first year, but disease problems associated with perenniality greatly reduced the potential for high seed wields.

Water use studies have shown that buffalo gourds under intensive culture have peak consumptive use rates similar to other crops (Nelson et al. 1988). However, they do appear to have somewhat lower total water requirements than conventional crops with similar growing seasons. The relatively low water use efficiency of the buffalo gourd is largely attributed to low seed yields. Although the plant has promising water use characteristics for arid-lands agriculture, low seed yields of presently available germplasm lines and cultivars appear to limit their potential as an oilseed crop.

Fruit and seed production are markedly affected by plant population density, and high wields were found to be limited by high plant populations. Conversely, low plant populations that were optimum for fruit and seed production resulted in low root yields. Nelson and coworkers (1983, 1988) experimented with various modifications in cropping systems and plant populations in an attempt to maximize either seed and oil or starch production of the roots. They were not successful in obtaining high seed yields, a primary requisite for high oil and protein production. They were reasonably successful in obtaining high root and starch production with high density plantings grown as an annual. They produced root yields as high as 34,550 kg/ ha with root starch content of 63.5% on a dry weight basis (Nelson et al. 1983).

Undoubtedly the relatively low seed and oil yields served to dampen enthusiasm for production and utilization by industry. The seed oil and proteins have been judged to be usable, but some problems in their processing and utilization, which are not insurmountable, do exist. The fact that neither oil or proteins are highly unique in character does little to stimulate interest in their utilization by industry. The somewhat unique characteristics of the root starch and their acceptable yields (Scheerens and Berry 1986, Nelson et al. 1983, Gathman and Bemis 1990) are positive factors. However, the economic feasibility of growing buffalo gourd solely for starch production has not been fully demonstrated. Byproduct utilization of the prodigious vine growth of buffalo gourds as an animal feed, as a fuel, or as a cellulose source for conversion to ethanol may be of some supplemental economic value.

The only real unique chemical constituent of the buffalo gourd is the presence of quantities of cucurbitacins, which are found in all parts of the plant. Cucurbitacins impart a bitter flavor to plant parts and are potent attractants to certain beetles and other insects. They may also be of value as sources of medicinal and pharmaceutical products (Gathman and Bemis 1990). More research is needed to determine the future potential of these compounds and to develop economically useful applications.

In summary, it appears that the lack of a truly unique, high-valued specialty product is a major constraint. In addition, the currently minimal economic prospects for the conventional oils, protein, and starch produced by the buffalo gourd have not generated sufficient interest by industry to push development and commercialization. However, future political and economic changes may be favorable for the development and utilization of this interesting, multifaceted, arid-land adapted plant.

Grindelia, Gumweed (Grindelia camporum Greene, Asteraceae)

The University of Arizona's Bioresources Research Facility conducted extensive research that surveyed and evaluated a wide array of desert plants for their biocrude production potential (Hoffmann 1983, McLaughlin and Hoffmann 1982, and McLaughlin et al. 1983). Biocrude is the hydrocarbon and hydrocarbon-like chemical fraction of plants that may be extracted by organic solvents and upgraded to liquid fuel and chemical feedstocks. They demonstrated that plants producing either latex or resinous exudates had the highest percentage of high energy extracts. On the basis of these observations, attention was focused upon those plants that produced resins.

One of the most promising of numerous species investigated was Grindelia camporum, which is an arid-adapted, herbaceous perennial found in the Central Valley area of California (Hoffmann et al. 1984, Hoffmann and McLaughlin 1986, Hinman 1984, Thompson 1985). This species produces significant quantities of extractable diterpene resin acids. The resins are produced in multicellular glands, which occur on the surfaces of stems, leaves, and involucres. The diterpene resins, which are composed of grindelic acid and several of its derivatives, are chemically similar to the resin acids that constitute rosin, a principal product of the naval stores industry. Naval stores is a generic term for a large class of chemicals that include turpentine, fatty acids, rosins, and their derivatives. Rosin is a complex mixture of diterpene resin acids that have wide and diverse industrial applications. The supply of high quality wood rosin, which is extracted from aged pine stumps is essentially exhausted. The recovery of gum rosin by tapping living pine trees is very labor intensive, and production within the United States has declined to nearly zero. The United States market has required more than 500 million kg of rosin in the recent past (Hoffmann and McLaughlin 1986).

Resins extracted from grindelia most likely could substitute for rosin in numerous industrial applications. If so, the production of sufficient acreage of grindelia in the and Southwest to meet the domestic demand for rosin would have a significant impact on the agricultural economy. Preliminary agronomic, breeding and genetic research were initiated in 1981. Hoffmann and McLaughlin (1986) reported that tetraploid lines of G. camporum will produce about 11,350 kg/ha-year of biomass by harvesting the stand twice and applying about 750 mm of irrigation water. This level of irrigation is low compared to the amount of water applied to most crops currently grown in the Southwest (McLaughlin 1985). The current germplasm of G. camporum produces about 10% crude resin, which equates to an annual yield of around 1,135 kg/ha. Economic projections indicate that yields of crude resin would need to be increased by breeding and selection to a level of 15-20% to be competitive (Hoffmann 1985, Hoffmann and McLaughlin 1986). Generic analyses and selection studies indicate that such an improvement in resin concentration and yield is feasible (McLaughlin 1986a, b). In addition to its high yield of crude resin, G. camporum also has other characteristics that favor domestication. It has an upright, herbaceous growth habit. Many accessions have an annual life cycle and the ability to regenerate growth from the root crown to produce two crops in a single growing season. The species has good tolerance to salinity and diseases as well as drought.

Preliminary research has been initiated on the characterization and utilization of grindelia resins (Timmermann et al. 1983). About 80% of the total extractable crude resins obtained from the grindelia plant consists of structurally different diterpene resin acids. It is apparent that the crude resins in the form obtained from the plant by solvent extraction will need to be further refined to obtain quality comparable to wood rosin. Grindelia produces a large number of related but chemically distinct forms of diterpene resins that may provide the opportunity for formulation of a new generation of improved rosin derivatives.

The bagasse, or material remaining after resin extraction, has value that must be considered in the economic assessment of grindelia as a new crop. It may have potential as animal feeds and certainly has value as a fuel in cogeneration of energy. Research is needed to determine the possible utilization of lignocelluloses and an array of natural products including steroids, terpenoids, polyphenols, and alkanes.

Current research on grindelia is now at a very low level. Funding from industrial sources supported initial research, but was subsequently terminated at a time when good progress was being made. It is regrettable that adequate funding is not currently available to carry forward this promising effort. The model employed in the funding of cuphea research maybe appropriate in developing commercial opportunities with grindelia. In supporting research with cuphea a three-way funding involving essentially equal financial inputs of federal, state, and industry sectors has been quite effective. Each concerned sector receives considerable leverage for each dollar invested. This also has the added advantage of involvement in all sectors in the planning and execution of the needed research and developmental efforts leading to full commercialization.

Euphorbia, Gopher Plant (Euphorbia lathyris L., Euphorbiaceae)

Euphorbia lathyris, a latex-bearing plant, received world-wide attention for several years as a possible source of liquid fuels. Dr. Melvin Calvin (1978, 1979) first brought attention to the plant as a candidate for "petroleum plantations" since he believed it to be adapted to dry, semi-arid lands. He estimated that energy plantations of this species would produce annual yields of at least the equivalent of 25 bbl of crude oil per hectare. He reasoned that cultivation of marginal semiarid arid and lands would make good use of the long growing season and the highly intense solar radiation in these regions. Another positive factor would be that such a cropping system would not be directly competitive with conventional food, feed, and fiber production systems. Unfortunately, the high hopes and expectations were not realized.

A rather comprehensive three-year research program was undertaken in 1979 at the University of Arizona at Tucson. The results of this research are well summarized by Kingsolver (1982). In brief, the developmental program was initiated with a logical, multidisciplinary approach. Germplasm was collected worldwide from 50 sources on six continents. Germplasm evaluation was conducted in greenhouse and field studies in 1980 and 1981. Agronomic studies were conducted to determine various cultural and water requirements. The first planting as a summer crop was a complete failure. It was found that euphorbia could be grown more successfully as a winter crop. Under these growing conditions it used 710 mm of water (irrigation requirement of about 1,000 mm) to produce a maximum of 15 tons of dry biomass and the equivalent of 7.5 bbl crude oil/ha. This yield was only about 30% of that originally estimated by Calvin, and clearly uneconomical. The germplasm evaluation further indicated that genetic variability was low for the amount of high-energy extractable materials. It was concluded that rapid development of improved germplasm would be unlikely within the existing plant accessions. In addition, E. lathyris was found to be extremely susceptible to Macrophomina phaseolina and other soil-borne diseases endemic in desert soils throughout the Southwest.

Another factor in the failure of euphorbia to develop into a successful new crop was the limited usefulness of the plants chemical composition. The oil of E. lathyris is similar to crude oil, in that it can be catalytically cracked to produce a significant portion of fuel fractions (Kingsolver 1982). However, since fossil fuel crude oil was and continues to remain relatively low priced and in good supply, competitive market factors effectively dampened enthusiasm and support to continue funding research on euphorbia and other potential plant oil sources. To have a fighting chance of reaching commercialization, a bioenergy crop needs to contain a chemical composition useful as a product or a feedstock for products that are in some way unique and significantly more valuable than crude oil. Unfortunately constituent analysis of E. lathyris did not identify any potentially useful bulk specialty chemicals.

The limited supply of fossil fuels may one day confer an economic and energetic advantage to the utilization of such plants as E. lathyris. When this point is reached, research and development may succeed in domesticating E. lathyris for commercial production of biocrude oil. However, since E. lathyris is mesophytic rather than xerophytic, development and production of euphorbia as a new crop most likely would occur in more temperate areas with higher rainfall than the and Southwest.

SUMMARY AND CONCLUSIONS

At least five of the six plants discussed have good potential for eventual domestication and development as new industrial crops for and lands. All examples have positive attributes as well as constraints to varying degrees.

Guayule is judged to have the best opportunity for successful adaption as a new crop. It produces a product, natural rubber, that is of critical importance and of sufficient demand to stimulate interest and participation of industry as well as the public sector. The research and development program is pursuing all aspects of production and processing to remove the various constraints to full acceptance. Sufficient rubber yield is recognized as the chief constraint, and good progress is being made in the plant breeding and genetic program involving state and federal cooperation. Additional financial support to this area is needed and would yield high dividends.

Jojoba has real potential as a source of liquid wax, but it is an example of where all facets of the new crops development process were not well coordinated. One of the major constraints is the minimal input in the area of plant breeding and selection of high yielding clones. Large areas of unselected material were planted and have been discarded due to very low yields. Another aspect is the lack of utilization research to develop new products and uses to absorb the increasing production and to maintain sufficient monetary return for the growers and processors.

Lesquerella is judged to have very good potential as a source of hydroxy fatty acids, and could be a successful new crop within a relatively short period of time. Current research is at a very minimal level. The scope of the research to cover all aspects of breeding, production, processing, and utilization needs to be defined and increased, and supported by both public and industry sectors to achieve rapid development and acceptance.

Buffalo gourd appeared to have outstanding attributes for development into a successful new crop for and areas. Much good research was conducted on all aspects of production and utilization. Serious constraints developed relative to disease problems of perennial plantings and low seed yields. Yields of starch from roots of plants grown as an annual were acceptable. One of the most serious constraints was the lack of production of any specific high-valued specialty chemicals. Cucurbitacins, which are natural insect attractants and have other potential uses, may provide this needed boost. The other main products—edible oil, protein and starch are not that unique and directly compete with other conventional crops grown in temperate climates. Economic conditions and supply needs do have a way of changing, which may one day favor full development of the potential of the buffalo gourd and related arid-adapted cucurbits.

Grindelia holds considerable promise as a domestic source of diterpene resins that have a variety of important industrial applications. Initial research conducted at a relatively minimal level appeared to be quite promising. The program received little public support, and now lacks a real push from industry to provide at least a minimal level of support to allow development to go forward. There appears to be sufficient potential for improving resin yields to an economically feasible level through plant breeding and agronomic research. Utilization research is needed to develop methods of extraction and refining, and the development of new products and uses to improve economic return.

Euphorbia lathyris was touted as a new plant source of liquid fuels. It was originally thought to be adapted to and conditions, but this did not prove to be true. The crop completely failed when planted during the summer growing period of the and Southwest. Plants tested from a worldwide collection showed little genetic variability, little adaption to and environments, and extreme susceptibility to soil-borne diseases endemic to and lands. It also lacked an identifiable high-valued specialty chemical that would increase its economic viability. While economic conditions may one day warrant revisiting euphorbia as a renewable source of liquid fuels, such development would most likely occur in temperate areas to which the species is better adapted.

From these examples it can be seen that development of new industrial crops for and lands holds considerable potential. However, to be fully successful many factors must come together and considerable multidisciplinary expertise and effort must be employed. It is also clear that some highly valued, specialty products such as natural rubber, resins, or an oil with a unique chemical structure and commercial application are needed to stimulate interest and support from both public and industry sectors. Interest and support of industry and active participation in the planning and funding of research and development are vital to successful commercialization. Another important factor is to recognize that new crop development requires strong and long-term commitment to allow sufficient time for orderly research and development. Finally, support must be supplied on a steady, sustainable level until the developmental process is successfully concluded.

REFERENCES


Last update February 28, 1997 by aw