Chrysothamnus Multiple -Use Shrub of the Desert

Chrysothamnus nauseosus (Rubber Rabbitbrush): Multiple-Use Shrub of the Desert

Item Type Article

Authors Weber, D. J.; Davis, T. D.; McArthur, E. D.; Sankhla, N.

Publisher University of Arizona (Tucson, AZ)

Journal Desert Plants

Download date 25/09/2021 07:00:53

Link to Item http://hdl.handle.net/10150/609066 172 Desert Plants 7(4) 1985

Introduction Chrysothamnus Shrubs achieve landscape dominance for the most part only in habitats that place plants under considerable stress. Conditions that promote shrubby habitats are drought or nauseosus (Rubber aridity, nutrient poor soils, fire, shade, poor soil aeration, winter cold, short growing seasons, and wind (Stebbins, Rabbitbrush): 1972; McArthur, 1984). Several of these conditions are met in the western United States where shrub genera from 15 Multiple -Use Shrub plant families are landscape dominants (McArthur, 1984). One common western plant is rabbitbrush -the genus Chrysothamnus. This western North American endemic of the Desert consists of 16 species (Anderson, 1986a). Three Chrysothamnus species are large and form species com- plexes consisting of several subspecies each (C. nauseosus, Rubber Rabbitbrush; C. parryi, Parry's Rabbitbrush; C. D. J. Weber viscidiflorus, Low Rabbitbrush). The most diversified Department of Botany species is Rubber Rabbitbrush, which occurs in various and Range Science, subspecific forms from the Sonoran to subalpine life zones, Brigham Young University, from Canada to Mexico, and from the Great Plains to the Pacific Ocean (Figure 1). Chrysothamnus, especially C. nauseosus, is a vigorous T. D. Davis pioneer plant in disturbed sites. It is common along road- Department of Agronomy sides and runoff areas where increased water supply in- and Horticulture, creases its biomass. It is a source of browse for deer and can Brigham Young University, be used by livestock (Hanks et al., 1975; McArthur et al., 1979a). Even more interesting is the fact that it contains natural rubber that, pending the results of current research, E. D. McArthur may have the potential for commercial production. The Intermountain Research Station, earliest record of rubber potential in Chrysothamnus U.S.D.A. Forest Service, nauseosus was in 1878 when Indians camped near St. Provo, Utah, George, Utah, taught some young boys how to make gum by chewing the inner bark of rabbitbrush. However, it was not noticed scientifically until about 1904 when A. J. N. Sankhla Davidson brought a specimen of Chrysothamnus nau- Department of Botany, seosus to the University of California for identification and University of Jodhpur, noted that the Indians use it as a gum. Jodhpur, India About 14 years later, the plant attracted national attention when Hall and Goodspeed (1919) published a paper on the presence of rubber in Chrysothamnus. At this time, the United States had recently been involved in a world war, and rubber was beginning to be an important component of Abstract the mechanized world. Hall and Goodspeed (1919) pub- Rubber Rabbitbrush (Chrysothamnus nauseosus), a lished an extensive study of over 60 western plant species common desert shrub native to the western United States, and indicated that certain subspecies of Chrysothamnus grows over a wide range of environmental conditions from nauseosus could be used to obtain natural rubber. They Mexico to Canada. Rabbitbrush grows well in disturbed estimated that over 300 million pounds of rubber were sites and can grow in saline soils. It has a high rate of net present in the native populations of C. nauseosus growing photosynthesis for a woody C3 plant and does not become in the western United States. light saturated at full sun. The many current and potential Some effort was made at that time, along with similar uses for the shrub include forage value for wildlife and efforts with guayule, to develop the potential of producing livestock, landscape use, production of natural rubber, po- our own rubber (Campos -Lopez and McGinnies, 1978; tential hydrocarbon crop, and potential source of natural McGinnies, 1979). Ostler et al. (1986) reported the rubber insecticides and fungicides. Its potential has not been fully from Chrysothamnus was of good quality. After World War recognized. I, interest in rabbitbrush rubber declined and was not pursued. However, when World War II occurred and the Acknowledgement plantations of natural rubber of the Asia Region were no This research was supported in part by National Science longer accessible to the United States, the need for natural Foundation Grant PCM- 8320462 (to Weber and McArthur) rubber once again increased interest in desert plants con- and was facilitated by a cooperative agreement between taining rubber. Both guayule and C. nauseosus were pro- Intermountain Research Station (USDA Forest Service) and moted as possible sources for natural rubber. The project Utah Division of Wildlife Resources Project W -82 -R. involved planting large acreages and considerable effort as.

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went into selecting those subspecies that contained a high t¡`tg 41111' content of rubber. However, as soon as World War II ended, ., ií ate" 1I , 1 the rubber project was suspended. After nearly 4 years of 4.044.%.'I work, the acres of cultivated Chrysothamnus plants were , I: tr i destroyed, and the project was essentially forgotten. Even ratadridia' the high yield acquisitions were not maintained and were ,, eventually lost. , `r r1.... More recently, additional interest has developed in this 111 kti-i 40* r ,I:LiME area and researchers 1 have again begun to look for different ':iill populations of C. nauseosus to examine the potential for rr,`1:ii: this desert shrub as a producer of natural rubber (Ostler et ,,r':'_-. . al., 1986). É~ 4 , , i+r,::::: . Taxonomy J Rubber Rabbitbrush is a shrub that ordinarily ranges in SS^ Ii,rai 12 r=\ size from to 70 inches in height. However, plants have .,c :.,....r been found in a natural setting that are 10 to 12 feet in ,:::::= height with large tree -like trunks (Figure 2). Several erect .,..,,. :-+ stems arise from the base, each with moderately flexible //i* leaflet branches (McArthur et al., 1979a; McMinn, 1980). ::::\m There is abundant variation in C. nauseosus as Hall 30° :::::::: (1919) recognized: Distribution of ¡ Nothing can be more 1, ... certain than that these attempts to *IMP1 recognize species and varieties do not by any means exhaust the (After Anderson 1985b) ,a; resources of the group. Every autumnal excursion into a new =o MA district brings to light one or more forms not previously described. The only limits set to the number of new species or varieties Figure 1. Distribution which might be set of Chrysothamnus nauseosus in up lie in one's ability to visit all parts of the North America. field during the flowering period and the failure or disinclination From Anderson I986ó to recognize minute variations. -(Hall, 1919).

Hall and Clements (1923) recognized 20 subspecies. to densely pubescent achene). During the flowering period, Some 50 years later, Anderson (1986 a and b) recognized 22 which occurs in the late summer, it is a spectacular plant to subspecies, several of them different than those recognized observe (Figure 5). It adds a brightly colored yellow flower by Hall and Clements. However, five subspecies are more in the fall to the otherwise relatively dull landscape. common and widespread than the others. These are ssp. The plant is self -fertile and thus the amount of hybridiza- albicaulis, hololeucus, nauseosus, consimilis, and gra- tion that occurs is somewhat limited. Examination of buds veolens. The first three subspecies are white or gray stem- in various stages of development reveals that the anthers med and also have white or gray mature leaves (young open to release pollen just as the buds are opening (McAr- leaves are green); the last two have green stems and leaves. thur et al., 1979a). As the buds continue to open, the anther Other subspecies of note include the montane ssp. tube is pushed above the corolla by elongating filaments. At salicifolius, which has white stems and broad green leaves, the same time, the style is elongated and pushes the stig- the sand -dwelling ssp. turbinatus, and the ephemeral mas up through the anther tube until the stigmas are leaved ssp. junceus (McArthur et al., 1979a; Anderson, completely exerted at full bloom. The stigmas then sepa- 1986a). The subspecies of C. nauseosus differ from one rate to expose their receptive inner anther tube of the same another by such characteristics as color of stem tomentum, flower. By this stage of development, most if not all of the pubescence of achenes and involucral bracts, shape of in- pollen from another tube of the same flower is shed. The volucral bracts, leaf width and pubescence, and stigma and later maturing stigmas, particularly from the first flowers corolla dimensions (McArthur et al., 1979b; Anderson, on an individual shrub, indicate that Chrysothamnus is 1986a). predominantly self -fertilized (Anderson, 1966; McArthur Rabbitbrush (Chrysothamnus nauseosus) flowers are et al., 1978). Pollen from the later development of flowers in born in heads that in turn are raised into cymes, racemes, or the same head or from other heads in the bush can be panicles (Figure 3). The heads contain five yellow disc transferred to receptive flowers on that bush. The genus is flowers and are subtended by involucral bracts (Figure 4) not apomictic (Anderson, 1966). Fruits mature in October arranged into five more -or -less distinct vertical ranks. Each and November and the seed can germinate almost im- flower contains a pappus of abundant white slender capil- mediately. There are 43,714 seeds per ounce (Plummer et lary bristles. The flower consists of a five -toothed or cleft al., 1968). tubular to funnel- formed corolla with five stamens united Rubber Rabbitbrush is entirely diploid (x =n =9) although by the anthers around the style and a pistil with two exerted polyploidy does occur to a limited extent in Low Rabbit- stigmas (an ovary that develops into a one -seeded glabrous brush, C. viscidiflorus (Anderson 1966, 1971). So, although Figure 2. Large plants of Chrysothamnus nauseosus near Palmettu, Nevada. Figure 3. Drawings of Chrysothamnus nauseosus subspecies. A: C. nauseosus ssp. albicaulis, McArthur and Blauer N -18, Wells, Elko Co., NV (0.8X). B: C. nauseosus ssp. consimilis, McArthur and Blauer N -42, Deeth, Elko Co., NV (0.6X). C: C. nauseosus ssp. graveolens, Blauer C 291A, Henryville, Garfield Co., UT (0.5X). D: C. nauseosus ssp. salicifolius, Tiernan s.n., Strawberry Valley, Wasatch Co., UT (1.1X) from McArthur et al. 1979a. l'h Desert Plants 7(4) 1985

Table 1. Net photosynthetic rates (Pn) of Chrysothamnus nauseosus ssp. albicaulis and six other woody species under similar environmental conditions. All plants were growing outdoors under irrigation except for A. tridentata, which was measured on a native site after a heavy rainfall. Plus /minus values indicate stan- dard or error of the mean (n = 4).*

Species mgCO2 dm-2 hr' mgCO2 g-' D. W. hr' Chrysothamnus nauseosus 45.9±1.2 31.3± 1.8 Acer saccharinum 16.8±1.9 21.0 ±2.4 Artemisia cana 26.8 ±2.9 17.4 ±2.3 Artemisia tridentata 30.0 ±3.8 13.9± 1.0 Atriplex canescens 55.8 ±2.7 30.2 ±2.0 Ephedra viridis -_ ** 5.2 ±0.5 Malus domestica 23.1 ±2.1 18.9±1.7 *Adapted from Davis et al (1985). **This species has photosynthetic stems and bears no leaves. Hence Pn on a leaf area basis cannot be calculated.

sandy matrix. Even though the species is widespread and often locally abundant, it does not form pure stands except in disturbed areas. Rather, in natural climax communities it is a component of a mixed plant community. It is successful in many distributed communities perhaps because of its highly mobile, aerially distrubed achenes and rapid seed- ling establishment (Hall and Clements, 1923; Hanks et al., 1975; McArthur et al., 1979a). In mixed communities the production of Rubber Rabbitbrush is often a bonus to grass productivity; that is, grass production is the same with or without rabbitbrush, and therefore the rabbitbrush production is a bonus (Frischknecht, 1963; Farnsworth et al., 1976). Physiology. Rubber Rabbitbrush fixes carbon dioxide by the C3 photosynthetic pathway as evidenced by its Ci3 /C12 isotope ratios (B. N. Smith, personal communication). We have, however, observed that this plant exhibits high rates of net photosynthesis (Pn) compared to most other woody C3 species (Table 1). On both a leaf area and dry weight basis, rabbitbrush Pn is similar to that of the Ca desert Figure 4. Flowers of Chrysothamnus: A: pappus; B: shrub, Atriplex canescens. The RuBP carboxylase and in- corolla; C: stigma; and D: flower head. A -C are C. parryi tercellular CO2 contents of rabbitbrush are similar to those ssp. attenuates (the arrow is on an involucral bract, the found in most C3 crop species (Davis et al., 1985). scale is in mm); D is C. nauseosus ssp. salicifolius (7X). Another interesting physiological of rab- From McArthur et al. 1979a. characteristic bitbrush is that Pn is not light saturated at light levels equivalent to full sun (Figure 6). This may be due to the presence of a tomentose vestiture on the leaf surface, which hybridization does not ordinarily occur between the sub- probably shades the chloroplasts (Figure 7). Many desert species, such hybridization might be possible through the plants possess pubescence, which presumably is of adap- medium of biotechnology. tive significance in reducing light absorbance. This results in reduced heat load and lower leaf temperatures (Ehle- Ecology and Physiology ringer and Bjorkman, 1978; Ehleringer and Mooney, 1978). Ecology. With its inherent variation and wide distribu- High rates of Pn in rabbitbrush are accompanied by high tion (Figure 1), Rubber Rabbitbrush, as might be expected, stomatal conductance values (Figure 6). However, these occurs over a wide range of habitats. For example, ssp. values were obtained on well- watered plants, and it is not consimilis is sometimes referred to as "Salt -rubber rabbit - known how rabbitbrush stomata respond to water stress. In brush" because it occurs in association with Black Grease - any case, Rubber Rabbitbrush is capable of maintaining wood on alkaline flats; ssp. salicifolius is a montane taxon high Pn and stomatal conductance under non -stress peri- occurring usually with mountain Big Sagebrush, (Ar- ods, hence the potential exists for high rates of dry matter temisia tridentata ssp. vaseyana), and Quaking Aspen, accumulation per unit of biomass. (Populus tremuloides); and ssp. turbinatus only grows in a Some preliminary evidence from Farnsworth et al. (1976) Figure 5. Chrysothamnus nauseosus in bloom. 178 Desert Plants 7(4) 1985

.. Reproduction and Propagation 50 .M Seeds of Chrysothamnus. Chrysothamnus seeds, techni- 500 N ó ^ cally achenes, are harvested late in the year after the fruit 40 E ..- set. The seeds are small in size but relatively easily col- E «o N 400 - lected in the field (Plummer et al., 1968). 74 m Investigation of the seed germination properties of s..30 C 4- l- Chrysothamnus suggests the following points: c 300 `v O 2`o u" Under cool nights (40.5 °F) and warm days (59 °F), ÿ 20 ' D 0 C a. Chrysothamnus germinates in as little as 2 days. Under a -- ''' 200 0 0 0 0 V standarized single cool- temperature seed germination con- 10 dition, the seeds collected in the southern region germinate á To E 100 ` more rapidly (about 2 weeks) compared to seeds collected in a) a , the northern region, which take about a month (McArthur Z et al., unpublished). Seeds do not appear to have a high 1000 2000 temperature requirement for germination (Khan et al., un- j publ.). While Chrysothamnus plants are tolerant to saline Incident Quantum was (pmolm-2s-1) soil, it is of interest to note that seed germination inhibited by increased concentrations of salts. This Figure 6. Net photosynthesis (Pa) stomatal conductance suggests that rains are important in leaching the salts so (gH2O), and intercellular CO2 (ci) of Chrysothamnus that germination can occur. Stevens et al. (1986) have nauseosus ssp. albicaulis [taken from Davis et al. (1985)1. shown that placement of the achene with the tip down in the soil (pappus up) is important. Propagation by Division. The rabbitbrush crown can be cut and divided into several new plants (Hall and Clements, suggested that Chrysothamnus viscidiflorus might be ca- 1923). Only a limited number of new plants can be obtained pable of nitrogen fixation. This work needs confirmation, by this method, however. Propagation by division is most however, in light of the fact that the Farnsworth et al. (1976) successfully achieved when the plants are dormant. report that Artemisia ludoviciana fixed nitrogen could not Propagation by Cuttings. Thus far, it has been difficult to be confirmed (Wullstein and Harker, 1982). Frischknecht propagate Rubber Rabbitbrush from cuttings (Everett et al., (1963) reported that the yield of Crested Wheatgrass forage 1978; McArthur, unpublished). Softwood cuttings placed was higher in areas where White Rubber Rabbitbrush was under mist tend to rot before adventitious roots form. Some growing or had been growing prior to seeding. Yield was rooting has been obtained with semihardwood cuttings reduced in comparable areas where plants had been re- (shoot diameter approximately .08 inches) taken from moved several years prior to seeding of the wheatgrass, plants that were not growing rapidly. About 25% of these which suggested that rabbitbrush may have had a beneficial cuttings rooted without mist within 6 weeks after place- effect on the soil. ment into a perlite rooting medium. To date, we have had Rabbitbrush contains high amounts of rubber and resins little success in propagating dormant hardwood cuttings indicating that the isoprenoid biosynthetic pathway is taken from stock plants in mid -winter. Even without mist, quite active in this species (Ostler et al., 1986; Weber and these cuttings tend to rot after several weeks. McArthur, unpublished). However, the factors that control Root -inducing chemicals have thus far not been very the formation of these secondary products are not known useful in propagating rabbitbrush. Our trials have been and would make a worthwhile future investigation. limited, however, and more work is needed to develop Galls. Several distinctive galls occur on Rubber Rabbit- techniques for improving rooting. brush stems and flower heads (Wangberg 1976, 1981; Propagation by Tissue Culture Regeneration. In contrast McArthur et al., 1979b; McArthur, 1985). Two of the most to propagation by cuttings, considerable success has been distinctive are "callus" and "cotton" galls, which are in- achieved in regenerating White Rubber Rabbitbrush using duced by fruit fly larvae on stems of several subspecies of tissue culture techniques (Upadhyaya et al., 1985). When Rubber Rabbitbrush (Figure 8). The two galls are induced by apical meristems of stock plants are removed by pruning or two different but closely related fly species of the genus pinching, a large number of axillary buds are released from Aciurina (Diptera: Tephritidae). The fly taxonomy is still apical dominance. When about 0.5 inch long, these axillary being worked out. Nevertheless, it appears that in areas of shoots can be excised, surface -sterilized, and placed on a concurrent fly species and rabbitbrush sympatry, the fly Murashige and Skoog (1962) basal medium. When the cul- species A. bigeloviae induces cotton galls on Green - ture medium is supplemented with auxin (1 mg/1), roots stemmed Rubber Rabbitbrush (C. nauseosus ssp. graveo- begin to form within about 1 week after initiation of the lens, turbinatus, and consimilis), whereas the fly species A. cultures (Fig. 9). When placed on a medium supplemented trixa induces galls on White- stemmed Rubber Rabbitbrush with cytokinins, axillary stem explants produce many (C. nauseosus ssp. albicaulis and hololeucus). In these offshoots that can be transferred to an auxin -containing sympatric areas then, the fly- induced galls aid in plant medium. Callus formation generally becomes evident after identification. In uniform rabbitbrush populations the host about 8 weeks. Initially this callus is morphologically specifity of gall forms is not as clear -that is, flies are not heterogeneous, but upon subculturing becomes very uni- bound as closely to "their" rabbitbrush subspecies. form and grows rapidly. The callus formed in the cultures Weber, Davis, McArthur and Sankhla Chrysothamnus 179

Figure 7. Tomentose vestiture of Chrysothamnus nau- Figure 8. Callus (left) and cotton (right) galls on C. nauseosus ssp. albicaulis leaves shown using scanning elec- seosus ssp. hololeucus and ssp. graveolens, respectively, tron microscopy (300X). from McArthur et al. 1979b. may be useful in future studies using genetic engineering most livestock and game will graze the flowers and occas- and protoplast fusion techniques to manipulate the rubber sionally a few leaves and tender stems. During the winter, or resin content in rabbitbrush. rabbitbrush is browsed heavily. Rubber Rabbitbrush was Successful in vitro regeneration of rabbitbrush can also found in 48% of the deer stomachs examined on a winter be achieved using 0.4 to 0.5 -inch long excised stem seg- range in Owen's Valley in California, even though it repre- ments, provided proper -sized sections are used. Stem seg- sented only about 6% of the total food ingested (Sampson ments that are about .01 inch in diameter are more success- and Jesperson, 1963). Crude protein content ranges from fully regenerated than small or larger explants (Upadhyaya 9% during the dormant months to 11.8% in the spring after et al., 1985). the new leaves are formed (Sampson and Jesperson, 1963). Most of the subspecies of Chrysothamnus nauseosus are Current and Potential Uses of Rubber Rabbitbrush among the latest bloomers of the genus. This is of practical Forage Value. Rabbitbrush is a browse plant that can be value to foraging insects at that time of the year when most used by game and livestock. The browse value of the nectar sources are no longer producing. Late -season nectar individual species vary according to subspecies and collected by bees produces a strong -flavored honey (McAr- ecotypes. The white or gray subspecies such as albicaulis thur et al., 1979a). and salicifolius are more palatable to livestock and big Landscape Uses. Rubber Rabbitbrush, especially the game than are the green subspecies graveolens and con - white -stemmed subspecies (ssp. albicaulis, hololeucus, similis (McArthur et al., 1974; Hanks et al. 1975). During salicifolius, and nauseosus), has potential value as an or- most of the summer, wildlife and livestock will browse the namental landscape plant (Figure 10). Over the past few plant only lightly and in many cases not at all. However, in years considerable concern has arisen about the availability the late summer and fall when rabbitbrush is in bloom, of water for use in irrigating landscape plantings in the arid Figure 9. Root formation in Chrysothamnus nauseosus treated with auxins, tubes 1 -3 -IBA 1 mg/ml, tubes 4 -5 -NAA i mglml (left to right). western United States. For this reason, there has been a demand for natural rubber will outstrip the supply during trend toward the use of native plant materials that require the 1980's. In addition, the production areas that are capa- little water for survival. Rabbitbrush characteristically re- ble of growing the Rubber Tree (Hevea brasiliensis) are quires little water and exhibits several desirable ornamen- somewhat limited because of the tree's requirement for tal qualities. The plant's rugged appearance blends nicely tropical conditions. Another plant, Guayule (Partheni um into the general surroundings of most arid Western land- argentatum ), is a potential rubber- producing desert shrub scapes. The gray -green foliage of White Rubber Rabbit- that has attracted a lot of attention (Polhamus, 1962; brush contrasts well with both the dark greens of other Hayman et al., 1983; Johnson and Hinman, 1980; Benedict shrubs and with the brilliant colors of annual and perennial et al., 1983). In many ways, Chrysothamnus and Guayule flowers. The fall- blooming characteristic of rabbitbrush is have similar characteristics in that they are both nonlatex desirable because few landscape shrubs bloom at this time rubber producing plants of the aster or sunflower family. and the brilliant yellow flowers blend nicely with the The harvesting and extraction process will probably be autumn colors of other woody species. The plant could be similar, and the same rubber processing plant could likely useful in a number of adverse landscape situations such as be used for both plant tissues. parking strips, hot /dry slopes, or wherever alkaline soils are Natural rubber consists of cis 1, 4 polyisoprene units. a problem. White Rubber Rabbitbrush generally does best While natural rubber occurs in over 200 species of plants, in sunny locations, although we have observed plants grow- including even dandelions and goldenrod, the major com- ing nicely on native canyon sites that receive only about 2 mercial source is from the Hevea brasiliensis tree. The hours of direct sun per day. majority of natural rubber is used in rubber tires because of its durability. The increased cost of raw materials for mak- Potential Use of Chemical Components in the Plant ing synthetic rubber is an important factor in the value of Chrysothamnus nauseosus is an impressive chemical these desert shrubs as potential rubber sources. In 1910, factory. Preliminary chemical analysis indicates that about guayule provided as much as 10% of the rubber resource in 500 secondary metabolite compounds (terpenes, phenols, the United States. Chrysothamnus has similar concentra- etc.) are present. Only about half of these compounds have tion of rubber as guayule and potentially could be used just been identified at this time. They indicate a rich source of as easily. There appear to be no structural differences chemical diversity. The rubber content has attracted the between the rubber from guayule, Hevea, and Chryso- most interest because of the increased demand for natural thamnus. Hall (1919) evaluated the quality of rubber. For example, McGinnies (1979) estimated that the (Continued on page 208) 208 Desert Plants 7(4) 1985

12 RESIN level and rubber level did not always correlate. Some plants

lo with low resin had high rubber content, others had high resin and low rubber. In still other cases, both high resin e and high rubber were present. Some biomass studies have been done on Chrysotham- 6 % nus. Plants that have been clipped and allowed to grow for 2 4 years yielded average values of 200 oz per year (McKell and Van Epps, 1980). Hall and Goodspeed (1919) reported an 2 average growth rate for Chrysothamnus of 118 to 134 oz per year in natural populations. If one used a growth rate of 197 o 14 14 14 14 14 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 oz per year and assuming only 2% rubber with plants 3 feet 07 96 97 98 99 02 04 05 06 07 08 09 10 1L 13 14 15 16 19 20 21 22 23 24 25 6- apart, a plantation would yield about 326 pounds of rubber per acre after 6 years growth. 5- A tremendous biochemical diversity of compounds is present in this plant. Under study is the potential of natural RUBBER % 4 - insecticides and fungicides. Previous reports indicate the 3 . polyacetylenes have a potential as natural insecticides. Rose et al. (1980) found that the polyacetylenes were an- 2 tifeedants for the Colorado potato beetle. Others have found that treatment of plants with polyacetylenes stimu- lated the plants to produce natural insect repellents (Maugh, 1982). Bohlmann et al. (1979a, 1979b) found six 14 14 14 14 14 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 IS 15 15 new types of Labdane type acids in Chrysothamnus. 95 96 97 98 99 02 04 05 06 07 08 09 10 11 13 14 15 16 19 20 21 22 23 24 25 Buchannon et al. (1978) evaluated over 100 plant species SAMPLE NUMBER including guayule and rabbitbrush as potential hydrocar- Figure 11. Rubber and resin concentrations in Chry- bon crops. Rabbitbrush had a slightly higher botanical use sothamnus nauseosus. value than guayule. The values of polar and oil fractions obtained by solvent extraction were 11.1°/0 dry weight for guayule and 11.5% dry weight for rabbitbrush. Both plants were rated as having excellent potential as a hydrocarbon crop. Chrysothamnus Because of the chemical variation in Chrysothamnus, it Continue from page 180 is possible to select characteristics from natural popula- Chrysothamnus natural rubber and concluded that the tions or to use biotechnological techniques -for example, Chrysothamnus rubber had mechanical properties that somaclonal variates that will give high yields of resin and were similar to Hevea rubber and that it could vulcanize. rubber. Once a selection has been made, there is the poten- Nuclear Magnetic Resonance and infrared analysis on tial of further improvements by traditional selection tech- extracts indicate that Chrysothamnus natural rubber is niques or by biotechnical application. Once superior plants essentially a cis isoprene polymer and is almost identical to are located or synthesized they can be propagated by veg- Hevea and guayule rubber. The molecular weight was etative means. determined to be 4.5 x 104. However, the molecular weight decreases in the extraction of guayule (Campos -Lopez and Summary McGinnies, 1978) suggesting that neither plant has an Chrysothamnus nauseosus is a widely distributed and antioxidant. The evidence suggests that Chrysothamnus highly adaptable desert shrub whose potential uses have rubber is of good quality and should be acceptable in corn - not been fully recognized. Future research on the use of mercial use (Ostler et al., 1986). chemicals extracted from rabbitbrush may result in a new Within natural populations of Chrysothamnus, there is source of natural rubber, insecticides, fungicides, or all considerable variability in the rubber content on a dry three. The use of both traditional plant breeding and new weight basis. The average rubber yield reported by Hall and biotechnology may greatly improve the chemical value of Goodspeed (1919) was 1.7% (dry wt) from 140 different this plant. samples. This, however, does not take into account the extreme values and at least two subspecies contained 6.5% References rubber (dry wt). A survey in 1982 yielded similar results Anderson, L. C. 1966. Cytotaxonomic studies in Chrysothamnus Botany 204 -212. (Ostler et al., 1986), but the number of individual popula- (Astereae, Compositae). Amer. Journ. 53: Anderson, L. C. 1971. Additional chromosome numbers in for rubber content is still tions that have been analyzed Chrysothamnus (Asteraceae). Bull. Torrey Botanical Club 98: relatively limited. We found considerable variability in 222 -225. rubber content in our own analysis (Figure 11). Anderson, L. C. 1986a. An overview of the genus Chrysothamnus When the resin content was determined, considerable (Asteraceae), p. 29 -45. In: E. D. McArthur and B. L. Welch variation existed; the value of 21% was highest (Ostler et (compilers), Proceedings- Symposium on the Biology of Ar- al., 1986). In our collection, the highest level was 14% resin temisia and Chrysothamnus. USDA Forest Service General (Figure 11). Our results (Figure 11) indicate that the resin Technical Report INT- Ogden, Utah. 398 p. Figure 10. Chrysothamnus nauseosus used as an ornamen- tal landscape plant near Cougar Stadium in Provo, Utah. 210 Desert Plants 7(4) 1985

Anderson, L. C. 1986b. Sympatric subspecies in Chrysothamnus nauseosus subspecies. p. 205 -210. In: E. D. McArthur and B. L. nauseosus. p. 98 -103. In: E. D. McArthur and B. L. Welch Welch (compilers), Proceedings- Symposium on the Biology of (compilers), Proceedings- Symposium on the Biology of Ar- Artemisia and Chrysothamnus. USDA Forest Service General temisia and Chrysothamnus. USDA Forest Service General Technical Report INT -200. Ogden, Utah. 398 p. Technical Report INT -200. Ogden, Utah. 398 p. McArthur, E. D., A. C. Blauer, A. P. Plummer, and R. Stevens. Benedict, C. R., P. H. Reibach, S. Madhavan, R. V. Stipanovic, J. M. 1979a. Characteristics and Hybridization of Important Inter- Keithly, and H. Yokoyama. 1983. Effect of 2- (3, 4- mountain Shrubs. III. Sunflower Family. USDA Forest Service Dichlorophenoxy) -triethylamine on the synthesis of cis - Research Paper INT -220. 82p. polyisoprene in guayule plants (Parthenium argentatum (Gray)). McArthur, E. D., B. C. Giunta, and A. P. Plummer. 1974. Shrubs for Plant Physiology 72: 897 -899. restoration of depleted ranges and disturbed areas. Utah Science Bohlmann, F., L. Dutta, H. Robinson and R. M. King. 1979a. New 35: 28 -33. labdane derivatives from Chrysothamnus nauseosus. Phyto- McArthur, E. D., D. L. Hanks, A. P. Plummer, and A. C. Blauer. chemistry 18: 1889 -1892. 1978. Contributions to the taxonomy of Chrysothamnus vis - Bohlmann, F., C. Zdero, H. Robinson, and R. M. King. 1979b. New cidiflorus and other Chrysothamnus species using paper

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