GERMINATION AND GROWTH INHIBITORS IN GUAYULE (PARTHENIUM ARGENTATUM GRAY) CHAFF AND THEIR POSSIBLE INFLUENCE IN SEED DORMANCY

Guayule (Parthenium argentatum Gray) is a rubber-producing plant native to the semi-arid region of north central Mexico and southwestern Texas. As a member of the family Asteraceae, the seed dispersal unit in guayule is comprised of an achene enclosed by two staminate florets and a bract. The seeds in this condition are dormant and need special treatment in order to germinate. Threshing, prolonged washing, and/or chemical treatments prove effective in improving the germination. Experiments showed that chaff influenced germination and seedling emergence. Bioassays of aqueous extracts of guayule chaff and the seed coat showed a significant inhibition of germination and radicle growth of guayule, lettuce, and tomato seeds. High-performance liquid chromatography enabled the identification of at least seven phenolic acids from guayule chaff extract. These, in order of decreasing concentrations, included p-hydroxybenzoic, protocatechuic, p-coumaric, ferulic, benzoic, vanillic, and cinnamic acids. All of them are well-known germination and growth inhibitors, and seem to play an important role in the dormancy of guayule seed.     

ARTIFICIAL HYBRIDIZATION OF RUBBER-BEARING GUAYULE WITH COLD-TOLERANT PARTHENIUM LIGULATUM

ABSTRACT Caespitose and cold-tolerant plants of Parthenium ligulatum (Jones) Barneby (Asteraceae) from a native population in the Uinta Basin, Utah, were uprooted, potted, and transferred to a greenhouse in California. Approximately two years after transfer, the plants flowered and subsequently were crossed to diploid guayule (Parthenium argentatum Gray), the rubber-bearing species, native to the state of Durango, Mexico. Only female guayule × male P. ligulatum crosses produced F₁ hybrids. Only crosses involving guayule as female parent and F₁ plants as male parents produced backcross (BC,) plants. Hybrid plants were variable with respect to their growth habit, inflorescence, and leaf shape. Both parents and F₁ hybrids had 2n = 36 chromosomes. Unlike the parents, however, meiosis was irregular in the hybrids which showed a range of 0–5 and an average of 2.1 univalents at metaphase I. Hybrids averaged 0.87 laggards at anaphase I and 0.83 micronuclei at the tetrad stage. The crossability of guayule and P. ligulatum, the high degree of chromosome pairing of the F₁ hybrids, and the production of BC₁ plants indicate that the two species are related in spite of their distinct morphological and ecological differences. This study suggests that the cold-tolerance trait of P. ligulatum may be transferred to guayule through interspecific hybridization followed by backcrossing. The development of cold-tolerant guayule cultivars is expected to expand the areas of guayule production beyond that of the Chihuahuan desert and similar climates.     

STEM ANATOMY OF PARTHENIUM ARGENTATUM,P. INCANUM AND THEIR NATURAL HYBRIDS

Guayule (Parthenium argentatum Gray) contains rubber in the parenchymatous cells of stems and roots. Stem anatomy of P. argentatum is described along with that of P. incanum H.B.K. (mariola). Anatomy of these species differs significantly. Phloem rays in both species increase in width by cell division and expansion; however, the increase observed in mariola is less as compared to that in guayule. Axial xylem parenchyma in guayule is generally a two-cell strand as compared to the fusiform axial xylem parenchyma observed in mariola. Vascular ray cells and cells of the pith region of guayule are parenchymatous, whereas those of mariola are sclerenchymatous. As a result of introgression between guayule and mariola, three forms of guayule exist in the native stands of Mexico. Morphological differences between these guayule plants have been described previously. The stem anatomy of these three groups of plants differ importantly. Group I guayule plants, least introgressed by mariola, have taller rays with the cells of pith region and vascular rays parenchymatous. Group III plants, highly introgressed by mariola, have a few to many cells of vascular rays and pith with lignified secondary walls and shorter rays. Many of the anatomical characteristics of group II plants, somewhat introgressed by mariola, are intermediate between group I and III plants.     

The effect of a rosette-crown fly, Botanophila turcica, on growth,biomass allocation and reproduction of the thistle Carthamus lanatus

Plant growth and reproductive output of the winter annual invasive thistle, Carthamus lanatus was characterised in relation to plant size in three native populations in southern France. The effects of the rosette-crown feeding fly Botanophila turcica on these plant characteristics were assessed by comparing unattacked with naturally attacked plants at each site and by a field experiment. Indirect effects of B. turcica on plant seed production were also compared with direct seed loss caused by a guild of capitulum-feeding insects that incidentally attacked the marked plants at these sites. C. lanatus showed no size or weight requirement for flowering, but larger flowering plants produced less total receptacle surface and less seed production (female reproductive potential) in proportion to plant weight than smaller flowering plants. B. turcica did not select hosts on the basis of size or density. B. turcica reduced plant relative growth rate (RGR) in all situations, but attacked plants compensated fully at two of three sites as attack failed to halt rosette growth. Attacked plants suffered 12 % mortality, and 71 % lower seed production than unattacked plants at the site with the lowest RGR. This corresponded to 9 % lower seed production for the whole thistle population compared to 8.6–19.5 % direct seed loss to capitulum insects across all sites.     

Responses of guayule (Parthenium argentatum) seedlings to plant growth promoting fluorescent pseudomonads

Summary The potential of a number of fluorescent pseudomonad strains to promote growth of guayule plants in the greenhouse and in the field was studied. A number of bacterial strains collected from guayule roots and rhizospheres promoted growth of greenhouse-grown plants but not field-grown plants. Percent increase in shoot dry weight of 12-week-old, greenhouseinoculated guayule plants ranged from 17 to 75 nine weeks after inoculation compared to non-inoculated plants. The increased growth of plants in the greenhouse could reduce production cost by shortening the time required to maintain plants in the nursery prior to transplanting to the field.Journal Series Article no 3816 of the Arizona Agricultural Experiment Station.     

Effect of strain and cultural conditions on the production of cytochalasin B by the potential mycoherbicide Pyrenophora semeniperda (Pleosporaceae,Pleosporales)

The seed pathogen Pyrenophora semeniperda has demonstrated potential as a mycoherbicidal biocontrol for eliminating persistent seed banks of annual bromes on western North American rangelands. This pathogen exhibits variation in virulence that is related to mycelial growth rate, but direct laboratory tests of virulence on seeds often have low repeatability. We developed a rapid and sensitive high pressure liquid chromatography method for quantification of the phytotoxin cytochalasin B in complex mixtures in order to evaluate its use in virulence screening. All 10 strains tested produced large quantities of this metabolite in solid wheat seed culture, with production varying over a fourfold range (535–2256 mg kg^?1). No cytochalasin B was produced in liquid potato dextrose broth culture, showing that its synthesis is strongly dependent on cultural conditions. In a Bromus tectorum coleoptile bioassay, solid culture extracts showed mild toxicity similar to the cytochalasin B standard at a concentration equivalent to 10^?4 M cytochalasin B (72–95% of control), whereas at 10^?3 M equivalent, the extracts exhibited significantly higher toxicity (8–18% of control) than the cytochalasin B standard (34% of control). This suggests the possible presence of other phytotoxic metabolites. Cytochalasin B production in solid wheat seed culture exhibited the predicted significant negative correlation with mycelial growth rate on potato dextrose agar, but the correlation was not very strong, possibly because cytochalasin B production and growth rate were measured under different cultural conditions.     

Photosynthesis and assimilate partitioning between carbohydrates and isoprenoid products in vegetatively active and dormant guayule: physiological and environmental constraints on rubber accumulation in a semiarid shrub

The stems and roots of the semiarid shrub guayule, Parthenium argentatum, contain a significant amount of natural rubber. Rubber accumulates in guayule when plants are vegetatively and reproductively dormant, complicating the relationship between growth/reproduction and product synthesis. To evaluate the factors regulating the partitioning of carbon to rubber, carbon assimilation and partitioning were measured in guayule plants that were grown under simulated summer‐ and winter‐like conditions and under winter‐like conditions with CO₂ enrichment. These conditions were used to induce vegetatively active and dormant states and to increase the source strength of vegetatively dormant plants, respectively. Rates of CO₂ assimilation, measured under growth temperatures and CO₂, were similar for plants grown under summer‐ and winter‐like conditions, but were higher with elevated CO₂. After 5 months, plants grown under summer‐like conditions had the greatest aboveground biomass, but the lowest levels of non‐structural carbohydrates and rubber. In contrast, the amount of resin in the stems was similar under all growth conditions. Emission of biogenic volatile compounds was more than three‐fold higher in plants grown under summer‐ compared with winter‐like conditions. Taken together, the results show that guayule plants maintain a high rate of photosynthesis and accumulate non‐structural carbohydrates and rubber in the vegetatively dormant state, but emit volatile compounds at a lower rate when compared with more vegetatively active plants. Enrichment with CO₂ in the vegetatively dormant state increased carbohydrate content but not the amount of rubber, suggesting that partitioning of assimilate to rubber is limited by sink strength in guayule.     

Performance of USDA guayule lines in the northern Negev of Israel

The rubber yield of the guayule plant (Tarthenium argentatum) is determined by its rubber concentration and biomass production, both of which are a function of genetic constituents and environmental conditions. With the aim of selecting best performing lines of guayule under the climatic conditions of the northern Negev of Israel, two-yr-old guayule plants from 13 USDA lines were evaluated for height, spread, canopy fresh and dry weight, branch and leaf dry weight, rubber and resin concentration, and rubber and resin yield per plant. Significant differences were found among the lines for all the characteristics tested. Lines 11600 and 11604 excelled in rubber and biomass production and were taller and more uniform than the other lines; whereas line N593, conventionally used as a standard, performed poorly and was less uniform. The correlation between rubber yield per plant and rubber concentration was poor, rubber yield being related mainly to biomass production and to a lesser degree to height and spread of the plants. Taken together with the fact that biomass production was more variable than rubber concentration, this finding suggests that breeding and selection of guayule for high rubber yield should be directed primarily towards improvement of biomass production rather than rubber concentration. In the northern Negev of Israel, USDA lines 11600 and 11604 performed well.     

Growth promotion of groundnut by IAA producing rhizobacteria Bacillus licheniformis MML2501

B. licheniformis MML2501 which was isolated from groundnut rhizosphere soil showed increased populations on spermozphere colonisation and significantly increased the seed germination and other growth parameters in groundnut under in vitro conditions. B. licheniformis MML2501 did not solubilise phosphate but produced indole acetic acid (IAA), with a maximum of 23 μg/ml under optimised conditions such as pH 7.0, temperature 35°C, tryphtophan at a concentration of 16 mM and at 200 rpm shaken conditions. The production of IAA by B. licheniformis MML2501 was further confirmed by TLC and HPLC analyses, in which the R_f value and retention time of 0.66 and 4.1 min respectively, match with that of the authentic IAA. Seed treatment of B. licheniformis MML2501 in groundnut showed a significant increase in seed germination, other growth parameters and yield parameters under potted plant experiments.     

Established native perennial grasses out-compete an invasive annual grass regardless of soil water and nutrient availability

Competition and resource availability influence invasions into native perennial grasslands by non-native annual grasses such as Bromus tectorum. In two greenhouse experiments we examined the influence of competition, water availability, and elevated nitrogen (N) and phosphorus (P) availability on growth and reproduction of the invasive annual grass B. tectorum and two native perennial grasses (Elymus elymoides, Pascopyrum smithii). Bromus tectorum aboveground biomass and seed production were significantly reduced when grown with one or more established native perennial grasses. Conversely, average seed weight and germination were significantly lower in the B. tectorum monoculture than in competition native perennial grasses. Intraspecific competition reduced per-plant production of both established native grasses, whereas interspecific competition from B. tectorum increased production. Established native perennial grasses were highly competitive against B. tectorum, regardless of water, N, or P availability. Bromus tectorum reproductive potential (viable seed production) was not significantly influenced by any experimental manipulation, except for competition with P. smithii. In all cases, B. tectorum per-plant production of viable seeds exceeded parental replacement. Our results show that established plants of Elymus elymoides and Pascopyrum smithii compete successfully against B. tectorum over a wide range of soil resource availability.     

Phytohormones and Antibiotics Produced by Bacillus subtilis and their Effects on Seed Pathogenic Fungi and on Soybean Root Development

Summary Bacteria belonging to the genus Bacillus were isolated from soil samples of Paraná State, Brazil, with the aim of evaluating their potential biological control of soybean seed pathogens. Strain PRBS-1 was selected, showing similar effectiveness to that of the strain AP-3, used as a reference due to its known antibiotic potential. The sequencing of the ribosomal 16S rRNA gene confirmed that both strains belong to the species B. subtilis, although showing high genetic diversity in relation to this species. Both strains inhibited five soybean seed pathogenic fungi in vitro, Rhizoctonia solani, Colletotrichum truncatum, Sclerotinia sclerotiorum, Macrophomina phaseolina and Phomopsis sp. Furthermore, the metabolites of AP-3 increased production of root hairs, while the metabolites of PRBS-1 stimulated outgrowth of lateral roots in soybean. The antibiotic effect of both strains seemed to be related to compounds of the iturin group, while the root growth promotion by PRBS-1 was at least partially related to the production of indoleacetic acid. The results have shown the potential of using selected strains of B. subtilis in the biological control of seed pathogens, as well as in promoting soybean growth.     

Latex content and biomass increase in mycorrhizal guayule (Partheniurn argentatum) under field conditions*

Guayule seedlings were inoculated with two Glomus species in pasteurised soil and grown in the glasshouse without added fertiliser for 8 wk prior to transplanting to the field. The survival rate of transplanted guayule seedlings was increased by inoculation with vesicular arbuscular mycorrhizal fungi compared with uninoculated controls. Inoculated guayule had greater concentrations of Ca, Fe, Mg and Mn at six months of age, and greater concentrations of Ca, Mg, and Zn at 12 months of age than did uninoculated plants. The latex content of both roots and shoots of guayule was greater in inoculated than in uninoculated guayule plants at 12 and 18 months of age. The resin content remained unchanged between treatments irrespective of sampling date.     

Morphological,chemical, and cytogenetic characters of F1 hybrids betweenParthenium argentatum (Guayule) andP. fruticosum var.fruticosum (Asteraceae) and their potential in rubber improvement

Interspecific hybrids betweenParthenium argentatum, the guayule rubber plant, andP. fruticosum var. fruticosum were evaluated for their potential rubber content and quality. Fifteen-mo-old field-grown plants ofP. fruticosum var.fruticosum measured four times more in height and spread than those ofP. argentatum, but contained less than 0.05% rubber of low mol wt.Parthenium argentatum showed 2% rubber content, with a mol wt of about one million. Resin contents varied little among parents or hybrids. The same age F₁ hybrids were intermediate in height and spread and had low rubber content, but showed presence of high mol wt rubber like the guayule parent. This indicates that high mol wt rubber is expressed over the low mol wt rubber in F₁ hybrids. Despite low rubber content but favorable biomass production, F₁ hybrids revealed irregular meiotic chromosome behavior and low pollen and seed germination. These results suggest that interspecific F₁ hybrids may be used in backcross programs to increase biomass and rubber content in guayule.     

Fermentation production of keratinase from Bacillus licheniformisPWD-1 and a recombinant B. subtilis FDB-29

Bacillus licheniformis PWD-1, the parent strain, and B. subtilis FDB-29, a recombinant strain. In both strains, keratinase was induced by proteinaceous media, and repressed by carbohydrates. A seed culture of B. licheniformis PWD-1 at early age, 6–10 h, is crucial to keratinase production during fermentation, but B. subtilis FDB-29 is insensitive to the seed culture age. During the batch fermentation by both strains, the pH changed from 7.0 to 8.5 while the keratinase activity and productivity stayed at high levels. Control of pH, therefore, is not necessary. The temperature for maximum keratinase production is 37°C for both strains, though B. licheniformis is thermophilic and grows best at 50°C. Optimal levels of dissolved oxygen are 10% and 20% for B. licheniformis and B. subtilis respectively. A scale-up procedure using constant temperature at 37°C was adopted for B. subtilis. On the other hand, a temperature-shift procedure by which an 8-h fermentation at 50°C for growth followed by a shift to 37°C for enzyme production was used for B. licheniformis to shorten the fermentation time and increase enzyme productivity. Production of keratinase by B. licheniformis increased by ten-fold following this new procedure. After respective optimization of fermentation conditions, keratinase production by B. licheniformis PWD-1 is approximately 40% higher than that by B. subtilis FDB-29. Received 16 July 1998/ Accepted in revised form 07 March 1999     

Reciprocal distribution of two congeneric trees, Betula platyphylla var. japonica and Betula maximowicziana, in a landscape dominated by anthropogenic disturbances in northeastern Japan

Aim Information has been compiled on disturbance regimes and the life‐history characteristics of Betula platyphylla var. japonica (Miq.) Hara and B. maximowicziana Regel to investigate the impact of humans on the present distribution patterns of these two congeneric tree species. Location The study area is in the central region of the northern Kitakami Mountain Range, located in the northeast of Honshu Island, Japan. Methods First, the present distributions of B. maximowicziana and B. platyphylla var. japonica were mapped at the landscape scale. To examine the factors affecting the distribution patterns, topographic features and past land use were taken into account. Second, life‐history traits of both species were clarified at various growth stages either by fieldwork or through a literature search. Previous studies have provided some information on seed production, seed dispersal, seedling dynamics, sprouting, and growth. In the present study, field observations and experiments were conducted regarding seed‐bank formation, size and age at reproduction, and the life span of canopy trees. Results Betula platyphylla var. japonica and B. maximowicziana were spatially segregated in the studied landscape (14,000 ha). The distribution of each species was correlated more strongly with land use at the beginning of the twentieth century than with site environmental factors such as altitude or slope angle. Betula platyphylla var. japonica was distributed more frequently on former grasslands, whereas B. maximowicziana was almost exclusively limited to past old‐growth forests. As typical pioneers, the two species showed similar life‐history traits but differed in several critical points. Betula platyphylla var. japonica has a vigorous sprouting ability, which might increase its resistance to burning and logging, whereas B. maximowicziana forms a persistent seed bank in the soil, indicating an advantage in regenerating in disturbances found in forest communities. Other critical differences were detected in age‐related characteristics such as minimum age of reproduction and life span. Main conclusions The earlier reproductive maturity and the shorter life span of B. platyphylla var. japonica indicate a shorter population cycle than that for B. maximowicziana. The latter would be excluded from grasslands that were burned frequently, as a result of the longer time span before initial reproduction and its poor sprouting ability. In contrast, B. platyphylla var. japonica would be excluded from old‐growth forests, where disturbance was infrequent, owing to its shorter life span and lack of a persistent seed bank.     

Complex Growth Regulator Increases Alfalfa Seed Production

The effects of thermophilic methane fermentation products on alfalfa (Medicago sativa L.) growth, nitrogen-fixing activity, and seed production were studied in pot and field experiments. Plant treatment with the preparation at the stages of stooling and flower bud formation resulted in an increase in the root nodule weight and their nitrogen-fixing activity, the accumulation of cytokinins (zeatin and zeatin riboside), and an increase in the green mass yield and protein content, especially at a low (0.25 of the full rate) mineral nitrogen rate. Crop seed production was considerably improved during the first (pot experiments) and second (field experiments) growing seasons. The conclusion was drawn that the causes for improved alfalfa seed production were the effects of group B vitamins, phytohormones, their interaction, and the switching of metabolic pathways toward cytokinin synthesis.     

TRICHOME MORPHOLOGY AS AN INDICATOR OF HIGH RUBBER BEARING GUAYULE (PARTHENIUM ARGENTATUM GRAY) PLANTS IN NATIVE POPULATIONS

Parthenium argentatum Gray (guayule) and P. incanum (mariola) grow in close associations in their native habitat of Mexico. Variation in rubber concentration and morphology of guayule has been known for a long time. Studies of over 75 native guayule plants indicated the presence of at least three prominent forms of guayule plants. Group I guayule plants have oblanceolate leaves and leaf margins are entire to two-toothed. T-shaped leaf trichomes are with centrally attached stalk and cap cell with two blunt ends. Plants in this group are high in rubber, containing on the average 17% rubber. Group II guayule plants have narrow elliptic leaves and leaf margins are entire to four-toothed. T-shaped trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and straight. Rubber content in these plants averages 10%. Group III guayule plants have ovate leaves and leaf margins are four- to eight-toothed. T-trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and wavy or curved. These plants on the average contain 6% rubber. Morphological as well as biochemical data indicate the presence of mariola genes in the last two groups of plants and this has resulted in an increase in trichome length and a decrease in the rubber content. Group II guayule plants are of more common occurrence than the others. Based on the data presented here, high rubber bearing guayule plants in native stands can be easily selected by analyzing trichome morphology.     

The effects of pollen limitation on population dynamics of snow lotus (<Emphasis Type="Italic">Saussurea medusa</Emphasis> and <Emphasis Type="Italic">S. laniceps</Emphasis>, Asteraceae): Threatened Tibetan medicinal plants of the eastern Himalayas

Pollen limitation reduces seed production and may reduce plant population growth rate. Plants may be particularly prone to pollen limitation if they require pollinators, occur at high elevation, and have human-mediated reductions in plant density due to harvesting. We found that two rare monocarpic Tibetan plant species, known as the Himalayan Snow Lotus, both require pollinators and that seed production in Saussurea medusa (Asteraceae) but not S. laniceps is limited by pollen receipt. We created deterministic and stochastic stage-structured matrix models for S. medusa, and found that pollen supplementation significantly increases population growth rate. However, even when pollen is not limiting, S. medusa is likely at risk for extinction in the next 50 years. Our results for this monocarpic plant differ from other population studies on pollen limitation in polycarpic plant species since the magnitude of pollen limitation for seed production was relatively low, and yet the sensitivity of population growth to changes in seed production was relatively high.     

Growth allocation between height and stem diameter in nonsuppressed reproducing Abies mariesii trees

To understand the growth patterns with respect to competition and leaf‐mass increase in reproducing trees, growth allocation between height and stem diameter was examined for nonsuppressed reproducing Abies mariesii trees in a subalpine forest in northern Honshu, Japan. The growth allocation was analyzed by dividing the relative growth rate of the stem volume into the relative contributions of height and stem‐diameter growth. During a 9‐yr period, height growth and seed‐cone production showed obvious annual variation, while stem‐diameter growth recorded moderate variation. For two of three years of seed‐cone production during the 9‐yr period, trees with larger seed‐cone production were associated with less height growth in the following year of seed‐cone production; however, there was no trend of height growth in the year of seed‐cone production. In the following year of mast seeding, trees with larger stem‐volume growth were associated with less height growth. This trend was also shown for the relationship between the cumulative stem‐volume growth during the 9‐yr period and growth allocation to height, suggesting that trees with a larger biomass increase depress the allocation of photosynthate to competition with a large expenditure for reproduction. In contrast to this, trees with a smaller biomass increase might allocate photosynthate to competition with surrounding trees. The results of this study suggest that an increase in reproductive organs during life history and annual variation in reproduction are closely associated with the growth patterns of the stem in A. mariesii trees.     

SPATIAL VARIABILITY IN SEED PRODUCTION OF THE PERENNIAL BUNCHGRASS BOUTELOUA GRACILIS (GRAMINEAE)

The effects of soil texture and grazing by cattle on the production of seeds of Bouteloua gracilis were evaluated for a semiarid grassland in northeastern Colorado. Ten locations were chosen to represent the range in soil textures and grazing intensities found at the Central Plains Experimental Range research site. Number of flowering culms, inflorescences and seeds, length of each flowering culm, total biomass of reproductive structures (culms, inflorescences, and seeds), and basal area were assessed for 96 B. gracilis plants at each location. Community-level estimates of density of flowering culms and density of viable seeds were made for each location. Both soil texture and grazing by cattle were important to spatial variability in seed production and other indicators of reproductive effort by B. gracilis. Grazing was important in mediating effects of soil texture. On locations protected from grazing, soil texture had significant effects on seed production; the largest number of seeds was produced on the coarsest-textured soil and the fewest number on the finest-textured soil. Relationships between seed production and clay content and between seed production and other indicators of reproductive effort by B. gracilis were different for grazed and ungrazed locations. Spatial variability in seed production of B. gracilis as a result of spatial variability in soil texture and grazing may be important to the continued dominance of this species in the presence of disturbances that vary in time and space.