Mature Plant Stage Research Articles

Overexpression of the DEAD-Box RNA Helicase Gene AtRH17 Confers Tolerance to Salt Stress in Arabidopsis.

Plants adapt to abiotic stresses by complex mechanisms involving various stress-responsive genes. Here, we identified a DEAD-box RNA helicase (RH) gene, AtRH17, in Arabidopsis, involved in salt-stress responses using activation tagging, a useful technique for isolating novel stress-responsive genes. AT895, an activation tagging line, was more tolerant than wild type (WT) under NaCl treatment during germination and seedling development, and AtRH17 was activated in AT895. AtRH17 possesses nine well-conserved motifs of DEAD-box RHs, consisting of motifs Q, I, Ia, Ib, and II-VI. Although at least 12 orthologs of AtRH17 have been found in various plant species, no paralog occurs in Arabidopsis. AtRH17 protein is subcellularily localized in the nucleus. AtRH17-overexpressing transgenic plants (OXs) were more tolerant to high concentrations of NaCl and LiCl compared with WT, but no differences from WT were detected among seedlings exposed to mannitol and freezing treatments. Moreover, in the mature plant stage, AtRH17 OXs were also more tolerant to NaCl than WT, but not to drought, suggesting that AtRH17 is involved specifically in the salt-stress response. Notably, transcriptions of well-known abscisic acid (ABA)-dependent and ABA-independent stress-response genes were similar or lower in AtRH17 OXs than WT under salt-stress treatments. Taken together, our findings suggest that AtRH17, a nuclear DEAD-box RH protein, is involved in salt-stress tolerance, and that its overexpression confers salt-stress tolerance via a pathway other than the well-known ABA-dependent and ABA-independent pathways.

Forage Legumes as Sources of Bioactive Phytoestrogens for Use in Pharmaceutics: A Review.

Alfalfa and red clover are the most widespread and most important perennial legumes, primarily used as a high-quality feed for livestock. Both alfalfa and red clover, as well as some other plant species from Fabaceae family, are a rich natural source of phytoestrogens, nonsteroidal compounds with an estrogenic activity whose beneficial effects in the prevention and treatment of many diseases are demonstrated in numerous scientific studies. Nowadays, various herbal preparations are present on the world market and their use is constantly increasing, as well as the growing demands of consumers for environmentally sound and health-safe production of plant species used as sources of active substances. Because of their widespread distribution, the possibility of organic breeding, and also significant increases in surface area under genetically modified crops in most EU countries, alfalfa and red clover have become more interesting alternative sources of phytoestrogens. The most common phytoestrogens in these forage legumes are genistein, daidzein, glycitein, formononetin, biochanin, coumestrol, kaempferol and apigenin. The content of these substances is significantly influenced by a number of factors including genotype, environment, production technology, plant maturity stage, and individual plant parts. Available evidence suggests that forage legumes represent high promising sources of health-promoting phytoestrogens. Due to numerous favorable features, they can find commercial application in different industries such as pharmaceutical, nutraceutical, cosmetic, and agriculture.

The Grape VlWRKY3 Gene Promotes Abiotic and Biotic Stress Tolerance in Transgenic Arabidopsis thaliana.

WRKY transcription factors are known to play important roles in plant responses to various abiotic and biotic stresses. The grape WRKY gene, WRKY3 was previously reported to respond to salt and drought stress, as well as methyl jasmonate and ethylene treatments in Vitis labrusca × V. vinifera cv. ‘Kyoho.’ In the current study, WRKY3 from the ‘Kyoho’ grape cultivar was constitutively expressed in Arabidopsis thaliana under control of the cauliflower mosaic virus 35S promoter. The 35S::VlWRKY3 transgenic A. thaliana plants showed improved salt and drought stress tolerance during the germination, seedling and the mature plant stages. Various physiological traits related to abiotic stress responses were evaluated to gain further insight into the role of VlWRKY3, and it was found that abiotic stress caused less damage to the transgenic seedlings than to the wild-type (WT) plants. VlWRKY3 over-expression also resulted in altered expression levels of abiotic stress-responsive genes. Moreover, the 35S::VlWRKY3 transgenic A. thaliana lines showed improved resistance to Golovinomyces cichoracearum, but increased susceptibility to Botrytis cinerea, compared with the WT plants. Collectively, these results indicate that VlWRKY3 plays important roles in responses to both abiotic and biotic stress, and modification of its expression may represent a strategy to enhance stress tolerance in crops.

Sweet Onion (Allium cepa L.) as Influenced by Organic Fertilization Rate: 1. Plant Growth, and Leaf and Bulb Mineral Composition

Vidalia onions (Allium cepa L.) are sweet, short-day, low pungency, yellow Granex-type bulbs that are popular in the United States because of their mild flavor. There are limited studies on sweet onion plant growth in response to organic fertilization rate. The objective of this report was to evaluate the effects of organic fertilizer rates on sweet onion plant growth, and leaf and bulb mineral nutrients. Experiments were carried out at the Horticulture Farm, Tifton Campus, University of Georgia, in the Winters of 2012–13 and 2013–14. There were five treatments [organic fertilizer 3–2–3 equivalent to 0, 60, 120, 180, and 240 kg·ha−1 nitrogen (N)]. During the season and at the mature plant stage, root, stem, and bulb biomass increased whereas the root-to-shoot ratio decreased with increasing fertilization rate up to 120 kg·ha−1 N. Foliar concentrations of N and Ca decreased whereas Cu concentration increased with increasing organic fertilization rate. Bulb Mg and Mn increased whereas P and Cu decreased with increasing organic fertilization rate. The accumulation of mineral nutrients by onion whole plants increased quadratically (N, P, K, and S) or linearly (Ca and Mg) with increasing fertilization rate. The N use efficiency decreased with increasing organic fertilization rate; the agronomic efficiency of N (AEN) decreased quadratically and the marginal yield decreased linearly with increasing fertilization rate. Chlorophyll indices (CI) were highest with 240 kg·ha−1 N and lowest with 0 kg·ha−1 N. In conclusion, onion plant growth increased with increasing organic fertilizer rate probably because of augmented soil N levels. Observation of nutrient deficiencies late in the season, even at high organic fertilization rates, indicates that preplant application of organic fertilizer was sufficient to cover plant nutritional needs only partially and that applications of N fertilizer later in the season may be necessary. High application rates of organic fertilizer (above those required by the crop) may have resulted in significant N leaching because it is unlikely that the crop used most of the N that was mineralized. Bulb concentrations of P, K, Ca, Mg, S, B, Fe, Cu, and Mn were higher compared with values reported in the literature for onions produced with inorganic fertilizers.

OPEN GLUME1: a key enzyme reducing the precursor of JA, participates in carbohydrate transport of lodicules during anthesis in rice.

OG1 is involved in JA-regulated anthesis by modulating carbohydrate transport of lodicules in rice. Flowering plants have evolved a sophisticated regulatory network to coordinate anthesis and maximize reproductive success. In addition to various environmental conditions, the plant hormone jasmonic acid and its derivatives (JAs) are involved in anthesis. However, the underlying mechanism remains largely unexplored. Here, we report a JA-defective mutant in rice (Oryza sativa), namely open glume 1, which has dysfunctional lodicules that lead to open glumes following anthesis. Map-based cloning and subsequent complementation tests confirmed that OG1 encodes a peroxisome-localized 12-oxo-phytodienoic acid reductase-a key enzyme that reduces the precursor of JA. Loss-of-function of OG1 resulted in almost no JA accumulation. Exogenous JA treatment completely rescued the defects caused by the og1 mutation. Further studies revealed that intracellular metabolism was disrupted in the lodicules of og1 mutant. At the mature plant stage, most seeds of the mutant were malformed with significantly reduced starch content. We speculate that JA or JA signaling mediates the carbohydrate transport of lodicules during anthesis, and signal the onset of cell degradation in lodicules after anthesis. We conclude that the OPEN GLUME 1 gene that produces a key enzyme involved in reducing the precursor of JA in JA biosynthesis and is involved in carbohydrate transport underlying normal lodicule function during anthesis in rice.

Effects of agronomic factors on yield and quality of whole corn plants and the impact of feeding high concentrations of corn silage in diets containing distillers grains to finishing cattle.

Corn plants were sampled over 2 consecutive years to assess the effects of corn hybrid maturity class, plant population, and harvest time on whole corn plant quality and yield in Nebraska. A finishing experiment evaluated the substitution of corn with corn silage in diets with corn modified distillers grains with solubles (MDGS). The first 2 harvest dates were at the mid- and late-silage harvest times whereas the final harvest was at the grain harvest stage of plant maturity. Whole plant yields increased as harvest time progressed (yr 1 quadratic P < 0.01; yr 2 linear P < 0.01). However, differences in TDN concentration in both years were quite minimal across harvest time, because grain percentage increased but residue NDF in-situ disappearance decreased as harvest time was delayed. In the finishing experiment, as corn silage inclusion increased from 15 to 55% (DM basis) by replacing dry rolled and high moisture corn grain with corn silage in diets containing 40% MDGS, DMI, ADG, and G:F linearly decreased (P ≤ 0.01), with the steers on the 15% corn silage treatment being 1.5%, 5.0%, and 7.7% more efficient than steers on treatments containing 30, 45, and 55% corn silage, respectively. Calculated dietary NEm and NEg decreased linearly as corn silage inclusion increased indicating that net energy values were greater for corn grain than for corn silage. In addition, dressing percentage decreased linearly (P < 0.01) as silage inclusion increased suggesting more fill as silage inclusion increases in diets. Cattle fed greater than 15% corn silage in finishing diets based on corn grain will gain slower and be slightly less efficient and likely require increased days to market at similar carcass fatness and size. When 30% silage was fed with 65% MDGS, DMI, and ADG were decreased (P < 0.01) compared to feeding 30% silage with 40% MDGS suggesting some benefit to including a proportion of corn in the diet. Conversely, when 45% silage was fed with 40% MDGS, ADG, and G:F were greater (P < 0.04) than when 45% silage was fed with just grain implying a greater energy value for MDGS than for corn grain. Substituting corn silage for corn grain in finishing diets decreased ADG and G:F which would increase days to finish to an equal carcass weight; however, in this experiment, increasing corn silage levels with MDGS present reduced carcass fat thickness without significantly decreasing marbling score.

Compensation effect of winter wheat grain yield reduction under straw mulching in wide-precision planting in the North China Plain

Climate change and the growing demand for food security force growers to identify ways both to improve food production and to reduce agricultural carbon emissions. Although straw mulching is known to decrease CO2 emissions, winter wheat grain yield in the North China Plain was declined under straw mulching. In an effort to determine the most effective way to increase winter wheat yield under straw mulching, a field experiment was conducted using two planting patterns (wide-precision planting and conventional-cultivation planting) and two straw mulching rates (0 and 0.6 kg/m2). The results showed the wide-precision planting/non-mulching treatment significantly increased the leaf area index more than the other three treatments at the early growth stage. This treatment improved aboveground dry matter accumulation and was conducive to increased spike weight in the late growth stage. By contrast, straw mulching significantly reduced winter wheat grain yields by lowering both spike number and 1000-grain weight at the mature plant stage. In the wide-precision planting/mulching treatment, a significantly increased spike number compensated for grain yield losses. The results support the idea that wide-precision planting combined with straw mulching has the potential to decrease the winter wheat grain yield reduction previously observed with straw mulching in the North China Plain.

Understanding medusahead low intake and palatability through in vitro digestibility and fermentation kinetics

The low intake of medusahead grass (Taeniatherum caput-medusae ssp. asperum) by sheep is attributed to the high silica content of the plant and its negative impact on digestibility, making this weed a successful competitor in grazed plant communities. The goals of this study were to determine the influence of (1) plant maturity stage (from late vegetative stage to beginning of senescence and thatch), (2) particle size (1, 5, 10 and 20 mm), and (3) high-quality feeds (alfalfa hay and a high-energy concentrate) on fermentation kinetics and apparent digestibility of medusahead relative to palatable feeds (alfalfa and tall fescue hays, and high-energy concentrates). In vitro gas production was estimated and apparent digestible organic matter (DOM) of the substrates was assessed after incubation. Medusahead from late vegetative to senescence stage had greater DOM (65% to 71%; P<0.05) than alfalfa hay (53%), similar to tall fescue hay (67%; P>0.05), and lower than the high-energy concentrates assayed (77% to 79%; P<0.05). Fermentation kinetics showed slow fermentation rates for medusahead relative to alfalfa (P<0.05), and a decline in fermentation rates with plant maturity (P<0.05). Fermentation rates of the substrates were reduced with particle sizes ⩾5 mm (P<0.05), and apparent DOM for medusahead declined as particle size increased, a relationship not found for alfalfa or tall fescue hays (P<0.05). No effects (P>0.05) on digestibility parameters were observed by the addition of high-quality feeds to medusahead. Slow fermentation kinetics and a significant inhibitory effect of particle size on apparent digestibility of organic matter contribute to explain the low use of medusahead by sheep. Such inhibitory effect may also underlie the lack of positive associative effects observed during the study.

Seasonal Changes in the Chemical Composition of &lt;em&gt;Aspilia Africana&lt;/em&gt; Plant Grown in Nigeria

The aim of the study was to evaluate the effects of season on the chemical composition of <em>Aspilia Africana</em> leaf over a 12-month period. Biomass yield, proximate and mineral compositions were analyzed. Data collected were subjected to ANOVA in a completely randomized design using SAS software package. Post hoc analysis was conducted at 5% significance using the Duncan multiple range test. Five seasons (late dry, early rainy, peak rainy, late rainy and early dry) and three stages of plant maturity (growing, blooming and aging) were identified. Results showed no effect (p>0.05) of season on the proximate composition (except for moisture and crude ash) and fibre fractions of <em>Aspilia Africana</em> leaf but mineral concentrations were influenced (p<0.05) by season. Crude protein and ash contents were higher during the rainy season but declined with the inception of the dry season while, crude fibre and its fractions were higher during the dry season. Calcium, zinc and phosphorus concentrations were highest during the peak rainy season then decline gradually as dry season progressed. Correlation result showed that an increased biomass yield led to increased (p<0.05) crude protein content with decreased crude fat, moisture and ash contents. Though biomass yield was higher between the late rainy and early dry seasons, results showed that there was no temporal variations in the nutrient composition of <em>Aspilia Africana</em> leaf during the 12-month study. Therefore, <em>Aspilia Africana</em> plant could be a valuable feed resource for all year fodder production.

Overexpression of TaNAC2D Displays Opposite Responses to Abiotic Stresses between Seedling and Mature Stage of Transgenic Arabidopsis.

Environmental stresses frequently affect plant growth and development, and many genes have been found to be induced by unfavorable environmental conditions. Here, we reported the biological functions of TaNAC2D, a stress-related NAC (NAM, ATAF, and CUC) gene from wheat. TaNAC2D showed transcriptional activator activity in yeast. TaNAC2D-GFP fusion protein was localized in the nucleus of wheat mesophyll protoplasts. TaNAC2D transcript abundance was significantly induced by NaCl, PEG6000, and abscisic acid (ABA) at seedling stage, and repressed by NaCl and PEG6000 at mature plant stage. When TaNAC2D was introduced into Arabidopsis, the 35-day-old soil-grown TaNAC2D-overexpression (TaNAC2D-OX) plants displayed slower stomatal closure, higher water loss rate, and more sensitivity to salt and drought stresses compared with WT plants. In contrast, TaNAC2D-OX seedlings, grown on 1/2 MS medium supplemented with different concentrations of NaCl, Mannitol, and MV, had enhanced tolerances to salt, osmotic and oxidative stresses during seed germination and post-germination periods. The opposite stress-responsive phenotypes of transgenic Arabidopsis were consistent with the expression patterns of TaNAC2D in wheat. Moreover, under high salinity and dehydration conditions, three marker genes, including NCED3, RD29A, and RD29B, were down-regulated in 35-day-old TaNAC2D-OX plants grown in soil and up-regulated in 14-day-old TaNAC2D-OX seedlings grown on 1/2 MS medium. Our results suggest that the change in growth stages and environmental conditions may regulate TaNAC2D’s function.

Arabidopsis AtNAP functions as a negative regulator via repression of AREB1 in salt stress response.

AtNAP , an Arabidopsis NAC transcription factor family gene, functions as a negative regulator via transcriptional repression of AREB1 in salt stress response. AtNAP is an NAC family transcription factor in Arabidopsis and is known to be a positive regulator of senescence. However, its exact function and underlying molecular mechanism in stress responses are not well known. Here, we investigated functional roles of AtNAP in salt stress response. AtNAP expression significantly increased at the seedling stage, with higher expression in both shoots and roots under NaCl, mannitol, and ABA treatments. T-DNA insertional loss-of-function mutants of AtNAP were more tolerant to salt stress than wild type (WT), whereas AtNAP-overexpressing transgenic plants (OXs) were more sensitive to salt stress than WT during germination, seedling development, and mature plant stage. Transcript levels of stress-responsive genes in the ABA-dependent pathway, such as AREB1, RD20, and RD29B, were significantly higher and lower in atnap mutants and AtNAP OXs, respectively, than in WT under salt stress conditions, suggesting that AtNAP might negatively regulate the expression of those genes under salt stress conditions. Indeed, AtNAP repressed the promoter activity of AREB1 under normal and salt stress conditions. These results indicate that AtNAP functions as a negative regulator in the salt stress response. Our results, together with previous studies, suggest that AtNAP functions as a negative regulator in osmotic stress responses, whereas it functions as a positive regulator in senescence.

Expression of a grape (Vitis vinifera) bZIP transcription factor, VlbZIP36, in Arabidopsis thaliana confers tolerance of drought stress during seed germination and seedling establishment

Drought is one of the most serious factors that limit agricultural productivity and there is considerable interest in understanding the molecular bases of drought responses and their regulation. While numbers of basic leucine zipper (bZIP) transcription factors (TFs) are known to play key roles in response of plants to various abiotic stresses, only a few group K bZIP TFs have been functionally characterized in the context of stress signaling. In this study, we characterized the expression of the grape (Vitis vinifera) group K bZIP gene, VlbZIP36, and found evidence for its involvement in response to drought and the stress-associated phytohormone abscisic acid (ABA). Transgenic Arabidopsis thaliana lines over-expressing VlbZIP36 under the control of a constitutive promoter showed enhanced dehydration tolerance during the seed germination stage, as well as in the seedling and mature plant stages. The results indicated that VlbZIP36 plays a role in drought tolerance by improving the water status, through limiting water loss, and mitigating cellular damage. The latter was evidenced by reduced cell death, lower electrolyte leakage in the transgenic plants, as well as by increased activities of antioxidant enzymes. We concluded that VlbZIP36 enhances drought tolerance through the transcriptional regulation of ABA-/stress-related genes.

Downy Mildew Disease Progress in Resistant and Susceptible Cucumbers Tested in the Field at Different Growth Stages

Downy mildew, caused by the oomycete pathogen Pseudoperonospora cubensis (Berkeley &amp; Curtis) Rostov, is a major foliar disease of cucumber. Ten years after the reemergence of P. cubensis, downy mildew continues to be a major threat to cucumber production in the United States. Cucumber accessions with high levels of resistance have been identified. Development of cultivars with high levels of resistance remains an important objective of cucumber breeding programs. We tested a set of cucumber cultigens, including highly resistant PI accessions and susceptible control lines, to observe the effect of plant age on resistance. Cultigens responded differently to disease across plant developmental stages. In general, older plants had more disease symptoms, even those classified as resistant, such as PI 197088. However, PI 330628 and PI 605996 held their resistance even at late developmental stages. It is possible that these lines were resistant at late stages due to other factors, such as their rapid, indeterminate growth, that allows them to outgrow the disease. However, although PI 197088 appears to have a rapid, indeterminate growth habit, it did not have more resistance at later stages of plant maturity. Regardless of the mechanism involved, plant breeders should use the genetic resistance in PI 330628 and PI 605996 over PI 197088.

Effects of initial density, nutrient, and water level regime on the seedling survival and growth of Typha orientalis Presl

Seedlings’ successful establishment is of importance in the preemption process of pioneers in wetlands. Although Typha orientalis Presl has been reported as a pioneer in Asia countries, studies on the seedling phase of T. orientalis are not available yet. A mesocosm experiment was conducted to understand the effects of biotic (initial density) and abiotic (nutrient and water level regime) factors on the seedling survival and growth of T. orientalis. Most seedlings survived under low initial density (93.8%) and eutrophic (95.5%) rather than high initial density (64.3%) and ombrotrophic (62.5%). Seedlings under low initial density, eutrophic, and flooded conditions showed relatively higher growth in shoot height. The final number of ramets showed an adverse tendency compared to the survival rate and shoot height particularly depending on the water level regime. T. orientalis compensated its biomass production with producing less but longer shoots under the flooded condition, indicating the phenotypic plasticity of T. orientalis as a deep water species. However, the compensation seemed to be guaranteed only under the condition of sufficient nutrients. Asian T. orientalis seemed not to be a pioneer but a weak-competitor not only in mature plant stage but also in juvenile seedling stage unless sufficient nutrients are guaranteed.

Monitoring of Rhizosphere Bacterial Communities in Soil with Sewage Sludge Addition Using Two Molecular Fingerprinting Methods: Do These Methods Give Similar Results?

Abstract In this study, bacterial genetic diversity from the rhizosphere of barley and wheat were studied. The plants were sown in pots with aliquot amount of 15 t/ha concentration of soil additive derived from sewage sludge and agricultural by-products represented by wastes from grain mill industry and crushed corn cobs. The plants sown in pots without the addition of soil additive represented control samples. The rhizosphere samples were collected on two dates (plant flowering and maturity) and the composition of bacterial communities were detected using two molecular fingerprinting methods – automated ribosomal intergenic spacer analysis (ARISA) and terminal restriction fragment length polymorphism (T-RFLP). Microbial biomass expressed as the amount of metagenomics DNA was higher in soils with addition of soil additive, except during maturity stage in barley rhizosphere. Nevertheless, statistically significant differences between control and sludge samples were not detected in any case. Similarly, no changes were detected in the composition of bacterial community between control and sludge samples in barley and wheat rhizosphere by using cluster analysis. Only minor temporal changes in the composition of bacterial community between flowering and maturity periods were observed. These changes were related to the samples collected in the plant maturity stage. In this stage, plants were completely mature and their impact on the rhizosphere bacterial communities in the form of root exudates was limited. Statistically significant differences between ARISA and T-RFLP methods were detected in all measured values of diversity indices. Despite these differences, both methods gave results leading to similar conclusions.

Expression of a grape bZIP transcription factor, VqbZIP39, in transgenic Arabidopsis thaliana confers tolerance of multiple abiotic stresses

The basic region/leucine zipper (bZIP) transcription factors are known to play key roles in response to abiotic stress. In this study, a bZIP gene (VqbZIP39) was isolated from grape (Vitis quinquangularis) and constitutively expressed in Arabidopsis under control of the cauliflower mosaic virus 35S promoter. The transgenic Arabidopsis thaliana plants showed enhance salt and drought stress tolerance during seed germination and in the seedling and mature plant stages. Various physiological parameters related to stress responses were analyzed to gain further insight into the role of VqbZIP39 and it was found that osmotic stress caused less damage to the transgenic seedlings than to the corresponding wild type plants. This correlated with an increase in endogenous ABA content as a consequence of the constitutive over-expression of VqbZIP39, and the up-regulated expression of stress-inducible target genes associated with tolerance of drought, high-salt, and oxidative stresses. Our results suggest that the expression of VqbZIP39 in A. thaliana likely enhances the tolerance to multiple abiotic stresses through the ABA signaling pathway, and may therefore have a similar function in the response to abiotic stresses in grape.

Seasonal variation in the secondary chemistry of foliar and reproductive tissues of Delphinium nuttallianum

Plant secondary compounds are critical in affecting interactions between plants and their herbivores. The norditerpene alkaloids are secondary compounds in Delphinium (larkspur) species which are divided into two classes: the N-(methylsuccinimido) anthranoyllycoctonine (MSAL-type) and non MSAL-type, and are known to be toxic to herbivorous insects and livestock. Alkaloid concentrations were measured in a whole plant context in vegetative and reproductive tissues in Delphinium nuttallianum at different stages of plant maturity at two locations to explore how plant maturity affected alkaloid concentrations within a growing season. Alkaloid concentrations differed between vegetative and reproductive tissues, with vegetative tissues having significantly lower alkaloid concentrations than reproductive tissues. However, no systematic differences in alkaloid concentrations were observed at different plant maturity stages across the growing season. Based on the data we suggest that alkaloid allocation in different plant parts of D. nuttallianum is influenced by life history of the plant, consistent with plant defense theory. At one location, as pods mature the qualitative alkaloid composition changed through structural diversification of the alkaloids present. The ecological significance of this structural diversification awaits further exploration.

Chemical Composition and Antioxidant Activity of Essential Oils from Algerian Daucus Carota L. subsp. carota Aerial Parts

The essential oil content and their chemical composition of aerial part, flowers, and both leaves and stems of wild carrot growing in Algeria (Daucuscarota L. ssp. Carota) as well as aerial part at different plant maturity stages was examined. The qualitative and quantitative analyses of the essential oils were performed using GC, GC-MS and 13C-NMR. 57 compounds were identified representing more than 85% of the total oil in each sample. Generally, The main components in the essential oil of aerial part in full flowering were α-pinene (21.3 %) and asarone (18.4 %), while the essential oils isolated from flowers and both leaves and stems were dominated by asarone (9.8, 9.4 %), α-pinene(10.9, 10.6 %) and β-bisabolene (7.6, 9.3 %) respectively. Before flowering and after flowering the major constituents were the linalool (11.2 %) and asarone (20.8 %) respectively. The antioxidant potential of the different essential oils was evaluated using the inhibition of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. All essential oils showed a relatively weak antioxidant capacity. The results obtained from the essential oils of the aerial part in full flowering 50 showed the strongest activity against DPPH than the other samples (IC =96,4±1.1 µg/ml).

Grazing preference of Merino sheep for naturalized annual clover species relative to commonly sown clover species

Selective grazing of white clover (Trifolium repens) over grass species in temperate pastures results in reduced clover abundance and availability over time. Within sheep- and cattle-grazed dryland (<800 mm annual rainfall) hill and high country areas of New Zealand, naturalized unsown annual clover species show greater persistence and abundance over sown clovers. With a view to understanding legume abundance in these areas, Merino sheep grazing preference was investigated for pure swards of naturalized species Trifolium dubium, T. glomeratum, T. arvense and T. striatum and commonly sown species T. repens and T. subterraneum. The Chesson–Manly preference index was used to explore the hypothesis that grazing preference differs between these species and changes as plants mature. Herbage offtake was quantified at vegetative (mid–late spring; November) and reproductive (early summer; December) stages of plant maturity. Significant preference distinctions between species (P < 0·05) occurred in December, with relative preference ranging from 0·248 for T. repens to 0·065 for T. dubium. Reduced relative preference for naturalized species was related to decreasing nutritive value from spring to summer, reflecting increased stem and flower sward content. Relative preference was negatively related to increasing acid detergent fibre and neutral detergent fibre and positively related to greater crude protein and dry-matter digestibility. Naturalized annual clover species of lower grazing preference at reproductive maturity will benefit pasture sustainability via herbage and seed production and associated nitrogen-fixation inputs.

Evaluation of the virulence of Sclerotium rolfsii isolates on Arachis hypogaea and screening for resistant genotypes in greenhouse conditions

Summary Sclerotium rolfsii is a soil borne pathogen responsible for root and stem rot on a wide range of crops. This study was conducted to identify the virulence of different S. rolfsii isolates on a susceptible local peanut germplasm and determine the resistance of 20 peanut genotypes to the most virulent isolate and also the relationship between virulence and mycelial compatibility groups (MCGs). Seventy eight isolates of this fungus from 10 host plants and six known MCGs were used in the experiment. The experiment was done in greenhouse conditions (25±5°C) using a complete randomized block design with three replications. Pots containing sterile soil (pH=6.7) were inoculated with barley seeds colonized by each isolate separately before being seeded with the peanut germplasm. Disease severity was assessed by scoring the wilting, yellowing or death of plants, mycelia or sclerotia production on the soil surface or on plant stem, stem area affected (%) and stem lesion length, at the stage of plant maturity. Also, shoot wet weight and plant height were recorded at this stage. According to the results of the pathogenicity tests, all of the isolates were virulent on the susceptible peanut germplasm and the virulence diff ered signifi cantly between the isolates (P≤0.01). There was no relationship between the virulence of the five groups of isolates identified in the present study and the MCGs. The peanut genotype 140, which was better than the others based on seed size, plant height and the canopy size, was also the most resistant one