Mahesh K. Upadhyaya

Phytotoxicity of clove oil and its primary constituent eugenol and the role of leaf epicuticular wax in the susceptibility to these essential oils

Abstract Herbicidal activities of clove oil and its primary constituent eugenol on broccoli, common lambsquarters, and redroot pigweed and the role of crystalline leaf epicuticular wax (LEW) in susceptibility and retention of these essential oils were studied. Clove oil (2.5%) and eugenol (1.5%) were applied to leaves of greenhouse-grown broccoli, common lambsquarters, and redroot pigweed seedlings and effects on seedling growth and leaf cell membrane integrity were studied. Compared with eugenol, clove oil caused greater inhibition of seedling growth in all species. Both eugenol and clove oil caused greater loss of membrane integrity and inhibition of seedling growth in redroot pigweed, which has no crystalline LEW, compared with common lambsquarters, which has a thick layer of crystalline LEW. In broccoli seedlings with LEW, clove oil caused greater inhibition of growth than eugenol. Both clove oil and eugenol caused greater electrolyte leakage from broccoli leaves without LEW than in the leaves with LEW. Removal of LEW increased electrolyte leakage, an indicator of cell membrane damage, by 97% in eugenol-treated and 26% in clove oil–treated broccoli leaves. Susceptibility of broccoli seedlings and possibly some weed species may, therefore, be affected by factors (e.g., genetic, environmental) that influence the amount of LEW. Although the presence of LEW greatly reduced the retention of the essential oil solutions, there was no significant difference between the retention of clove oil and eugenol solutions, indicating that differences in their phytotoxicity to broccoli leaves was not due to differential foliar retention. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE; clove, Syzygium aromaticum (L.) Merr. & Perr.; purple sprouting broccoli, Brassica oleracea var. italica.

Postharvest moisture loss characteristics of carrot (Daucus carota L.) cultivars during short-term storage

Abstract Differences in moisture loss characteristics among carrot cultivars Imperator Special 58, Gold Pak 28, Caro-pride, Paramount, Eagle, Celloking, Top Pak and Caro-choice during short-term storage at 13 °C and at either 80% or 35% relative humidity were investigated. Experiments were conducted over two years with an early and late harvest in each year. Moisture loss was significantly greater when carrots were stored at low relative humidity compared to high relative humidity. Consistent cultivar differences in moisture loss characteristics were observed only in the late-harvested carrots at low relative humidity. Cultivars with higher specific surface area and relative electrolyte leakage, and lower water and osmotic potentials exhibited high moisture losses. Regression analysis, however, showed that moisture loss differences among cultivars were mainly associated with the specific surface area of the root.

The biology of Canadian weeds. 110. Tragopogon dubius Scop., Tragopogon pratensis L., and Tragopogon porrifolius L.

Several types of salsify or goats-beard, Tragopogon species (Asteraceae), are found in Canada as biennial or monocarpic perennial herbs with yellow or purple flowers. Introduced from Eurasia, T. pratensis and T. dubius have become established in all provinces in Canada except Newfoundland and the territories. Tragopogon porrifolius tends to be more local, but is also found in southern areas of most provinces. Tragopogon species hybridize readily, and the tetraploid species T. mirus and T. miscellus have resulted from crosses among the three diploid Tragopogon species in North America. Salsify species produce relatively large umbrella-like pappuses which promote long-distance dispersal. These species also invade rangeland, and are considered noxious weeds in some parts of Canada. Key words: Tragopogon dubius, Tragopogon pratensis, Tragopogon porrifolius, Tragopogon mirus, Tragopogon miscellus, salsify, goats-beard, Asteraceae, Compositae, hybridization, weed biology

Mechanism of seed dormancy in Cynoglossum officinale L.

Summary Roles of seed coat and methanol-extractable phenolic substances in regulation of Cynoglossum officinale L. seed dormancy were studied. Removal of the seed coat resulted in nearly complete germination of innately dormant seeds. The seed coat did not substantially retard water uptake nor did it contain any water soluble germination inhibitor, but the O 2 uptake of seeds increased approximately six-fold upon removal of the seed coat. The increase in O 2 uptake induced by seed-coat removal was due to both an increase in seed respiration (measured by CO 2 evolution) and a high level of non-respiratory O 2 consumption. C. officinale seeds contained high levels of phenolic substances, and seed extracts showed high polyphenol oxidase activity. Analysis of the pattern of methanol-extractable phenolic substances, however, showed no significant quantitative or qualitative correlation between changes in specific phenolic compounds and seed germination induced by stratification or seed-coat removal. It is concluded from this study that C. officinale seed coats inhibit seed germination by controlling O 2 availability to the embryo.

Phytotoxic Activity of Clove Oil, Its Constituents, and Its Modification by Light Intensity in Broccoli and Common Lambsquarters (Chenopodium album)

Abstract Herbicidal activity of clove oil and its main constituents eugenol, &bgr;-caryophyllene, and &agr;-humulene was studied by measuring their effects on cell membrane integrity in broccoli and common lambsquarters plants at the three- and nine-leaf stage, respectively. Roles of essential oil constituents in the overall phytotoxicity of clove oil, dose-response (10 to 160 mM) relationships of their phytotoxicity, and the effect of light intensity on phytotoxicity of clove oil and eugenol were studied. Most of the phytotoxicity of clove oil (2.5% solution) was due to eugenol, its largest constituent. &bgr;-caryophyllene and &agr;-humulene played little or no role. Dose-response relationships showed that at equimolar concentration, eugenol was the most phytotoxic essential oil constituent of the clove oil. On a per unit biomass basis, membrane damage in response to clove oil and eugenol sprays decreased with increasing light intensity. This suggests that efficacy of essential oil in causing plant damage could be affected by light intensity experienced by plants prior to the oil spray. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; Broccoli, Brassica oleracea L. var. italica Plenck, purple sprouting broccoli.

Influence of preharvest water stress on postharvest moisture loss of carrots (Daucus carota L.)

SummaryTo understand the relationship between preharvest water stress and postharvest moisture loss, carrot cvs Eagle and Paramount were grown in muck soil in 6 1 pots (eight carrots per pot) in a greenhouse at the University of British Columbia. The plants were watered to field capacity every second day for 5.5 months prior to receiving 100,75,50 and 25% field capacity water stress treatments (for 4.5 weeks), henceforth referred to as low, medium, high and severe water stress respectively. Postharvest moisture loss of carrots stored at 13μC and 32% relative humidity was monitored every second day for three weeks. The percent moisture loss was low in the low water stressed, and high in the severely water stressed carrots of both cultivars. Root crown diameter, weight, and water and osmotic potentials decreased, whereas specific surface area and relative solute leakage increased with increasing preharvest water stress. The results show that carrots adjust to water stress by lowering water and osmotic poten...

The Biology of Canadian Weeds. 149. Rumex acetosella L.

Stopps, G. J., White, S. N., Clements, D. R. and Upadhyaya, M. K. 2011. The Biology of Canadian weeds. 149. Rumex acetosella L. Can. J. Plant Sci. 91: 1037-1052. Rumex acetosella L., sheep sorrel, is a perennial herb originating from Europe and southwestern Asia, now found in at least 70 countries worldwide. A common weed, it appears in grasslands, pastures, rangelands, waste areas, and along roadsides across North America. It frequently occurs as a weed in lowbush blueberry fields in Atlantic Canada, particularly in Nova Scotia. Rumex acetosella thrives on poor, acidic, and disturbed soils across a broad range of climatic conditions. A persistent seed bank and vegetative reproduction from creeping roots contribute to the ability of R. acetosella to tolerate various methods of control including certain herbicides, fire, and tillage. Tart-tasting leaves, rich in vitamin C have led to the use of R. acetosella in European and North American cultures as both a source of food and a component of herbal medicines. Excessive consumption of the leaves, which contain oxalic acid, can be poisonous to horses and sheep. In addition, R. acetosella is a possible host of the tomato spotted wilt virus, which is detrimental to a variety of vegetable crops.

Potassium nutrition and postharvest moisture loss in carrots (Daucus carota L.)

SummaryThe effect of potassium (K) nutrition on the shelf life of carrots (Daucus carota L., cv. Paramount) was studied using a hydroponic system involving rockwool slabs as an inert support. Carrots were grown for 192 d under greenhouse conditions and with 0, 0.1,1.0,10 and 15 mM K supplied in the nutrient medium. Increase in K concentration in the nutrient medium up to 1 mM decreased postharvest moisture loss. Carrot root weight and tissue K concentration increased, and water potential, osmotic potential and relative solute leakage decreased with increasing K concentration up to 1 mM. Concentrations greater than 1 mM had little or no additional effect on postharvest moisture loss, root water and osmotic potentials and relative solute leakage. Root weight did not increase above 10 mM K. The best subset model obtained by backward stepping and the optimum Mallow’s coefficient showed that carrot root weight and relative solute leakage accounted for most of the variation in moisture loss. Root weight correla...

Allelopathic Influence of Houndstongue (Cynoglossum officinale) and Its Modification By UV-B Radiation

Influence of aqueous leaf extracts, leaf residue, and leached-leaf residue of houndstongue, a noxious rangeland weed, on seedling emergence of forage grasses was studied. Ultraviolet-B (UV-B) effects during houndstongue growth on subsequent germination and growth-inhibitory activity of leaf extracts were investigated. Addition of glasshouse-grown houndstongue leaf extract to mineral soil decreased emergence of crested wheatgrass by 13% and prairie junegrass by 20% at 14 d after sowing. Idaho fescue emergence was unaffected. Incorporation of houndstongue leaf- and leached-leaf residue into soil (0.4 g residue : 20 g soil) delayed emergence of forage grasses. At 14 d after sowing, houndstongue leaf residue spread on the soil surface (0.2 g residue : 20 g soil) tended to inhibit seedling emergence more than leaf residues incorporated into soil. In separate experiments, houndstongue plants were grown at 0, 4, 7, and 11 kJ/m2/d biologically effective UV-B radiation for 6 wk, and leaf extracts (0.5, 1, 2, and 4% wt/v) were prepared. Exposure of houndstongue to increasing UV-B dose during plant growth generally increased the inhibitory activity of their leaf extract on prairie junegrass germination. Crested wheatgrass and Idaho fescue seedlings incubated in extracts of houndstongue leaves exposed to UV-B, compared with leaves grown in a UV-B–free environment, had decreased root lengths. Leaf extracts of plants exposed to elevated UV-B levels had higher absorbance at 300 nm, indicating greater concentration of UV-B–absorbing compounds. This study suggests houndstongue leaf extracts and residues inhibit seed germination and seedling emergence and that UV-B may enhance their allelopathic influence on some forage grasses. Field studies are needed to confirm the allelopathic influence of houndstongue under rangeland conditions. Nomenclature: Houndstongue, Cynoglossum officinale L. CYWOF, crested wheatgrass, Agropyron cristatum (L.) Gaertn., alternate binomial, Elymus wawawaiensis J. Carlson & Barkworth var. Secar, Idaho fescue, Festuca idahoensis Elmer var. Joseph, prairie junegrass, Koeleria macrantha (Ledeb.) J.A. Schultes

Ultraviolet-B radiation and plant competition: experimental approaches and underlying mechanisms.

Abstract Under realistic stratospheric ozone depletion scenarios, ultraviolet-B radiation (280–320 nm) (UV-B) influences plant morphology and plant competitive interactions. Influence of UV-B on plant competition can be studied using a variety of experimental and analytical approaches including inverse yield-density models and allometric, neighborhood or size-structure analyses that provide links between plant and ecosystem responses. These approaches differ in their abilities to extract information regarding competitive interactions and their morphological underpinnings. Only a limited number of studies have been carried out to investigate UV-B effects on plant competition, and most of these have used the replacement series approach, which has received much criticism. Nonetheless, results to date indicate that slight differences in UV-B–induced morphological responses of species grown within associations can alter canopy structure thereby influencing photosynthetically active radiation (PAR) interception and relative competitive ability. Because the response of individuals of the same species is expected to be uniform, UV-B may influence intraspecific competition less than interspecific competition. Before we can make clear generalizations and predictions concerning the effects of this radiation on plant competition, an understanding is crucial of the mechanisms underlying UV-B–induced shifts in competitive interactions by assessing competition over time.