Paul B. Cavers

PATTERNS OF CHANGE IN SEED WEIGHT OVER TIME ON INDIVIDUAL PLANTS

Seeds from individual plants of eight herbaceous species exhibited the same general pattern over a period of time; the largest seeds were produced first and then progressively smaller seeds ripened as the plants aged. The difference between the mean weight of the largest seeds and the mean weight of the smallest was significant (P < .05) for all the eight species. Such differences averaged as much as 25% for one species (Melilotus alba) and were much greater for the seeds of some individual plants within certain species. All eight species are short-lived weeds, all grew in London, Canada, and all but one were in naturally occurring populations. For some species (e.g., Diplotaxis tenuifolia) all individual plants exhibited more or less the same patterns of seed weight change over the season, but for other species (e.g., Onopordum acanthium) there were great differences between plants in seed weight patterns. In a separate study also made in London, Ontario, Canada, 10 spaced plants of Amaranthus retroflexus were grown in a garden free of interference from other plants. Ripe seeds were collected on seven occasions for each plant. With all plants there was a significant decrease in mean weight per 100 seeds over the growing season. Our results suggest that some differences in seed weight between populations reported by other authors could be partly or wholly accounted for by differences in the maturity of the plants being sampled. Further, the great differences between individuals with respect to seed weight patterns suggest that any comparisons of seed weight between populations should be based on collections from a large number of plants in each habitat.

Population Dynamics of the Perennial Herbs Plantago Major L. and P. Rugelii Decne

Demographic information about plant populations has accumulated over the last few years, and some generalizations are now possible from these data. Sarukhan & Harper (1973) used published information on the survivorship of several herbs and grasses from different geographic regions, and from their own studies on buttercups, to show that established plants of perennials, including Plantago lanceolatat (Sagar 1959), suffer approximately constant annual mortality, though the mortality rate varies between species. Mortality rates appear to be affected by environmental conditions in the year of germination and during subsequent years (Williams 1970; Antonovics 1972). This information has been used to prepare preliminary models of the regulation of plant populations (Harper & White 1971). The complete life cycle has rarely been assembled in a life table (Sharitz & McCormick 1973), and then may be useful for annual species only. Sarukhan & Harper (1973) recognized that mortality rates of perennials need not be constant. Although most survivorship curves for plant populations approximate to the Type II described by Deevey (1947), those for range grasses studied by Canfield (1957) were negatively skewed (Deevey type I) while those of grasses studied by Williams (1970) were slightly positively skewed (Deevey type III). The few studies available on the survivorship of populations of seedlings show that the mortality rate declines with age (Sharitz & McCormick 1973; Sarukhan & Harper 1973), eventually attaining a constant loss rate (Harper 1967; Hett & Loucks 1971; Hett 1971; Antonovics 1972; Thomas 1972). Mortality rates in populations of dormant seeds, like those for established plants, are usually fairly constant (Roberts 1962; Sarukhan 1974). Only two studies are known to us where differences in longevity, mortality, natality, and density were examined in closely related species under natural conditions. Sarukhan & Harper (1973) investigated the demography of Ranunculus repens, R. bulbosus and R. acris, and Thomas (1972) investigated the dynamics of Hieracium florentinum, H. floribundum, and H. pratense. Such taxonomically related species can live in the same area if the factors regulating the size of their populations, at any stage of the life cycle, are different (Harper et al. 1961). For example, Sagar (1959) showed that Plantago major, P. media and P. lanceolata could cohabit, in part, because seeds of each species had different requirements for germination.

Role of the pigmented seed coat of proso millet ( Panicum miliaceum L.) in imbibition, germination and seed persistence

Proso millet ( Panicum miliaceum L.) is both a crop and a weed in many parts of the world. The weedy biotypes exhibit a wide range of seed colours, but the strains with the most persistent seeds are distinguished by darker seeds. This paper compares the seed biology of a range of biotypes from Canada and demonstrates that darker seeds have heavier seed coats, imbibe and germinate more slowly, and suffer less imbibition damage (measured as electrolyte leakage). It is concluded that all these attributes contribute to the increased persistence in the soil of the dark-seeded weedy biotypes. Imbibition damage is widely implicated in poor emergence and low vigour of crop seeds, but has not previously been considered in the context of weed seed persistence.

The biology of Canadian weeds. 116. Echium vulgare L.

Echium vulgare L., known as blueweed or viper’s bugloss, is a blue or purple flowered biennial or short-lived monocarpic perennial herb found in every province in Canada. A naturalized weed of European origin, E . vulgare grows in highly disturbed are as, typically in soils of limestone or dolomite parent material. It is not competitive with crops, but serves as an alternate host for fungal pathogens and contains hepatotoxic alkaloids detrimental to livestock when consumed in large amounts. E. vulgare is a noxious weed in Nova Scotia, Quebec, Manitoba, Alberta and parts of British Columbia. Beneficial aspects include contributions to honey production and herbal medicine. Key words: Echium vulgare, blueweed, vipers bugloss, weed biology

In Vivo Optical Analysis of Quantitative Changes in Collagen and Elastin During Arterial Remodeling

Abstract Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P < 0.05) after treatment with anti-inflammatory agents, and plaque area decreased on comparison with saline-treated rabbits after stent implant or angioplasty (P ≤ 0.013). Excellent correlations for FEI with elastin and collagen I, III and IV content measured by IH (R2 ≥ 0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2 ≥ 0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites.

Variation in germination response within Scotch thistle, Onopordum acanthium L., populations matured under greenhouse and field conditions.

Abstract The effects of two maturation conditions (greenhouse and field) on germination percentages and rates were determined for cypselas (seeds) of Scotch thistle, Onopordum acanthium L. Four collections from each of three populations were tested in 1996 and 1997 (one of the same 1996 populations was used again in 1997, but two were different). Cypselas from all collections were incubated within three days of collection at 25˚C and 10˚C, for 14 hours light, and 10 hours dark, respectively. In general, cypselas that matured under warmer temperatures (greenhouse) germinated at higher percentages than those that matured under cooler temperatures (field). For example, in the Environmental Sciences Western (ESW) population at least five times as many cypselas from each greenhouse collection germinated than from the comparable field collection. Cypselas that matured early in the season were usually more germinable than those that matured later. However, field-produced cypselas from half of the populations had the opposite trend. Overall, all populations that matured under warmer conditions germinated at higher percentages than those matured under cooler conditions. Germination rates showed no clear trends among collections or between greenhouse- and field-matured cypselas.

Parental Effects on Spatial Patterns of Plants: A Contingency Table Approach

We examined the effects of plant size and seed production on the seed shadows and mature offspring patterns of isolated parent plants of six biotypes of Panicum miliaceum. Spatial patterns of offspring were summarized in contingency tables that were classified by distance and orientation from the parent. These tables were analyzed with reciprocal averaging ordination and dispersion profile analysis. The first and second com- ponents of the ordination of a detailed data set reflected the distance and orientation, respectively, of the seed shadows from their parents. The mean infructescence height and the mean lateral spread of the parent plants were correlated with the first component of the ordination while the orientation of the parent plants was correlated with the second component. Little support was found for the hypothesis that biotypes with high numbers of seeds produced should have greater dispersal ability. However, when the individuals were grouped by seed production, irrespective of biotype, the more fecund groups had more distant cohorts of mature offspring. This latter trend was partly attributable to the increased density-dependent mortality near fecund parent plants and partly attributable to the larger sizes and hence larger seed shadows of these parents.

Interpopulation and interyear variation in germination in Scotch thistle, Onopordum acanthium L., grown in a common garden: Genetics vs environment

Germination patterns were studied among three populations of Scotchthistle, Onopordum acanthium L. (Asteraceae). Cypselas(seeds) were collected twice during the growing season for four consecutiveyears (1996–1999) from plants grown in the same location, theEnvironmental Sciences Western Field Station (ESW) near London, Ontario.Cypselas from 1996 came from plants that had been transplanted as rosettes fromtheir original sites to ESW, while those for 1997–1999 came from plantsgrown from cypselas collected in 1996. Fresh cypselas were put to germinate at25 °C, 14 hlight/10 °C, 10 h dark for 55 days.Consistent and significant differences in final germination percentages amongpopulations were obtained over the four years. There were also differencesbetween collections within populations in 1996 and 1998. In addition, the finalgermination percentage (collectively) differed widely among years. There was agreater than 30 percent correlation between germination percentage and meandaily maximum temperature during cypsela maturation. Since there were similardifferences among populations every year, it appears that germination patternsof O. acanthium populations have a genetic basis as wellasan environmental one.

Response of common lambsquarters (Chenopodium album) to glyphosate application timing and rate in glyphosate-resistant corn

Field studies were conducted over 3 yr at two locations to evaluate the effect of glyphosate rate and time of application on common lambsquarters control, density, dry weight, seed production, and the number of seedlings emerging from soil cores taken the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when common lambsquarters were at the two-, four-, or six-leaf stage of growth. Nicosulfuron was applied to all experimental areas to control annual grasses. Visual estimates of percent control increased, whereas density, dry weight, seed production, and seedlings emerging the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the glyphosate rate above 450 g/ha had little effect on these parameters. Corn yield declined only at glyphosate rates below 450 g/ha. Time of application had no effect on common lambsquarters control and corn yield because little emergence occurred after the first glyphosate application. There was no interaction between glyphosate rate and time of application for any of the parameters evaluated. In these studies, the application of glyphosate at half the manufacturers registered rate provided control of common lambsquarters equivalent to the full-registered rate with no measured increase in weed seed production and no increase in weed seedlings emerging from soil cores the year after herbicide application. The results suggest that in some cases the use of reduced herbicide rates can provide excellent weed control and maintain crop yields, while reducing the cost of production and the environmental impact of herbicides. The use of extremely low rates (112 or 225 g/ha), however, resulted in reduced corn yields, increased common lambsquarters seed production and seedlings emerging the year after application, and possibly increased weed management costs in subsequent years. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L. ‘Pride G4286’, ‘DeKalb 493RR’. Additional index words: Reduced rates, weed control, weed seed production. Abbreviation: DAA, days after application.

Isolation and structural characterization of a water-soluble germination inhibitor from Scotch thistle (Onopordum acanthium) cypselas.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.