bluuebunny/crossref_metadata_2025_split huggingface dataset:
Germination responses of buried seeds of Capsella bursa‐pastoris exposed to seasonal temperature changes
Authors: BASKIN J. M. , BASKIN Carol C. 
Published: July 2006

SummaryBuried seeds of Capsella bursa‐pastoris exhibit an annual conditional dormancy/non‐dormancy cycle. Seeds after‐ripen during summer and remain non‐dormant during autumn and winter. Seeds enter conditional dormancy in early spring, first showing marked decreases in ability to germinate at high (35/20°C) and then at lower (30/15, 25/15°C) temperatures. Seeds do not lose the ability to germinate to high percentages at March (15/6°C) and April (20/10°C) temperatures in March and April. Thus, C. bursa‐pastoris is a facultative winter annual, germinating in both autumn and spring if seeds are exposed to light. However, because some seeds retain the ability to germinate at 30/15 and 25/15°C, they could do so throughout the growing season in regions with cool, moist summers. Conditional dormancy developed in all seeds given 12 weeks at 5°C and subsequently kept for 4 weeks each at March (15/6°C), April (20/10°C) and May (25/15°C) temperatures. Thus, seeds of C. bursa‐pastoris enter conditional dormancy as temperatures increase in spring.
Changes of weed seed bank parameters according to species, time and environment
Authors: CHAUVEL B. , GASQUEZ J. , DARMENCY H. 
Published: July 2006

SummaryThe soil seed bank of weeds was studied in two fields, The first was not treated with herbicides for nine years and had a high weed seed density. The second was treated every year and had a low weed seed density. A study of the probability distributions of the weed seed populations in the soil showed that they were aggregated and appeared to have the negative binomial distribution. Transformations were therefore used to normalize the original values in order to compare the distributions and amounts of different species at different times and locations. However, normalizations were possible only with species having an average of at least two seeds per core. With the normalized values, it was observed that some species had similar statistical distributions in the same field. However, the distribution of a species may vary throughout the field, in time, and according to herbicide and culture rotations.
Uptake and metabolism of hexazinone in Rubus hispidus L. and Pyrus melanocarpa (Michx.) Willd
Authors: JENSEN K. I. N. , KIMBALL E. R. 
Published: July 2006

Summary:Rooted cuttings of Pyrus melanocarpa (Michx.) Willd. had a 3.5‐fold greater tolerance to soil‐applied hexazinone than those of Rubus hispidus L. in a greenhouse trial. R. hispidus accumulated four times more 14C‐label in the foliage following root uptake of 14C‐hexazinone than P. melano‐carpa. Here, the greater uptake and susceptibility of R. hispidus was related to its greater root:fol‐iage (weight) ratio compared to the tolerant P. melanocarpa. However, in whole plant metabolism studies employing younger plants there were no differences in 14C accumulation in the leaves. Here 14Chexazinone was converted to a number of hydroxylated and/or demethylated triazinone metabolites in both species following vacuum infiltration into leaf disks and root sections, or following root uptake in whole plants. A major difference in metabolism between the two species was the greater formation of the mono demethylated metabolite, B, [3‐cyclohexyl‐6‐methylamino‐l‐methyl‐l,3,5‐triazine‐2,4‐dione] in P. melanocarpa which may also contribute to its greater tolerance. A loss of total 14Clabel from all plant parts with time may reflect cleavage of the 14C‐ring‐labelled herbicide.
Effects of N, P and K on Striga asiatica (L.) Kuntze seed germination and infestation of sorghum
Authors: RAJU P. S. , OSMAN M. A. , SOMAN P. , PEACOCK J. M. 
Published: July 2006

Summary:Sorghum (Sorghum bicolor (L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kg−1 soil. With an increase of soil N, the Striga asiatica (L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induce Striga seed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1−1 range. The sorghum root exudate was considerably more active at 0 mg N 1−1, than at 30 mg N 1−1, and the stimulant produced at 150 mg N 1−1 failed to induce Striga seed germination. Presence of N in the growth medium considerably reduced the effectiveness of the stimulating substance produced by sorghum roots, whereas K promoted stimulant activity only in the absence of N. The presence or absence of P in the growth medium did not affect Striga seed germinability, probably due to the inability of this element to interfere with the production or activity of the stimulating substance from the host plants. It can be concluded, therefore, that sorghum plants seem to produce active root exudate only in conditions of N deficiency.
Competition between Silene vulgaris (Moench) Garcke and alfalfa (Medicago sativa L.)
Authors: WALL D. A. , MORRISON I. N. 
Published: July 2006

Summary:Growth indices describing the nature of the competitive relationship between Silene vulgaris and alfalfa during crop establishment were determined from experiments conducted outdoors in southem Manitoba in 1986 and 1987. The results of the experiments indicated that alfalfa dry matter yields were influenced more by intra‐ than interspecific competition. In comparison S. vulgaris was affected more by interspecific competition. Replacement diagrams and aggressivity indices both demonstrated that alfalfa and S. vulgaris were the aggressor and sub‐ordinate species, respectively. Relative replacement rates for alfalfa versus S. vulgaris were significantly greater than unity, indicating that alfalfa exerted a greater replacement pressure on S. vulgaris than did S. vulgaris on alfalfa. Over time alfalfa could be expected to replace S. vulgaris as the dominant species within a population. Barley was more competitive than alfalfa with S. vulgaris. Not only was S. vulgaris shoot dry weight reduced more by barley than by alfalfa during the establishment year, but fewer S. vulgaris seedlings emerged the following year in plots that had been seeded to barley than in those that had been seeded to alfalfa.
Environmental factors affecting the herbicidal activity of DPX‐A7881
Authors: BUCHANAN F. S. , GILLESPIE T. J. , SWANTON C. J. 
Published: July 2006

Summary:DPX‐A7881, methyl 2‐[(4‐ethoxy‐6‐methyl‐amino‐1, 3, 5‐triazin‐2‐yl)carbamoylsulphanoyl] benzoate, is a sulfonylurea herbicide being developed in Canada and Europe for post‐emergence broadleaf weed control in spring and winter rapeseed. Growth room studies were conducted to determine the environmental factors affecting the herbicidal activity of DPX‐A7881 applied post‐emergence on winter rapeseed (Brassica napusu L. ‘Tandem’) and on a closely related weed species, Sinapis arvensis L. (wild mustard).Laboratory tests were carried out at tempera tures ranging from 2–26°C, at relative humidities from near 40% to >95%, with rain‐free periods from 0.25–8 h after herbicide application, at soil moisture contents from 50–200% of field capacity, and with irradiances from 23–450 μEm−2s−1 Significant control of S. arvensis was demonstrated for all treatments except under poor growing conditions at the lowest temperatures and irradiances tested. After two weeks' exposure to each of the tem perature treatments, the herbicide maintained control of S. arvensis during a subsequent week of favourable growing conditions. Relative humidity, soil moisture or simulated rainfall did not significantly alter the herbicidal activity of DPX‐A7881 on S. arvensis. DPX‐A7881 showed a high degree of crop safety on B. napus. The herbicide did not significantly reduce the dry weights of B. napus grown under any of the environmental conditions tested.
A simple model of crop loss by weed competition from early observations on relative leaf area of the weeds
Authors: KROPFF M. J. , SPITTERS C. J. T. 
Published: July 2006

Summary:A new simple empirical model for early prediction of crop losses by weed competition was introduced. This model relates yield loss to relative leaf area of the weeds shortly after crop emergence using the relative damage coefficient q as the single model parameter. The model is derived from the hyperbolic yield density relationship and therefore accounts for the effects of weed density. It is shown that the model also accounts for the effect of different relative times of weed emergence. A strong advantage of the approach is that it can be used when weeds emerge in separate flushes.The regression model described experimental data on sugar‐beet – lambsquarters (Beta vulgaris L. –Chenopodium album L.) and maize‐barnyard grass (Zea mays L. –Echinochloa crus‐galli L.) competition precisely. The model describes a single relationship between crop yield loss and relative leaf area of the weeds over a wide range of weed densities and relative times of weed emergence. Possibilities for scientific and practical application of the model are discussed.
Attempts to transfer paraquat resistance from barley grass (Hordeum glaucum Steud.) to barley and wheat
Authors: ISLAM A.K.M.R. , POWLES S.B. 
Published: July 2006

Summary:A paraquat‐resistant biotype of barley grass (Hordeum glaucum Steud.) was hybridized with barley and wheat in an attempt to transfer paraquat resistance to these crops. Although hybridizations with barley did not result in the production of a plant, cytological evidence of chromosome elimination of one parent, presumably of H. glaucum, was obtained from squash preparations of young F1 embryos. Hybridizations of wheat with both diploid and tetraploid H. glaucum resulted in the production of wheat haploids. These results indicate that it may not be possible to transfer paraquat resistance to barley and wheat using conventional hybridization techniques.
The activity and mobility of triasulfuron in soil as influenced by organic matter, duration, amount and frequency of rain
Authors: OPPONG F. K. , SAGAR G.R. 
Published: July 2006

Summary: Résumé: ZusammenfassungThe influence of different levels of organic matter and of the duration, amount and frequency of rainfall on the biological activity and mobility of triasulfuron were investigated. Biological activity was inversely related to the organic matter content of the soil. Movement of the herbicide down the soil profile, assessed by bioassay, was inversely related to the organic matter content of the soil, and the amount and frequency of rain directly influenced the extent of leaching of the herbicide. Triasulfuron was moved to a depth of at least 22.5 cm when soil columns were exposed to a total of 528 mm of natural rainfall over a period of 6 months. The presence of phytotoxic levels of the herbicide in the surface layers of soil columns 6 months after exposure to outdoor temperatures and natural rainfall suggested that triasulfuron may persist in soils for relatively long periods. Influence de la matiére organique, et de la durée, niveau et fréquence des précipitations sur l'activité et la mobilité du triasulfuron dans le sol L'influence de différentes teneurs en matière organique et de la durée, quantité et fréquence des pluies sur l'activité biologique et la mobilité du triasulfuron a étéétudiée. L'activité biologique est inversement liée avec la teneur enmatière organique du sol. Le mouvement descendant de l'herbicide dans le profil du sol, estimé par bio essai, est inversement lié avec la teneur en matière organique du sol, et la quantité et la fréquence des pluies influencent directement l'importance de la lixiviation de l'herbicide. Le triasulfuron s'est déplacé jusqu'à une profondeur d'au moins 22,5 cm quand les colonnes de sols ont été exposées à un total de 52,8 cm de pluies naturelles sur une période de 6 mois. La présence de taux phytotoxiques d'herbicide dans les couches superficielles des colonnes de sol 6 mois après l'exposition aux températures extérieures et aux précipitations naturelles montre que le triasulfuron peut persister dans 1s sols pendant des périodes relativement longues. Einfluβ der organischen Substanz des Bodens sowie der Niederschlagsdauer, ‐menge und ‐frequenz auf Persistenz und Mobilität von Triasulfuron im Boden Die biologische Aktivität sowie die Verlagerung von Triasulfuron im Boden, mit Biotests bestimmt, waren umgekehrt proportional zum Gehalt an organischer Substanz. Die Regenmenge sowie ‐frequenz beeinflußten die Einwaschung des Herbizids direkt. Bei insgesamt 528 mm natürlichem Niederschlag innerhalb 6 Monaten wurde Triasulfuron in Bodensäulen mindestens 22,5 cm tief eingewaschen. Aus dem Vorhandensein phytotoxischer Mengen des Wirkstoffs in den oberen Schichten der Bodensäulen nach 6 Monaten unter Freilandbedingungen wurde auf relativ hohe Persistenz im Boden geschlossen.
Effect of hypoxia on buried weed seed germination
Authors: BENVENUTI S. , MACCHIA M. 
Published: July 2006

SummaryTrials were carried out in order to investigate the effect of hypoxia on seed germination of Datura stramonium L. in Petri dishes and when buried at various depths in soil. Hypoxia was found to cause a decrease in germination capacity and germination rate. This inhibition was partially alleviated by daily exchange of hypoxic gas surrounding the seeds during incubation. Similarly, seed scarification allowed maintenance of a higher germination capacity under conditions of low oxygen availability, showing that the seed coat was only partially gas permeable. Oxygen deficiency led to a decrease in respiratory capacity. However, this was probably compensated for by induction of fermentation metabolism. The possibility of removing the final products of fermentation exerts a decisive influence on seed germination, especially in an environment such as soil, where their diffusion into the surrounding environment is restricted. Thus daily nitrogen flushing partially eliminated this inhibition, even under conditions of low external oxygen availability. It was therefore postulated that the main depth–derived inhibition was not caused directly by oxygen deficiency but by the increasing difficulty in eliminating toxic fermentation products, which was found to be proportional to the degree of hypoxia. Finally, incubation for several days under completely anaerobic conditions induced secondary dormancy. This was probably due to an ecological adaptation mechanism that prevents germination under conditions that are unfavourable for survival.
The effect of temperature on sprouting and early establishment of Cynodon dactylon
Authors: SATORRE E. H. , RIZZO F. A. , ARIAS S. P. 
Published: July 2006

SummaryBud‐sprouting dynamics, sprouting base temperature and reserve mobilization of rhizomes and stolons of Cynodon dactylon (L.) Pers. were characterized in a laboratory experiment under dark conditions. In addition, the dynamics of sprout emergence were determined during 2 years under field conditions. In the laboratory experiment, buds from the vegetative structures did not sprout at temperatures below 7^C. The rate of sprouting increased with temperature within the range 11–33^C, and a base temperature of 7.71^C was determined for bud sprouting of rhizome and stolons of the weed. An exponential model is proposed relating the percentage of sprout emergence in the field to accumulated thermal units, calculated as the sum of the daily mean air temperature above the base temperature of bud sprouting. This model satisfactorily predicted the dynamics of C. dactylon sprout emergence in sunflower (Helianthus annuus L.) crop fields. The efficiency of carbohydrate reserve use during sprout growth was highly dependent on temperature and type of vegetative structure The efficiency was maximum at 20^C and was higher for rhizomes than for stolons. The main factors influencing bud sprouting and early weed establishment are discussed.
The potential for selecting wheat varieties strongly competitive against weeds
Authors: LEMERLE D. , VERBEEK B. , COUSENS R.D. , COOMBES N E 
Published: July 2006

SummaryThe competitive abilities of a wide range of genotypes of wheat (Trilicvm aestivum L.) and durum wheat (Triticum durum Desf.) against Lolium rigidum Gaud, (annual ryegrass) were examined 1o determine the potential for breeders to select strongly competitive varieties, Considerable potential within the wheat genome to breed varieties with greater competitive ability was demonstrated. In 1993, 250 genotypes from around the world were screened and in 1994 a subset of 45 (mainly Australian) genotypes were further examined. A uniform density of L. rigidum reduced grain yield of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated with L. rigidum dry matter. Wheats varied in competitive ability with source, and durum wheats were less competitive than T. aestivum. The ‘old’ standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight F1 hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass of L. rigidum by an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high density was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were tall with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discussed.
Precision of soil seedbank sampling: how many soil cores?
Authors: DESSAINT F. , BARRALIS G. , CAIXINHAS M.L. , MAYOR J.‐P. , RECASENS J. , ZANIN G. 
Published: July 2006

SummaryA prerequisite for a precise estimate of the abundance of weed seeds in sou is prior knowledge of sampling variability, Based on an analysis of EWRS working group trials, it is shown that the sampling variance (s2) of seed counts increases with the sampling mean (S2) and can be predicted with the logarithmic form of Taylor's power law: log10(sz)=a+b log10(x̄). This relationship is constant over time for means greater than 0.1 seeds per core within each of the five different sites studied (temporal variability) but differs slightly among sites (geographical variability). An attempt is made to use a general s2 : x̄ relationship to predict the number of samples as a function of precision and density.
Prediction of Heteranthera reniformis competition with flooded rice using day–degrees
Authors: FERRERO A. 
Published: July 2006

SummaryIn field studies carried out in 1992 and 1993, several durations of growth of Heteranthera reniformis Ruitz et Pavon were established in flooded rice (Oryza sativa L.) to evaluate weed influence on crop yield using day‐degree predictive models for weed growth. H. reniformis was allowed to emerge at 7‐day intervals from rice emergence until 49 days later. Weeds that emerged with the rice accumulated 403 day‐degrees during the first 49 days. Weeds allowed to utilize 308 day‐degrees had a dry weight reduction of 20% compared with plants that emerged with the rice. With the loss of all 403 day‐degrees dry weight was reduced by about 95%. Maximum leaf area index (LAI) was 2.8, reached at 308 day‐degrees. Weed density ranged from 48 to 5 plants m‐2 when all 403 day‐degrees were accumulated or lost by the plant respectively. When the weed lost only 95 day‐degrees out of the possible 403 (1 week's delay in emergence) rice yield was 34% and 39% lower in 1992 and 1993 respectively. When the weed was allowed to accumulate ail 403 day‐degrees yield reduction reached 62% in 1992 and 68% in 1993, very similar to the control plot, which were maintained weedy throughout (64% and 70.5%). After an accumulation of 403 day‐degrees the weed reduced the number of rice panicles by 45% in 1992 and 38% in 1993.
Basal cell carcinoma in outdoor versus indoor workers in Turkey
Authors: Dogan Gursoy 
Published: July 2006

AbstractBackground  Basal cell carcinoma remains a significant health problem, and is most common in people of Caucasian origin with significant sun exposure. This study investigated differences between two groups of Turkish patients with basal cell carcinoma: indoor workers versus outdoor workers.Methods  One hundred and twenty‐one patients with primary basal cell carcinoma were categorized as outdoor (Group OW) or indoor workers (Group IW), according to sun exposure at work. Findings for age, sex, skin type, tumor location, and histologic subtype/aggression were compared.Results  The mean age of Group IW was lower than that of Group OW (57.3 ± 9.2 vs. 65.8 ± 12.2 years, respectively). Group OW comprised more men than women (63.4% vs. 36.6%, respectively), whereas women predominated in Group IW (62% vs. 38%, respectively). The facial cheek was a more frequent tumor site in Group IW than in Group OW (20% vs. 7.0%, respectively). There were no statistical differences with respect to skin types or histological subtypes; however, Group OW had a higher proportion of aggressive subtypes than Group IW (25.4% vs. 10%, respectively).Conclusions  The results in the Turkish population of the study suggest that basal cell carcinoma may develop in indoor workers (intermittent sun exposure) earlier than in outdoor workers with chronic sun‐exposure, but more aggressive subtypes are more likely to be linked with chronic sun‐exposure.
Temporal structure of an ant community in semi‐arid Australia
Authors: BRIESE D. T. , MACAULEY B. J. 
Published: July 2006

AbstractThe activity of five seed‐harvesting and ten non‐harvesting species of ants was examined over a 2‐year period. The ant community appeared to be stable in the long term, but there was considerable variability in the numbers and species of ants active at any one time, both on a seasonal and diel basis. Only four species were active throughout the year, with activity reduced in winter. Two species were consistently nocturnal, nine were mainly diurnal, and the remaining four species switched from diurnal to more nocturnal activity with increasing temperatures.The changes in the diurnal pattern and intensity of foraging activity were shown to be controlled by several climatic and biotic variables. These were classed as either ‘stimulatory‐inhibitory’ which determined whether activity would occur or not, or ‘regulatory’, which set the physical limits to activity and controlled foraging intensity. Factors such as forage availability and colony satiation were placed in the first category, and soil temperature, moisture stress and light intensity were placed in the second.There was no simple response to the combination of variables, and individual species responded differently to the various factors. The resulting temporal separation probably reduces competitive interactions between species.
The functional response of a predatory mite and the nature of the attack rate
Authors: LONGSTAFF BARRY C. 
Published: July 2006

AbstractThe assumptions of the Random Predator equation are discussed and the problems associated with parameter estimation and prediction are pointed out.Experiments are described in which the functional response characteristics of a mesostigmatid mite Pergamasus crassipes, preying upon a collembolan, Onycbiurus armatus, were observed over four successive time intervals. In a series of separate experiments the handling‐time, Th, was estimated directly.A modification of the random predator equation is proposed in which a searching time sub‐model is incorporated. Predictions from this model suggest that the attack rate is not a constant but is a function of prey density. An attack rate sub model is formulated and the resultant functional response model is shown to be more accurate and more readily usable for prediction than the random predator equation.