Relative contribution of genotype, seed size and environment to secondary seed dormancy potential in Canadian spring oilseed rape (Brassica napus)

Secondary seed dormancy has been linked to seedbank persistence of volunteer oilseed rape (Brassica napus) in western Canada. It has been suggested that there is a genetic component to secondary seed dormancy expression in oilseed rape, but little is known of its importance in relation to non‐genetic factors. In a series of experiments we investigated the relative importance of genotype, seed size, time of windrowing and pre‐ and post‐harvest environment on the expression of secondary seed dormancy. We found that genotype contributed between 44 and 82% to the total variation in secondary seed dormancy. A broad range in secondary seed dormancy expression was observed among 16 genotypes examined. Nevertheless, three‐quarters of the genotypes investigated exhibited relatively high potential for the expression of secondary seed dormancy (back‐transformed mean 71% dormant seeds). Seed size contributed 21% to the total variation, while the influence of seed maturity (harvest regime) on secondary seed dormancy expression was negligible. Despite diverging environmental conditions during the four growing seasons spanning these experiments, the influence of pre‐harvest environment on seed dormancy expression was relatively small and ranged from 0.1% to 4.5%. Secondary seed dormancy potential decreased over time during seed storage. This decrease was greatest when seeds were stored at ambient temperatures and least when seeds were stored at ?70°C.     

Changes in seed bank size and dormancy characteristics of the glyphosate-resistant biotype of goosegrass (Eleusine indica[L.] Gaertn.)

A study on changes in the seed bank size of a glyphosate ( N -(phosphonomethyl)glycine)-resistant (R) Eleusine indica biotype was carried out on a naturally occurring infestation of a young oil palm plantation. The total number of shed seeds collected was 53% of the predicted potential total number of seeds produced by the plants. Ametryn ( N -ethyl- N' -(methylethyl)-6-(methylthio)-1,3,5-triazine-2, 4-diamine) was found to be able to control the R seed population in the soil. The periodicity of seedling emergence was influenced by rainfall subsequent to the 1 month period of seed shedding. Seed burial at 2, 10 and 20 cm depths showed that 39, 33 and 79%, respectively, of viable seed persisted in the soil after 2 years. Seeds in the state of enforced dormancy played an important role in maintaining the seed population throughout the 2 year period of burial in the soil.     

The roles of light and pericarp on seed dormancy and germination in feral Raphanus sativus (Brassicaceae)

The timing of seed germination may determine the success of a weed species in an agroecosystem, and its expression is modulated by environmental conditions, but also by seed physiology and anatomy. The aims of this study were to investigate the roles of light, pericarp, dry storage and cold stratification on seed dormancy and germination in feral radish, a troublesome agricultural weed in temperate zones of the Americas that reduces crop yields. To this end, we used isolated intact pods and extracted seeds to test germination over time under contrasting temperature, light and storage conditions. Here, we showed that fresh seeds were non‐dormant, but that light and the presence of the pericarp reduced germination, especially under low temperatures. The pericarp reduced the final water content absorbed by seeds inside pods and decreased absorption/dehydration rates. The pericarp showed several small lignified cell layers in the endocarp, and x‐ray images displayed the lack of space between the partially embedded seed and the endocarp. Dry storage and cold stratification were ineffective in breaking the dormancy imposed by the pericarp. The apparent requirement for darkness and the mechanical restriction of the pericarp may have the potential to induce dormancy, spreading the timing of seed germination over a more extended period and hindering the control of feral radish.     

Effects of relative humidity and substrate on the spatial association between glyphosate and ethoxylated seed oil adjuvants in the dried deposits of sessile droplets

BACKGROUND: In recent years, several studies have shown the impact of adjuvants on the characteristics of herbicide deposits on leaf surfaces. Until now, most studies have addressed the distribution of active ingredients (AIs), whereas few experiments have focused on the location of the adjuvants. The objective of this study was a systematic examination of the particle distribution profile of both the AI (glyphosate, Gly) and the adjuvants after the application of sessile microdroplets on hydrophobic (Teflon) and hydrophilic (glass and aluminium) model surfaces. RESULTS: The association degree (AD) was surface dependent and specific for the tested adjuvants. In general, the rather hydrophobic adjuvant RSO 5 showed decreasing AD with Gly at increasing relative humidity (RH) levels. The rather hydrophilic RSO 60 adjuvant displayed higher AD between the compounds at a higher RH. A high concentration of the adjuvant reduced the AD for both of the RSO adjuvants evaluated. CONCLUSION: The combination of surface properties, the type of adjuvant and the relative humidity determines the degree of association between Gly and the adjuvants. The present results suggest that the interaction between the AI and an adjuvant determines whether spatial separation occurs, whereas physical processes (e.g. capillary particle movement, inward and outward Marangoni flows and the evaporation rate) are decisive for the extent of the separation. Coffee‐ring structures were formed exclusively with the adjuvant + Gly mixtures, whereas Gly alone formed either one big deposit or several small islands distributed within the droplet footprint. Copyright © 2011 Society of Chemical Industry     

Effects of temperature and light on seed germination of ephemeral plants in the Gurbantunggut Desert,China: implications for vegetation restoration

Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light. Therefore, research on the effects of temperature and light on seed germination is extremely meaningful for vegetation restoration, especially in desert ecosystems. Seeds of 28 ephemeral plants collected from the Gurbantunggut Desert of China were incubated at different temperatures (5°C/1°C, 15°C/5°C, 20°C/5°C, 25°C/10°C and 30°C/15°C) in 12-h light/12-h darkness or continuous darkness regimes, and the responses of seed germination to temperature and light and the germination speed were studied in 2016. Results showed that seed germination percentage of the 28 ephemeral plants significantly differed to temperature and light. We classified the studied plants as the following groups based on their responses to temperature: 1 low temperature responsed plants, 12 moderate temperature responsed plants, 7 high temperature responsed plants, 4 non-responsed plants and 5 plants of no germination. It should be noted that Corispermum lehmannianum Bunge is sensitive to both moderate and high temperatures. There were 4 groups of plant in response to light, i.e., 7 light responsed plants, 10 dark responsed plants, 6 light non-responsed plants and 5 plants of no germination. Based on seed germination speed of the 28 ephemeral plants, we divided them into 4 patterns of germination, i.e., very rapid, moderately rapid, moderate and slow. Combining variations of temperature, precipitation and sand dune types in the study area, we suggested that very rapid and moderately rapid germinated plants could be used to moving sand dunes in early spring during vegetation restoration, moderate germinated plants could be used to semi-fixed sand dunes in late autumn, and slow germinated plants could be used to sand plain in summer. Thus, seedling establishment and vegetation restoration would be improved by considering seed germination characteristics of these ephemeral plants in the Gurbantunggut Desert, China.     

The effect of initial concentration of carbofuran on the development and stability of its enhanced biodegradation in top‐soil and sub‐soil

Carbofuran was incubated in top‐soil and sub‐soil samples from a pesticide‐free site at a range of initial concentrations from 0.1 to 10 mg kg⁻¹. Amounts of the incubated soils were removed at intervals over the subsequent 12 months, and the rate of degradation of a second carbofuran dose at 10 mg kg⁻¹ was assessed. An applied concentration as low as 0.1 mg kg⁻¹ to top‐soil resulted in more rapid degradation of the fresh addition of carbofuran for at least 12 months. The degree of enhancement was generally more pronounced with the higher initial concentrations. When the same study was conducted in sub‐soil samples from the same site, an initial dose of carbofuran at 0.1 mg kg⁻¹ resulted in only small increases in rates of degradation of a second carbofuran dose. However, degradation rates in the sub‐soil samples were, in many instances, considerably greater than in the corresponding top‐soil samples, irrespective of pre‐treatment concentration or pre‐incubation period. Initial doses of 0.5 mg kg⁻¹ and higher applied to sub‐soil successfully activated the sub‐soil microflora. Application of the VARLEACH model to simulate carbofuran movement through the soil profile indicated that approximately 0.01 mg kg⁻¹ of carbofuran may reach a depth of 70 cm 400 days after a standard field application. The results therefore imply that adaptation of the sub‐soil microflora (c 1 m depth) by normal field rate applications of carbofuran is unlikely to occur. In experiments to investigate this in soils exposed to carbofuran in the field, there was no apparent relationship between top‐soil exposure and degradation rates in the corresponding sub‐soils. The results further confirmed that some sub‐soil samples have an inherent capacity for rapid biodegradation of carbofuran. The high levels of variability observed between replicates in some of the sub‐soil samples were attributed to the uneven distribution of a low population of carbofuran‐degrading micro‐organisms in sub‐surface soil. There was no apparent relationship between soil microbial biomass and degradation rates within or between top‐soil and sub‐soil samples. © 2001 Society of Chemical Industry     

Effect of temperature,organic amendment rate and moisture content on the degradation of 1,3‐dichloropropene in soil

1,3‐Dichloropropene (1,3‐D), which consists of two isomers, (Z)‐ and (E)‐1,3‐D, is considered to be a viable alternative to methyl bromide, but atmospheric emission of 1,3‐D is often associated with deterioration of air quality. To minimize environmental impacts of 1,3‐D, emission control strategies are in need of investigation. One approach to reduce 1,3‐D emissions is to accelerate its degradation by incorporating organic amendments into the soil surface. In this study, we investigated the ability of four organic amendments to enhance the rate of degradation of (Z)‐ and (E)‐1,3‐D in a sandy loam soil. Degradation of (Z)‐ and (E)‐1,3‐D was well described by first‐order kinetics, and rates of degradation for the two isomers were similar. Composted steer manure (SM) was the most reactive of the organic amendments tested. The half‐life of both the (Z)‐ and (E)‐isomers in unamended soil at 20 °C was 6.3 days; those in 5% SM‐amended soil were 1.8 and 1.9 days, respectively. At 40 °C, the half‐life of both isomers in 5% SM‐amended soil was 0.5 day. Activation energy values for amended soil at 2, 5 and 10% SM were 56.5, 53.4 and 64.5 kJ mol^?1, respectively. At 20 °C, the contribution of degradation from biological mechanisms was largest in soil amended with SM, but chemical mechanisms still accounted for more than 58% of the (Z)‐ and (E)‐1,3‐D degradation. The effect of temperature and amendment rate upon degradation should be considered when describing the fate and transport of 1,3‐D isomers in soil. Use of organic soil amendments appears to be a promising method to enhance fumigant degradation and reduce volatile emissions. Published in 2001 for SCI by John Wiley & Sons, Ltd     

Inheritance mode and realized heritability of resistance to imidacloprid in the brown planthopper,Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: The brown planthopper, Nilaparvata lugens (Stål), is a serious pest that causes enormous losses to the rice crop in Asia. The genetic basis of imidacloprid resistance was investigated in N. lugens. RESULTS: The resistant strain, selected for imidacloprid resistance from a field population of N. lugens collected from Nanjing, Jiangsu Province, China, showed a 964‐fold resistance compared with the laboratory strain. Progenies of reciprocal crosses (F₁ and F₁′) showed similar dose–mortality responses (LC₅₀) to imidacloprid, and also exhibited a similar degree of dominance (D), 0.58 for F₁ and 0.63 for F₁′. Chi‐square analyses of self‐bred and backcross progenies (F₂, F₂′ and BC respectively) rejected the hypothesis for a single gene control of the resistance. The estimated realized heritability (h²) of imidacloprid resistance was 0.1141 in the resistant strain of N. lugens. CONCLUSION: The results showed that imidacloprid resistance in N. lugens was autosomal and was expressed as an incompletely dominant trait, probably controlled by multiple genes. Copyright © 2009 Society of Chemical Industry     

Insecticidal activity and nicotinic acetylcholine receptor binding of dinotefuran and its analogues in the housefly, Musca domestica

The insecticidal activity of dinotefuran and 23 related compounds against the housefly, Musca domestica (L) was measured by injection with metabolic inhibitors. Dinotefuran was less active than imidacloprid and clothianidin by a factor of 10 in molar concentrations. Their binding activities to the fly-head membrane preparation were measured by using [125I]alpha-bungarotoxin ([125I]alpha-BGTX) and [3H]imidacloprid ([3H]IMI) as radioligands. The activity of some selected compounds measured with [3H]IMI was 10(4)-fold higher than that measured with [125I]alpha-BGTX. With [3H]IMI as a radioligand, dinotefuran was 13-fold less active than imidacloprid. The inhibitory effect of dinotefuran on the binding of [3H]IMI to the membrane preparation was in a competitive manner. Quantitative analysis of the insecticidal activity of the test compounds with the binding activity measured with [3H]IMI showed that the higher the binding activity, the higher was the insecticidal activity.     

Residues of the herbicide fenoxaprop‐P‐ethyl,its agronomic safener isoxadifen‐ethyl and their metabolites in rice after field application

BACKGROUND: Fenoxaprop‐P‐ethyl is a herbicide used on cereals and in particular on rice, the degradation of which leads to several relevant metabolites. The herbicide is used together with an agronomic safener such as isoxadifen‐ethyl, which also generates some metabolites. The present work was aimed at developing and validating an analytical method for the determination of the above parent compounds and their main metabolites in the edible fractions of rice. Parent compounds were extracted in acetonitrile and determined by gas chromatography with a mass spectrometer detector, while metabolites were extracted in acetonitrile and analysed by liquid chromatography tandem mass spectrometry. RESULTS: The method was validated through recovery tests in rice straw, grain and plant: accuracy was in the range 76–86% and 90–103% for parent compounds and metabolites respectively. Precision, as relative standard deviation, was in the range 3–11% and 6–17% for parent compounds and metabolites respectively. The limit of detection was 0.01 mg kg^?1 for each analyte, while the limit of quantification was set at 0.05 mg kg^?1. CONCLUSION: The analytical method is suitable for quantitative determination of each analyte considered in rice commodities. Copyright © 2010 Society of Chemical Industry     

Effect of cutting frequency on above‐ and belowground biomass production of Rumex alpinus,R. crispus,R. obtusifolius and the Rumex hybrid (R. patienta × R. tianschanicus) in the seeding year

Rumex species are important weeds in grasslands and on arable land. The Rumex hybrid (R. patienta × R. tianschanicus; cv. OK‐2, Uteusha) has been planted as a forage and energy crop since 2001 in the Czech Republic, but its ecological requirements and its potential to become a new weedy species have never been investigated. In 2010 and 2011, we performed a pot experiment to investigate the effect of none, one and two cuts per year on biomass production of Rumex OK‐2 and common broad‐leaved Rumex species (Rumex obtusifolius, R. crispus and R. alpinus). The higher cutting frequency can reduce the belowground biomass, but no effect on the aboveground biomass was detected. Flowering in the seeding year was recorded in only 50% of R. obtusifolius plants. Non‐flowering R. obtusifolius plants produced significantly more belowground biomass than flowering plants under no cutting or one cut treatments. The growth response of Rumex OK‐2 to different cutting treatments was very similar to R. crispus. These similarities indicate the weed potential of the hybrid to become a troublesome weedy species, similar to R. crispus.     

Dynamics of above‐ground and below‐ground biomass of Rumex crispus,Rumex obtusifolius and the new weedy species Rumex hybrid cv. OK‐2 (R. patientia x R. tianschanicus) in the seeding year

Docks can be serious weeds of arable land and permanent grasslands where they can persist through well‐established root systems. A Rumex hybrid (R. patientia x R. tianschanicus; cv. OK‐2, Uteusha) has been planted as a forage and energy crop since 2001 in Czechia and has now become a new weed species. As its ecological characteristics are unknown, there is a need for improved knowledge for developing control measures and strategies. In 2010 and 2011, we performed a tube pot experiment to investigate above‐ground and below‐ground biomass growth dynamics and below‐ground biomass allocation of Rumex OK‐2. We compared the hybrid with Rumex crispus and Rumex obtusifolius during the vegetation season in the seeding year. Above‐ground and below‐ground biomass of Rumex species tended to increase from July to September. In the seeding year, flowering was recorded only for one plant of Rumex OK‐2 and 27.5% of R. obtusifolius plants, whereas R. crispus did not flower. The proportion of below‐ground biomass of Rumex species in the upper 30 cm was about 70–80%. The growth dynamics and allocation of below‐ground biomass of Rumex OK‐2 were more like R. crispus than to R. obtusifolius. These similarities indicate the potential of Rumex OK‐2 to become a troublesome weedy species, comparable with R. crispus.