Variation in seed dormancy and light sensitivity in Alopecurus myosuroides and Apera spica-venti

Variation in seed dormancy and light sensitivity was studied in Alopecurus myosuroides and Apera spica-venti . Seeds were collected from different populations, at different dates and from plants emerging in autumn or spring, and used in four experiments. In the first experiment, initial dormancy was investigated in light and darkness. In Expt 2, buried seeds were exhumed on 16 occasions, from September 1997 to March 2000, and germinated in light, in darkness and after a 5-s light exposure. In Expt 3, emergence was recorded for seeds sown in pots outdoors. In Expt 4, stratified seeds of A. myosuroides only were exposed to photon irradiance ranging from 0.1 to 25 600 μmol m⁻². Variation was high among seed collections, but both species showed winter annual dormancy patterns. Apera spica-venti germinated to high percentages in autumn but negligibly in spring. Alopecurus myosuroides germinated less in spring when tested in darkness and after a short light exposure and emerged poorly in spring, which reflected photo-desensitisation during cold stratification. We conclude that the peak of emergence in A. myosuroides , and to some extent in A. spica-venti , is largely regulated by exposure to light interacting with low-level dormancy. This offers valuable information regarding optimal timing of weed control measures.     

THE NATURE AND CONSEQUENCE OF INTERFERENCE BY ALOPECURUS MYOSUROIDES HUDS. ON THE GROWTH OF WINTER WHEAT

Summary. In a field experiment with different densities of Alopecurus myosuroides , 10 plants/m² caused no significant reduction in total dry weight of winter wheat at harvest. When autumn- or spring-germinated plants at 100/m² remained until harvest, crop weight was reduced by about 30%. A study of root-zone competition between A. myosuroides and winter wheat in the glasshouse showed that suppression of the weed by the crop was greater at high nitrogen levels; the practical implications of this are discussed.
La nature de l'interférence d' Alopecurus myosuroïdes Huds. sur la croissance du blé d'hiver, et ses conséquences     

Effect of environmental conditions on Alopecurus myosuroides germination. I. Effect of temperature and light

Summary Control of Alopecurus myosuroides with a minimum amount of herbicide may be improved by models describing the impact of cropping system effects on the weed's demography. In order to develop the submodel relating the weed seedbank to the emerged seedlings, a series of laboratory experiments was set up to analyse and quangify the effects on A. myosuroides germination of temperature, storage location, seed age and light incidence for various seed populations. The minimum temperature requirement for germination was estimated at 0 °C, and it did not depend on seed population or weight. In the subsequent experiments, a four-parameter non-linear equation depending on accumulated day-degrees was fitted to the observed germination data, resulting in the estimation of parameters quangifying germination proportion and rate. Storage location had little influence on germination. Germination proportion and rate increased with seed age and were higher in light than in darkness. The later the germinating seeds were submitted to light, the less was their germination stimulated. These observations were synthesized by a series of equations quangifying the relative variation in germination parameters as a function of storage and light conditions, independent of seed population.     

Longevity of seeds of four annual grass and two dicotyledon weed species as related to placement in the soil and straw disposal technique

Persistence of seeds of the four winter annual grass species, Alopecurus myosuroides , Bromus sterilis , Bromus hordeaceus and Vulpia myuros , were studied under field conditions. The studies also included the two dicotyledon species, Tripleurospermum inodorum and Galium aparine . Seed samples were stored in the field at different depths in the plough layer for a year. Following germination, seedling emergence was taken as an indicator of field persistence. In a supplementary investigation, seed samples were placed on the soil surface or buried at 2 cm for a month and then tested for viability. Persistence of the two Bromus species was very short, irrespective of depth and duration of burial. Persistence of the other species was positively correlated with incorporation of seeds to a few centimetres depth. Increasing the depth of incorporation below 2 cm had a variable influence on persistence. Persistence of seeds placed directly on the soil surface was short, whether they were left there for a year or a month. Whether seeds at the soil surface were left uncovered or covered with chopped straw had limited influence on seed persistence. However, straw cover significantly increased persistence of A. myosuroides seeds and there was the same tendency with T. inodorum .     

A rapid reliable test for screening aryloxyphenoxy- propionic acid resistance within Alopecurus myosuroides and Lolium spp. populations

A reliable seedling bioassay was developed and tested for the rapid screening for resistance to aryloxyphenoxypropionic (APP) herbicides in Alopecurus myosuroides and Lolium spp. populations. It is based upon the difference in coleoptile length of resistant and susceptible A. myosuroides and Lolium seedlings, respectively, exposed to fenoxaprop-P acid and diclofop acid solution for 6 days in a plastic box. A 6 mg L⁻¹ fenoxaprop-P acid solution was selected as the best concentration for a reliable screening of resistant biotypes within A. myosuroides populations. At this concentration, coleoptile lengths of susceptible and resistant seedlings were shorter and longer than 10 mm respectively. Similarly, resistant seedlings within Lolium populations were easily detected at 10 mg L⁻¹ diclofop acid. At this concentration, coleoptile lengths of susceptible and resistant seedlings were shorter and longer than 20 mm respectively. For both populations, the coleoptile length distributions appear to discriminate between two kinds of APP-resistant biotypes (highly and slightly resistant).     

Vernalization responses and subsequent fertility of two climatically distinct populations of rattail fescue (Vulpia myuros [L.] C.C. Gmel.)

Rattail fescue has become increasingly problematic in North America as a result of the greater adoption of no‐till practices. While rattail fescue is described generally as a winter annual, there exists a wide variation in the life history documentation of the species. In some instances, rattail fescue has been observed behaving as a spring annual. In order to assess the vernalization plasticity of rattail fescue, laboratory‐germinated seedlings from two climatically different rattail fescue populations, eastern versus western Oregon, were exposed to 4, 7 or 10°C temperatures for 0, 2, 4, 5, 6, 6.5, 7 or 8 weeks of vernalization. Following vernalization, the seedlings were transferred to a greenhouse and the developmental stages were recorded. After 13 weeks, the emergent inflorescences were clipped and the seeds were tested for germinability. The initiation of sexual development in the eastern population was affected significantly by the vernalization temperature and length, while the western population only responded to the vernalization length. In general, a faster progression through the reproductive stages of development was associated with longer vernalization lengths. Lastly, there was an increase in the germination rate of the seeds that were produced on the parent plants that were subjected to longer vernalization lengths, regardless of the population or vernalization temperature. The level of plasticity in the vernalization response between the two tested populations indicates that land managers should monitor local population life history traits in order to ensure that effective weed control is implemented at the correct growth stage.     

Weed suppression by soil steaming in combination with activating compounds

The aim of this study was to determine the weed suppression potential of soil steaming plus activating compounds (KOH or CaO) to boost soil temperature. Different combinations between the compounds and rates were tested in experiments carried out in the field and in a controlled environment. Treatment effects were assessed on field weed vegetation and on seedbank and seedling emergence of three winter ( Alopecurus myosuroides , Matricaria chamomilla and Raphanus raphanistrum ) and four spring annuals ( Amaranthus retroflexus , Echinochloa crus-galli , Fallopia convolvulus and Setaria viridis ), were assessed on field weed vegetation. Neither maximum soil temperature (from 72 to 85°C) nor duration of high temperature in the 3 h following application consistently affected weed suppression. In the field, no significant effects on total weed density were recorded, but there were some significant effects on individual species. The weed seedbank was clearly suppressed by activated steaming: total seedling emergence was inversely related to increasing KOH rates both in the 0–10 and 10–20 cm soil layers, while for CaO the relationship was significant only in the 0–10 cm layer. Winter annuals were more sensitive to KOH than CaO and spring annuals had a more pronounced species-specific response to treatments. There was a strong negative relationship between compound rate and seedling emergence for all species. Alopecurus myosuroides was the most sensitive to the steam-alone treatment (77% reduction), whereas M. chamomilla and E. crus-galli were the least sensitive. Results from this study indicate that the type and rates of activating compounds for soil steaming must be adjusted to the weed community composition.     

PCR-based detection of resistance to acetyl-CoA carboxylase-inhibiting herbicides in black-grass (Alopecurus myosuroides Huds) and ryegrass (Lolium rigidum gaud)

A simple method based upon allele-specific PCR was developed to detect an isoleucine-leucine substitution in the gene encoding chloroplastic acetyl-coenzyme A carboxylase (ACCase) in two gramineous weeds: Lolium rigidum Gaud and Alopecurus myosuroides Huds. Analysis of 1800 A myosuroides and 750 L rigidum seedlings showed that the presence of ACCase leucine allele(s) conferred cross-resistance to the cyclohexanedione herbicide cycloxydim and to the aryloxyphenoxypropionate herbicides fenoxaprop-P-ethyl and diclofop-methyl. Seedlings containing ACCase leucine allele(s) could be either sensitive or resistant to the aryloxyphenoxypropionate herbicides haloxyfop-P-methyl and clodinafop-propargyl. Successful detection of resistant plants in a field population of A myosuroides was achieved using this PCR assay. Using it with basic molecular biology laboratory equipment, the presence of resistant leucine ACCase allele(s) can be detected within one working day.     

A model of the effects of cultivation on the vertical distribution of weed seeds within the soil

A matrix model was constructed for the prediction of vertical seed movement within the soil. This was inserted into a model of the life-cycle of Alopecurus myosuroides in order to predict seed population dynamics. Parameter values were obtained from published sources and from a single field cultivation experiment using coloured plastic beads. In simulations, stability of vertical distribution was reached sooner under ploughing than under rigid tine cultivation. Stable distributions were very different for the two cultivation methods, being reached by damped oscillations in the case of ploughing and asymptotically in the case of rigid tine cultivation.     

Effect of environmental conditions on Alopecurus myosuroides germination. II. Effect of moisture conditions and storage length

Summary More effective control of Alopecurus myosuroides with a minimum amount of herbicide may be achievable by using models describing the impact of cropping system effects on the weed's demography. In order to develop the submodel relating the weed seedbank to the emerged seedlings, a series of laboratory experiments was set up to analyse and quangify the effects on A. myosuroides germination of length of seed storage in dry conditions, soil water potential and dryness during imbibition. The base soil water potential for germination was estimated at −1.5 MPa. A four-parameter non-linear equation depending on accumulated day–degrees was fitted to the observed germination data, resulting in the estimation of parameters illustrating germination proportion and rate. Germination proportion and rate increased with seed storage length, and were increased by short and decreased by long dry periods occurring after imbibition. These results showed that, in contrast to crop species, A. myosuroides germination cannot be expressed simply as a function of hydrothermal time, but also requires the determination of the proportion of non-dormant seeds as a function of seed age and environmental conditions.     

The effect of pre-germination chilling on subsequent growth and flowering in three arable weeds

This experiment investigated the effect of pre-germination moist chilling of seeds (for 3 weeks at 2^C) of 10 common arable weeds on the subsequent growth and flowering of the plants. In only three of the species (Alopecurus myosuroides Huds., Veronica persica Poir. and Trifolium dubium Sibth.) was flowering markedly increased by the seed chilling treatments. At 3 months, the mean number of flowers and seed heads per plant on the treated plants was greater than that on the controls by factors of 13.9, 2.02 and 1.74 respectively. Shoot lengths of the seed-chilled plants were also significantly greater in all three species, though dry weights did not differ significantly from those of the controls. Thus, the plants showed morphological changes associated with reproduction but no significant alteration in total dry weight. The ecological implications of the data are discussed in relation to possible effects of climatic change on species which require seed vernalization.     

大穗看麦娘与日本看麦娘的DNA条形码鉴定

大穗看麦娘是我国麦田新发生的恶性杂草,与日本看麦娘苗期形态相近,导致难以识别和有效监测。本研究利用4个DNA 条形码候选序列(rbcL、matK、trnH-psbA和ITS2)对13份大穗看麦娘和10份日本看麦娘叶片材料进行分子鉴定,采用Vector NTI分析扩增的DNA序列峰图质量并比对碱基差异,通过MEGA 6.0软件中的K2P模型计算样本种内和种间的双参数遗传距离,采用邻接法构建系统发育树。结果表明,4个DNA 条形码序列中仅matK扩增测序结果不理想。日本看麦娘在4种DNA条形码序列中不存在种内差异,大穗看麦娘在rbcL、matK和ITS2序列中无种内差异,仅在trnH-psbA序列中存在7个差异位点。大穗看麦娘和日本看麦娘种间各DNA条形码序列均有差异,trnH-psbA、rbcL、matK和ITS2序列存在的差异位点数分别为6、3、14和28。ITS2的种间平均遗传距离大于rbcL,且具有特异性,适宜用于大穗看麦娘和日本看麦娘的准确鉴定。     

A method to determine the pollen-mediated spread of target-site resistance to acetylcoenzyme A carboxylase inhibitors in black grass (Alopecurus myosuroides Huds.)

Journal of Plant Diseases and Protection - In this study the spread of target-site resistance to ACCase inhibitors via pollen was characterized in a population of Alopecurus myosuroides. The spread...     

Interactions Between Chill-Hours and Degree-Days Affect Carpogenic Germination in Monilinia vaccinii-corymbosi

ABSTRACT The relationship of cumulative chill-hours (hours with a mean temperature <7.2 degrees C) and heating degree-days (base 7.2 degrees C) to carpogenic germination of pseudosclerotia of Monilinia vaccinii-corymbosi, which causes mummy berry disease of blueberry, was investigated. In two laboratory experiments, pseudosclerotia collected from rabbiteye blueberry in Georgia were conditioned at 5 to 6 degrees C for 26 to 1,378 h prior to placement in conditions favorable for germination and apothecium development. The number of chill-hours accumulated during the conditioning period affected the subsequent proportion of pseudosclerotia that germinated and produced apothecia, with the greatest incidence of carpogenic germination occurring after intermediate levels of chilling ( approximately 700 chill-hours). The minimum chilling requirement for germination and apothecium production was considerably lower than that reported previously for pseudo-sclerotia from highbush blueberry in northern production regions. The rate of carpogenic germination was strongly affected by interactions between the accumulation of chill-hours and degree-days during the conditioning and germination periods; pseudosclerotia exposed to prolonged chilling periods, once transferred to suitable conditions, germinated and produced apothecia more rapidly (after fewer degree-days had accumulated) than those exposed to shorter chilling periods. Thus, pseudosclerotia of M. vaccinii-corymbosi are adapted to germinate carpogenically following cold winters (high chill-hours, low degree-days) as well as warm winters (low chill-hours, high degree-days). Results were validated in a combined field-laboratory experiment in which pseudosclerotia that had received various levels of natural chilling were allowed to germinate in controlled conditions in the laboratory, and in two field experiments in which pseudosclerotia were exposed to natural chilling and germination conditions. A simple model describing the timing of apothecium emergence in relation to cumulative chill-hours and degree-days was developed based on the experiments. The model should be useful for better timing of field scouting programs for apothecia to aid in management of primary infection by M. vaccinii-corymbosi.     

Characterisation of target-site resistance to ACCase-inhibiting herbicides in the weed Alopecurus myosuroides (black-grass)

Resistance to aryloxyphenoxypropionate (AOPP), cyclohexanedione (CHD) and phenylurea herbicides was determined in UK populations of Alopecurus myosuroides Huds. Two populations (Oxford AA1, Notts. A1) were highly resistant (Resistance indices 13-->1000) to the AOPP and CHD herbicides fenoxaprop, diclofop, fluazifop-P and sethoxydim, but only marginally resistant to the phenylurea, chlorotoluron. Analyses of acetyl coenzyme A carboxylase (ACCase) activity showed that an insensitive ACCase conferred resistance to all the AOPP/CHD herbicides investigated. Another population, Oxford S1, showed no resistance to sethoxydim at the population level, but contained a small proportion of plants (<10%) with an insensitive ACCase. Genetic studies on the Notts A1 and Oxford S1 populations demonstrated that target site resistance conferred by an insensitive ACCase is monogenic, nuclearly inherited with the resistant allele showing complete dominance. Investigations of the molecular basis of resistance in the Notts A1 population showed that sethoxydim resistance in A myosuroides was associated with the substitution of an isoleucine in susceptible with a leucine in resistant plants, which has also been found in three other resistant grass-weed species (Setaria viridis (L) Beauv, Avena fatua L, Lolium rigidum Gaud).     

A review of the effects of crop agronomy on the management of Alopecurus myosuroides

This study reviews 52 field experiments, mostly from the UK, studying the effects of cultivation techniques, sowing date, crop density and cultivar choice on Alopecurus myosuroides infestations in cereal crops. Where possible, a statistical meta‐analysis has been used to calculate average responses to the various cultural practices and to estimate their variability. In 25 experiments, mouldboard ploughing prior to sowing winter cereals reduced A. myosuroides populations by an average of 69%, compared with non‐inversion tillage. Delaying drilling from September to the end of October decreased weed plant densities by approximately 50%. Sowing wheat in spring achieved an 88% reduction in A. myosuroides plant densities compared with autumn sowing. Increasing winter wheat crop density above 100 plants m^?2 had no effect on weed plant numbers, but reduced the number of heads m^?2 by 15% for every additional increase in 100 crop plants, up to the highest density tested (350 wheat plants m^?2). Choosing more competitive cultivars could decrease A. myosuroides heads m^?2 by 22%. With all cultural practices, outcomes were highly variable and effects inconsistent. Farmers are more likely to adopt cultural measures and so reduce their reliance on herbicides, if there were better predictions of likely outcomes at the individual field level.     

Localized origins of herbicide resistance in Alopecurus myosuroides

The process of evolution of resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides was investigated in four distinct patches of Alopecurus myosuroides Huds. (black-grass) that occur within adjacent fields on a cereal farm in Nottinghamshire, UK. In one field, there was a `main' patch containing 96% resistant plants and two `satellite' patches containing ≈2.9% and 4.4% resistant plants, and in an adjacent field another patch contained 25% resistant plants. Genome fingerprinting by simple sequence repeat (SSR)-anchored polymerase chain reaction (PCR) was used to analyse variation at 30 genetic loci in at least 20 resistant and 20 sensitive individual plants from each patch, from additional resistant populations from Essex and Lincolnshire, and from a sensitive reference population. Banding patterns were found to be highly repeatable. Each patch contained a high level of genetic diversity, regardless of its resistance status, and there was evidence for genetic differences between the patches (Gst = 0.14, Nei's distances up to 0.26). There was no evidence that resistance had spread from the `main' patch to the others, as resistant and sensitive plants in the same patch were more closely related on average than were resistant plants from neighbouring patches. The most likely explanations of this distribution, and their implications, are discussed.     

New, quick tests for herbicide resistance in black-grass (Alopecurus myosuroides Huds) based on increased glutathione S-transferase activity and abundance

Black-grass (Alopecurus myosuroides Huds) is a major grass weed in winter cereals in Europe. It reduces yields and can act as a secondary host for a range of diseases. Herbicide resistance in this species was first detected in the UK in the early 1980s, and has now been reported in thirty counties. To successfully manage herbicide resistance it is vital that suspect populations are tested so that appropriate action can be taken. Ideally, a test will be quick, cheap and easy to use. Furthermore, it should provide an unequivocal result before post-emergence herbicides are to be applied, allowing alternative strategies to be adopted where necessary. This paper reports the development of new tests for herbicide resistance based on our observation that the resistant black-grass biotype Peldon contains approximately double the activity of the enzyme glutathione S-transferase (GST) compared with susceptible biotypes. Data are presented on the production of a monoclonal antiserum to a novel 30 kDa GST polypeptide purified from the biotype Peldon. An ELISA using this antiserum is described and the utility of this assay to detect resistant black-grass biotypes in plants grown under glass and in the field is presented. In addition, a microtitre assay for GST activity is described, which allows the rapid assessment of GST activities of plants. Both abundance and activity of GSTs are discussed as markers for herbicide resistance in black-grass.     

The survival of Alopecurus myosuroides Huds. seeds in soil

The survival of Alopecurus myosuroides seeds was studied in soil under arable cropping and short term grass leys in which seed return was prevented. At two winter wheat sites, where weed seeds were sown, the mean annual seed decline was 73–83% over a 2- or 3-year period. The rate of decline was similar with all the cultivation systems studied: ploughing, tine cultivation and direct drilling. Seeds buried initially by ploughing, and then not disturbed by cultivation, were slightly more persistent. At five arable sites with natural populations of A. myosuroides, seed numbers declined to an average of 3% of the original amount present after 3 years, and to 1% after 4 years. Initial populations of over 50 000 seeds m^?2 were recorded. Plant populations were not always proportional to the total seed content of the soil, especially on ploughed land. Seed decline in two grass fields was similar to that under arable cropping. A. myosuroides plants were recorded in a wheat crop following a 2-year grass ley. Weed plants did not persist in the vegetative state in grass used for conservation and grazing. At all sites, appreciable quantities of seeds were still present in the soil after 2–4 years. Although a relatively small proportion of seeds survived, the actual number of seeds surviving was substantial. For this reason, it was concluded that any eradication policy is unlikely to be effective in a cropping system dominated by winter cereals.     

Predicting the growth and competitive effects of annual weeds in wheat

The growth and competitiveness of 12 annual weed species were studied in crops of winter wheat, in which weeds were sown to give a wide range of plant densities. Weed growth patterns were identified; early species which senesced in mid-summer were less competitive than those with a growth pattern similar to that of the crop. Most species had little effect on crop yield in 1987, and this was attributed to a high crop den sity. Crop yield-weed density relationships for all species in 1988 and for Galium aparine in 1987 were well described by a rectangular hyperbola. Species were listed in the following competitive order based on the percentage yield loss per weed m^?2: Avena fatua > Matricaria perforata > Galium aparine > Myosotis arvenis > Poa trivialis > Alopecurus myosuroides > Stellaria media > Papaver rhoeas > Lamiumpur-pureum > Veronica persica > Veronica hederi-folia > Viola arvensis. Prediction of yield loss is discussed. The assumptions inherent in using Crop Equivalents (based on relative weights of weed and crop plants), are challenged; with intense competition, weed biomass at harvest failed to replace lost crop biomass, and harvest index was reduced. It is concluded that a competi tive index, derived from yield density relation ships, and expressed as the percentage yield loss per weed m^?2, is more likely to reflect the com petitive ability of a species than an index obtained from plant weights in the growing crop.