首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Velvetleaf seeds have been found in imported grains in Japan. The plants from these seeds show a weedy growth habit, such as that seen in the noxious velvetleaf which has recently emerged in Japan and noted in our previous study. To elucidate the genetic background of the velvetleaf strains found in imported grains we evaluated the genetic variation of six strains and an additional 39 worldwide velvetleaf accessions using the intersimple sequence repeat (ISSR) polymorphism. Cluster analysis based on the ISSR polymorphism emitted two major clusters which corresponded well with classification by growth habit, that is, crop type and weed type. Five of the six strains from the imported grains formed a small cluster. All six strains united into one major cluster containing the weed type accessions, while all of the old Japanese accessions formed another major cluster containing the crop type accessions. The genetic difference between imported weedy velvetleaf and old Japanese accessions suggests that imported velvetleaves are the source of the recent outbreak of the noxious velvetleaf in Japan.  相似文献   

2.
Hybridisation between genetically distinct lineages results in increases in overall genetic diversity and is a potential mechanism for the origin and spread of adaptive alleles. Weed and crop hybridisation may result in weedy ecotypes, which have, in addition to classic weedy traits such as seed shattering and long seed dormancy, crop traits that enhance weediness, such as adaptation to field cultivation and harvest strategies. Weedy rice (Oryza sativa) hybridises with cultivated rice and, in the process, may produce new (pink‐awned) weedy rice varieties. Pink‐awned (PA) weedy rice plants have been observed in rice fields in Arkansas. We explored the genetic relationships between PA weedy rice, crop rice, global rice accessions and other weedy rice ecotypes present in the southern United States. Gene sequencing of 48 sequence‐tagged sites (STS loci) revealed a pattern of hybridisation and gene flow between blackhull weedy rice and tropical japonica rice (O. sativa subsp. japonica) cultivars. Our data suggest that PA rice originates from hybridisation between blackhull weedy rice and tropical japonica rice. PA rice offspring segregate phenotypic traits associated with weediness in rice. This segregation could lead to adaptive allele combinations in PA rice, which could potentially move into other weedy rice types through subsequent hybridisation events.  相似文献   

3.
Agricultural practices exert selective forces on weed populations. As these practices change over time, weed adaptive traits also evolve, allowing weeds to persist in the new environment. However, only weeds having individuals showing the trait with adaptive significance will be able to cope with these changes, thus allowing a sub‐population to be selected for persistence. In addition, changes in agricultural practices can select new weed species showing functional traits with characteristics adaptive to the modified system. Seed dormancy has long been recognized as a trait with enormous adaptive value to adjust weed biology to cropping systems. In this paper, we illustrate with examples of success and failure, the value of seed dormancy as a functional trait to cope with long‐term changes in crop production systems. We show that successful outcomes are mostly related to the existence of sufficient variability for the functioning of physiological mechanisms that control dormancy characteristics as influenced by the agricultural environment. Presented examples illustrate how knowledge about the relationship that exists between agricultural practices and their selective pressure on seed dormancy can be instrumental in predicting changes in weed biotype dormancy characteristics or foreseeing the appearance of new weed species in future agricultural scenarios. © 2019 Society of Chemical Industry  相似文献   

4.
Weeds and weed control are major production costs in global agriculture, with increasing challenges associated with herbicide‐based management because of concerns with chemical residue and herbicide resistance. Non‐chemical weed management may address these challenges but requires the ability to differentiate weeds from crops. Harvest is an ideal opportunity for the differentiation of weeds that grow taller than the crop, however, the ability to differentiate late‐season weeds from the crop is unknown. Weed mapping enables farmers to locate weed patches, evaluate the success of previous weed management strategies, and assist with planning for future herbicide applications. The aim of this study was to determine whether weed patches could be differentiated from the crop plants, based on height differences. Field surveys were carried out before crop harvest in 2018 and 2019, where a total of 86 and 105 weedy patches were manually assessed respectively. The results of this study demonstrated that across the 191 assessed weedy patches, in 97% of patches with Avena fatua (wild oat) plants, 86% with Raphanus raphanistrum (wild radish) plants and 92% with Sonchus oleraceus L. (sow thistles) plants it was possible to distinguish the weeds taller than the 95% of the crop plants. Future work should be dedicated to the assessment of the ability of remote sensing methods such as Light Detection and Ranging to detect and map late‐season weed species based on the results from this study on crop and weed height differences.  相似文献   

5.
International trade is a major route by which non‐indigenous organisms are introduced into new habitats. Various kinds of weed seeds have been introduced through grain trade. The objectives of this study were to understand the factors that affect the initial assemblage of plant species introduced by the international grain trade and to extract their general attributes. We surveyed weed seed contamination of spring wheat imported from Canada to Japan and analysed the effects of the field abundance of each weed and of harvesting and cleaning on the quantity of weed seed included in the imported wheat. The field abundance was positively correlated with the weed seed quantity. Seeds of short weeds and seeds with a pappus were eliminated from the wheat by the harvesting or cleaning process. Many other crop plants contaminated the wheat. Because various transportation vehicles, temporary storage sites and port elevators are used commonly with all exported crops and it is difficult to remove all residues from them, other crops might be carried over into the wheat commodity. These relationships also apply to other grains.  相似文献   

6.
Transgenic herbicide‐resistant rice is needed to control weeds that have evolved herbicide resistance, as well as for the weedy (feral, red) rice problem, which has been exacerbated by shifting to direct seeding throughout the world—firstly in Europe and the Americas, and now in Asia, as well as in parts of Africa. Transplanting had been the major method of weedy rice control. Experience with imidazolinone‐resistant rice shows that gene flow to weedy rice is rapid, negating the utility of the technology. Transgenic technologies are available that can contain herbicide resistance within the crop (cleistogamy, male sterility, targeting to chloroplast genome, etc.), but such technologies are leaky. Mitigation technologies tandemly couple (genetically link) the gene of choice (herbicide resistance) with mitigation genes that are neutral or good for the crop, but render hybrids with weedy rice and their offspring unfit to compete. Mitigation genes confer traits such as non‐shattering, dwarfism, no secondary dormancy and herbicide sensitivity. It is proposed to use glyphosate and glufosinate resistances separately as genes of choice, and glufosinate, glyphosate and bentazone susceptibilities as mitigating genes, with a six‐season rotation where each stage kills transgenic crop volunteers and transgenic crop × weed hybrids from the previous season. Copyright © 2009 Society of Chemical Industry  相似文献   

7.
Data from the literature and recent experiments with herbicide-resistant (HR) canola (Brassica napus L) repeatedly confirm that genes and transgenes will flow and hybrids will form if certain conditions are met. These include sympatry with a compatible relative (weedy, wild or crop), synchrony of flowering, successful fertilization and viable offspring. The chance of these events occurring is real; however, it is generally low and varies with species and circumstances. Plants of the same species (non-transgenic or with a different HR transgene) in neighbouring fields may inherit the new HR gene, potentially generating plants with single and multiple HR. For canola, seed losses at harvest and secondary dormancy ensures the persistence over time of the HR trait(s) in the seed bank, and the potential presence of crop volunteers in subsequent crops. Although canola has many wild/weedy relatives, the risk of gene flow is quite low for most of these species, except with Brassica rapa L. Introgression of genes and transgenes in B rapa populations occurs with apparently little or no fitness costs. Consequences of HR canola gene flow for the agro-ecosystem include contamination of seed lots, potentially more complex and costly control strategy, and limitations in cropping system design. Consequences for non-agricultural habitats may be minor but appear largely undocumented.  相似文献   

8.
Weedy rice is morphologically similar to cultivated rice (Oryza sativa L.). It has biological characteristics that identify it as a weed. Its important weedy characteristics, that is, early and heavy seed shattering, makes it very difficult to control. Weedy rice has not been reported to be an important weed problem in transplanted, flooded rice. However, the shift to direct‐seeded rice (DSR) due to water issues and high costs of labor has increased reports of weedy rice becoming an expanding important problem in Vietnam, Malaysia, Thailand, and the Philippines. Experts believe that the growing adoption of DSR in Asian countries will result in the rise of weedy rice as one of the top troublesome weeds in rice production. Early and recent surveys in the Philippines have indicated the urgent need to increase awareness of weedy rice among farmers to allow the implementation of a number of effective location‐specific weed management strategies. These surveys and other studies conducted since weedy rice was first reported in 1991 confirmed that weedy rice and grass weed species caused major problems in DSR areas. About 35% of the 4.56 M ha harvested area in the country is planted with DSR. As cultivated and weedy rice are close relatives, it would be very difficult to implement management options very early in crop growth. However, a deeper understanding of the underlying traits of weedy rice can help develop a holistic approach toward effective and economic weed management.  相似文献   

9.
The presence of weeds in crop fields often causes yield reductions. However, the effects of weed diversity have not been fully examined. This study tested the hypothesis that, holding density constant, increased weed species richness would decrease the effects of competition on spring wheat target plant performance. Measurements were taken from circular neighbourhoods (16.5 cm radius) with a single spring wheat plant surrounded by combinations of Setaria viridis , Avena fatua , Kochia scoparia , Thlaspi arvense and spring wheat plants, representing all combinations of neighbour species at four density levels. Using regression models, we found that species richness had no significant direct effect on spring wheat biomass, yield, or relative growth rate and that there were no significant neighbour species interaction terms. For weedy target plants, the presence of negative interaction terms suggested that increasing species richness had negative effects on growth of individual weed species. Additional analysis suggested that increased species richness may limit competitive ability of dominant weeds. Although we found no evidence of a direct effect of weed species richness on crop performance, increased weed species richness had no negative effect on spring wheat performance. Further, species richness of the weed community appears to influence weedy plant performance, which may offer a future opportunity to influence crop performance.  相似文献   

10.
Early growth and nutrient content of crops and weeds from weed-free and weedy no-tillage maize (Zea mays L, cv. TZB), cowpea (Vigna unguiculata (L) Walp. cv. VITA-5) and maize/cowpea intercrop at populations of 40000, 50000 and 30000 + 40000 plants ha?1 grown on a loamysand Oxic Ustropept in a subhumid tropical location were monitored in the early and late 1979 cropping seasons. In the first 6 weeks of growth in the early season, cropping pattern had no effect on weed growth; weeds did not suppress crop growth significantly until 5–6 weeks after sowing and total crop dry weights were not affected by cropping pattern. Three weeks after sowing, weeds from weedy crop plots had taken up two to four times as much nutrient (N, P, K, Ca + Mg) as was taken up by corresponding weed-free crops. In the late season, weed dry weight 6 weeks after sowing was depressed in the intercrop compared to monocultures and dry-matter production of the intercrop was higher than those of monocultures. The resource use index (RUI), defined as the amount of an environmental resource used by a weed-free crop divided by the combined amount of the same resource used by the corresponding weedy crop and the associated weeds, increased with age of crop and was higher for the intercrop than the monocultures only in the late season.  相似文献   

11.
Digitaria sanguinalis is a troublesome annual weed that causes important yield losses in different crops. Despite this, there is scarce information about different aspects of its biology under field conditions. New knowledge about the establishment process of this species will be of paramount importance in order to maximise the effectiveness of weed management. The aims of this paper were to evaluate the effect of stubble found on the surface on seed dormancy levels through the season, the effects of stubble and soyabean crop canopy on seedling emergence and to determine the field emergence pattern as a consequence of seed dormancy level at dispersal time. Seeds on the soil surface, which showed a high dormancy level at the beginning of autumn, were released from dormancy by low winter temperatures and germinated during spring as temperatures rose, showing a transient surface seedbank. Seeds covered by stubbles had delayed the emergence in the field due to lower alternating temperatures perceived by the surface seedbank. On the other hand, the presence of a soyabean crop and stubble together reduced the number of seedlings. Seeds with a high dormancy level at dispersal time showed a delayed emergence in the next season when compared with seeds with a lower dormancy level. However, the final number of seedlings was similar. Both stubble on surface and crop canopy are useful factors to lessen and delay the seedling emergence allowing the design of weed management strategies in order to diminish the population levels of this species.  相似文献   

12.
Galinsoga parviflora , an annual dicot species of the family Asteraceae, is a common herb that is often found in disturbed habitats and agricultural areas in many parts of the temperate and subtropical regions of the world. It is a native of tropical America and the center of its origin is thought to be the mountainous area of Central America. Galinsoga parviflora is considered to be a common weed in several crops of major importance, such as wheat, corn, cotton, tobacco, sugarbeet, tomato, pepper, potato, bean, onion, cabbage, garlic, coffee, citrus, banana, and strawberry; it is frequently found in gardens and uncultivated areas. It succeeds particularly in moist soils and it is favored by a long photoperiod and high light intensity. The significant features of the plant, such as the lack of seed dormancy, rapid growth and development, early flowering, many generations per growing season, production of a great number of seed in a wide range of environmental circumstances, and the ability for easy vegetative reproduction under favorable conditions predispose the plant to be a troublesome weed. These features allow the easy distribution and rapid establishment of the weed in large populations, a fact that often makes this weed difficult to control. Galinsoga parviflora competes strongly, particularly with irrigated crops of short height, and it might also hinder crop harvest. The management of G. parviflora can be achieved by manual weeding, repeated soil cultivation, crop rotation, mulching, and herbicide application. The plant is reported to be edible and is used also for medicinal purposes.  相似文献   

13.
Competition between annual weeds and vining peas (Pisum sativum L.) at five target population densities between 11 and 194 plants/m2 was examined by means of periodic destructive sampling of weedy and weed-free plots. A further area of each plot was cut and vined to assess yields. Weeds impaired vegetative development, particularly by reducing tillering in low density crops. This resulted in weedy plots having fewer pods per plant at harvest but a lower proportion of flat pods than weed-free plots. Weeds had no effect on numbers or weights of peas in full pods nor on tenderometer values of samples of vined peas. Adverse effects of weeds on the growth of individual crop plants decreased with increasing crop density. However, at lower crop densities many of the additional pods on weed-free plots contributed little to vined yield, while at higher densities, direct or indirect effects of weeds increased the problem of maintaining sufficient photosynthetic area during pod swelling to prevent pod abscission and poor ovule development. Regression analysis of yield on crop density and of yield on numbers of pods per plant showed that vined yield per hectare was reduced by weeds by a constant amount across the range of densities and numbers of pods examined. Vining throughput was also reduced in weedy as compared with weed-free crops, even on high density plots where little or no weed vegetation remained at harvest. In general, weed presence had effects similar to those caused by increasing crop density, but without the additional contribution to yield made by extra plants. Higher density crops suppressed weeds very effectively but were no less vulnerable to yield loss than those of lower density; they therefore merit just as much attention to effective weed control as crops suffering more visibly from competition by weeds.  相似文献   

14.
The onion, Allium cepa, is an important vegetable crop around the world. Globally, India ranks second in onion production, but yields are often much lower than in many other onion producing countries. This study reports on one major contributing factor to low onion yields in India: the presence of a weedy mimic that is morphologically similar to onion until the onset of flowering. We used morphological and molecular methods to identify this mimic as Asphodelus fistulosus, an exotic weed not previously reported in India. Our study indicated that molecular markers derived from the rbcL and/or matK chloroplast genes in a DNA barcoding approach allow accurate identification of this weed using any tissue and even at early developmental stages. Our results also showed that visual examination of seed lots coupled with DNA barcoding analysis of samples of 5–10 individual seeds can be used to confirm identification. The ability to easily identify contaminating material before and during cultivation can allow farmers to minimise production losses and prevent further spreading of this weed.  相似文献   

15.
In a field trial in 1978 at Mokwa, southern Guinea savanna zone of Nigeria, metolachlor at 1.5 and 3.0, prometryne at 2.0 and norflurazon and diuron at 1.6 kg/ha combined good weed control with high grain yield of cowpeas. The grain yields with these herbicides were comparable to those of the hoe-weeded and significantly higher than the weedy controls. In 1979, under wetter conditions, crop injury was observed with prometryne and linuron at 2.0 kg/ha. However, the grain yields obtained with alachlor, metolachlor, chloramben, pendimethalin and norflurazon and their mixtures with prometryne, linuron, diuron or metobromuron were comparable to that of the hoe-weeded treatment. In 1979 at Samaru, northern Guinea savanna, pendimethalin at 1.5, metolachlor at 3.0 and chlorbromuron and linuron at 1.0 kg/ha gave selective weed control. Prometryne at 2.0 kg/ha was the only herbicide that gave a significantly lower broad-leaved weed weight than the weedy check but it reduced the crop stand. At 1.0 kg/ha it was tolerated by the crop but failed to control grasses. Metolachlor at 1.5 kg/ha had a significantly higher broad-leaved weed weight than the weedy check. All theherbicides, except pendimethalin at 3.0 kg/ha, controlled the annual sedges at Samaru.  相似文献   

16.
Weedy rice ( Oryza sativa f. spontanea ) is a problematic weed in the Thai Hom Mali rice production areas of Thung Kula Ronghai in north-eastern Thailand. There is a great need to initiate studies of weedy rice populations in order to perform basic studies to learn about the seed morphology and genetic diversity. The aims of this study were to determine the seed morphological traits and amylose content and to evaluate the genetic variation, based on the polymorphisms of nuclear and chloroplast DNA, of weedy rice. The seeds and flag leaves were collected from a total of 125 weedy rice plants at six rice fields in the region. For the samples, four morphological traits, the amylose content, and the chloroplast identity (ID) sequence and microsatellite genotypes at the waxy locus were determined. The weedy rice that was collected from the Thung Kula Ronghai region varied considerably in its amylose content and both the seed morphology and genotypes. Some of the weedy rice shared the common microsatellite alleles and chloroplast ID sequence with Thai Hom Mali and wild rice, Oryza rufipogon , indicating that the weedy rice in this region might originate from the introgression between cultivated rice and O. rufipogon , which often takes place in nature, mostly in a one-way process from cultivated rice to O. rufipogon.  相似文献   

17.
Cultivated plants are known to readily hybridise with their wild relatives, sometimes forming populations with weedier life‐history strategies than their progenitors. Due to altered precipitation patterns from human‐induced global climate change, crop‐wild hybrid populations may have new and unpredictable environmental tolerances relative to parental populations, which would further challenge farming and land‐management weed control strategies. To recognise the role of seed dormancy variation in weed invasion, we compared seedbank dynamics of two cross‐type populations (wild radish, Raphanus raphanistrum, and crop‐wild hybrid radish, R. raphanistrum × R. sativus) across a soil moisture gradient. In a seed‐burial experiment, we assessed relative rates of seed germination, dormancy and seed mortality over two years across cross types (crop‐wild hybrid or wild) and watering treatments (where water was withheld, equal to annual rainfall, or double annual rainfall). Weekly population censuses in 2012 and 2013 assessed the frequency and timing of seedling emergence within a growing season. Generally, germination rates were two times higher and seed dormancy was 58% lower in hybrid versus wild populations. Surprisingly, experimental soil moisture conditions did not determine seedbank dynamics over time. Yet, seed bank dynamics changed between years, potentially related to different amounts of annual rainfall. Thus, variation in seedbank dynamics may be driven by crop‐wild hybridisation rates and, potentially, annual variation in soil moisture conditions.  相似文献   

18.
Since the introduction of rice production in Japan, lowland areas have been managed for rice production with the purpose of better rice growth, as well as lesser weed infestation. Rice is cropped every year in lowland fields by repeated cultivation of a single crop, with high yields and without soil sickness usually being observed in upland fields. This is probably because the irrigation water supplies various nutrients for healthy rice growth and the drainage washes out and removes harmful factors. However, until recently, the wet or flooded conditions of lowland fields in the Asian monsoon region never have allowed humans to cultivate useful summer crops, except rice or some aquatic plants. Therefore, the management of lowland areas in the Asian monsoon region has been significantly different from European field management, where crop rotation has been the traditional standard practice. Paddy weeds are aquatic plants or hygrophytes that have adapted to lowland fields. Traditionally, tillage and puddling were practiced seasonally in lowland fields on a regular schedule every year. Rice cultivation technology was developed and supported by regional irrigation systems that created stable environments for typical paddy weeds to complete their life cycle. After the introduction of chemical weed control, rice fields became very severe habitats for these paddy weeds, where they could not grow and reproduce without strategies for survival under herbicide exposure. Even so, many of the traditional paddy weeds survived because of their accumulated or uneradicated seed banks, although several aquatic plants were listed as endangered or threatened species. The important weed species changed, sometimes rapidly and sometimes slowly, depending both on their reproductive system and their biological response towards field management and weed control systems. Very recently, the level of perennial weeds, herbicide‐resistant weeds, and weedy rice has increased in paddy fields that are highly dependent on herbicide use. In addition, several hygrophyte species have invaded paddy fields. In order to address these issues, the improvement and application of integrated weed management methods are expected to be critical.  相似文献   

19.
Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize.  相似文献   

20.
Variations in climate are widely recognized as central factors governing the competitive balance in mixed‐species plant communities. In agricultural systems, highly variable patterns of crop yield reduction as a function of weed density have been documented across sites and among years at the same site for several crop–weed combinations. This variation is typically attributed to contrasting environmental conditions. Despite broad acknowledgement of their importance, experimental and temporal limitations have constrained the investigation and systematic understanding of environmental controls on the dynamics of competition. For several well‐studied crop–weed associations, aggregating historical data from similar competition experiments provides an opportunity to explore interference relationships over an array of conditions. In this study, 19 site‐years of maize –Abutilon theophrasti (velvetleaf) data were compiled and the weather characterized (i.e. average ambient temperature and moisture regime) for discrete portions of each growing season. These features were then related to patterns of maize yield loss from A. theophrasti interference at high weed densities. Results of this analysis suggest that temperatures following establishment, together with the presence or absence of water stress during the maize crop's exponential growth phase, account for over 60% of the observed variation in relative yield loss.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号