Wild Oat Populations Research Articles

Wild Oat ( Avena fatua ): Crop Mimicry and Herbicide Resistance

Abstract Wild oat ( Avena fatua ) is a weed species that through crop mimicry survive in conventional managed farmlands, particularly in cereal crops such as wheat and barley. Adaptation of wild oat likely dates back around 9000 years when domestication of cereal species began in the Fertile Crescent and around the Mediterranean Sea. So far, wild oat has been described as a troublesome weed in 44 countries across temperate parts of the world. Wild oat reduces crop yields due to its competition for nutrients, water and light. Variable seed dormancy results in early maturing plants that add to the soil’s seed bank, and later maturing plants that contaminate the harvested grain. Since wild oat seeds resembles cereal grain, they are difficult to remove by mechanical seed cleaning. Seed lots contaminated with wild oat seeds are downgraded since it reduces the suitability as food and feed. Contaminated seedlots used for planting is a source of long distance spread of the weed. Herbicide application is an important part of wild oat control in areas with intensive wheat and barley production. Herbicide labels typically recommend the optimal size of wild oat seedlings and crop plants for best control. However, timing of an application can be difficult when wild oat plants are at different growth stages. The majority of herbicides are grouped according to the mode-of-action in cells of weed plants either inhibiting specific enzymes or entire metabolic pathways. Repeated use of herbicides with the same mode-of-action creates a selection pressure that can result in development of wild oat populations resistant to these herbicides. There is a direct relationship between the number of wild oat plants treated with herbicides and the risk of selecting for resistant plants. Thus, best management practices (BMP) aim to reduce the number of wild oat seed in the field, and include rotating between herbicides with different mode-of-action, and following recommendations on herbicide labels regarding plant growth stages and dosage. Cultural practices include rotating crop species and optimizing crop health, planting of weed-free seed, and cleaning of machinery between fields. Wild oat’s adaptations for crop mimicry and herbicide resistance make it problematic to manage but incorporating BMPs into an integrated approach can help. Information © His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada.

Development and Validation of Avena Integrated Management (AIM): A Bioeconomic Decision Support Tool for Wild Oat Management in Australian Grain Production Systems

Abstract Wild oat is a long-standing weed problem in Australian grain cropping systems, potentially reducing the yield and quality of winter grain crops significantly. The effective management of wild oat requires an integrated approach of diverse control techniques that suit specific crops and cropping situations. This research aimed to construct and validate a bioeconomic model that enables the simulation and integration of weed control technologies for wild oat in grain production systems. The Avena spp. integrated management (AIM) model was developed with a simple interface to provide outputs of biological and economic data (crop yields, weed control costs, emerged weeds, weed seedbank, gross margins) on wild oat management data in a cropping rotation. Uniquely, the AIM was validated against real-world data on wild oat management in a wheat and sorghum cropping rotation, where the model was able to reproduce the patterns of wild oat population changes as influenced by weed control and agronomic practices. Correlation coefficients for 12 comparison scenarios ranged between 0.55 and 0.96. With accurate parameterization, AIM is thus able to make useful predictions on the effectiveness of individual and integrated weed management tactics for wild oat control in grain cropping systems.

Current Status of Herbicide Resistance of Wild Oats (Avena spp) in Wheat Fields in Mardin and Şanlıufa Provinces of Türkiye

Wheat is a strategic crop with its role in human nutrition. In Türkiye, it has importance in agriculture and economy as well as being a staple crop. Mardin and Şanlıurfa provinces of Türkiye approximately produces 1.6 million tons of wheat on 600 thousand ha fields. One of the important factors limiting wheat production is weeds. Weeds compete with the wheat plant and cause significant yield and quality loss. Wild oat (Avena spp.) species are an important problem in wheat fields in both provinces. Herbicide applications are widely used to control wild oats due to their ease of use, short duration of action and low cost. Wheat fields were surveyed to supply data for strategies to be followed via determining the current situation of herbicide resistance in these provinces where herbicide resistant wild oats had been reported. Out of 95 fields visited, 65 fields had significant wild oat populations of which 61 A. sterilis and four A. fatua. Then these populations were tested to find out herbicide resistance levels against clodinafop-propargyl (ACCase inhibitor) and formulated mix of mesosulfuron-methyl and iodosulfuron-methyl sodium (ALS inhibitors). Only two populations, one low level and the other medium level were found to be resistant to the formulated mix of mesosulfuron and iodosulfuron while 11 populations were resistant to clodinafop, one high level, three medium level and the remaining low level. It was assumed that longer use history and wider use of clodinafop as well as herbicides used in winter rotational crops might cause more clodinafop resistant populations. It was concluded that a strategy to prevent or delay herbicide resistance in these provinces should be prepared because herbicide resistance has continued evolving.

Wild Oats Offer New Possibilities for Forage Because of the Higher Nutrition Content and Feed Value

Oats (Avena sativa L.) are mostly used as a germplasm resource for forage. This experiment showed the differences in the nutrient composition and the forage quality of five wild leather oat populations from Israel and one cultivated leather oat population from China. It also showed the correlation of the indicators with the geo-environmental factors in the places of origin of the six populations that were analysed. Three replicated experiments were conducted during a three-year period from 2018.10 to 2020.03, mainly from 11 indicators of nutrient composition and forage quality. In this experiment, Spearman’s correlation was used to analyse the differences between different groups (p < 0.05), the relationship between components was analysed by principal component analysis (PCA), and the kinship relationship between six groups was also analysed based on the data of 11 components. In terms of nutrient content, the cultivated group Hu had significantly lower ash (8.92%), crude protein (11.96%), and soluble sugar content (10.51%) than the wild oat groups. In terms of forage quality, the lignin content (3.31%) of the Hu population was 2.3 times higher than that of Evolution Canyon, and the fibre content was 8 times higher than that of Sede Boqer. This indicates that wild oats have better nutritional value and palatability. Following the correlation analysis, it was found that the environmental factors of the origin had a significant effect on the indexes of ash, crude protein, and soluble sugar of oat straw, but had less effect on the content of crude fat, total phosphorus, and total potassium. Meanwhile, the annual rainfall and the number of rainfall days in the origin had a significant effect on the fibre content. In conclusion, the higher variability of wild oat populations due to the influence of different environmental and geographical factors may be a new possibility brought by forage oats.

Evaluation of panicle removal methods and crop topping applications as supplemental tools for wild oat (Avena fatua) management

AbstractIncreased frequency and occurrence of herbicide-resistant biotypes heightens the need for alternative wild oat management strategies. This study aimed to exploit the height differential between wild oat and crops by targeting wild oat between panicle emergence and seed shed timing. Two field studies were conducted either in Lacombe, AB, or Lacombe, AB and Saskatoon, SK, from 2015 to 2017. In the first study, we compared panicle removal methods: hand clipping, use of a hedge trimmer, and a selective herbicide crop topping application to a weedy check and an industry standard in-crop herbicide application in wheat. These treatments were tested early (at panicle emergence), late (at initiation of seed shed), or in combination at one location over 3 yr. In the second study, we investigated optimal timing of panicle removal via a hedge trimmer with weekly removals in comparison to a weedy check in wheat and lentil. This study was conducted at two locations, Lacombe, AB, and Saskatoon, SK, over 3 yr. Among all the tested methods, the early crop topping treatment consistently had the largest impact on wild oat density, dockage, seedbank, and subsequent year crop yield. The early (at panicle emergence) or combination of early and late (at initiation of seed shed) treatments tended to reduce wild oat populations the following season the most compared to the late treatments. Subsequent wild oat populations were not influenced by panicle removal timing, but only by crop and location interactions. Panicle removal timing did significantly affect wild oat dockage in the year of treatment, but no consistent optimal timing could be identified. However, the two studies together highlight additional questions to be investigated, as well as the opportunity to manage wild oat seedbank inputs at the panicle emergence stage of the wild oat lifecycle.

Mechanistic basis for synergism of 2,4-D amine and metribuzin in Avena sterilis.

The combination of herbicides with different modes of action has been adopted not only to improve weed control but also to increase the environmental sustainability of plant-protection products. In this study, we showed a synergistic effect of the auxin herbicide 2,4-D amine with the PSII-inhibiting herbicide metribuzin to control the global grass weed wild oat (Avena sterilis) population and investigated the underlying mechanisms. Pretreatment with 2,4-D amine did not change the foliar absorption of metribuzin but did increase metribuzin translocation to the roots and new leaves, although enhancement of the metribuzin metabolism was also observed. Considering that the expression level of the target site psbA gene is significantly higher in leaves than in roots, increased metribuzin translocation to new leaves is likely the major cause of the observed synergism, even though enhanced metribuzin metabolism may offset the metribuzin efficacy. This is the first report on the synergistic mechanism between 2,4-D amine and metribuzin in weed control.

Determination of Effects on Weed Height and Weed Biomass of Wild Oat (Avena sterilis L.) Populations in Wheat Fields against ALS and ACCase Herbicides

Bu çalışma 2013 ve 2014 yıllarında farklı etki mekanizmasına sahip olan ALS (Mesosulfuron-methyl + Iodosulfuron-methyl sodium) ve ACCase (Clodinafop-propargyl) inhibitörü herbisitlerin Osmaniye ili buğday ekim alanlarında sorun olan kısır yabani yulaf (Avena sterilis L.) popülasyonların bitki boyu ve yaş ağırlıklarına olan etkilerinin belirlenmesi amacıyla yapılmıştır. Osmaniye ili yoğun buğday ekimi yapılan alanlarda Mayıs ayında her 3 km’de bir 50 noktada duruş yapılarak sadece 15 tarlada kısır yabani yulaf popülasyonlarına ait örneklemeler gerçekleştirilmiştir. Bu sayede aynı tarlalardan iki yıl üst üste 1 da’lık alanda olgun kısır yabani yulaf tohumları toplanmıştır. Daha sonra buğday tarlalarından toplanan olgun kısır yabani yulaf tohumlarıyla sera denemeleri kurulmuştur. Popülasyonlarda bitki boyu ve yaş ağırlığa olan etkinin belirlenmesinde iki farklı etki mekanizmasına sahip herbisitin 3 farklı (N/2, N: tavsiye dozu, 2N) dozu uygulanmıştır. Bitki boylarına göre tavsiye dozlarında ALS inhibitöründe popülasyonların %50’sinin, ACCase inhibitöründe ise %27’sinin etkilendiği belirlenmiştir. Populasyonların yaş ağırlıklarının ALS inhibitöründe %50’sinin, ACCase inhibitöründe %20’sinin tavsiye dozunda etkilendiği saptanmıştır. ALS ve ACCase inhibitörlerinin popülasyonlar üzerindeki etkileri incelendiğinde gerek bitki boyuna, gerekse yaş ağırlığa olan etkilerinin ALS inhibitörü tavsiye dozunda daha fazla olduğu saptanmıştır. Popülasyonlar birbiri arasında kıyaslandığında bitki boyları açısından tavsiye dozunun yarısında Düziçi 3 popülasyonu, yaş ağırlık açısından tavsiye dozunun yarısında Kadirli 9 popülasyonu ile tavsiye dozunda Kadirli 6 popülasyonu iki farklı etki mekanizmasında da benzer şekilde en etkili bulunmuştur. Bitki boyu ve yaş ağırlığa olan genel etkiler incelendiğinde, toplanan popülasyonlar üzerinde ALS inhibitörünün ACCase inhibitörüne göre hemen hemen bütün uygulama dozlarında daha yüksek etkiye sahip olduğu saptanmıştır.

Avena fatua L. escapes and delayed emergence in wheat (Triticum aestivum L.) crops of Argentina

Avenafatua (L.) is one of the most important weed grasses in wheat crops on the most important wheat (Triticum aestivum L.) production area of Argentina. It is present in 60% of the fields of an area of 750,000 ha not only reducing crop yields but also contaminating the wheat and barley (Hordeum vulgare L.) grain. The most frequent practice for its control is the application of ACCase inhibitors or ALS inhibitors herbicides. However, the presence of wild oat is frequent in wheat crops at harvest even in those fields where herbicides were applied and thus, regarded as resistant individuals. Thus, the objective of this study was to identify the processes that explain the persistence of wild oat individuals during the crop cycle. Seeds from cultivated and from uncultivated areas were harvested and then the response to ACCase inhibitors and ALS inhibitors herbicides was studied over 20 selected populations from different areas of both conditions (cultivated and uncultivated). Emergence dynamic from seeds of both conditions was also studied and in addition, the effect of mature environment on seeds germination was also assessed. The results indicate that none of the populations were resistant to herbicides studied. However, emergence dynamic was different depending on the seeds coming from agricultural fields or not cropping condition. Seeds from cultivated areas had higher dormancy and emerged later in the field than those from no cropped areas. The ripening environment did not modify the emergence pattern suggesting differences in emergence dynamic are based on genetic nature. These results show dormancy levels and therefore germination and establishment dynamic on the field was hierarchically more important than response to herbicides to favor the persistence of this weed in wheat production systems. Thus, it is still possible to apply proactive agronomic strategies with the aim of avoiding the growth of wild oat populations resistance to herbicides.

Cross-resistance patterns of winter wild oat (Avena ludoviciana) populations to ACCase inhibitor herbicides

The level of resistance and patterns of cross-resistance to clodinafop, sethoxydim, and pinoxaden were examined in 12 putative resistant and one susceptible populations of winter wild oat (Avena ludoviciana) collected from Fars Province, in the southwest of Iran. The responses of biomass and length of coleoptiles to the increasing dosages of the three herbicides were determined in both whole-plant and seed bioassays. In the whole-plant bioassay, all 12 putative resistant populations were found to be resistant to clodinafop with resistance ratios (R/S) ranging from 1.76 to >47.04. Most clodinafop-resistant populations exhibited low levels of cross-resistance to sethoxydim. Three highly sethoxydim-resistant populations, F2, S2, and ES4, were slightly resistant to clodinafop. Six populations (M1, M2, F2, S2, S4, and ES4) showed high cross-resistance to pinoxaden with R/S values as large as 10.73 to 40.29. A highly clodinafop-resistant population, M2, was more sensitive to pinoxaden than the susceptible population. The results of the seed bioassay resembled those obtained from the whole-plant experiment suggesting seed bioassay as an inexpensive, rapid method for screening-resistant genotypes.

Identifying Critical Control Points in the Wild Oat (Avena fatua) Life Cycle and the Potential Effects of Harvest Weed-Seed Control

Wild oat is a problematic weed species that requires new management techniques in the face of herbicide resistance; harvest weed-seed control (HWSC) may be an option. Wild oat demographic information was collected in long-term, rotational field studies in Lacombe, AB, Canada, in 2006 and 2007, and a periodic matrix model was parameterized using management extremes (no IPM, no herbicide to high IPM, and full herbicide). Population growth rates were calculated for each treatment and year. Prospective (elasticity) and retrospective (LTRE) analyses were conducted alongside a rearrangement of the model equation in which population growth rates were designated and the required proportion of newly shed seed survival that gives that growth rate was solved for. All populations had λ > 1 or increasing populations. Elasticity analyses indicated that λ was most-highly elastic to the overwinter seedbank (Esw = 1), followed by seedling survival, fecundity, and survival of newly shed seed (0.63 to 0.86 across treatments). The latter may be the most-accessible vital rate for management of herbicide resistant populations. LTRE exposed the stochasticity of wild oat population growth rates between years and their ability to take advantage of lapses in control. Decreasing the proportion of newly shed seeds (snew) that survives was the most-effective and available control strategy until reduced to 0.1 to 0.3 when the summer seedbank becomes more critical. When averaged across treatments, > 80% of newly shed seed must be eliminated to stop the population from growing, resulting in a stable population, but not a decline. Because of preharvest shattering, HWSC will likely not be effective enough alone to cause wild oat populations to decline. New management techniques for wild oat control that can be used in combination with HWSC and integrated weed management strategies are needed.

The frequency of herbicide-resistant wild oat (Avena spp.) populations remains stable in Western Australian cropping fields

Avena is a problematic weed of cropping regions of southern Australia and many areas of the world. In 2010, a random survey was conducted across 14 million hectares of the Western Australian grain belt to monitor the change in herbicide resistance levels by comparing resistance frequency results with a survey conducted in 2005. Screening Avena populations with herbicides commonly used to control this weed revealed that 48% of Avena populations displayed resistance to the commonly used acetyl-Co A carboxylase-inhibiting herbicides, which was lower than that found in 2005 (71%). The broad-spectrum herbicides glyphosate and paraquat provided good control of all Avena populations. Resistance to acetolactate synthase-inhibiting herbicides and to flamprop were detected for the first time in Western Australia in this survey. Therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future.

Characterisation of Avena fatua populations with resistance to multiple herbicides

SummaryAvena fatua (wild oat) populations with resistance (R) to one or more herbicides have been described in numerous cropping systems worldwide. We previously reported that the R3 and R4 wild oat populations from Montana, USA, were resistant to four herbicides representing three different modes of action: tralkoxydim [acetyl‐CoA carboxylase (ACCase] inhibitor), imazamethabenz and flucarbazone [acetolactate synthase (ALS) inhibitors] and difenzoquat (growth inhibitor). We now quantify resistance levels of these populations to triallate [very long chain fatty acid (VLCFA) biosynthesis inhibitor], pinoxaden (ACCase inhibitor) and paraquat (photosystem I inhibitor). Glasshouse dose–response experiments showed that, compared with the means of two susceptible (S) populations, the R3 and R4 populations were 17.5‐ and 18.1‐fold more resistant to triallate, 3.6‐ and 3.7‐fold more resistant to pinoxaden, respectively, and 3.2‐fold (R3) more resistant to paraquat. Pre‐treatment of R plants with the cytochrome P450 inhibitor malathion partially reversed the resistance phenotype for flucarbazone (both populations), imazamethabenz (R4), difenzoquat (R4) and pinoxaden (R3), but not for tralkoxydim, fenoxaprop‐P‐ethyl or triallate. Target site point mutations known to confer resistance to ALS or ACCase inhibitors were not detected via DNA sequencing and allele‐specific PCR assays in R plants, suggesting the involvement of non‐target site resistance mechanism(s) for these herbicides. Together, our results complete the initial characterisation of wild oat populations that are resistant to seven (R3) or six (R4) herbicides from five or four mode of action families respectively.

Identification of glyphosate-resistant Lolium rigidum and Raphanus raphanistrum populations within the first Western Australian plantings of transgenic glyphosate-resistant canola

Transgenic glyphosate-resistant canola was first commercially grown in Western Australia (WA) in 2010, providing an opportunity to obtain important baseline data regarding the level of glyphosate resistance in weeds following the exclusive use of glyphosate for in-crop weed control. In this study, two surveys (2010 and 2011) were conducted across the 14 Mha of the grainbelt of WA. The 2010 survey was carried out at the late-flowering stage of glyphosate-resistant canola, whereas the 2011 survey was conducted at an earlier growth stage (6–8 leaves), ~2–3 weeks after the second in-crop glyphosate application. During the surveys, 239 fields were visited, representing an estimated combined area of 24 000 ha. The 2011 survey alone represented a subsample of 23% of the total glyphosate-resistant canola planting in the WA grainbelt for that season. Glyphosate resistance was identified in one population of wild radish (Raphanus raphanistrum L.) and in eight annual ryegrass (Lolium rigidum L.) populations. None of the tested capeweed (Arctotheca calendula (L.) Levyns) populations were glyphosate-resistant. In this survey, no populations of barley grass (Hordeum spp.), brome grass (Bromus spp.), wild oat (Avena spp.) or small-flowered mallow (Malva parviflora L.) survived glyphosate application. Despite a long history of pre-seeding and fallow glyphosate use in WA, this survey found that glyphosate still provides excellent in-crop control of most species; however, some resistance is evident, requiring diverse weed control techniques to limit their spread.

Impact of Biotic and Abiotic Stresses on the Competitive Ability of Multiple Herbicide Resistant Wild Oat (Avena fatua)

Ecological theory predicts that fitness costs of herbicide resistance should lead to the reduced relative abundance of resistant populations upon the cessation of herbicide use. This greenhouse research investigated the potential fitness costs of two multiple herbicide resistant (MHR) wild oat (Avena fatua) populations, an economically important weed that affects cereal and pulse crop production in the Northern Great Plains of North America. We compared the competitive ability of two MHR and two herbicide susceptible (HS) A. fatua populations along a gradient of biotic and abiotic stresses The biotic stress was imposed by three levels of wheat (Triticum aestivum) competition (0, 4, and 8 individuals pot−1) and an abiotic stress by three nitrogen (N) fertilization rates (0, 50 and 100 kg N ha−1). Data were analyzed with linear mixed-effects models and results showed that the biomass of all A. fatua populations decreased with increasing T. aestivum competition at all N rates. Similarly, A. fatua relative growth rate (RGR) decreased with increasing T. aestivum competition at the medium and high N rates but there was no response with 0 N. There were no differences between the levels of biomass or RGR of HS and MHR populations in response to T. aestivum competition. Overall, the results indicate that MHR does not confer growth-related fitness costs in these A. fatua populations, and that their relative abundance will not be diminished with respect to HS populations in the absence of herbicide treatment.

Multiple Herbicide Resistance in Wild Oat and Impacts on Physiology, Germinability, and Seed Production

The evolution of weed biotypes resistant to multiple herbicide modes of action, here termed multiple herbicide resistance, is a growing problem around the world. We investigated two multiple herbicide resistant (MHR) wild oat (Avena fatua L.) populations from Montana and hypothesized that they would exhibit fitness costs compared with two herbicide‐susceptible (HS) populations. Dose‐response tests showed that the MHR populations were resistant to difenzoquat (a membrane disruptor), imazamethabenz (an acetolactate synthase [ALS] inhibitor), flucarbazone (an ALS inhibitor), and tralkoxydim (an acetyl‐CoA carboxylase inhibitor). In greenhouse studies, we assessed differences between MHR and HS populations in seed germination, photosynthetic parameters, plant growth, and reproduction. Seeds of one HS population germinated more at cold temperature (4.9°C) and less at high temperature (29.6°C) compared with the other populations. Plants of this HS population also had lower stomatal conductance (23%), intercellular CO2 concentration (7.5%), and transpiration (15.3%) than the other populations, but there were no differences in photosynthetic rates between any populations. Also, there were no differences in relative growth rate among all HS and MHR populations. The MHR populations initiated seed production several days sooner than the HS populations; however, HS populations produced 67% more tillers, and one HS population ultimately produced 43% more seeds than the MHR populations, indicating a potential fitness cost of resistance. With the exception of seed production differences, our results do not indicate a consistent fitness cost. More research is needed in field settings and with resource competition to further evaluate fitness costs in MHR populations.

Herbicide Resistance Endowed by Enhanced Rates of Herbicide Metabolism in Wild Oat (Avenaspp.)

The biochemical basis of resistance to the acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicide diclofop-methyl was investigated in a resistant wild oat population (R1), which does not exhibit a resistant ACCase. Rates of foliar uptake and translocation of [14C]-diclofop were the same in the R1 vs. susceptible (S) populations. However, the level of phytotoxic diclofop acid was always found to be lower in the R1 vs. S plants, with a concomitant higher level (up to 1.7-fold) of nontoxic polar diclofop metabolites in R1 relative to the S plants. These results indicate that a non–target-site-based mechanism of enhanced rate of diclofop acid metabolism confers resistance in population R1. Moreover, the high-performance liquid chromotography elution profile of the major diclofop metabolites in R1 is similar to that of wheat, suggesting resistance in individuals of population R1 involves a wheat-like detoxification system mediated by cytochrome P450 monooxygenases. In addition, lower level of tissue diclofop acid was also observed using nonradioactive ultra-performance liquid chromatography–mass spectrometry analysis in resistant individuals of three other resistant wild oat populations (R2, R3, and R4) known to posses ACCase gene resistance mutations. These results establish that either one or at least two independent resistance mechanisms (target-site ACCase resistance mutations and non–target-site enhanced rates of herbicide metabolism) can be present in individual wild oat plants.

Herbicide resistance-endowing ACCase gene mutations in hexaploid wild oat (Avena fatua): insights into resistance evolution in a hexaploid species

Many herbicide-resistant weed species are polyploids, but far too little about the evolution of resistance mutations in polyploids is understood. Hexaploid wild oat (Avena fatua) is a global crop weed and many populations have evolved herbicide resistance. We studied plastidic acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicide resistance in hexaploid wild oat and revealed that resistant individuals can express one, two or three different plastidic ACCase gene resistance mutations (Ile-1781-Leu, Asp-2078-Gly and Cys-2088-Arg). Using ACCase resistance mutations as molecular markers, combined with genetic, molecular and biochemical approaches, we found in individual resistant wild-oat plants that (1) up to three unlinked ACCase gene loci assort independently following Mendelian laws for disomic inheritance, (2) all three of these homoeologous ACCase genes were transcribed, with each able to carry its own mutation and (3) in a hexaploid background, each individual ACCase resistance mutation confers relatively low-level herbicide resistance, in contrast to high-level resistance conferred by the same mutations in unrelated diploid weed species of the Poaceae (grass) family. Low resistance conferred by individual ACCase resistance mutations is likely due to a dilution effect by susceptible ACCase expressed by homoeologs in hexaploid wild oat and/or differential expression of homoeologous ACCase gene copies. Thus, polyploidy in hexaploid wild oat may slow resistance evolution. Evidence of coexisting non-target-site resistance mechanisms among wild-oat populations was also revealed. In all, these results demonstrate that herbicide resistance and its evolution can be more complex in hexaploid wild oat than in unrelated diploid grass weeds. Our data provide a starting point for the daunting task of understanding resistance evolution in polyploids.

Influence of Time of Emergence on the Growth and Development of Wild Oat (Avena fatua)

Successful control of wild oat in cereal crops requires an accurate prediction of the developmental stages of wild oat plants that emerged during the growing season. The main objective of this research was to evaluate wild oat growth and to predict the phyllochron of wild oat plants that emerge at various times in the Red River Valley region of Minnesota and North Dakota. Field experiments were conducted in 2002 and 2003 in Crookston, MN, and Fargo, ND. Four emergence cohorts were established in 4 successive wk. Research plots were arranged in randomized complete blocks with six replications. From the naturally emerged wild oat population, 10 randomly selected plants per plot were evaluated for plant height, leaves on main stem, tillers per plant, total leaves per plant, days to flag leaf emergence and to heading, biomass per plant, and seeds per plant. Haun's numerical cereal development scale was regressed on days after emergence (DAE), day length (DL), growing degree days (GDD), or photothermal units (PTU). Wild oats that emerged first required more time for flag leaf emergence and heading, were taller, and had more biomass, leaves, tillers, and seed production than wild oat plants that emerged later. Wild oat phyllochron intervals were 5.3 d, 94 GDD, or 1,468 PTU, regardless of emergence timing. These data suggest that wild oat phyllochron is primarily driven by air temperature and is relatively stable during the extended emergence period. Later-emerging wild oat plants, although not as competitive as earlier emerging ones, still have the potential to contribute to the seed bank if left uncontrolled.

Tillage and weed control effects on productivity of a dry seeded rice–wheat system on a Vertisol in Central India

A 3-year (2006–2007 to 2008–2009) field study was conducted to evaluate the effect of four tillage systems {zero tillage (ZT) in rice (Oryza sativa L.) and wheat (Triticum aestivum L.), conventional tillage (CT) in rice and wheat, and two rotational tillage sequences that alternated between CT and ZT} with three weed management levels (weedy check, recommended herbicide and herbicide+1 hand weeding) in rice–wheat cropping system on a clay-loam soil. Continuous ZT increased the population density of awnless barnyard grass [Echinochloa colona (L.) Link] and rice flat sedge (Cyperus iria L.) in rice but reduced the population of wild oats [Avena ludoviciana (L.) Dur.] and common lambsquarters (Chenopodium album L.) in subsequent wheat. Pendimethalin (1.0kga.i.ha−1) fb 2,4-D (0.50kga.i.ha−1) significantly reduced the population density of E. colona, C. iria and sessile joyweed [Alternanthera sessilis (L.) D.C.], but did not control pink node flower (Caesulia axillaris Roxb.) in rice. In wheat, clodinafop propargyl (0.06kga.i.ha−1) fb 2,4-D (0.50kga.i.ha−1) significantly reduced the population of A. ludoviciana, but had no effect on toothed burclover (Medicago hispida Gaertn.). Continuous ZT resulted in significantly higher yield of rice (2.94Mgha−1), wheat (4.45Mgha−1) and rice–wheat system (7.39Mgha−1) compared to continuous CT (2.35, 3.86 and 6.21Mgha−1, respectively). For the total soil depth sampled (0–20cm), weed seed population was significantly greater under continuous ZT (165 weeds 500g−1 soil) and CT (101 weeds 500g−1 soil), compared to rotational tillage (71–85 weeds 500g−1 soil). Rotational tillage systems significantly reduced the seed density of C. iria, A. ludoviciana and M. hispida compared to continuous ZT or CT. Total weed seed density was 66% lower in herbicide treated than in untreated plots. Continuous ZT with effective weed management using recommended herbicide+1 hand weeding was more remunerative and energy efficient. These results suggest that conventional till-based rice–wheat system could be replaced with zero-till-based crop establishment method with effective weed control to save labor and energy in Vertisols of Central India.

Basis for Herbicide Resistance in Canadian Populations of Wild Oat (Avena fatua)

Wild oat is the second-most abundant, but most economically important, weed across the Canadian Prairies of western Canada. Despite the serious economic effects of resistance to acetyl-CoA carboxylase (ACC) or acetolactate synthase (ALS) inhibitors or both in this weed throughout the Northern Great Plains of North America, little research has examined the basis for herbicide resistance. We investigated target-site and nontarget-site mechanisms conferring ACC- and ALS-inhibitor resistance in 16 wild oat populations from across western Canada (four ACC-inhibitor resistant, four ALS-inhibitor resistant, and eight ACC- and ALS-inhibitor resistant). TheACC1mutations were found in 8 of the 12 ACC inhibitor-resistant populations. The Ile1781Leu mutation was detected in three populations, the Trp2027Cys and Asp2078Gly mutations were in two populations each, and the Trp1999Cys, Ile2041Asn, Cys2088Arg, and Gly2096Ser substitutions were in one population each. Three populations had twoACC1mutations. Only 2 of the 12 ALS inhibitor-resistant populations had anALStarget-site mutation—Ser653Thr and Ser653Asn substitutions. This is the first global report ofALStarget-site mutations inAvenaspp. and four previously undocumentedACC1mutations in wild oat. Based on these molecular analyses, seedlings of five ACC + ALS inhibitor-resistant populations (one with anACC1mutation; four with noACCorALSmutations) were treated with malathion, a known cytochrome P450 monooxygenase inhibitor, followed by application of one of four ACC- or ALS-inhibiting herbicides. Malathion treatment often resulted in control or suppression of these populations, suggesting involvement of this enzyme system in contributing to resistance to both ACC and ALS inhibitors.