The world’s first glyphosate-resistant case of Avena fatua L. and Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne and alternative herbicide options for their control

Avena fatua and A. ludoviciana (commonly known as wild oats) are the most problematic winter grass species in fallows and winter crops in the northeast region of Australia. A series of experiments were conducted to evaluate the performance of glyphosate and alternative post-emergence herbicides on A. fatua and A. ludoviciana. This study reports the world’s first glyphosate-resistant (GR) biotypes of A. fatua and A. ludoviciana. The glyphosate dose required to kill 50% of the plants (LD50) and to reduce 50% of the biomass (GR50) for the GR biotype of A. fatua was 556 g a.e./ha and 351 g a.e./ha, respectively. These values for A. ludoviciana were 848 g a.e./ha and 289 g a.e./ha. Regardless of the growth stage (3–4 or 6–7 leaf stages), clethodim (120 g a.i./ha), haloxyfop (78 g a.i./ha), pinoxaden (20 g a.i./ha), and propaquizafop (30 g a.i./ha) were the best alternative herbicide options for the control of A. fatua and A. ludoviciana. The efficacy of butroxydim (45 g a.i./ha), clodinafop (120 g a.i./ha), imazamox + imazapyr (36 g a.i./ha), and paraquat (600 g a.i./ha) reduced at the advanced growth stage. Glufosinate (750 g a.i./ha), flamprop (225 g a.i./ha), and pyroxsulam + halauxifen (20 g a.i./ha) did not provide effective control of Avena species. This study identified alternative herbicide options to manage GR biotypes of A. fatua and A. ludoviciana.

Identification of sentinel plant species for evaluating phytotoxicity of veterinary antibiotics in mediterranean europe

Background Antibiotics used to treat livestock species enter agricultural fields when they are excreted by grazing animals or are present in manure that is added to fields as fertiliser. In the European Union, the potential effects of such antibiotics on terrestrial plants must be evaluated following the standardised OECD 208 method, which specifies the crop and wild species that should serve as “sentinels” for assessing antibiotic exposure. The present study aimed to compare this approved list of sentinel species against crop and wild plant species actually present in agricultural and pasture lands in Mediterranean Europe in order to identify the most appropriate sentinel plants for the region. The study focused on Spain as a region representative of Mediterranean Europe. Georeferenced layers for wild plant species and cultivated areas (crops), livestock density and land cover were combined, and then selection criteria were applied, leading to the identification of sentinel crop species for agriculture and pasture scenarios. Results In the agriculture scenario, the sentinel crop species were barley, wheat, corn, sunflower, dried pie, alfalfa, vetch, oilseed rape and sugar beet; the sentinel wild species were Papaver rhoeas, Galium aparine and Chenopodium album. In the pasture scenario, sentinel wild species were Bromus tectorum, Agrostis capillaris, Trifolium pratense, Lotus corniculatus and Galium aparine. The following common weed species in field boundaries or in pasture lands also emerged as potential sentinel species for risk assessment, even though they are not listed in the OECD 208 method: Sonchus oleraceus, Avena sterilis, Dactylis glomerata, Hordeun murinum and Lolium rigidum. Conclusions The sentinel species identified in this study may be useful in risk assessment procedures covering Mediterranean Europe. The method developed for this study could be useful for identifying sentinel species for other geographical areas.

Differences in Germination of ACCase-Resistant Biotypes Containing Isoleucine-1781-Leucine Mutation and Susceptible Biotypes of Wild Oat (Avena sterilis ssp. ludoviciana)

Herbicide resistance can affect seed germination and the optimal conditions required for seed germination, which in turn may impose a fitness cost in resistant populations. Winter wild oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet and Magne] is a serious weed in cereal fields. In this study, the molecular basis of resistance to an ACCase herbicide, clodinafop-propargyl, in four A. ludoviciana biotypes was assessed. Germination differences between susceptible (S) and ACCase-resistant biotypes (WR1, WR2, WR3, WR4) and the effect of Isoleucine-1781-Leucine mutation on germination were also investigated through germination models. The results indicated that WR1 and WR4 were very highly resistant (RI > 214.22) to clodinafop-propargyl-contained Isoleucine to Leucine amino acid substitution. However, Isoleucine-1781-Leucine mutation was not detected in other very highly resistant biotypes. Germination studies indicated that resistant biotypes (in particular WR1 and WR4) had higher base water potentials than the susceptible one. This shows that resistant biotypes need more soil water to initiate their germination. However, the hydrotime constant for germination was higher in resistant biotypes than in the susceptible one in most cases, showing faster germination in susceptible biotypes. ACCase-resistant biotypes containing the Isoleucine-1781-Leucine mutation had lower seed weight but used more seed reserve to produce seedlings. Hence, integrated management practices such as stale seedbed and implementing it at the right time could be used to take advantage of the differential soil water requirement and relatively late germination characteristics of ACCase-resistant biotypes.

Discovery and Chromosomal Location a Highly Effective Oat Crown Rust Resistance Gene Pc50-5

Crown rust, caused by Puccinia coronata f. sp. avenae, is one of the most destructive fungal diseases of oat worldwide. Growing disease-resistant oat cultivars is the preferred method of preventing the spread of rust and potential epidemics. The object of the study was Pc50-5, a race-specific seedling crown rust resistant gene, highly effective at all growth stages, selected from the differential line Pc50 (Avena sterilis L. CW 486-1 × Pendek). A comparison of crown rust reaction as well as an allelism test showed the distinctiveness of Pc50-5, whereas the proportions of phenotypes in segregating populations derived from a cross with two crown rust-susceptible Polish oat cultivars, Kasztan × Pc50-5 and Bingo × Pc50-5, confirmed monogenic inheritance of the gene, indicating its usefulness in oat breeding programs. Effective gene introgression depends on reliable gene identification in the early stages of plant development; thus, the aim of the study was to develop molecular markers that are tightly linked to Pc50-5. Segregating populations of Kasztan × Pc50-5 were genotyped using DArTseq technology based on next-generation Illumina short-read sequencing. Markers associated with Pc50-5 were located on chromosome 6A of the current version of the oat reference genome (Avena sativa OT3098 v2, PepsiCo) in the region between 434,234,214 and 440,149,046 bp and subsequently converted to PCR-based SCAR (sequence-characterized amplified region) markers. Furthermore, 5426978_SCAR and 24031809_SCAR co-segregated with the Pc50-5 resistance allele and were mapped to the partial linkage group at 0.6 and 4.0 cM, respectively. The co-dominant 58163643_SCAR marker was the best diagnostic and it was located closest to Pc50-5 at 0.1 cM. The newly discovered, very strong monogenic crown rust resistance may be useful for oat improvement. DArTseq sequences converted into specific PCR markers will be a valuable tool for marker-assisted selection in breeding programs.

Competition of Weeds Dominated by Wild Oat (Avena sterilis) in Wheat (Triticum durum Desf.) in Jordan

Wheat is the main field crop grown in Jordan. Productivity is low due to different factors, including erratic rainfall, poor soil fertility and weed competition. A field experiment was carried out at the University of Jordan Research Station for two growing seasons to determine the effect of weed competition on growth and yield of wheat (Triticum durum Cv. “Hourani”). Treatments consisted of either allowing weeds to infest the crop or maintaining the crop weed-free for increasing durations after emergence. Results showed that, the longer the periods of weed competition, the greater the loss in crop growth and yield. Average reductions in grain and straw yields were 41% and 37%, respectively. The highest grain yield obtained was from weed-free, and the lowest was in weed-infested plots for the entire growing season. Average grain yield was not significantly different at 14 to 49 days of weed-infested periods, while none of the weed-free periods produced a yield similar to that of the weed-free control. However, maintaining a weed-free crop for three weeks after emergence significantly increased grain yield compared with the weed-infested control. High rainfall in the first season almost doubled weed growth and greatly reduced wheat growth and yield compared with the second season. To determine the critical period of weed competition and the influence of weed infestation on wheat grain yield, Gompertz and logistic equations were fitted to data representing increasing duration of weed-free and weed-infested periods, respectively. Based upon an arbitrary 5% level of average grain yield loss in the two years, the critical period of weed competition occurred at 0–49 days after wheat emergence, which corresponded with the rapid increase in weed biomass.

Interference of Wild Oats (Avena fatua) and Sterile Oats [Avena sterilis ssp. ludoviciana (Durieu)] in Wheat

Wild oat (Avena fatua L.) and sterile oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne; referred to as A. sterilis here], winter season weeds, are increasing their prevalence in the eastern grain region of Australia. Biological attributes of these weeds enable them to survive in a wide range of environments and under different weed infestation levels. The interference of A. fatua and A. sterilis in a wheat (Triticum aestivum L.) crop was examined in southeast Queensland, Australia through field studies in 2019 and 2020. Different infestation levels (0, 3, 6, 12, 24, and 48 plants m−2) of A. fatua and A. sterilis were evaluated for their potential to cause yield losses in wheat. Based on a three-parameter logarithmic model, the A. fatua and A. sterilis infestation levels corresponding to 50% wheat yield loss were 15 and 16 plants m−2, respectively. The yield reduction was due to a reduced spike number per unit area because of an increased weed infestation level. At the highest weed infestation level (48 plants m−2), A. fatua and A. sterilis produced a maximum of 4,800 and 3,970 seeds m−2, respectively. A. fatua exhibited lower seed retention (17-39%) than A. sterilis (64-80%) at wheat harvest, as most of the seeds of A. fatua had shattered at crop maturity. Our results implied that there is a good opportunity for harvest weed seed control if the paddock is infested with A. sterilis. This study suggests that in the absence of an integrated weed management strategy (using both chemical and nonchemical options), a high infestation of these weeds could cause a severe crop yield loss, increase weed seed production, and replenish weed seedbank in the soil.

Novel sensor-based method (quick test) for the in-season rapid evaluation of herbicide efficacy under real field conditions in durum wheat

Optimum herbicide use is a key factor affecting the success of any integrated weed management strategy. The main objective of the current study was to implement a method based on spectrometer measurements for the in situ evaluation of herbicide efficacy and the detection of potentially herbicide-resistant weeds. Field trials were conducted in Greece between 2018 and 2020 in several durum wheat fields (Triticum durum Desf.). In all trials, the overall effect of herbicide application on the recorded Normalized Difference Vegetation Index (NDVI) values (at 1 and 2 wk after treatment [WAT]) was significant (P ≤ 0.001). For the majority of the surveyed fields, low NDVI values were recorded after 2,4-D application and a mixture of clopyralid + florasulam from 1 WAT, suggesting their increased efficacy. In several cases, the application of pyroxsulam + florasulam resulted in significant NDVI reductions at 2 WAT. As observed at the end of the growing seasons, the herbicides that reduced NDVI resulted in lower weed biomass. Strong correlations were observed between weed aboveground biomass and NDVI (2 WAT). In particular, R2 values were 0.8234 to 0.8649, 0.8453, 0.8595, 0.8149, and 0.8925 for the Aliartos, Thiva, Domokos, Larissa, and Orestiada fields, respectively. The overall effects of herbicide application on wheat grain yield were also significant (P ≤ 0.001). Pot experiments confirmed that the high NDVI values in some cases could be attributed to the presence of herbicide-resistant weeds. For instance, the resistance indices of two accessions of catchweed bedstraw (Galium aparine L.) to mesosulfuron-methyl + iodosulfuron-methyl-sodium ranged between 9.7 and 13.2, whereas one sterile oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet & Magne] accession was 8.8 times more resistant to fenoxaprop-p-ethyl than a susceptible one. The present study is targeted at making a significant contribution toward establishing cause–effect relationships and presenting a useful tool for developing more effective weed management practices in more arable crops and under different soil and climatic conditions.

Modeling emergence of sterile oat (Avena sterilis ssp. ludoviciana) under semiarid conditions

Winter wild oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne; referred to as A. sterilis here] is one of the major weed species of the Avena genus, given its high competitive ability to infest cereal crops worldwide, with special concern in Spain. A nine-location field experiment was established across Spain where a total of 400 A. sterilis seeds per location were sowed in four replicates in autumn 2016 to monitor the emergence during two growing seasons in dryland conditions. The data were used to test the prediction ability of previously published thermal (TT) and hydrothermal time (HTT) models and to develop new models, if required. Overall, the average percentage of emergence was 30% during the first season and 21% during the second season. In both seasons, the main emergence flush occurred between November and February. According to the phenological stage, A. sterilis achieved the tillering earlier in southern sites, between November 25 and the end of December, compared with northern sites, where this stage was reached at the end of January. The newly developed model described the emergence with precision, using three cardinal temperatures to estimate the TT. The three cardinal points were established at −1.0, 5.8, and 18.0 C for base (Tb), optimum (To), and ceiling temperature (Tc), while the base water potential (Ψb) was established at −0.2 MPa for the HTT estimation. This study contributes to improving prediction of the emergence of A. sterilis and provides knowledge for decision support systems (DSS) for the control of this weed.