¿Deben los modelos de emergencia de Lolium rigidum adaptarse en función de las condiciones climáticas?

Lolium rigidum es una problemática mala hierba a nivel mundial que en España produce importantes pérdidas de cultivo y económicas. El grupo de Biología y Agroecología de Malas hierbas (BAMh) de la SEMh ha estudiado la emergencia de esta especie durante dos campañas, 2016-17 y 2017-18. Para ello, se estableció un experimento en 10 localidades con una población de L. rigidum recolectada en Cataluña y se realizó el seguimiento de su emergencia cada 2-7 días. La emergencia se parametrizó en función de registros de temperatura y humedad procedentes de un datalogger enterrado a 2 cm. Los resultados muestran que el uso de los grados térmicos horarios es suficiente para una correcta descripción de la emergencia, desechando la opción de aplicar los grados hidrotérmicos, más comunes en los modelos de malas hierbas de invierno. Sin embargo, la emergencia de esta población de L. rigidum fue diferente en el centro y noreste de España respecto al sur, sugiriendo un efecto ambiental debido a su adaptación climática. Por ello, se plantea la necesidad de incluir poblaciones locales con el fin de adaptar el modelo desarrollado en el presente trabajo para los biotipos climáticos existentesPostprint (published version

Natural hybridization between wheat (Triticum aestivum L.) and its wild relatives Aegilops geniculata Roth and Aegilops triuncialis L

8 Pág.Cultivated bread wheat (Triticum aestivum L.) spontaneously hybridizes with wild/weedy related Aegilops populations, but little is known about the actual rates at which this hybridization occurs under field conditions. It is very important to provide reliable empirical data on this phenomenon in order to assess the potential crop-wild introgression, especially in the context of conducting risk assessments for the commercialization of genetically modified (GM) wheat, as gene flow from wheat to Aegilops species could transfer into the wild species genes coding for traits such as resistance to herbicides, insects, diseases or environmental stresses.This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) from Spain under the project AGL2004-07101-C02-01/AGRPeer reviewe

Pollen-mediated movement of herbicide resistance genes in Lolium rigidum

The transfer of herbicide resistance genes by pollen is a major concern in cross-pollinated species such as annual ryegrass (Lolium rigidum). A two-year study was conducted in the greenhouse, under favorable conditions for pollination, to generate information on potential maximum cross-pollination. This maximum cross-pollination rate was 56.1%. A three-year field trial was also conducted to study the cross-pollination rates in terms of distance and orientation to an herbicide-resistant pollen source. Under field conditions, cross-pollination rates varied from 5.5%to 11.6%in plants adjacent to the pollen source and decreased with increasing distances (1.5 to 8.9%at 15 m distance and up to 4.1%at 25 m in the downwind direction). Environmental conditions influenced the cross-pollination both under greenhouse and field conditions. Data were fit to an exponential decay model to predict gene flow at increasing distances. This model predicted an average gene flow of 7.1%when the pollen donor and recipient plants were at 0 m distance from each other. Pollen-mediated gene flow declined by 50%at 16.7 m from the pollen source, yet under downwind conditions gene flow of 5.2%was predicted at 25 m, the farthest distance studied. Knowledge of crosspollination rates will be useful for assessing the spread of herbicide resistance genes in L. rigidum and in developing appropriate strategies for its mitigation. © 2016 Loureiro et al. This is an open ccess article distributed under the terms of the reative Commons Attribution License, which permits nrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Population variability in the response of ripgut brome (Bromus diandrus) to sulfosulfuron and glyphosate herbicides

Ripgut brome has become a problematic weed in Spain both as a consequence of the continuous cropping of winter wheat through minimal tillage systems and its difficult control with selective herbicides. Ripgut brome populations collected in the regions of Castilla-León and Cataluña, two main cereal-growing areas in Spain, were screened in the greenhouse for response to sulfosulfuron, a selective herbicide for the control of brome grasses in wheat, and to glyphosate, often used as a pre-plant knockdown to control bromes in no-till systems. The fresh weight percentage relative to the untreated controls was calculated for each ripgut brome population and herbicide and was used as a measure of the herbicide response. Results showed variation in fresh weight response to both herbicides among populations. Fresh weight of the populations after sulfosulfuron was applied at the two-leaf stage at a rate of 20 g ai ha-1 varied from 3% in the most susceptible population to 35% in the most resistant; the response was similar (6 to 38%) when the herbicide dose was reduced to half. For glyphosate at 800 g ae ha-1, fresh weight varied from 2 to 25% among populations, but the range of variation in fresh weight response increased as herbicide dose decreased to one half, with rates of from 4% to 90% among populations. The location of the collection site (inside the field or in-margin) showed no differences in response to both herbicides, but there was a statistically significant, geographically correlated differentiation for glyphosate response, with a greater resistance in the populations from Castilla-León. Undamaged plants were found after treatments with both herbicides, showing differences in resistance among plants. The study shows inter- and intrapopulation variability for the response of ripgut brome to sulfosulfuron and glyphosate. The implications for resistance development are discussed within the framework of relationships of the structure of the populations relative to their herbicide response. © 2011 Weed Science Society of America

In vitro culture selection increases glyphosate tolerance in barley

In vitro culture of barley calluses has been used to produce plants with increased glyphosate tolerance. Calluses from immature embryos of barley Hordeum vulgare L. 'Jeff') were cultured on Murashige and Skoog medium with 10-6, 10-5, 10-4, 5x10-4, 10-3 or 10-2 M glyphosate for one, four or thirty months. Plants were regenerated from calluses maintained in glyphosate medium at 10-6, 10-5 or 10-4 M for four months, at 10-5 or 5x10-4 M for one month and at 10-5 M for thirty months. The progeny of each regenerated plant was analyzed for response to glyphosate. Some progenies showed increased tolerance to glyphosate

The response of Bromus diandrus and Lolium rigidum to dalapon and glyphosate I Baseline sensitivity

The establishment of Bromus diandrus and Lolium rigidum baseline sensitivity to glyphosate and dalapon herbicides was studied for the North Central region of Spain. A rapid method in Petri dishes and a plant assay method were evaluated. The studied populations of both weed species showed sensitivity to both herbicides. The rapid method to establish the sensitivity baseline for these species worked properly for dalapon and a good correlation was found between Petri dish and plant assays. In the case of glyphosate, the rapid method was not sensitive enough, so baseline sensitivity establishment would have to be determined with plant assays. The baseline sensitivities will allow us to determine quickly and accurately any variation in the sensitivity of these weeds against these herbicides over time and to detect, at an early stage, the beginning of any trends towards resistance. © 2010 The Authors. Journal Compilation © 2010 European Weed Research Society

Inheritance of tolerance to metribuzin in durum wheat

The inheritance of tolerance to the herbicide metribuzin was studied in two durum wheat cultivars, one of which, 'Anton', is resistant and one, 'Nita', susceptible. Parents, F1, F2 and F3 of the crosses 'Anton' x 'Nita' and 'Nita' x 'Anton' were tested for herbicide response. The character evaluated was the increase in weight of plants treated with the herbicide. As there were no significant differences between progenies of reciprocal crosses, cytoplasm was not involved in tolerance. Tolerance was semi-dominant with means values of F1, F2 and F3 progenies in the range of mid-parent. The heritability of this trait estimated by regression of the average of progeny F3 in their parent F2 had a value of 0.23 ± 0.063 and a value of 0.52 ± 0.150 estimated by the relation V(G)/V(P) for full-sib F2 families

Hybridization, fertility and herbicide resistance of hybrids between wheat and Aegilops biuncialis

Genetically modified crops are now grown worldwide and their area of cultivation is increasing yearly. Although transgenic crops offer benefits, several risks have been identified associated with their cultivation. One such risk is their potential for hybridization with wild species, and weed-related species, and the possible escape and subsequent introgression of the transgenes into these species. Transgenic wheat varieties are being successfully developed and field-tested, primarily on herbicide-tolerant wheat. If genetically modified herbicide-tolerant wheat is commercialized in the near future this may result in the escape of the inserted gene from the crop and its incorporation into closely related wild species. This fact could give a competitive advantage to the recipients. For risk assessment purposes it is necessary to determine the frequency of crop-wild transgene flow and the fertility of hybrids. Most wheat-wild hybridization studies have been conducted with the purpose of breeding with wheat acting as the female parent in crosses, but very limited information is available focused on hybrid production with wheat as the male parent. Here, we studied (1) the potential hybridization between wheat and the wild related Aegilops biuncialis, and (2) the fertility of the hybrids. Hybridization was quantified in crossing experiments over 5 years in a greenhouse using three wheat cultivars as pollen donors and emasculated plants of one A. biuncialis population as pollen recipients. Hybridization was estimated as the ratio of number of seeds set to the number of flowers pollinated in percentage terms. Our results show that hybrids between wheat and A. biuncialis are formed easily, with hybridization rates ranging from 8.5 to 75%. The fertility of the hybrids, measured as the number of seeds per spikelet (%), was also evaluated by self-pollination and by backcrossing. Most of the hybrids were self-sterile but 11 F seeds were obtained from 191 A. biuncialis-wheat hybrids. However, backcrossing seeds were found in all BC combinations at average rates of 3.7% (0-19.6%) for greenhouse experiments, and 4.6% (0-28.9%) for field experiments. In subsequent generations, although few plants were available, BCF exhibited a certain degree of fertility, up to 3.57% with the cultivar Chinese Spring. F and BC were also checked for resistance to the herbicide difenzoquat that was present in the parental wheat, while A. biuncialis was susceptible. Difenzoquat resistance was maintained in the F hybrids and also in the derived BC plants. This information on hybridization and fertility of the first A. biuncialis-wheat hybrid generations could be an initial step to assess the relative advantage of hybridization in the adaptive ability of A. biuncialis and hybrid derivatives and the impact thereof on the environment and agricultural system. This needs to be studied in depth when wheat and A. biuncialis share habitat. © 2008 INRA EDP Sciences

Activity of 5-enolpyruvylshikimate-3-phosphate synthase in glyphosate treated and untreated barley

EPSPS (5-enolpyruvilshikimate-3-phosphate syn-thase) inhibition has been described as the main target for the herbicide glyphosate. Total soluble protein concentration and EPSPS activity were measured after 4 hr, 1 day and 7 day of glyphosate treatment, at a dose equivalent to 0.94 Kg ha-1. After seven days of glyphosate treatment, EPSPS activity reduced to 80% as compared to the activity in untreated seedlings. Glyphosate at 2 μM concentration inhibited EPSPS by 18% at a PEP concentration of 1 mM, but inhibition increased to 64% when PEP concentration was 0.1 mM. Moreover, 1.5 μM glyphosate concentration reduced EPSPS activity by 50% at 0.1 mM of PEP, instead 0.1 mM of glyphosate was necessary when 1 mM was present in the reactions

Pollen-mediated gene flow in wheat (Triticum aestivum L.) in a semiarid field environment in Spain

Transgenic wheat (Triticum aestivum L.) varieties are being developed and field-tested in various countries. Concerns regarding gene flow from genetically modified (GM) crops to non-GM crops have stimulated research to estimate outcrossing in wheat prior to the release and commercialization of any transgenic cultivars. The aim is to ensure that coexistence of all types of wheat with GM wheat is feasible in accordance with current regulations. The present study describes the result of a field experiment under the semi-arid climate conditions of Madrid, Spain, at two locations ("La Canaleja" and "El Encin" experimental stations) in Madrid over a 3-year period, from 2005 to 2007. The experimental design consisted of a 50 × 50 m wheat pollen source sown with wheat cultivars resistant to the herbicide chlortoluron ('Deganit' and 'Castan' respectively) and three susceptible receptor cultivars ('Abental', 'Altria' and 'Recital') sown in replicated 1 × 1 m plots at different distances (0, 1, 3, 5, 10, 20, 40, 80 and 100 m) and four directions. Outcrossing rates were measured as a percentage of herbicide-resistant hybrids using an herbicide-screening assay. Outcrossing was greatest near the pollen source, averaging 0.029 % at 0 m distance at "La Canaleja" and 0.337 % at "El Encin", both below the 0.9 % European Union regulated threshold, although a maximum outcrossing rate of 3.5 % was detected in one recipient plot. These percentages declined rapidly as the distance increased, but hybrids were detected at different rates at distances of up to 100 m, the maximum distance of the experiment. Environmental conditions, as drought in 2004-2005 and 2005-2006, may have influenced the extent of outcrossing. These assays carried out in wheat under semi-arid conditions in Europe provide a more complete assessment of pollen-mediated gene flow in this crop. © 2012 Springer Science+Business Media B.V