Crops In Argentina Research Articles

Identification of potassium phosphite responsive miRNAs and their targets in potato.

Micro RNAs (miRNAs) are small single strand non-coding RNAs that regulate gene expression at the post-transcriptional level, either by translational inhibition or mRNA degradation based on the extent of complementarity between the miRNA and its target mRNAs. Potato (Solanum tuberosum L.) is the most important horticultural crop in Argentina. Achieving an integrated control of diseases is crucial for this crop, where frequent agrochemical applications, particularly fungicides, are carried out. A promising strategy is based on promoting induced resistance through the application of environmentally friendly compounds such as phosphites, inorganic salts of phosphorous acid. The use of phosphites in disease control management has proven to be effective. Although the mechanisms underlying their effect remain unclear, we postulated that miRNAs could be involved. Therefore we performed next generation sequencing (NGS) in potato leaves treated and non treated with potassium phosphite (KPhi). We identified 25 miRNAs that were expressed differentially, 14 already annotated in miRBase and 11 mapped to the potato genome as potential new miRNAs. A prediction of miRNA targets showed genes related to pathogen resistance, transcription factors, and oxidative stress. We also analyzed in silico stress and phytohormone responsive cis-acting elements on differentially expressed pre miRNAs. Despite the fact that some of the differentially expressed miRNAs have been already identified, this is to our knowledge the first report identifying miRNAs responsive to a biocompatible stress resistance inducer such as potassium phosphite, in plants. Further characterization of these miRNAs and their target genes might help to elucidate the molecular mechanisms underlying KPhi-induced resistance.

Monitoring the Evolution of Resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) to the Cry1F Protein in Argentina.

Maize (Zea mays L.) is one of the most important and widely cultivated crops in Argentina. Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a common maize pest capable of causing significant yield losses and is most destructive in late-planted maize in subtropical regions, going through five to six generations per growing season. The Bacillus thuringiensis (Bt) trait Herculex I Insect Protection technology by Dow AgroSciences and Pioneer Hi-Bred (HX I, event DAS-Ø15Ø7-1), expressing Cry1F protein, was launched in the 2005-2006 season in Argentina and was widely adopted because of the high level of efficacy against S. frugiperda, as well as other pests such as Diatraea saccharalis (J.C. Fabricius). However, increased late-season plantings, limited adoption of refuge, and properties of S. frugiperda biology (high number of generations and migratory behavior) have led to high S. frugiperda exposure to Cry1F and resistance selection pressure. Field efficacy monitoring has been conducted throughout the main maize production areas in Argentina from 2009 to 2016. Laboratory monitoring has been conducted throughout the same areas from 2010 to 2015. Here, we describe changes in field efficacy of HX I and the results of laboratory-based susceptibility monitoring conducted using purified Cry1F protein. Increases in larval survival and crop damage were evident throughout the 2012-2016 period and spanned the majority of maize production areas in Argentina. Over the same period, random larval collections showed increasing survivorship on diet containing purified Cry1F protein. These field and laboratory studies confirmed that resistance to Cry1F has developed and is now widely distributed in S. frugiperda populations in Argentina.

First report of spot lesion of wheat caused by Pyrenophora teres f. sp maculata observed in Argentina

Pyrenophora tritici-repentis, causal agent of tan spot, is the species commonly associated with leaf spotting symptoms on wheat (Triticum aestivum L.) worldwide and in Argentina. On the other hand, P. teres is a major constraint on barley (Hordeum vulgare L.) production, however the pathogen has not been reported in association with wheat crop in Argentina. In 2018, following a routine survey of wheat fields, leaves showing symptoms compatible with those caused by Pyrenophora spp. were observed in the principal wheat production areas in Buenos Aires and Entre Rios Provinces of Argentina. The disease incidence varied from 30% to 80%. Symptomatic wheat plants were collected from production fields and spotted foliar tissue with symptoms was plated onto PDA 2% growth medium. The isolates were tentatively identified as putative Pyrenophora spp. based on its colonies and conidia characteristics. Given the possibility of confusion by similar characteristics between some Pyrenophora species that infect wheat plants, the aim of this work was to clarify the identity of the fungus infecting this crop.In this study, we were able to confirm field observations in greenhouse assays on wheat plants using the fungal isolates. The seedling symptoms rate under artificial inoculation of five commercial wheat varieties was 100%. Pathogenicity tests and morphological studies as well as analyses indicated that the disease was caused by Pyrenophora teres. Molecular identification of the two isolates was doubled checked by PCR. First, the internal transcribed spacer (ITS) amplification and sequencing and specific PCR assay using PTT and PTM primers allowed to confirm that two monosporic isolates were P. teres f. maculata. This is a novel disease on wheat in Argentina caused by this pathogen. This finding is of great importance from the epidemiological point of view of the biodiversity of the fungus and also to contribute with the future management of the disease.

Molecular Mechanisms Endowing Cross-resistance to ALS-Inhibiting Herbicides in Amaranthus hybridus from Argentina

Amaranthus hybridus L. is one of the most problematic weeds in summer crops in Argentina. However, 20 years after the detection of the first case of resistance to ALS-inhibiting herbicides in this country, no extensive reports of the molecular mechanisms endowing resistance were published. In this work, we sequenced the acetolactate synthase gene of resistant plants belonging to five different populations of A. hybridus from Santa Fe and Cordoba provinces. We found that every population presented at least one of the previously documented substitutions W574L and D376E in ALS amino acid sequence. These results explain the cross-resistance to ALS-inhibiting herbicides and should alert about the usage of herbicides with a different site of action after an ineffective control of this species. This is the first report of these target-site mechanisms endowing resistance to ALS-inhibiting herbicides in A. hybridus populations from Argentina.

Lethal and sublethal effects of chlorantraniliprole on Spodoptera cosmioides (Lepidoptera: Noctuidae).

The Spodoptera cosmioides (Walker, 1858) population has increased in Bacillus thuringiensis Berliner (Bt) soybean crops in Argentina. As there are no registered products for its control, the recommended insecticides for S. frugiperda are used. The aim of this study was therefore to determine the lethal concentration (LC) of chlorantraniliprole and its sublethal effects on the biological and reproductive functions of S. cosmioides, an emerging soybean pest in Argentina. An ingestion toxicity bioassay showed that chlorantraniliprole was active against larvae of the second instar, and after 48 h of exposure LC50 was 0.054 µg mL-1 H2 O. In the study of sublethal effect, chlorantraniliprole induced changes in the life cycle of exposed S. cosmioides, which required more time to complete all stages of development (larval, pupal and adult stages). Pupal weight was also higher in larvae exposed to sublethal concentrations of chlorantraniliprole. Adult fecundity was decreased: the number of eggs laid by each adult female moth, as compared with control females, was two (LC15 ) and eight (LC30 ) times lower. These results indicate that chlorantraniliprole has toxicity against S. cosmioides larvae. Sublethal effects on the biological and reproductive performance of this species can help optimize integrated pest management programs. © 2018 Society of Chemical Industry.

Metabolic and physiologic profile during the fruit ripening of three blueberries highbush (Vaccinium corymbosum) cultivars

BACKGROUND: Blueberry was introduced as a crop in Argentina about 30 years ago. Its harvesting period ranges from September to December, during the northern hemisphere (its main export destination) fall season, which makes it a profitable commercial crop. As most part of the production is exported fresh, the understanding of biochemical aspects connected with fruit firmness is crucial to improve marketable conditions. OBJECTIVE: The main purpose of this work is to explore the metabolic and physiologic changes in three highbush blueberry cultivars during maturation and the possible association with their contrasting firmness features. METHODS: Vaccinium corymbosum cv. ‘Emerald’, ‘Snowchaser’ and ‘O’Neal’, in order of decreasing firmness, were collected at green and ripe stages. Metabolites were analyzed by gas chromatography-mass spectrometry (GC-MS) and HPLC. Total phenolic compounds, pectin methyl esterase (PME) and β-galactosidase activities were quantified by colorimetric assays. RESULTS: Multivariate analysis of metabolites differentiated fruit regarding their maturation state in the first place. Malic, citric and phosphoric acids, asparagine (Asn) and mannitol were more abundant in green fruits. Conversely, mature fruits were distinguished by their higher content of citrulline and turanose. Other compounds were responsible for the differentiation between varieties: histidine (His), valine (Val), arginine (Arg), methionine (Met) and sucrose where high in ripe Snowchaser, while green and ripe Emerald had more tryptophane (Trp), glycine (Gly), phenylalanine (Phe), Trp, Gly and glucose. An interesting finding is that Emerald, the firmer variety, had less xylose content at both stages, possibly owing to a minor degree of cell wall degradation. Fold change of PME and β-galactosidase activity from green to ripe fruit demonstrated a divergent tendency in Emerald and Snowchaser compared to O’Neal. A correlation study strongly and positively connected firmness with citric acid and phenylalanine (Phe) content, while xylose, leucine (Leu) and shikimic acid were negatively related to this attribute. CONCLUSIONS: This study suggests that changes in the content of a few metabolite and activities of cell wall modifying enzymes during maturation period could be correlated with the observed difference in firmness of the blueberries studied. These findings may yield clues for improvements in fertilization protocols as well as to serve to the guided development of new varieties based on biochemical quality traits.

Primer registro de Argyrotaenia tucumana (Lepidoptera: Tortricidae) en montes de duraznero, Prunus persicae (L.) Batsch, del sur de la provincia de Santa Fe

Argyrotaenia tucumana Trematerra & Brown, 2004 (Lepidoptera: Tortricidae) was detected feeding on peach fruit crops in the south of Santa Fe province. The damages observed in January 2017 were superficial and close to the peduncle of the fruit. This is the first record of this pest on this crop in Argentina

Distribution and genetic variability of alfalfa dwarf virus, a cytorhabdovirus associated with alfalfa dwarf disease in Argentina.

In 2010, a novel cytorhabdovirus named alfalfa dwarf virus (ADV) was detected for the first time in lucerne crops in Argentina showing dwarfism, in mixed infections with several other viruses. ADV appears to be endemic to Argentina and has not been reported elsewhere. In this study, we have investigated the genetic variability of ADV based on the complete nucleoprotein (N) gene of 13 isolates from different lucerne-growing regions in Argentina. Phylogenetic and sequence identity analyses showed that all ADV isolates are closely related and have not diverged more than 1% in the N gene despite geographical separation. These data provide further evidence that ADV is new to science and emerged and spread very recently. A total of 43 single-nucleotide polymorphisms were identified between the ADV isolates studied. Analysis of N gene ORF sequence revealed a mutational bias, with more transitions than transversions. In all cases, the ratio of non-synonymous/synonymous nucleotide changes was <1, indicating that ADV N gene is under predominantly purifying selection.

Characterization and competitive ability of non-aflatoxigenic Aspergillus flavus isolated from the maize agro-ecosystem in Argentina as potential aflatoxin biocontrol agents

Aspergillus flavus is an opportunistic pathogen and may produce aflatoxins in maize, one of the most important crops in Argentina. A promising strategy to reduce aflatoxin accumulation is the biological control based on competitive exclusion. In order to select potential biocontrol agents among isolates from the maize growing region in Argentina, a total of 512 A. flavus strains were isolated from maize kernels and soil samples. Thirty-six per cent of the isolates from maize kernels did not produce detectable levels of aflatoxins, while 73% of the isolates from soil were characterized as non-aflatoxin producers. Forty percent and 49% of the isolates from maize kernels and soil samples, respectively, were not producers of cyclopiazonic acid (CPA). Sclerotia morphology was evaluated using Czapek Dox media. Eighty-six per cent of the isolates from maize kernels and 85% of the isolates from soil samples were L sclerotia morphotype (average diameter > 400 μm). The remaining isolates did not produce sclerotia. All isolates had MAT 1-1 idiomorph. The competitive ability of 9 non aflatoxigenic strains, 4 CPA(+) and 5 CPA(−), was evaluated in co-inoculations of maize kernels with an aflatoxigenic strain. All evaluated strains significantly (p < 0.05) reduced aflatoxin contamination in maize kernels. The aflatoxin B1 (AFB1) reduction ranged from 6 to 60%. The strain A. flavus ARG5/30 isolated from maize kernels would be a good candidate as a potential biocontrol agent to be used in maize, since it was characterized as neither aflatoxin nor CPA producer, morphotype L, MAT 1-1 idiomorph, and reduced AFB1 content in maize kernels by 59%. This study showed the competitive ability of potential aflatoxin biocontrol agents to be evaluated under field trials in a maize agro-ecosystem in Argentina.

Characterization of Argentinian Endemic Aspergillus flavus Isolates and Their Potential Use as Biocontrol Agents for Mycotoxins in Maize.

Maize (Zea mays L.) is a highly valuable crop in Argentina, frequently contaminated with the mycotoxins produced by Aspergillus flavus. Biocontrol products formulated with atoxigenic (nontoxic) strains of this fungal species are well known as an effective method to reduce this contamination. In the present study, 83 A. flavus isolates from two maize regions of Argentina were characterized and evaluated for their ability to produce or lack of producing mycotoxins in order to select atoxigenic strains to be used as potential biocontrol agents (BCA). All of the isolates were tested for aflatoxin and cyclopiazonic acid (CPA) production in maize kernels and a liquid culture medium. Genetic diversity of the nonaflatoxigenic isolates was evaluated by analysis of vegetative compatibility groups (VCG) and confirmation of deletions in the aflatoxin biosynthesis cluster. Eight atoxigenic isolates were compared for their ability to reduce aflatoxin and CPA contamination in maize kernels in coinoculation tests. The A. flavus population was composed of 32% aflatoxin and CPA producers and 52% CPA producers, and 16% was determined as atoxigenic. All of the aflatoxin producer isolates also produced CPA. Aflatoxin and CPA production was significantly higher in maize kernels than in liquid medium. The 57 nonaflatoxigenic strains formed six VCG, with AM1 and AM5 being the dominant groups, with a frequency of 58 and 35%, respectively. In coinoculation experiments, all of the atoxigenic strains reduced aflatoxin from 54 to 83% and CPA from 60 to 97%. Members of group AM1 showed a greater aflatoxin reduction than members of AM5 (72 versus 66%) but no differences were detected in CPA production. Here, we described for the first time atoxigenic isolates of A. flavus that show promise to be used as BCA in maize crops in Argentina. This innovating biological control approach should be considered, developed further, and used by the maize industry to preserve the quality properties and food safety of maize kernels in Argentina.

Variations in pest bird density in Argentinean agroecosystems in relation to land use and/or cover, vegetation productivity and climate

Context Changes in environmental conditions may influence bird populations, including pest bird species, and their distribution. In Argentina, particularly in the Pampas region, agricultural expansion has resulted in important changes in agroecosystems, with impacts on bird species. Aims This study analysed the relationship between pest bird densities and the environmental variables associated with land use and/or cover, vegetation productivity and climate. The study focused on the most important pest bird species to grain crops in Argentina and Uruguay: the eared dove (Zenaida auriculata) and the monk parakeet (Myiopsitta monachus). Methods An area in Central Argentina was divided into three agro-productive regions, one predominantly agricultural and two with mixed production activities: agricultural rangeland and agricultural forested rangeland. Bird populations were sampled on a yearly basis between 2003 and 2011 in point-transects located along secondary roads (47 routes in total). Linear mixed models and a multi-model inference approach were used to compare the effects of individual predictive variables on bird densities. Key results Mean estimated density for the eared dove was 0.39 individuals per ha (±0.02), almost three times the density of the monk parakeet (0.10 individuals per ha±0.02). The spatial distribution of changes in density of the eared dove and monk parakeet showed irregular patterns across the study area. Density of eared dove was directly related to cover of native and exotic woodlots and inversely related to cover of fallow and weedy fields, and to temperature and rainfall. Monk parakeet density, in turn, was directly related to cover of woodlots. Conclusions The density of eared doves and monk parakeets changed mostly in relation to land use and/or cover and, to a lesser extent, to climatic conditions. Information of pest bird populations in a long-term period allowed us to understand spatial patterns in bird population distribution and to identify the main environmental factors explaining them. Implications The consideration of land use and/or cover, vegetation productivity and climate variables at regional scale, measured during a long-term period, would be critical for anticipating population increases and, possibly, increases in crop damage.

Natural occurrence of the entomopathogenic genus Pandora on spittlebug pests of crops and pastures in Argentina

AbstractThe natural occurrence of entomophathogenic fungi infecting spittlebugs (Hemiptera: Cercopidae) considered serious pests to pasture grasses and crops in Argentina was investigated during summer˗autumn (December to May) from 2013 to 2016. Adults and nymphs of spittlebugs were collected from Sorghum halepense and Setaria parviflora var. parviflora in San Miguel de Tucumán, Tucumán province. The entomopathogenic fungal species were characterized on the basis of morphological keys and molecular techniques. Microscopic characters were described from material mounted in lactophenol/aceto‐orcein (1% w/v), and the amplification of the fungal SSU rDNA was carried out using the universal primers nu‐SSU‐0021‐5′ and nu‐SSU‐1780‐3′. Summarized information about occurrence of fungal infections on spittlebugs populations is provided. This study reports for the first time the occurrence of the genus Pandora infecting adults of the economically important spittlebugs Deois (Deois) mourei, D. (D.) knoblauchii, Isozulia christenseni christenseni and Notozulia entreriana from Argentina expanding the host range and geographical distribution of entomophthoralean fungi.

Complete genome sequence of maize yellow striate virus, a new cytorhabdovirus infecting maize and wheat crops in Argentina.

A rhabdovirus infecting maize and wheat crops in Argentina was molecularly characterized. Through next-generation sequencing (NGS) of symptomatic leaf samples, the complete genome was obtained of two isolates of maize yellow striate virus (MYSV), a putative new rhabdovirus, differing by only 0.4% at the nucleotide level. The MYSV genome consists of 12,654 nucleotides for maize and wheat virus isolates, and shares 71% nucleotide sequence identity with the complete genome of barley yellow striate mosaic virus (BYSMV, NC028244). Ten open reading frames (ORFs) were predicted in the MYSV genome from the antigenomic strand and were compared with their BYSMV counterparts. The highest amino acid sequence identity of the MYSV and BYSMV proteins was 80% between the L proteins, and the lowest was 37% between the proteins 4. Phylogenetic analysis suggested that the MYSV isolates are new members of the genus Cytorhabdovirus, family Rhabdoviridae. Yellow striate, affecting maize and wheat crops in Argentina, is an emergent disease that presents a potential economic risk for these widely distributed crops.

The sunflower crop in Argentina: past, present and potential future

Sunflower was a crop of great importance in Argentina until 2002; it was ranked among the countries with the largest production, about 18% of the world total. Currently, it is in the fourth place, with only 7%. Several factors caused Argentina to lose its leadership, the most important being that farmers preferred the soybean crop because of its competitiveness pushing sunflower to areas where the former crop was not adapted. However, in 2016/2017 there was an increase in area and production of sunflower, probably associated with the reduction of state intervention in farmer's income because export duties were totally eliminated, while those for soybean remained high. International forecasts suggest that an increase in the demand for sunflower oil and by-products is expected. Argentinean farmers can make a significant contribution to meeting these needs. The whole sunflower chain of value, grouped in the association ASAGIR, makes continuous efforts to improve the sunflower product, by research programs and other activities which will render sunflower more attractive for farmer. It is likely that, in a short time, Argentina could regain its place on the podium of sunflower producing countries.

Characterization of dark septate endophyte fungi associated with cultivated soybean at two growth stages

Dark Septate Endophytes (DSE) is a diverse group of Ascomycetes that colonize the roots of a wide range of plants species. They can be found in all ecosystems, from deserts to the tropics, but also in agroecosystems associated to the crops. Despite the ubiquitous of these fungi, only a few major crops were assessed for this association in field conditions. In general terms, a complex consortium of DSE fungi were observed to colonize the roots of some crops. In this work we study the DSE community associated to soybean in the most productive area of this crop in Argentina. We hypothesized that DSE root colonization level, and the identity/frequency of the isolates switch according to the growth stage of the crop. A total of 34 dark fungal colonies were isolated from two growth stages, being only six isolates asyntomatic in the resynthesis assay. Some taxa as Boeremia sp., Cadophora sp., Coniothyrium sp., Corynespora cassicola, Peyronellaea sp. and Phaeosphaeria sp. were exclusively isolated from seedlings, supporting the hypothesis of DSE fungal consortium switching. The soybean pathogens Corynespora cassicola and Macrophomina phaseolina were isolated from young and mature plants respectively. Additional studies should focus on a fine analysis of the dynamics of these fungi, considering also the driving factors that could determine these changes. To understand these mechanisms may be fundamental for a better sustainable management of the crop.

Primer registro de &lt;i&gt;Chloridea (Heliothis) subflexa&lt;/i&gt; (Lepidoptera: Noctuidae: Heliothinae) en uchuva en Brasil

Chloridea (Heliothis) subflexa (Guenée) (Lepidoptera: Noctuidae: Heliothinae) es una especie frugívora y monófoga con hospederos que consta de las plantas del género Physalis. En los últimos años, gusano del tomato de cascara se convirtió en la principal plagas-insectos en cultivos de tomatillo (Physalis ixocarpa Brotero de México) y cultivo de la uchuva (Physalis peruviana L.) en Argentina. El objetivo fue reportar el primer registro de C. subflexa en P. peruviana en Brasil. Los especímenes se recogieron en la fase larvaria y se mantuvieron en una dieta natural hasta llegar a la etapa adulta. La identificación de especies se realizó en base a criterios morfológicos. Se registraron la presencia y daños causados por C. subflexa en frutos de P. peruviana, producidos en un sistema orgánico. Este es el primer registro para Brasil.

Estimating Net Primary Productivity and Carbon Inputs by Soybean Crops in Argentina

ABSTRACTMonitoring crop net primary productivity (NPP) and its proportion returned to soil in the form of carbon (C) input is vital to better understand the ecological responses to environmental and anthropogenic changes. However, quantification of NPP and C inputs from cropping systems at a regional scale is challenging due to the temporal and spatial variability of soils, climate, and management practices. The aim of this study was to estimate (i) the NPP from soybean crop [Glycine max (L.) Merr.] and (ii) the C inputs from soybean residues into soils of the Pampas and Extra-Pampas regions of Argentina between 1993 and 2005 using a simple approach based on the crop yield census records, a C budget equation, and crop-specific conversion factors at regional scale. Soybean NPP (t ha−1 year−1) at a regional scale was estimated by grain yields and harvested areas reported in the long-term (1993–2005) National database for several districts within each province. The mean annual soybean NPP in the Pampas was 0.3 t ha−1 higher (P < 0.05) than in the Extra-Pampas, resulting in a higher C input from soybean residues of 0.4 t ha−1 year−1 in the Pampas region. Due to improved cultivars and higher nutrient inputs in the Pampas region, the mean NPP and C inputs increased by about 25% from 1999 to 2005. Crop NPP and C inputs from residues into soils play a major role in C dynamics and should be considered for further studies at different scales to understand soil organic C modifications through agricultural changes.

Temporal and spatial dynamics of Tomato spotted wilt virus and its vector in a potato crop in Argentina

ABSTRACTThe nature of spatial and temporal dynamics of Tomato spotted wilt virus (TSWV) and its vector in a potato crop cv. Innovator without insecticide application is analysed. Seed tuber was analysed for the presence of TSWV as a source of initial inoculum. The presence of plants with symptoms of TSWV was evaluated by visual observation and DAS‐ELISA analysis to confirm the virus infection. Thrips species were collected from leaves and inflorescences and identified under stereomicroscope. The distribution of symptomatic plants and thrips species was recorded five times at 14 days intervals. The initial seed tuber infection was of 1.1%. Disease incidence was 0% at 29 days after planting (DAP), 0.2% at 43 DAP, 2.2% at 56 DAP, 11.6% at 70 DAP and 14.6% at 84 DAP. The progress of the disease was adequately described by a Logistic model [y = 0.15/(1 + 1205372.93 × exp (−0.22 × DAP))]. Thrips vector species identified as resident in the crop during the whole cycle were Thrips tabaci (n = 423), Frankliniella occidentalis (n = 141) and as occasional species, F. schultzei (n = 34) and F. gemina (n = 5) were found. At 43 and 56 DAP a random distribution pattern was observed and the thrips species found were T. tabaci (n = 188) and F. occidentalis (n = 105). An aggregated pattern was determined at 70 and 84 DAP. Spatial patterns of the disease spread suggest a polycyclic epidemic with TSWV secondary spread in the potato crop. Multiple control measures were deduced from these epidemiological results like virus testing in tubers, removal of external virus infection sources and thrips control.

Role of seed environment and covering structures on large crabgrass germination

The success of large crabgrass (Digitaria sanguinalis) growing among summer crops in Argentina, may be partly explained by its escape from weed controls related to the emergence of different seedlings cohorts determined by seed dormancy and germination requirements. The objectives of this work were to evaluate the effect of temperature, red (R):far-red (FR) ratio and the possible role of the caryopses covering structures on the release of seed dormancy in D. sanguinalis. Therefore, the effects of moist pre-treatment duration, light and temperature, as well as the caryopsis covering structures, and imbibition with H2O2 and the extract of caryopses covers on seed germination, were investigated. Moist pre-treatment at 5 and 20°C promoted dormancy release and fluctuating temperatures between 20/30°C and light promoted germination. However, exposure to 30min of light with a high R:FR ratio reduced germination. Removing or puncturing some of the caryopsis covering structures, as well as imbibition with 2.6M H2O2 enhanced seed germination. Results suggest that the extended seedling emergence throughout the season could be due to the influence of the environmental factors studied here on dormancy release and germination, and that seed covering structures have an important role in seed dormancy imposition for this species.

Arthropod communities and biological control in soybean fields: Forest cover at landscape scale is more influential than forest proximity

Natural habitats surrounding annual crops influence biodiversity and the provision of ecosystem services within the cultivated habitats. Soybean, an important crop worldwide and the main crop in Argentina, is affected by several pest species, including stink-bugs that damage soybean pods. Here, we studied the effects of Chaco Serrano forests on arthropod herbivores and natural enemies and on biological control of stink bugs on soybean, at landscape (forest cover) and local (forest proximity) scales. We sampled arthropods on soybean plants by using the beating-sheet method, on nine landscapes (with low and high forest cover) and at 5, 25, 50 and 100m from the forest, during soybean flowering and pod-filling stages. Biological control of stink bug eggs was assessed via sentinel-egg experiments in soybean and forest habitats. We found that landscapes with high forest cover presented higher richness and abundance of natural enemies and higher levels of biological control on stink bug eggs (both in the cropland and in the forest), while a similar trend for herbivores was restricted to soybean flowering stage. Community composition of both functional groups was also affected by forest cover and crop phenological stage. Forest proximity had more limited effects: natural enemies showed more species and individuals at 5m from the forest than at larger distances and, conversely, stink bug abundance was lower at the closest distance to the forest. We conclude than forest amount at landscape scale is more influential for arthropod biodiversity and biological control in soybean than forest proximity. Moreover, our results suggest that maintaining remnants of forest in agricultural landscapes can be effective for conservation of arthropod biodiversity while contributing to biological control of stink bugs in soybean fields.