Cereal Aphids Research Articles

Identifying drivers of spatio-temporal dynamics in barley yellow dwarf virus epidemiology as a critical factor in disease control.

Barley yellow dwarf virus (BYDV) is one of the most important viral diseases of small grains worldwide. An understanding of its epidemiology is crucial to control this disease in a sustainable way. The virus moves through the agricultural landscape via cereal aphids as vectors. Understanding movement of these aphids in space and time is of key importance and in doing so, the spatial and temporal variables that influence BYDV epidemiology can be identified. The presence of summer hosts, crop rotation, crop diversity, agricultural practices and climate variables are crucial. Through digitalization, spatial (e.g. land‐use) and temporal (e.g. weather) information is becoming more readily available. Including this information into a prediction model could improve decision support systems that will rationalize the decision‐making process towards a more integrated control of the disease. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Host-parasitoid network in extreme conditions: the case of cereal aphids in wheat crops in Saskatchewan, Canada

Host-parasitoid network in extreme conditions: the case of cereal aphids in wheat crops in Saskatchewan, Canada

Learning‐induced switching costs in a parasitoid can maintain diversity of host aphid phenotypes although biocontrol is destabilized under abiotic stress

Aphid populations frequently include phenotypes that are resistant to parasitism by hymenopterous parasitoid wasps, which is often attributed to the presence of 'protective' facultative endosymbionts residing in aphid tissues, particularly Hamiltonella defensa. In field conditions, under parasitoid pressure, the observed coexistence of aphids with and without protective symbionts cannot be explained by their difference in fitness alone. Using the cereal aphid Rhopalosiphum padi as a model, we propose an alternative mechanism whereby parasitoids are more efficient at finding common phenotypes of aphid and experience a fitness cost when switching to the less common phenotype. We construct a model based on delay differential equations and parameterize and validate the model with values within the ranges obtained from experimental studies. We then use it to explore the possible effects on system dynamics under conditions of environmental stress, using our existing data on the effects of drought stress in crops as an example. We show the 'switching penalty' incurred by parasitoids leads to stable coexistence of aphids with and without H. defensa and provides a potential mechanism for maintaining phenotypic diversity among host organisms. We show that drought-induced reduction in aphid development time has little impact. However, greater reduction in fecundity on droughted plants of symbiont-protected aphids can cause insect population cycles when the system would be stable in the absence of drought stress. The stabilizing effect of the increased efficiency in dealing with more commonly encountered host phenotypes is applicable to a broad range of consumer-resource systems and could explain stable coexistence in competitive environments. The loss of stable coexistence when drought has different effects on the competing aphid phenotypes highlights the importance of scenario testing when considering biocontrol for pest management.

Evidence of Pyrethroid Tolerance in the Bird Cherry-Oat Aphid Rhopalosiphum Padi in Ireland

Results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rose-grain aphid (Metopholophium dirhodum) and the bird-cherry – oat aphid (Rhopalosiphum padi), are used to measure levels of pyrethroid resistance. Aphid pests on cereals in the British Isles are predominantly controlled by pyrethroid insecticides, especially since the implementation of the recent ban on neonicotinoid seed treatments on all outdoor crops. Resistance to pyrethroids has been detected in one of the main aphid pests, the grain aphid (Sitobion avenae), probably brought on by the sustained use of these pyrethroid sprays to control cereal aphids, which can transmit plant viruses, especially Barley Yellow Dwarf Virus (BYDV). The withdrawal of several insecticide compounds (e.g. pirimicarb, dimethoate, chlorpyrifos and the aforesaid neonicotinoids) for cereal aphid control will probably increase the selection pressure, leading to increased levels of resistance in S. avenae, and, potentially, the evolution of resistance in other cereal aphid species. In this article we present the results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rosegrain aphid (Metopholophium dirhodum) and the bird-cherry– oat aphid (Rhopalosiphum padi), in order to measure levels of pyrethroid resistance. At present, little is known about the extent of pyrethroid resistance in S. avenae beyond the UK and in other cereal aphids. It therefore becomes increasingly important to monitor these pests to inform crop management decisions in light of the recent loss of other insecticides. The unintended consequences of the rapid withdrawal of insecticides, together with a failure to prepare and install alternative products and control approaches in advance, will probably ultimately lead to the loss of effectiveness of insecticidal compounds like pyrethroids.

Integrated protection of winter wheat from a complex of harmful causes in european non-chernozem region of the RF

The results of many years of research on the effectiveness of the integrated use of crop protection means and fertilizers with the application of various tillage systems for cultivation of winter wheat of Moskovskaya variety 39 are presented. The studies were conducted in the European nonchernozem soil of Moscow Region on sod-podzolic medium loamy medium-cultivated soil. It was shown that weeds are mainly represented by broadleaved species with an amount of 270 to 370 pcs/ m2. Among pests, cereal aphids and capsid bugs dominate. Among diseases, Helminthosporium and Fusarium root rot (up to 30–40%) and aerogenic infections – brown leaf rust (15-28%) and leaf spot (17-25%) were noted. Studies showed high individual effectiveness in eliminating harmful causes by using appropriate means of protection – seed disinfectants, herbicides, fungicides and insecticides. Weed infestation decreased by 78-85%, root rot development – by 78-81, leaf diseases – by 91-98, pests – by 78-100%. At the same time, the weak effectiveness of the Alto-super fungicide against Septoria and Karate insecticide against wheat thrips was noted. The effect of protective measures on the stored crop was as follows: seed disinfectants – 18%, insecticides – 21, herbicides – 39, fungicides – 22%. The highest economic effect was obtained with the integrated use of plant protection products – up to 1.07 t / ha of grain. At the same time, the quality of grain, content of protein and gluten, and grain class increased. The economic effi ciency of the integrated protection system ranged from 4.7 to 8.1 roubles for each rouble spent. The best result in terms of economic effi ciency was obtained with moldboard tillage and the use of a full dose of NPK90 mineral fertilizers and a full integrated protection scheme.

Monitoring the form of resistance of populations of schools of culture and culture to the insecticide

Goal. To study the toxicity of the modern variety of insecticides from different classes of chemical substances at the level of the mean concentration (СК50, %) of the active substance for the common cereal aphids, cabbage flea, rape blossom weevil, common spider mite. Based on these data to determine the rate of resistance of natural populations of these species of phytophagous arthropods to insecticides.
 Methodology. The sensitivity of phytophagous arthropods was studied on natural populations collected on crops of winter wheat, canola, soybeans in the Kiev region in 2015—2018. For the poisoning of cereal aphids and mites using the method of immersion of the populated lists wheat and soybeans, and flea beetles and pollen beetle — dip them in a gauze bag for 3 seconds in the appropriate solution of insecticides. Were taken 24 hours after poisoning. Toxicological parameters were calculated by using Proban.
 Results. Identifies the different sensitivity of the natural arthropod populations to current insecticides. In terms of the mean concentration (СК50, %) of the active substance rapeseed pollen beetle were most sensitive to Configure, while the rest of the drugs is almost the same. Over the years research is more resistant to Decis Profi turned ordinary spider mites. This pest was a higher resistance.
 Conclusions. The sensitivity of arthropods to insecticides of different chemical classes depends on the characteristics of the pest and the properties of the drug. Indicators of resistance are determined by the biology of the phytophage and terms of use of insecticide. The highest PR was observed for polyvoltine species (aphids, mites). Low levels of resistance to phytophagous pyrethroid insecticides can be explained by two factors: a smaller volume of use or reversion (return of chuvstvitelnosti to the initial level).

Predicting aphid abundance on winter wheat using suction trap catches

The relationship between the number of cereal aphids in flight (recorded by a national grid of suction traps in the Czech Republic) and their occurrence on winter wheat (in Prague) was established between 1999–2015. The flight of all the species was bimodal. Except for Rhopalosiphum padi, whose flight activity peaked in autumn, > 80% of individuals were trapped during April to mid-August. The species frequency was different between the winter wheat and aerial populations. R. padi, the dominant species in the trap catches, formed a small proportion of the aphids on the winter wheat, while Sitobion avenae and Metopolophium dirhodum, which were underrepresented in the suction traps, alternately dominated the populations on the wheat. The aphid abundance in the wheat stands was correlated with the suction trap catches in the “spring” peak (April to mid-August), and the maximum flight activity occurred 4–10 days after the peak in the number of aphids on the wheat. In contrast, the prediction of the aphid abundance in the wheat stands using the total suction trap catches until the 15th of June (the final date for the application of crop protection actions) was reliable only for M. dirhodum. Its maximum abundance on the wheat exceeded 40 aphids per tiller if the total suction trap catch until the 15th of June was ≥ 60 individuals per trap. The prediction of R. padi and S. avenae abundance using the suction trap catches was not reliable.

Drought Stress and Nitrogen Fertilization Affect Cereal Aphid Populations in Wheat Fields

Water stress and nitrogen deficiency are two constraints that negatively affect growth and productivity of wheat plants. Moreover, the interaction between these two stresses could affect the susceptibility of wheat plants to insect attack. In order to examine the influence of drought stress and nitrogen fertilization on piercing-sucking insect pests, the population abundance of four cereal aphid species; English grain aphid Sitobion avenae, wheat aphid Schizaphis graminum, Bird cherry-oat aphid Rhopalosiphum padi, and corn leaf aphid Rhopalosiphum maidis has been monitored in two water treatments (water stress and well-watered) and two nitrogen levels (120 and 180 kg N ha-1). Results revealed that S. graminum was the most dominant specie in all treatments, followed by S. avenae. The population of all aphids tends to increase in the second half of the season coinciding with the emergence of wheat spikes. Stressed-wheat plants attracted more aphids, especially when water deficit synchronizes with an increase in N fertilization. Aphids vigorously thrive better on stressed plants amended with high nitrogen level. Contrary, the lower infestation rate was observed in well-watered plots with lower nitrogen rate. Plant characteristics, such as days to heading, plant height, and chlorophyll content were significantly decreased in drought-stressed plants, while higher N rates increased such parameters. Grain yield and its components were reduced with drought stress and reduced nitrogen fertilization. The current study advocates avoiding severe drought concurrently with an increasing in nutritional augmentation which it might contribute in an increase in insect pest infestation and decreasing in wheat plant traits.

Taxonomic Status and Population Oscillations of Aphidius colemani Species Group (Hymenoptera: Braconidae) in Southern Brazil.

Aphidius colemani (Viereck) was reported in Brazil before the Biological Control Program of Wheat Aphids (BCPWA) when Mediterranean genotypes were introduced from France and Israel. This species was re-described as a complex called A. colemani group composed of three species. Consequently, uncertainty remains about which parasitoid of the group is occurring in southern Brazil. This study has two main objectives: (i) re-examine the species status of A. colemani group collected during the introduction of parasitoids and from a 10-year (2009-2018) monitoring program in wheat fields in northern Rio Grande do Sul (RS), Brazil; (ii) describe the variation in the population density of parasitoids and its association with meteorological factors during this period. We examined 116 specimens from the Embrapa Wheat entomological collection, and those collected in Moericke traps in Coxilha, RS. All the parasitoids of the A. colemani group from the BCPWA period were identified as Aphidius platensis (Brèthes). In traps, 6541 cereal aphid parasitoids were collected, of which 61.9% (n = 4047) were from A. colemani group and all those were identified as A. platensis. Temperature was the factor that effected population density with the highest number of parasitoids recorded in the winter months. Sex ratio changed between years varying from 0.50 to 0.97. The parasitoid A. platensis was the only species in the A. colemani group sampled during 10 years of monitoring.

Transgenic Winter Wheat Expressing the Sucrose Transporter HvSUT1 from Barley does not Affect Aphid Performance.

Winter wheat expressing the sucrose transporter HvSUT1 from barley (HOSUT) has an increased yield potential. Genetic engineering should improve cultivars without increasing susceptibility to biotic stresses or causing negative impacts on ecosystem services. We studied the effects of HOSUT wheat on cereal aphids that feed on the sugar-rich phloem sap. Three HOSUT winter wheat lines, their conventional parental cultivar Certo, and three conventional cultivars were used. Clip cage experiments in the greenhouse showed no differences in life-table parameters of Rhopalosiphum padi and Sitobion avenae (Hemiptera: Aphididae) on transgenic lines compared to Certo, except higher fecundity of S. avenae on one HOSUT line. Population development of both aphid species over three weeks on caged flowering tillers did not reveal differences between the HOSUT lines and Certo. When aphids were monitored in a Swiss field study over two years, no differences between HOSUT lines and Certo were observed. We conclude that HOSUT wheat did not have consistent effects on aphids compared to the parental cultivar and measured parameters were generally in the range observed for the conventional winter wheat cultivars. Thus, HOSUT wheat is unlikely to suffer from increased aphid damage.

Intercropping impacts the host location behaviour and population growth of aphids

AbstractIncreasing intrafield plant diversity has been shown to regulate pest populations in various agroecosystems. Among the suggested mechanisms for this bottom‐up pest control, the disruptive crop hypothesis states that herbivores' abilities to locate and colonize their host plants are reduced by the presence of non‐host plants. Under laboratory conditions, we evaluated how intercropping wheat and legumes modifies the behaviour of apterous cereal aphids,Sitobion avenae(Fabricius) (Hemiptera: Aphididae), in terms of host plant location and population growth. We compared two intercropping systems – soft winter wheat,Triticum aestivumL. (Poaceae), associated with winter pea,Pisum sativumL., or with white clover,Trifolium repensL. (both Fabaceae) – and sole stands of soft winter wheat. Aphids needed more time to locate their wheat host plant and then spent less time on wheat when it was intercropped with clover. At the population level, and accounting for host plant biomass, only intercropping wheat with clover significantly reduced aphid densities on wheat, as this was particularly disruptive toS. avenaebehaviour and population growth.Our laboratory study points out that the species used as non‐host plants and their density are important parameters that should be taken into account in field studies on intercropping systems.

Identification and Genetic Differentiation of Sitobion avenae (Hemiptera: Aphididae) Biotypes in China.

The development of biotypes of the cereal aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), was initially found only on wheat, but barley can also be critical in the process. To address this issue, S. avenae clones were collected on barley and wheat, genotyped with six microsatellite markers, and tested with 58 wheat/barley varieties. Based on the virulence response profiles on different resistant wheat/barley varieties and three susceptible controls, six biotypes of S. avenae were identified. We developed a new system to distinguish between S. avenae biotypes by using only five barley/wheat varieties (i.e., barley: Dulihuang, Zaoshu No.3, Xiyin No.2; wheat: Zhong 4 wumang, 186-TM12-34). The unique virulence profiles of different S. avenae biotypes were further verified by testing their life-history traits (i.e., 10-d fecundity and total developmental time of nymphs) on the abovementioned five barley/wheat varieties. Among all the identified biotypes, biotype 1 was predominant, occupying over 82% of the total in each province. Biotype 5 was found only in Xinjiang, whereas biotype 6 occurred only in Zhejiang. The principal coordinate analysis with microsatellite data suggested apparently low genetic differentiation between biotypes 1 and 2. In most cases, extents of genetic divergence between different S. avenae biotypes could reflect differences in virulence response profiles of these biotypes, implying a genetic component for evolutionary relationships among these biotypes. Our study provides insights into the development and evolution of aphid biotypes, and a firm basis for clarifying the underlying genetic and evolutionary mechanisms.

EFFECT OF NITROGEN FERTILIZER DOSE AND ROW SPACING ON AMARANTH PRODUCTIVITY

Amaranth is a valuable food and feed crop that can solve the problem of vegetable protein in animal husbandry. The aim of the research was to study elements of amaranth cultivation technology: the dose of nitrogen fertilizers (without fertilizers, N15, N20, N25) and the row spacing (15, 30, 45 cm). The work was carried out on sod-podzolic medium loamy gleyic soil on the experimental field of FSBEI HE Yaroslavl State Agricultural Academy in 2018. The studied parameters were determined according to generally ac-cepted methods. The use of nitrogen fertilizers contributed to a significant increase in leaf area and pho-tosynthetic potential of amaranth crops at the highest values of the background N20 – 4.7 thousand m2 / ha and 324.08 thousand m2 / ha × days, respectively. Increase in row spacing when sowing amaranth raised the leaf surface area value, accumulation of dry aboveground mass, photosynthetic potential, ger-mination and safety at maximum values in the variant with a row spacing of 45 cm. abundance of weed flea, cereal aphid and sunflower fire. Sowing amaranth with a width of 45 cm between rows caused a sta-tistically significant decrease in the number of studied pests, as well as the number and dry weight of young and perennial weeds. The use of nitrogen fertilizers in a dose of 25 kg AI / ha contributed to a sig-nificant decrease in the yield of amaranth green mass from 145.12 q / ha on the «no-fertilizer» variant to 127.93 q / ha, with maximum values for the background N20 – 156, 55 kg / ha. Thus, the greatest effi- 128 ciency was shown by the introduction of nitrogen fertilizers at a dose of 20 kg ai / ha when sown with a row spacing of 45 cm.

Previous Aphid Infestation Induces Different Expression Profiles of Genes Associated with Hormone-Dependent Responses in Near-Isogenic Winter Wheat Lines.

Hormone-dependent responses in host plants induced by herbivore infestation have species-specific effects. This study focused on determining the relative expression profiles of the genes associated with hormone-dependent pathways in two near-isogenic wheat lines when attacked by cereal aphids. Infestation with Rhopalosiphum padi Linnaeus (Hemiptera: Aphididae) and/or Sitobion avenae Fabricius (Hemiptera: Aphididae) significantly upregulated the expression of marker genes related to the salicylic acid (SA)- and jasmonic acid (JA)-dependent pathways in the tested lines. In the resistant line 35-E4, previous infestation with R. padi significantly increased the relative expression of plant pathogenesis-related protein 1 at all sampling times but did not have a significant effect on the expression of the phenylalanine ammonia-lyase (PAL) gene. In addition, the expression levels of the lipoxygenase (LOX) and allene oxide synthase (AOS) genes immediately increased after the aphid attack. In susceptible line 35-A20, infestation with either R. padi or S. avenae led to significantly increased expression levels of the AOS and PAL genes. Moreover, sequential aphid infestation induced higher expression of AOS compared with a single-species aphid infestation, whereas the expression of the PAL gene was antagonistically affected by sequential aphid infestation. Overall, these results showed that aphid infestation induced SA- and JA-dependent responses in host plants. However, the expression profiles of these genes in resistant and susceptible host lines were significantly different.

ESTIMATION OF THE COLLECTION RICE ACCORDING TO RESISTANCE TO CEREAL APHID

Ordinary cereal aphid causes great damage to rice plants in the Rostov region and the Krasnodar Territory. Its harmful effects can be limited with the help of plant genetic resistance. The study of resistance of collection rice material to aphids has only recently begun. Therefore, there is a need to analyze the hereditary polymorphism of rice samples according to resistance to ordinary cereal aphid. 494 collection samples of the laboratory for rice breeding and seed production at the FSBSI Agricultural Research Center “Donskoy” were the material for the research. In laboratory VIR conditions, young rice plants were infected by the Krasnodar ordinary aphid, after which there was performed a phenotypic damage assessment using a scale from 0 (no damage) to 10 (plant death). Due to the study it was found that most of the samples were unstable or weakly stable. There were identified 15.1% of relatively stable forms, their damage was 1–4 points. Most samples showed a wide range of variation in plant damage from 1 to 10 points. Only 41 samples out of the 494 studied ones were homogeneous, all plants of which received the same point (1, 2, 3, 4, 8, or 10); the rest samples were heterogeneous. 167 samples received two variants of points, 226 samples received three, 60 samples received four. The rice samples ‘Kandidat’, ‘Komandor’, ‘PF-4186’, ‘Norin 31’, ‘Priozerny 61’, ‘Don 7243’, ‘Don 4237’ can be recommended as sources of resistance to ordinary cereal aphid to develop new rice varieties.

Population dynamics of wheat aphid on different landraces of wheat under field conditions

Wheat (Triticum aestivum L.) is the leading food grain and staple diet in Pakistan. Cereal aphids are a severe problem in wheat growing areas. Among environmentally safe and economical methods for the control of aphids, the use of resistant wheat cultivars is one of the promising approach in pest management programs which can overcome the economic damage caused by aphid infestation. In the present study, the population dynamics of wheat aphid was observed on 114 landraces of wheat. The results showed that during March, nine landraces showed the highest population of Rhopalosiphum padi while the lowest R. padi population was recorded on fourteen different landraces with aphid populations ranging from 3.25 to 4.08. In the month of April, the highest population of R. padi was recorded on 81 landraces while the lowest population was recorded on 33 landraces with mean aphid numbers ranging from 2.91 to 6.9. The peak population was recorded during the month of May on 78 landraces of wheat and proved to be the susceptible while the remaining thirty eight landraces of wheat proved to be resistant with low aphid densities. The mean aphid population varied from 4.25 to 6.95. The results obtained from the month of March were non-significant while those obtained during the months of April and May were significant

Correction to: Harbouring the secondary endosymbiont Regiella insecticola increases predation risk and reproduction in the cereal aphid Sitobion avenae

The author would like to include the following changes in the published article.

Cereal aphid performance and feeding behaviour largely unaffected by silicon enrichment of host plants

There is growing interest in using silicon (Si) for pest and disease management in cropping systems, notably in cereals which have the capacity to hyper-accumulate Si from the soil. Si-mediated pest resistance is thought to operate via physical and allelochemical mechanisms, but it is unclear whether phloem-feeders (e.g. aphids) are as adversely affected as chewing pests. To date, the role of Si in wheat (Triticum aestivum) against aphid pests has focussed almost exclusively on one species (Schizaphis graminum). We investigated the impacts of Si supplementation on plant growth and foliar chemistry (concentrations of carbon, nitrogen and Si) and associated changes in performance parameters of two global aphid pests (Rhopalosiphum maidis and Diuraphis noxia). In addition, we used electrical penetration graphs to determine how Si supplementation affected aphid feeding behaviour. Si supplementation increased foliar Si concentrations by 170% and decreased foliar C by c. 5%. Si impacts on aphid performance were only observed for D. noxia. Longevity and intrinsic rates of increase (rm) decreased by c. 8 days and were c. 13.5% lower, respectively, on Si-supplemented plants. The performance of R. maidis was unaffected by Si supplementation, and neither species was affected in terms of feeding behaviour. We conclude that Si enrichment of wheat is unlikely to be an effective pest control strategy for R. maidis and D. noxia. In reporting these findings, we aim to help identify patterns in Si-based crop resistance and inform future directions (e.g. alternative pest species) for research.

Wheat genotypic diversity and intercropping to control cereal aphids

Increasing intrafield plant diversity has been shown to regulate pest populations. Mixing wheat cultivars and intercropping winter wheat and white clover are both promising agroecological practices. On field experiments over two growing seasons, we combined both practices and examined the impact on aphid populations and on wheat production. Results show that combining intra- and interspecific diversity did not outperform each practice individually in reducing aphid populations. Taken separately, intercropping tended to have lower aphid infestation, while it was intermediate in cultivar mixtures. Yearly variation in climatic conditions impacted wheat and clover development, as well as the appearance of aphid peaks. Wheat yields and grain nitrogen content were reduced in intercropping by 10% and 7%, respectively, but not in cultivar mixtures. Our findings suggest that intrafield diversification may regulate wheat aphids to some extent, but combining two diversification practices did not result in an attractive trade-off between pest regulation and wheat production in real farming conditions.

Asexual reproduction of a few genotypes favored the invasion of the cereal aphid Rhopalosiphum padi in Chile.

BackgroundAphids (Hemiptera: Aphididae) are insects with one of the highest potentials for invasion. Several aphid species are present globally due to introduction events; they represent important pests of agroecosystems. The bird cherry-oat aphid Rhopalosiphum padi (Linnaeus) is a major pest of cereals and pasture grasses worldwide. Here, we report the genetic features of populations of R. padi that colonize different cereal crops in central Chile.MethodsRhopalosiphum padi individuals were collected in central Chile and genotyped at six microsatellite loci. The most frequent multilocus genotype (MLG) was then studied further to assess its reproductive performance across cereal hosts under laboratory conditions.ResultsPopulations of R. padi in Chile are characterized by a low clonal diversity (G/N = 62/377 = 0.16) and the overrepresentation of a few widely distributed MLGs. One of the MLGs constituted roughly half of the sample and was observed in all sampled populations at high frequencies. Furthermore, this putative aphid “superclone” exhibited variations in its reproductive performance on cereals most commonly cultivated in Chile. The sampled populations also exhibited weak signs of genetic differentiation among hosts and localities. Our findings suggest that (1) obligate parthenogenesis is the primary reproductive mode of R. padi in Chile in the sampled range and (2) its introduction involved the arrival of a few genotypes that multiplied asexually.