Greenbug Populations Research Articles

Diversity of barley accessions from the Asian part of Russia in greenbug resistance

Background. The use of barley cultivars resistant to greenbug (Schizaphis graminum Rondani) is an effective, economical and ecology-friendly way to control the dangerous phytophage. The insect is able to overcome the resistance of the host plant, which necessitates a relentless search for new genes to ensure reliable protection of barley fields from the pest.Materials and methods. Resistance to the Krasnodar greenbug population was assessed in 345 barley accessions from the Asian part of Russia. Besides, resistance to S. graminum was studied in cv. ‘Post’ (carrier of the Rsg1 gene), a pure line derived from cv. ‘Onokhoisky’ (k-16626, Buryatia) heterogeneous for this trait, and landraces from Mongolia (k-3885, k-3904, and k-4080). Juvenile plants were infested with aphids in the laboratory, and when a susceptible control died, the damage to experimental barley accessions was assessed using a scoring scale. Genetic control of greenbug resistance in the line derived from cv. ‘Onokhoisky’ was studied using the insect’s test clones and an analysis of the segregation in F2 hybrids from crossing the resistant line with cv. ‘Belogorsky’ susceptible to the aphid, when the plants were infested with the Krasnodar population of the phytophage and with clones of S. graminum.Results and conclusions. We identified 7 accessions heterogeneous for aphid resistance. Among them, plants with a high level of greenbug resistance were found in three landraces from Tuva (k-14714, k-14718, and k-14733). Resistance was also clearly expressed in the line derived from cv. ‘Onokhoisky’. This cultivar is protected by a dominant allele that differs from the previously identified Rsg1, as well as from the alleles found in Mongolian landraces k-3904, k-4080, and k-3885. ‘Onokhoisky’ also has genes with low expressivity, which manifest themselves when the main gene for resistance to S. graminum appears ineffective.

Greenbug resistance in barley landraces from Uzbekistan

Background. The greenbug (Sсhizaphis graminum Rondani) can significantly reduce the yield of barley and other cereals in the southern regions of Russia. Cultivation of resistant varieties can significantly limit the pathogen’s harmfulness. At the same time, specific interaction with the genotypes of the host plant, characteristic of S. graminum, requires a continuous search for new resistance donors to broaden the genetic diversity of barley cultivars. Materials and methods. The resistance of 178 accessions of barley landraces from Uzbekistan to the Krasnodar greenbug population was tested in laboratory experiments. Juvenile plants were infested with aphids of different ages, and when the susceptible control died (cv. ‘Belogorsky’), resistance was assessed on a 0 to 10 (plant death) rating scale. Plants with a damage rate of 1–4 points (up to 30% of the leaf surface being damaged) belonged to the resistant class; damage rate of 5–8 points indicated moderate resistance of plants, and that of 9–10 meant susceptibility. In addition, we assessed the aphid damage of the winter barley cultivar ‘Post’, protected by the previously identified resistance gene Rsg1.Results and conclusions. We identified 52 barley accessions as heterogeneous for the studied trait. In six accessions, plants with high (points 3 to 4) and moderate (5 to 8) resistance were identified; 6 accessions were differentiated into 3 phenotypic classes: resistant, moderately resistant, and susceptible; and in 40 accessions the manifestation of the resistance component varied within 5 to 7 points (from 31 to 60% of the leaf surface being damaged). The distinctly expressed resistance of 12 accessions is controlled by alleles of resistance genes that differ from Rsg1. After selection for resistance, the identified accessions can be used in breeding.

Resistance to greenbugs in the sorghum nested association mapping population

The greenbug, Schizaphis graminum, is a serious pest of sorghum (Sorghum bicolor). For the past several decades, resistant sorghum hybrids have been used to control greenbug populations. However, the durability of plant resistance is frequently challenged by evolution of new greenbug biotypes, and there is a continuous need for screening of resistant germplasm for its effective management in the field. Natural variation in sorghum plants/populations provides distinct approaches to identify novel sources of resistance against greenbugs. In this study, we used the recently developed sorghum nested association mapping (NAM) population parental lines to understand sources of sorghum resistance to greenbugs. Using choice and no-choice assays, we have identified SC265 and Segaolane as the resistant and susceptible lines, respectively, to greenbugs compared to the wild-type plants. The Electrical Penetration Graph (EPG) analysis revealed that the greenbugs spent significantly lesser time in the xylem and sieve element phases while feeding on the resistant NAM parental line, SC265, compared to the susceptible (Segaolane) and wild-type (RTx430) sorghum lines. In addition, the EPG results indicated that there is no significant difference in the time to first probe, time to reach first sieve element, pathway phase, and non-probing phase among the three sorghum plants, which suggests that the resistance factors present in the vascular tissues of the resistant line (SC265) potentially contribute to the resistance mechanisms against greenbugs. Overall, SC265 NAM parental line showed a combination of antixenotic and antibiotic-mediated resistance mechanisms against greenbugs, whereas the susceptible line Segaolane displayed the least resistance to greenbugs.

ВЛИЯНИЕ СМЕНЫ РАСТЕНИЯ-ХОЗЯИНА НА ГЕНЕТИЧЕСКУЮ СТРУКТУРУ КРАСНОДАРСКОЙ ПОПУЛЯЦИИ ОБЫКНОВЕННОЙ ЗЛАКОВОЙ ТЛИ SCHIZAPHIS GRAMINUM RONDANI (HOMOPTERA, APHIDIDAE)

Characteristics of the new malting spring barley cultivar ‘Omsky 100’ are presented. This cultivar, bred at the Siberian Research As a result of studying the Krasnodar Schizaphis graminum population, a high level of the insect’s overall and seasonal variability in its virulence to sorghum resistance genes was detected. The greenbug population feeding on sorghum was shown to be labile in virulence to barley accessions as well. The selection of S. graminum genotypes specifically adapted to host plant species was observed. During the reproduction of the insect on barley plants, the individuals without “redundant” genes of virulence to sorghum had an advantage in competition. Replacement of the host led to rapid accumulation of clones virulent to the sorghum resistance genes Sgr1 - Sgr4 and Sgr12.

Greenbug (Schizaphis graminum) resistance in oat (Avena spp.) landraces from Asia

Among 371 oat accessions from the world collection of the Vavilov Institute of Plant Genetic Resources (VIR) mostly represented by the landraces from Asia (Maritime Territory of Russian Federation, Mongolia, China, Japan, North Korea, India, Iran, Afghanistan, and Bhutan) ninety five were heterogeneous for resistance to the North Caucasus populations of the greenbug (Schizaphis graminum Rondani). Damage ratings of resistance in 47 accessions were high, low level of resistance was identified in 48 genotypes. Higher frequency of greenbug resistant accessions (60.5%) was found among landraces from Mongolia. Lines with high expression of the resistance were selected from seven landraces with wide range of damage ratings. North Caucasus populations of S. graminum from Krasnodar area and Dagestan significantly differ by the frequencies of virulence to host plant. Seven virulence phenotypes differentially interacting with oat genotypes were found in the Krasnodar population and 10 phenotypes were revealed in the Dagestan population. Results of the experiments with the greenbug test clones revealed that all the lines selected from the accessions VIR-2490, VIR-2539, VIR-4074, VIR-12213, VIR-12214 (Mongolia), VIR-6688 (India) and VIR-13624 (North Korea) are protected by diverse alleles of resistance genes which differ from the earlier identified gene Grb3. These lines are supposed to have aphid resistance genes nonidentical to the Grb1 and Grb2. The accessions VIR-6688, VIR-4074 and VIR-12214 possess high resistance to Krasnodar and Dagestan greenbug populations and the accession VIR-13624 is protected by the most effective gene (genes) of resistance to the both populations from North Caucasus.

Greenbug resistance in barley accessions from East and South Asia

Heterogeneous forms differing in level of expressing resistance to the Krasnodar greenbug population have been revealed as a result of studying 1358 barley accessions from East and South Asian countries. High resistance of 98 accessions is controlled by alleles not identical to alleles of the earlier identified Rsg1 gene. A difference in genetic control of resistance in barley landraces from China and North Korea was found.

Molecular characterization of aphids infesting sorghum in China

Sorghum aphid (Melanaphis sacchari), greenbug (Schizaphis graminum) and corn leaf aphid (Rhopalosiphum maidis) are the main pests of sorghum in China. Genotype characterization and/or biotype identification of pests is the first step for cereal breeding programme to obtain resistant cultivars. DNA barcoding technique provides an effective tool for species and biotype diagnosis in various organism. In this study, we sequenced a fragment of 680 bp of cytochromecoxidase I (COI) gene from above aphid species collected from 16 sorghum growing regions in China. The results revealed that (i) No polymorphism was found in the mitochondrial DNA from different sorghum aphid and greenbug populations. The diversity in these two species was not as much as we expected, (ii) Three haplotypes were identified in corn leaf aphid clones. The most common haplotype was the same as that in Canada, USA and UK and (iii) Mitochondrial COI sequences could effectively distinguish different aphid species, and further different haplotypes within an aphid species.

Demographic parameters of greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), on six Iranian genotypes of barley

Greenbug, Schizaphis graminum (Rondani), is one of the injurious aphids of cereals in various regions of the world. This study has measured the life table parameters of the greenbug on six barley genotypes at 25 ± 2 °C, 55 ± 10% RH and 16:8 L:D in greenhouse. According to the results, significant differences were not observed for aphids’ developmental times among the genotypes. Also, the nymphs underwent no mortality on any of the tested genotypes. The longevity of the aphids was obtained from 23.7 to 35.9 days. The least mean number of offsprings was on Raihan cultivar and the highest on line13 (Legia/CWB117-5-9-5). R0 value was significantly higher on line 20 (Mall-4-3094-2//Alpha/Cum/3/Victoria/ICB01-1368-0AP) and line 13 than on the Raihan cultivar. However, the rm and λ values were significantly higher on line 44 (Sls/Bda//Sararood-1) than on Raihan cultivar. T (mean generation time) and DT (doubling time) values of the Raihan cultivar were longer than the other genotypes. Results of this research indicated that among the tested genotypes, the Raihan cultivar is the most unsuitable host for greenbug aphid and lead to the decrease of greenbug population growth.

Dynamics of the genetic structure of the Krasnodar greenbug population under host plant alteration

A high level of overall and seasonal variability of the Krasnodar greenbug population in terms of its virulence to sorghum and barley resistance genes, as well as RAPD markers, was discovered. Selection of insect genotypes specifically adapted to host plant species was recorded. Aphid clones that were avirulent to resistant sorghum samples were most abundant on barley. Greenbug migration from barley to sorghum led to rapid accumulation of clones that are virulent to sorghum resistance genes: Sgr1-Sgr4 and Sgr12. After alteration of the host, a significant shift of genotype groups similar in RAPD profiles was observed. Distribution of RAPD markers was independent of alleles of virulence of the insect.

Long-term seasonal polymorphism of the Krasnodar greenbug population for virulence to sorghum varieties carrying different resistance genes

The genetic structure of the Krasnodar population of the greenbug (Schizaphis graminum Rondani) was analyzed in 2002 to 2010. A high level of general and seasonal polymorphism for the insect virulence to different sorghum accessions was revealed. Abiotic factors were shown to play an important role in the seasonal variation of the frequencies of virulence phenotypes: they can alter the relative competitiveness of greenbug clones, and, therefore, changes in environmental conditions lead to differential selection in the S. graminum population.

Field efficacy of wintertime insecticide applications against greenbugs, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) on winter wheat ( Triticumaestivum L.)

Winter wheat producers in Oklahoma often combine an insecticide with a top-dress application of nitrogen during late fall and winter to control existing greenbug populations. We evaluated the efficacy of three classes of insecticides applied in cold weather field conditions ranging from −13.3 to 28.9 °C from 2002 to 2004 for greenbug control in winter wheat in replicated small plots. Insecticides provided control ranging from 0% to 98%, but generally responded similarly to temperature. Percent control of greenbugs resulting from applications of dimethoate, chlorpyrifos and λ-cyhalothrin was correlated with maximum, minimum and average daily temperatures that occurred two days post-treatment. While percent control was unique for each insecticide, a combined regression of percent control against average daily temperature predicted that a 95% level of control would be achieved when post-treatment temperatures exceeded 13.6 °C. Rainfall that occurred post-treatment affected the efficacy of dimethoate but did not affect the other insecticides. Insecticide persistence was extended under cooler temperatures, allowing acceptable control 14 days post-treatment if temperatures warmed. The decision to apply insecticides should be made based on existing treatment thresholds for greenbug, but if treatment with an insecticide is warranted, winter wheat producers can expect reasonable control of greenbugs from insecticides applied during the winter, as long as post-treatment temperatures exceed 13 °C within the following 14 days.

Biotypic Diversity in Greenbug (Hemiptera: Aphididae): Microsatellite-Based Regional Divergence and Host-Adapted Differentiation

Nineteen isolates of the cereal aphid pest greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), were collected from wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; or noncultivated grass hosts in five locations from Colorado and Wyoming. Parthenogenetic colonies were established. Biotypic profiles of the 19 isolates were determined based on their abilities to damage a set of host plant differentials, and 13 new biotypes were identified. Genetic diversity among the 19 isolates and five previously designated greenbug biotypes (E, G, H, I, and K) was examined with 31 cross-species transferable microsatellite (simple sequence repeat) markers. Neighbor-joining clustering analysis of marker data revealed host-adapted genetic divergence as well as regional differentiation of greenbug populations. Host associated biotypic variation seems to be more obvious in "agricultural biotypes," whereas isolates collected from noncultivated grasses tend to show more geographic divergence. It seems that the biotype sharing the most similar biotypic profiles and the same geographic region with current prevailing one may have the greatest potential to become the new prevailing biotype. Close monitoring of greenbug population dynamics especially biotypic variation on both crop plants and noncultivated grasses in small grain production areas may be a useful strategy for detecting potentially new prevailing virulent biotypes of the greenbug.

Population dynamics of greenbug biotypes “E” and “F” on Texas bluegrass

AbstractCool‐season perennial forage grasses are known to serve as alternate hosts of the greenbug, Schizaphis graminum (Rondani) in the southern Great Plains of the USA. Texas bluegrass (Poa arachnifera Torr.) is a cool‐season perennial forage grass indigenous to this region and because of its persistence under grazing is being bred for improved forage production. An experiment was conducted to determine the population dynamics of greenbug biotype “E”, the predominant biotype found in this region and biotype “F” which is known to infest bluegrass species. Twenty‐five Texas bluegrass genotypes, three Kentucky bluegrass (Poa pratensis L.) genotypes, a Canada bluegrass (Poa compressa L.) genotype, two Texas × Kentucky bluegrass hybrids, and a Texas × Canada bluegrass hybrid were screened for their abilities to support greenbug population growth. Bluegrass species and genotypes varied significantly in their ability to support greenbug biotypes E and F. On the basis of higher aphid numbers, biotype E had a higher population growth rate as compared with biotype F on Texas bluegrass. Some Texas bluegrass genotypes were not included in both biotype trials due to lack of availability of uniform plant material for inoculation. Nine of 25 Texas bluegrass genotypes did not support biotype E greenbug population growth. Similarly, 13 of 22 Texas bluegrass genotypes did not support biotype F population growth. Both Canada and Kentucky bluegrass supported high populations of biotype F and interspecific hybrids varied in their host suitability to both biotypes.

Genetic diversity of sorghum in greenbug resistance

Resistance of the sorghum gene pool to the Krasnodar greenbug population is investigated. A high level of resistance is established in accessions of cultivated sorghum species. Genetic uniformity of resistance donors widely used in Russian and US breeding programs is shown. Fifteen greenbug resistance genes are identified.

USING THE CUMULATIVE-SIZE MECHANISTIC MODEL FOR ANALYZING INSECT DATA

Two data sets of aphid abundance are analyzed using a new cumulative-size based mechanistic model. The first data set pertains to the cotton aphid, and its analysis demonstrates the power of the mechanistic model-based approach. The second data set pertains to greenbug populations, and its analysis shows the key role that birth and death rate coefficients may play in predicting the peak and the cumulative population sizes.

Inheritance of greenbug resistance in several forms of grain sorghum and sudangrass

The inheritance of resistance against the Krasnodar population of common greenbug Schizaphis graminum Rond. was analyzed in nine accessions of grain sorghum and sudangrass. The dominant gene of cultivar Capbam (k-455, United States) was effective against some greenbug clones and differed from the Sgr1-Sgr11 resistance genes. The gene was designated as Sgr12. The cultivar Capbam was proposed for use as a differentiator in population genetic studies in S. graminum. The cultivar Sarvasi (k-3852, Hungary) contains not only the dominant Sgr1 gene, but also a recessive gene (most likely Sgr2), which is effective against some greenbug clones. Grain sorghum accessions k-928 and k-929 (Gugara Belaya, western China) each carry two highly effective dominant resistance genes, which differ from Sgr1-Sgr4, Sgr6, Sgr9, and Sgr10. In addition, the resistance genes of accession k-929 differ from the Sgr5 gene. Accession k-928 proved to contain an additional dominant resistance gene, which is expressed in response to some greenbug clones. The gene was designated as Sgr13. Sudangrass accessions k-100 and k-122 (Ukraine) each carry two dominant resistance genes. Accessions k-62, k-99 (Ukraine), and k-96 (Russia) each carry one dominant and one recessive resistance gene. The dominant resistance genes that are expressed in the cultivar Odesskaya 25 (k-122) in response to infestation with some clones from the natural greenbug population were designated as Sgr14 and Sgr15.

Spatial and Temporal Distribution of Induced Resistance to Greenbug (Homoptera: Aphididae) Herbivory in Preconditioned Resistant and Susceptible near Isogenic Plants of Wheat

Interactions between biotype E greenbugs, Schizaphis graminum (Rodani), and two near isogenic lines of the greenbug resistance gene Gb3 of wheat, Triticum aestivum L., were examined for 62 d after infestation. By comparing aphid performance and host responses on control and greenbug-preconditioned plants, we demonstrated that systemic resistance to greenbug herbivory was inducible in the resistant genotype with varying intensities and effectiveness in different parts of the plants. Preconditioning of susceptible plants resulted in modification of within-plant aphid distribution and reduction of cumulative greenbug densities, but it showed no effect on reducing greenbug feeding damage to host plant. Preconditioning of resistant plants altered greenbug population dynamics by reducing the size and buffering the fluctuation of the aphid population. Preconditioning in the first (oldest) leaf of the resistant plant had no phenotypically detectable effect in the stem and induced susceptibility locally in the first leaf within the first 2 d after infestation. The preconditioning-induced resistance reduced greenbug density, delayed aphid density peaks and extended the life of younger leaves in resistant plants. Expression of induced resistance was spatially and temporally dynamic within the plant, which occurred more rapidly, was longer in duration, and stronger in intensity in younger leaves. Host resistance gene-mediated induced resistance was effective in lowering greenbug performance and reducing damage from greenbug herbivory in host plants. Results from this study supported the optimal defense theory regarding within-plant defense allocation.

Phenotypic mechanisms of host resistance against greenbug (Homoptera: Aphididae) revealed by near isogenic lines of wheat.

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10-14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.

Phenotypic Mechanisms of Host Resistance Against Greenbug (Homoptera: Aphididae) Revealed by Near Isogenic Lines of Wheat

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10–14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.

Resistance to greenbug (Heteroptera: Aphididae) biotype I in Aegilops tauschii synthetic wheats.

The greenbug, Schizaphis graminum (Rondani), is a major pest of wheat in North America, reducing U.S. wheat production by 60 to 100 million dollars each year. In this research, 149 wheat lines containing genes from Aegilops tauschii (Coss.) Schmal. were evaluated for resistance to greenbug biotype I. More than 50% of the lines sustained moderate foliar chlorosis from greenbug feeding, and approximately one third of all the lines were highly resistant. All lines with chlorosis scores similar to the resistant control 'Largo' expressed high levels of antibiosis, producing greenbug populations with mean weights ranging from 0.05 to 11.8 mg. There was no significant difference between greenbug weights on these lines and those reared on 'Largo', but the mean weight of individuals reared on the susceptible control 'Thunderbird' was significantly greater than those reared on 'Largo' or any of the test lines. The mean population size of greenbugs produced on plants of each line was significantly correlated with mean greenbug weight. Tolerance was not evident in any of the lines examined, but was unexpectedly apparent in 'Thunderbird' at a level similar to that in the tolerant control cultivar 'Largo'.