Russian Wheat Aphid Infestation Research Articles

Confirmatory detection and identification of biotic and abiotic stresses in wheat using Raman spectroscopy.

Wheat is one of the oldest and most widely cultivated staple food crops worldwide. Wheat encounters an array of biotic and abiotic stresses during its growth that significantly impact the crop yield and consequently global food security. Molecular and imaging methods that can be used to detect such stresses are laborious and have numerous limitations. This catalyzes the search for alternative techniques that can be used to monitor plant health. Raman spectroscopy (RS) is a modern analytical technique that is capable of probing structure and composition of samples non-invasively and non-destructively. In this study, we investigate the accuracy of RS in confirmatory diagnostics of biotic and abiotic stresses in wheat. Specifically, we modelled nitrogen deficiency (ND) and drought, key abiotic stresses, and Russian wheat aphid (Diuraphis noxia) infestation and viral diseases: wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV), economically significant biotic stresses in common bread wheat. Raman spectra as well as high pressure liquid chromatography (HPLC)-based analyses revealed drastically distinct changes in the intensity of carotenoid vibration (1185 cm-1) and in the concentration of lutein, chlorophyll, and pheophytin biomolecules of wheat, triggered in response to aforementioned biotic and abiotic stresses. The biochemical changes were reflected in unique vibrational signatures in the corresponding Raman spectra, which, in turn could be used for ~100% accurate identification of biotic and abiotic stresses in wheat. These results demonstrate that a hand-held Raman spectrometer could provide an efficient, scalable, and accurate diagnosis of both biotic as well as abiotic stresses in the field.

Cell-wall structural carbohydrates reinforcements are part of the defence mechanisms of wheat against Russian wheat aphid (Diuraphis noxia) infestation

Russian wheat aphid (RWA) is one of the most challenging pests for wheat crops globally. In South Africa, RWA has breached the strategy of introducing resistant genes into wheat plants, and so far, five RWA biotypes with different virulence levels have been documented in the field. Our study investigated how the cell wall plays a defensive role in Tugela-Dn1 (susceptible) and-Dn5 (resistant) cultivars infested with South African RWA-biotype 2 (RWASA2). The activities of enzymes related to defense responses were measured. The cell wall's holo-cellulose content, soluble lignin and physicochemical changes were quantified in the infested susceptible and resistant cultivars. Lastly, in vitro RWASA2 saliva-associated CWDEs activity was determined on cell wall-related model substrates. The results show that apoplastic peroxidase and β-1,3-glucanase activities were significantly higher in Tugela-Dn5 relative to the control during the infestation periods. Peroxidase activity is associated with lignin cross-linking of the cell wall, which could deter RWASA2 feeding. The total phenolic and holo-cellulose contents were significantly induced in Tugela-Dn5 at 72 and 120 h post infestation (hpi). These findings were corroborated by the FTIR results, which showed that holocellulose and lignin regions of the resistant and susceptible wheat were affected by infestation at 72 hpi. However, Tugela-Dn5 reinforced cell wall content at 120 hpi. An increased crystallinity index in the resistant cultivar validated the cell wall reinforcement at 120 hpi, while Tugela-Dn1 delayed cell wall reinforcement. This study demonstrates that cell wall reinforcement's modification is part of defense responses against Russian wheat aphid infestation.

Yield Reductions of Wheat Cultivar Obora (UTIQUE96/FLAG-1) due to Russian Wheat Aphid (Diuraphis noxia) Infestation under Field Conditions at Selected Districts of West Showa Zone, Ethiopia

Background: Wheat (Triticum aestivum L.) is an important cereal crop as being consumed as staple food in the world as well as in Ethiopia. The production of wheat in Ethiopia decreased due to the incidence of insect pests. Out of insects’ pests the Russian wheat aphid (Diuraphis noxia) is the recent one that causes yield loss either directly or indirectly. Methods: The experiment was carried out at selected districts of West Showa zone, Ethiopia during off cropping season 2019 to evaluate the yield reduction in wheat crop due to the invasion of Russian wheat aphids. Malamar, Dimethoate, neem seeds, leaves, Beaveria bassiana and Metarhizium anisopliae were used in form of spray. Result: However, Malamar and Dimethoate highly significantly lowered the population of Diuraphis noxia. The combination of Beaveria bassiana and Metarhizium anisopleae significantly lowered the population of Russian wheat aphid. The combination of Neem leaf and Neem seeds, as well as Beaveria bassiana, proved to be effective against Russian wheat aphid yet they were protected and sound against the environments. Malamar showed the maximum decrease in Diuraphis noxia populations followed by Dimethoate, the combination of Beaveria bassiana and Metarhizium anisopleae.

Evaluation of Dryland Wheat Cultivars on the Market in South Africa for Resistance against Four Known Russian Wheat Aphid, <i>Diuraphis noxia</i>, Biotypes in South Africa

An increased wheat yield potential under changing environmental conditions is a challenge in agriculture. Resistant wheat lines can yield more than susceptible wheat lines in the presence of Russian wheat aphid infestation. There are currently four Russian wheat aphid (RWA) biotypes known in South Africa with different virulence against different wheat cultivars. To keep up with the ever-changing patterns it is necessary to screen the cultivars for resistance against these Russian wheat aphid (RWA) biotypes. All the dryland wheat cultivars on the market were evaluated for resistance against the four known Russian wheat aphid (RWA) biotypes in South Africa. Through this evaluation, the status of Russian wheat aphid (RWA) resistance in South African dryland wheat cultivars can be updated to adapt to environmental changes and the wheat industry can adapt to changes in virulence of Russian wheat aphid (RWA) biotypes that may cause damage to Russian wheat aphid (RWA) resistant cultivars, subsequently affecting yield. Evaluations were done in the glasshouse by screening wheat cultivars against four different South African Russian wheat aphid (RWA) biotypes, RWASA1-RWASA4, under controlled conditions. The glasshouse evaluations showed that out of the 19 dryland wheat cultivars currently on the market in South Africa 16 are resistant against RWASA1, 7 are resistant against RWASA2, 7 are resistant against RWASA3 and 5 are resistant against RWASA4. Dryland wheat cultivars were also evaluated under field conditions at four different field localities. In the field, 5 cultivars were resistant to RWASA3 at two localities, respectively, and 3 and 5 cultivars were resistant to RWASA4 at two localities, respectively. Since Russian wheat aphid (RWA) damage can influence the final yield of a wheat cultivar significantly, changing conditions can influence both resistant cultivars, and the virulence of Russian wheat aphid (RWA). It is advisable to evaluate wheat cultivars on the market under different conditions and with all known Russian wheat aphid (RWA) biotypes in an area.

Cultural management of russian wheat aphid infestation of bread wheat varieties in Kenya

Wheat (Triticum aestivum L.) is ecologically suited to East African countries and is the second important cereal after maize in Kenya. It is an important source of food, livestock feeds and income. However, its production (442,000 MT) does not meet annual domestic demand (1,750,000 MT), due to cereal aphids infestation. The most serious cereal aphid in Kenya is the Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov), causing yield losses of >90% when not controlled. The objective of this study was to develop low cost cultural, sustainable and environmentally safe practices for the management of the RWA in East Africa. Treatments included nine varieties, three seeding rates and three rates of nitrogen application. Nine commercial wheat varieties, K. Tai, K. Kingbird, K Wren, K. Korongo, K. Hawk, K. Sunbird, Robin, K. Eagle, and NBWII were sown. Main plots were assigned to wheat varieties, sown at three seeding rates 75, 100 and 125 kg ha-1. Sub-plots were assigned to three rates of nitrogen, 75, 100 and 130 kg N ha-1, applied at tillering stage (GS 22). Variety K. Korongo supported the lowest aphid count of 3.6 per 5 plants; followed by K. Hawk (3.8) and Robin (2.9 aphids). Robin gave the highest grain yield (2.9 t ha-1), followed by K. Korongo (2.7 t ha-1) and K. Hawk (2.5 t ha-1). Application of 100 kg N ha-1 and seeding at 100 kg ha-1 were the best rates.Key Words: Diuraphis noxia kurdjumov, nitrogen, Triticum aestivum

Alexin™ treatment boosts defence responses in wheat against Russian wheat aphid (Diuraphis noxia) infestation

Alexin™ treatment boosts defence responses in wheat against Russian wheat aphid (Diuraphis noxia) infestation

High spectral and spatial resolution hyperspectral imagery for quantifying Russian wheat aphid infestation in wheat using the constrained energy minimization classifier

The effects of insect infestation in agricultural crops are of major ecological and eco- nomic interest because of reduced yield, increased cost of pest control and increased risk of environmental contamination from insecticide application. The Russian wheat aphid (RWA, Diuraphis noxia) is an insect pest that causes damage to wheat (Triticum aestivum L.). We pro- posed that concentrated RWA feeding areas, referred to as hot spots, could be identified and isolated from uninfested areas within a field for site specific aphid management using remotely sensed data. Our objectives were to (1) investigate the reflectance characteristics of infested and uninfested wheat by RWA and (2) evaluate utility of airborne hyperspectral imagery with 1-m spatial resolution for detecting, quantifying, and mapping RWA infested areas in commercial winter wheat fields using the constrained energy minimization classifier. Percent surface reflec- tance from uninfested wheat was lower in the visible and higher in the near infrared portions of the spectrum when compared with RWA-infested wheat. The overall classification accuracies of >89% for damage detection were achieved. These results indicate that hyperspectral imagery can be effectively used for accurate detection and quantification of RWA infestation in wheat for site-specific aphid management. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.8.083661)

Involvement of Nitric Oxide in the Russian Wheat Aphid Resistance Response of Wheat

The involvement of nitric oxide (NO) in the Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), resistance response of wheat (Triticum aestivum L.) was investigated. Resistant (cv. Tugela DN) and near isogenic susceptible (cv. Tugela) wheat plants grown under green-house conditions were used. Russian wheat aphid infestation induced an early accumulation of NO to a higher level in the resistant than susceptible plants. Nitric oxide accumulation corresponded with increased nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NiR, EC 1.7.7.1) activities, suggesting a possible association with NO production. Inhibition studies confirmed the involvement of NR in NO production during the RWA resistance response. The use of a NO donor or NR inhibitor revealed that NO could act as another early signal for induction of the secondary defence enzymes, intercellular β-1,3-glucanase and peroxidase.

Increased feeding damage under elevated Co2: The case of the Russian wheat aphid

We report the results of a baseline study on the effects of Russian wheat aphid infestation on barley lines grown under ambient and elevated (450 and 550μmolmol−1) CO2 concentrations [CO2]. Elevated CO2 impacted on plant biomass, C:N ratios and leaf nitrogen concentrations. Visible manifestation of aphid feeding related damage was assessed by examining resultant chlorosis and leaf roll under ambient and two elevated [CO2] levels using a control and three resistant barley host combinations. Elevated [CO2] had a significant positive effect on the growth of the four barley lines that were not infested by the aphids. However under the same conditions aphid feeding under elevated CO2 conditions caused very high biomass loss, which was more noticeable in experiments involving non-resistant PUMA than in the resistant barley lines. The results of this study demonstrate that CO2 enrichment substantially increases aphid populations of RWASA1 and RWASA2 on the four barley lines investigated. Furthermore, aphid populations were higher on non-resistant PUMA than the three resistant lines and the RWASA2 biotype out-performed RWASA1 in each case. Under elevated [CO2], aphid feeding, resulted in a significant increase in the leaf C:N ratios (as a percentage change) in most treatments, compared to levels recorded on uninfested plants. The resistant lines also showed a significant reduction in leaf nitrogen (~40% for PUMA and not less than 30% for the resistant STARS lines tested). C:N ratio changes and N loss correlated to [CO2] and aphid biotype. By 28days of infestation, most of the non-resistant PUMA line in particular showed significant irrecoverable levels of leaf chlorosis. At level 9 rating on the chlorosis scale (i.e. plant death when recovery was not possible), experiments were terminated. As aphid success is unlikely to be the sole product of [CO2], but also of other limiting nutrients such as N, it may be worth further investigating the effect of plant quality and ultimately plant nutrition on the population growth of aphids.

The selective induction of the phenylalanine ammonia-lyase pathway in the resistance response of wheat to the russian wheat aphid

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is notorious for causing severe yield losses in many of the wheat producing areas of the world. The phenylpropanoid pathway is involved in many plant defence mechanisms. Phenylalanine ammonia-lyase (PAL) is a key enzyme leading to biosynthesis of phenolic acids, some of which are involved in plant defence mechanisms. The effect of RWA infestation on PAL activity and phenolic acid composition was studied in resistant (Tugela DN) and susceptible (Tugela) wheat cultivars. PAL activity was selectively induced in the infested resistant wheat. The increase in PAL activity was reflected in the selective increase in certain phenolic acid concentrations. The phenolic acids that were selectively induced in resistant wheat upon RWA infestation were identified using the authentic phenolic acids p-hydroxybenzoic acid, gallic acid, resorcylic acid, gentisic acid, caffeic acid, p-hydroxyphenylacetic acid, and ferulic acid. The induced levels of these phenolic acids corresponded to the peak PAL activities. It is evident that the phenylpropanoid pathway contributes to the resistance of wheat to the RWA.

Inhibition of Xanthine Oxidase Activity Results in the Inhibition of Russian Wheat Aphid-Induced Defense Enzymes

The role of xanthine oxidase (XO) in the defense response of wheat (Triticum aestivum L.) against the Russian wheat aphid (RWA) (Diuraphis noxia) was studied. Xanthine oxidase catalyzes the oxidation of hypoxanthine to xanthine to uric acid, and oxygen radicals that are formed as a by-product at both of these oxidation steps may participate in plant defense reactions. A resistant wheat cultivar (Tugela DN), and a close isogenic susceptible cultivar (Tugela), were infested with 20-30 aphids per plant before inhibiting xanthine oxidase by adding allopurinol as a soil drench to the resistant plants. Increases in H(2)O(2) content were detected early after infestation in the resistant wheat, and the downstream defense related responses, chitinase and peroxidase activities, were selectively induced by RWA infestation. These downstream defense responses were substantially inhibited in allopurinol treated-resistant wheat, presumably as a response to inhibition of XO, and superoxide dismutase (SOD). We conclude that the production of active oxygen species through the XO system plays an important role in the induction of defense reactions in wheat against the RWA.

Aphid feeding activates expression of a transcriptome of oxylipin-based defense signals in wheat involved in resistance to herbivory.

Damage by the Russian wheat aphid (RWA), Diuraphis noxia, significantly reduces wheat and barley yields worldwide. In compatible interactions, virulent RWA populations flourish and susceptible plants suffer extensive leaf chlorophyll loss. In incompatible interactions, RWA reproduction and population growth are significantly reduced and RWA-related chlorophyll loss in resistant plants is minor. The objectives of this study were to develop an understanding of the molecular and phytochemical bases of RWA resistance in plants containing the Dnx resistance gene. Microarray, real-time polymerase chain reaction, and phytohormone assays were conducted to identify transcriptome components unique to RWA-infested Dnx plants and susceptible (Dn0) plants, and to identify and characterize putative genes involved in Dnx plant defense responses. We found that RWA-infested Dnx plants upregulated >180 genes related to reactive oxygen species, signaling, pathogen defense, and arthropod allelochemical and physical defense. The expression of several of these genes in RWA-infested Dnx plants increased significantly from 6- to 24-h post infestation (hpi), but their expression in Dn0 plants, when present, was delayed until 48- to 96 hpi. Concentrations of 16- and 18-carbon fatty acids, trans-methyl-12-oxophytodienoic acid, and abscisic acid were significantly greater in Dnx foliage than in Dn0 foliage after RWA infestation, suggesting that Dnx RWA defense and resistance genes may be regulated via the oxylipin pathway. These findings provide a foundation for the elucidation of the molecular basis for compatible- and incompatible plant-aphid interactions.

Stronger induction of callose deposition in barley by Russian wheat aphid than bird cherry‐oat aphid is not associated with differences in callose synthase or β‐1,3‐glucanase transcript abundance

The effects of infestation by the bird cherry-oat aphid (BCA), (Rhopalosiphum padi L) and the Russian wheat aphid (RWA) (Diuraphis noxia Mordvilko) on callose deposition and transcription of genes related to callose accumulation were investigated in barley (Hordeum vulgare L. cv. Clipper). The BCA, which gives no visible symptoms, induced very limited callose deposition, even after 14 days of infestation. In contrast, RWA, which causes chlorosis, white and yellow streaking and leaf rolling, induced callose accumulation already after 24 h in longitudinal leaf veins. The deposition was pronounced after 72 h, progressing during 7 and 14 days of infestation. In RWA-infested source leaves, callose was also induced in longitudinal veins basipetal to the aphid-infested tissue, whereas in sink leaves, more callose deposition was found above the feeding sites. Eight putative callose synthase genes were identified in a database search, of which seven were expressed in the leaves, but with similar transcript accumulation in control and aphid-infested tissue. Five out of 12 examined beta-1,3-glucanases were expressed in the leaves. All five were upregulated in RWA-infested tissue, but only two in BCA-infested tissue, and to a lesser extent than by RWA. The results suggest that callose accumulation may be partly responsible for the symptoms resulting from RWA infestation and that a callose-inducing signal may be transported in the phloem. Furthermore, it is concluded that the absence of callose deposition in BCA-infested leaves is not because of a stronger upregulation of callose-degrading beta-1,3-glucanases in this tissue, as compared to RWA-infested leaves.

Antioxidative enzymes and the Russian wheat aphid (Diuraphis noxia) resistance response in wheat (Triticum aestivum)

A crucial function of antioxidative enzymes is to remove excess reactive oxygen species (ROS), which can be toxic to plant cells. The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the activities of antioxidative enzymes was investigated in the resistant (cv. Tugela DN) and the near-isogenic susceptible (cv. Tugela) wheat (Triticum aestivum L.). RWA infestation significantly induced the activity of superoxide dismutase, glutathione reductase and ascorbate peroxidase to higher levels in the resistant than in susceptible plants. These findings suggest the involvement of antioxidative enzymes in the RWA-wheat resistance response, which was accompanied by an early oxidative burst. The results are consistent with the role of ROS in the resistance response and the control of their levels to minimise toxic effects.

Airborne Multi-Spectral Remote Sensing of Russian Wheat Aphid1Injury to Wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a severe pest of wheat in the High Plains region of the United States. Remote sensing may be an effective way to detect RWA infestations in fields for pest management decision-making purposes. We evaluated an airborne multi-spectral remote sensing system for its ability to differentiate varying levels of injury caused by RWA infestation in winter wheat fields. Two fields located in southeastern Colorado were studied in spring 2004 and two fields located in far western Oklahoma were studied in spring 2005. The proportion of wheat stems damaged by RWA in each field was measured in 20 to 24 3×3-m plots with varying levels of RWA infestation. Prior to sampling plots, multi-spectral imagery was obtained using an SSTCRIS® multi-spectral imaging system mounted NADIR in a Cessna 172 aircraft. The multi-spectral data were compared with the intensity of RWA damage to wheat plants within the plots. Correlations between vegetation indices calculated from the multi-spectral data with the proportion of RWA damaged wheat tillers per plot were negative for all vegetation indices. Regressions of vegetation indices versus the proportion of RWA damaged wheat tillers per plot were usually significant and had negative slopes. However, slopes and intercepts of regressions differed significantly among fields. Any one or a combination of differences in time of day, atmospheric conditions, edaphic factors (e.g. soil type and soil moisture), wheat variety, and possibly other factors could have caused the differences observed in regressions.

Reflectance characteristics of Russian wheat aphid (Hemiptera: Aphididae) stress and abundance in winter wheat

The Russian wheat aphid ( Diuraphis noxia (Mordvilko)) infests wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.), and other small grains and grasses. Russian wheat aphid infestations are unpredictable in time and space. In favorable conditions, Russian wheat aphid feeding can result in heavy damage to wheat and barley in a short period of time. A repetitive monitoring strategy that allows for rapid assessment of aphid infestation and damage over the growing season is critically needed. Tracking the irregular infestation patterns of Russian wheat aphid in order to optimize control efforts is central to the successful management of this aphid. One method that has been shown over a number of years to be useful for monitoring some insect outbreaks is to measure the light reflected by the infested canopy, plant, or leaf. Hence, this research was designed to investigate: (1) the potential use of remotely sensed data to discern and identify differences in spectral reflection patterns (spectral signatures) of winter wheat canopies with and without Russian wheat aphid infestation, and (2) the relationship between spectral indices and Russian wheat aphid abundance in wheat canopies growing in field conditions. Russian wheat aphid-infested wheat canopies had significantly lower reflectance in the near infrared region and higher in the visible range of the spectrum when compared with noninfested canopies. Linear regression analyses showed that there were varying relationships between Russian wheat aphid density and spectral vegetation indices, with coefficients of determination ( r 2) ranging from 0.91 to 0.01. These results indicate that remote sensing data have the potential to distinguish damage by Russian wheat aphid and quantify its abundance in wheat. However, success for Russian wheat aphid density estimation depends on the selection of spectral vegetation indices.

Field evaluation of emmer wheat-derived synthetic hexaploid wheat for resistance to Russian wheat aphid (Homoptera: Aphididae).

Broadening the genetic base for resistance to Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), in bread wheat, Triticum aestivum L., is desirable. To date, identified Russian wheat aphid resistance genes are either located to the D chromosomes or to rye translocation of wheat, and resistance derived from the A or B genomes of tetraploid Triticum spp. would therefore be highly beneficial. Fifty-eight synthetic hexaploid wheat, derived from interspecific crosses of Triticum dicoccum Schrank. and Aegilops tauschii (Coss.) Schmal. and their parents were evaluated for resistance to Russian wheat aphid under field conditions. Plots infested with aphids were compared with plots protected with insecticides. The T. dicoccum parents were highly resistant to Russian wheat aphids, whereas the Ae. tauschii parents were susceptible. Resistance levels observed in the synthetic hexaploids were slightly below the levels of their T. dicoccum parents when a visual damage scale was used. but no major resistance suppression was observed among the synthetics. Russian wheat aphid infestation on average reduced plant height and kernel weight at harvest in the synthetic hexaploids and the T. dicoccum parents by 3-4%, whereas the susceptible control 'Seri M82' suffered losses of above 20%. Because resistance in the synthetic hexaploid wheat is derived from their T. dicoccum parent, resistance gene(s) must be located on the A and/or B genomes. They must therefore be different from previously identified Russian wheat aphid resistance genes, which have all been located on the D genome of wheat or on translocated segments.

Field Evaluation of Emmer Wheat-Derived Synthetic Hexaploid Wheat for Resistance to Russian Wheat Aphid (Homoptera: Aphididae)

Broadening the genetic base for resistance to Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), in bread wheat, Triticum aestivum L., is desirable. To date, identified Russian wheat aphid resistance genes are either located to the D chromosomes or to rye translocation of wheat, and resistance derived from the A or B genomes of tetraploid Triticum spp. would therefore be highly beneficial. Fifty-eight synthetic hexaploid wheat, derived from interspecific crosses of Triticum dicoccum Schrank. and Aegilops tauschii (Coss.) Schmal. and their parents were evaluated for resistance to Russian wheat aphid under field conditions. Plots infested with aphids were compared with plots protected with insecticides. The T. dicoccum parents were highly resistant to Russian wheat aphids, whereas the Ae. tauschii parents were susceptible. Resistance levels observed in the synthetic hexaploids were slightly below the levels of their T. dicoccum parents when a visual damage scale was used, but no major resistance suppression was observed among the synthetics. Russian wheat aphid infestation on average reduced plant height and kernel weight at harvest in the synthetic hexaploids and the T. dicoccum parents by 3–4%, whereas the susceptible control ‘Seri M82′ suffered losses of above 20%. Because resistance in the synthetic hexaploid wheat is derived from their T. dicoccum parent, resistance gene(s) must be located on the A and/or B genomes. They must therefore be different from previously identified Russian wheat aphid resistance genes, which have all been located on the D genome of wheat or on translocated segments.

Plant damage and yield response to the Russian wheat aphid (Homoptera: Aphididae) on susceptible and resistant winter wheats in Colorado.

Plant damage and yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), were evaluated on a susceptible (TAM 107) and a resistant (RWA E1) winter wheat, Triticum aestivum L., in three Colorado locations in the 1993 and 1994 crop years. Russian wheat aphid was more abundant on TAM 107 than on RWA E1. Russian wheat aphid days per tiller were greater at the higher infestation levels. Yield losses as a result of Russian wheat aphid infestation occurred most of the time with TAM 107 but rarely with RWA E1. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. Russian wheat aphids per tiller had a negative relationship to yield in TAM 107 but not in RWA E1. In TAM 107 yield decreased as aphid densities increased, but yield remained constant regardless of initial aphid abundance on RWA E1 in all environments. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. The resistance conferred by the Dn4 gene seems to be an effective management approach across a range of field conditions.

Salicylic acid is involved in resistance responses in the Russian wheat aphid-wheat interaction

Summary The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the salicylic acid (SA) content and catalase (EC 1.11.1.6) activity were studied in resistant (cv. Tugela DN) and near-isogenic susceptible (cv. Tugela) wheat ( Triticum aestivum L.). The aim was to gain information on the involvement of SA in the resistance responses in wheat against the RWA. RWA infestation selectively induced SA accumulation and peroxidase (EC 1.11.1.7) activity in the resistant wheat. Catalase activity was, however, inhibited in both resistant and susceptible wheat plants. Intercellularly applied SA confirmed the possible inhibitory effect of SA on catalase and stimulating effect on defense responses as indicated by peroxidase used as a marker. Results suggest the involvement of SA in the resistance of wheat against the RWA. A SA inhibitable catalase is also present in wheat; indications are that it may not be involved in SA-mediated defence responses.