Tolerance of antibiotic and susceptible cereal seedlings to the aphids Metopolophium dirhodum and Rhopalosiphum padi

Some cereal seedlings exhibit antibiotic and antixenotic resistance to the aphids Metopolophium dirhodum (Walker) and Rhopalosiphum padi (L.), because the seedlings contain hydroxamic acids or gramine. The association between tolerance to aphids and aphid antibiosis was investigated for three cereals, Dollarbird wheat Vulcan wheat and Yagan barley. The dry biomass gained by the aphids and the simultaneous reduction in the biomass of the plants (biomass conversion ratio) quantified tolerance. Biomass production and the density dependence of biomass production by the aphids quantified antibiosis more effectively than fecundity. Vulcan wheat, which has more hydroxamic acid than Dollarbird wheat showed the highest level of antibiosis, and the barley was not antibiotic for either aphid. The biomass conversion ratio was a constant; the biomass of an infested plant was reduced by 3 mg for each mg of aphid biomass gained, regardless of aphid species, plant cultivar, or aphid density. The three plants showed no differential tolerance to the aphids, and therefore tolerance is not associated with antibiosis in this case.     

Electronic recording of plant penetration by the cereal aphids Rhopalosiphum padi and Metopolophium dirhodum on resistant and susceptible wheat seedlings

Plant penetration by the aphids Rhopalosiphum padi and Metopolophium dirhodum was monitored using an electronic recording method. Recordings over 3 h showed that phloem ingestion was reduced on resistant wheat, when compared with a more susceptible species, but this trend was reversed when results from longer (12 h) experiments were used. Plant penetration by M. dirhodum was reduced by attachment to the electronic system, but the behaviour of R. padi was relatively unaffected. The results are discussed in relation to prospects for using electronic methods as a screening procedure.     

Honeydew production and sap ingestion by the cereal aphids Rhopalosiphum padi and Metopolophium dirhodum on seedlings of resistant and susceptible wheat species

Measurements of the frequency and rate of honeydew excretion by Rhopalosiphum padi and Metopolophium dirhodum, feeding on seedlings of resistant and susceptible wheat (Triticum monococcum and T. aestivum) were used to estimate the quantity of sap ingested over 24 h. Ingestion was significantly reduced on the more resistant T. monococcum and for M. dirhodum this may be due in part to a reduction in the success of phloem location.     

Laboratory assessments of resistance to the aphids Sitobion avenae and Metopolophium dirhodum in three Triticum species and two modern wheat cultivars

Three ancient varieties of wheat and two spring-sown modern varieties were screened in the laboratory to assess their resistance to the cereal aphids Sitobion avenae and Metopolophium dirhodum. Resistance was measured in terms of non-preference and antibiosis on plants at three growth stages. The ancient variety Einkorn was the most resistant in terms of both non-preference and antibiosis to both species of aphids at all growth stages examined. The ancient variety Emmer and the modern Sicco exhibited some resistant properties, whereas the ancient Spelt and modern Timmo were relatively susceptible to aphid attack.     

Insecticide resistance status and detoxification enzymes of wheat aphids Sitobion avenae and Rhopalosiphum padi

正Dear Editor,Wheat aphids are serious pests in wheat growing areas of China,and can lead to from 10%to over 30%reduction in wheat production(Wang et al.,2006).The main wheat aphids are Sitobion avenae(Fabricius),Rhopalosiphum padi(Linnaeus),Metopolophium dirhodum(Walker),and Schizaphis graminum(Rondani).In the Huang-Huai area of China,the dominant wheat aphid species are S.avenae and R.padi.For many years,farmers have applied chemical pesticides to control wheat aphids.The number of wheat aphids in north     

Grain subproteome responses to nitrogen and sulfur supply in diploid wheat Triticum monococcum ssp. monococcum

Wheat grain storage proteins (GSPs) make up most of the protein content of grain and determine flour end‐use value. The synthesis and accumulation of GSPs depend highly on nitrogen (N) and sulfur (S) availability and it is important to understand the underlying control mechanisms. Here we studied how the einkorn (Triticum monococcum ssp. monococcum) grain proteome responds to different amounts of N and S supply during grain development. GSP composition at grain maturity was clearly impacted by nutrition treatments, due to early changes in the rate of GSP accumulation during grain filling. Large‐scale analysis of the nuclear and albumin‐globulin subproteomes during this key developmental phase revealed that the abundance of 203 proteins was significantly modified by the nutrition treatments. Our results showed that the grain proteome was highly affected by perturbation in the N:S balance. S supply strongly increased the rate of accumulation of S‐rich α/β‐gliadin and γ‐gliadin, and the abundance of several other proteins involved in glutathione metabolism. Post‐anthesis N supply resulted in the activation of amino acid metabolism at the expense of carbohydrate metabolism and the activation of transport processes including nucleocytoplasmic transit. Protein accumulation networks were analyzed. Several central actors in the response were identified whose variation in abundance was related to variation in the amounts of many other proteins and are thus potentially important for GSP accumulation. This detailed analysis of grain subproteomes provides information on how wheat GSP composition can possibly be controlled in low‐level fertilization condition.     

Field assessments of resistance to the aphids Sitobion avenae and Metopolophium dirhodum in old and modern spring-sown wheats

Three ancient varieties of wheat and two modern spring-sown cultivars were investigated in the field to assess their resistance to the cereal aphids Sitobion avenae and Metopolophium dirhodum; the monitoring of natural populations and detailed observations using clip-cages were both undertaken. The ancient variety Einkorn showed both antixenotic and antibiotic resistance to S. avenae, and antibiotic resistance to M. dirhodum. The resistance to S. avenae was greater than that to M. dirhodum. The value of Einkorn as a component of a resistance-breeding programme is discussed with reference to its agronomic and genetic characteristics and with reference to the pest status of cereal aphids.     

Effects of feeding position of the aphids Sitobion avenae and Metopolophium dirhodum on wheat yield and quality

The effects of feeding site of Sitobion avenae and Metopolophium dirhodum on grain weight, number and nitrogen content were investigated in the laboratory and in the field. When the latter species was confined to particular leaves in a growth room, grain weight reductions occurred only when the aphid fed on the flag leaf; reductions in percentage grain protein, but not grain weight, followed lower leaf feeding. Leaves which had borne aphids had a higher proportion of nitrogen at death than control leaves, but this explained little of the shortfall in grain nitrogen, which was mainly due to direct removal during aphid feeding. Multiple regressions of grain weight on aphid species/feeding site in the field confirmed the lack of grain weight effects when lower leaves were colonised; because grain size was greatly reduced by aphid feeding, percentage grain nitrogen increased with increasing aphid density in one cultivar and in others was unchanged. Successive comparison of control grain weights with those from tillers bearing an increasing range of aphid densities resulted in a significant reduction in weight with tillers bearing 21 to 25 aphid units on their ear and flag leaf combined, one unit comprising one adult or fourth-instar aphid or three of earlier instars. These and other factors affecting the nature and extent of cereal aphid damage are discussed.     

Effect of gramine in the resistance of barley seedlings to the aphid Rhopalosiphum padi

Gramine (N,N-Dimethyl-3-aminomethylindole) content in various barley cultivars varied from 0 to 2.6 mmoles/kg fresh weight. Those cultivars which were lacking gramine were the most susceptible to the aphid Rhopalosiphum padi (L.). The population growth rate of R. padi negatively correlated with gramine content in leaves of barley seedlings. In addition, gramine incorporated in artificial diets decreased survival, amount of diet ingested and reproduction of aphids at concentrations similar to those found in plant leaves. Thus, it is suggested that gramine may be one of the factors responsible for the resistance of barley seedlings to R. padi.

---

Résumé La teneur de gramine (N,N-dimethyl-3-aminomethyl-indole) dans différentes cultures de seigle présente des variations comprises entre 0 et 2,8 mmoles/Kg (poids frois). Les varietés dépourvues de gramine sont plus sensibles à l'attaque des pucerons. Le taux de croissance de la population des Rhopalosiphum padi a une correlation négative avec la teneur en gramine des feuilles de plantules de seigle. D'ailleurs, la gramine diminue les taux de nourrissement, de survie et de réproduction des pucerons alimentés avec des diètes artificielles contenant des concentrations du produit testé, similaire à celles trouvées pour les feuilles des plantes. Donc, on suggèrent que la gramine peut être un des facteurs responsables de la résistance des plantules de seigle contre l'attaque de Rhopalosiphum padi.

     

The nature of the effects of the aphids Sitobion avenae and Metopolophium dirhodum on the growth of wheat

Field-caged, post-anthesis populations of the aphids Sitobion avenae and Metopolophium dirhodum reduced grain weight of wheat by 14 and 7% respectively and induced changes in the senescence of the flag leaf. Spikelet number and grain number were unaffected as they are normally determined by pre-anthesis factors. Percentage grain protein was significantly reduced by both aphid species. The pattern of grain weight reduction within the ear was consistent with known limitations on the distribution of flag leaf assimilates among the grains. The relative effects of the two aphid species apparently resulted from the degree of nutrient drain imposed at particular feeding sites and the reduction in the leaf area duration of the flag leaf.     

麦长管蚜和禾谷缢管蚜对小麦植株挥发物及蚜害诱导挥发物的行为反应

用四臂嗅觉计测定了麦长管蚜Macrosiphum avenae和禾谷缢管蚜Rhopalosiphum padi对小麦植株挥发物及麦蚜取食诱导挥发物的行为反应,揭示了2种麦蚜的嗅觉及小麦植株的诱导防御反应特点.在所选的13种小麦植株挥发物及蚜害诱导挥发物组分中,6-甲基-5-庚烯-2-酮、6-甲基-5-庚烯-2-醇和水杨酸甲酯对这2种蚜虫表现出强的驱拒作用;反-2-己烯醛对麦长管蚜的有翅和无翅蚜的吸引作用最强;反-2-己烯醇对禾谷缢管蚜的无翅蚜吸引作用最强,反-3-己酰醋酸酯对禾谷缢管蚜有翅蚜的吸引作用最强.说明麦蚜取食能诱导小麦植株的防御反应,麦长管蚜和禾谷缢管蚜及其不同蚜型间嗅觉反应的特点不同.     

Triticum monococcum lines with distinct metabolic phenotypes and phloem‐based partial resistance to the bird cherry–oat aphid Rhopalosiphum padi

Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.     

The spatial distribution of canopy-resident and ground-resident cereal aphids (Sitobion avenae and Metopolophium dirhodum) in winter wheat

We investigated, within two cereal fields in Southern England, the within-canopy spatial distribution of the aphids Sitobion avenae and Metopolophium dirhodum in relation to crop yield and plant nitrogen. We extended the study to investigate the spatial distribution of aphids that fell to, or returned from, the ground in order to estimate availability of the within-canopy aphid population to ground-active predators. We revealed that crop canopy aphid spatial pattern was associated with nitrogen or yield. Differences were evident between species: S. avenae was generally negatively associated with yield or plant nitrogen, whilst M. dirhodum exhibited positive association. For both aphid species, we observed strong spatial pattern for aphids falling to the ground and conclude that this could, in part, mediate the effectiveness of ground-active predators as pest control agents.     

Suspension and protoplast culture of hexaploid wheat (Triticum aestivum L.)

Suspension cultures have been initiated from embryogenic callus of hexaploid wheat (Triticum aestivum L.). Most commonly, these suspensions are composed of callus-like clusters (up to 2 mm in diameter). Two rapidly-growing lines (MBE6 and C82d) have been obtained, which consist of smaller aggregates of cytoplasmic cells, and these have been maintained for more than 4 years. These lines show very limited morphogenetic capacity and only a single plantlet has been regenerated, from line MBE6, after 9 months in culture. Protoplasts isolated from line MBE6 are unable to divide, but protoplasts from line C82d consistently undergo sustained divisions to form callus or secondary cell suspensions.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog (1962) medium     

Reproductive strategy of winged and wingless morphs of the aphids Sitobion avenae and Metopolophium dirhodum

The reproduction of apterous and alate morphs of the aphids Sitobion avenae and Metopolophium dirhodum is compared on the basis of fecundity in 5- and 10-day periods of adult life. Apterae of both species are consistently more fecund than alatae of comparable weight, producing about three more nymphs on average in any 5-day period. The reproductive differences are related to the number and quality of embryos at eclosion and to ovulation rates, both of which in turn appear to be linked to wing-muscle maintenance. These relationships between weight, embryos and reproduction may be used to predict a newly moulted adult aphid's fecundity, a method which may facilitate the assessment of resistance to aphids in new cereal varieties, by obviating lengthy recording of reproduction. The strategies by which alatae of these and other aphid species minimize the difference between their fecundity and that of apterae are discussed.     

Genetic control of the wheat Triticum monococcum L. resistance to powdery mildew

Using hybrid analysis and test-clone method, 102 accessions of Triticum monococcum L. from the collection of the Vavilov All-Russia Institute of Plant Industry have been studied. This species of wheat has been found to by considerably polymorphic with respect to the resistance to the fungus Erysiphe graminis DC. f. sp. tritici Marchal. causing powdery mildew. The resistance of most accessions to the fungus population and clones is determined by dominant genes. In rare cases, the resistance was determined by recessive genes or one, two, or three oligogenes. A group of einkorn wheat accessions has been found in which the resistance to powdery mildew was determined by the same dominant factor or different but closely linked ones. Recessive resistance genes of T. monococcum differ from the recessive gene pm5 determining the resistance of T. aestivum plants. The genome of T. monococcum contains various genes of resistance to powdery mildew and is a potential source of effective genes to be used when selecting cultivated species of wheat for immunity.     

Genetic control of the wheat Triticum monococcum L. resistance to powdery mildew

Using hybrid analysis and test-clone method, 102 accessions of Triticum monococcum L. from the collection of the Vavilov All-Russia Institute of Plant Industry have been studied. This species of wheat has been found to by considerably polymorphic with respect to the resistance to the fungus Erysiphe graminis DC. f. sp. tritici Marchal. causing powdery mildew. The resistance of most accessions to the fungus population and clones is determined by dominant genes. In rare cases, the resistance was determined by recessive genes or one, two, or three oligogenes. A group of einkorn wheat accessions has been found in which the resistance to powdery mildew was determined by the same dominant factor or different but closely linked ones. Recessive resistance genes of T. monococcum differ from the recessive gene pm5 determining the resistance of T. aestivum plants. The genome of T. monococcum contains various genes of resistance to powdery mildew and is a potential source of effective genes to be used when selecting cultivated species of wheat for immunity.     

Diallelic analysis of quantitative traits in hexaploid wheat (Triticum aestivum L.)

Abstract

A complete diallel study of crosses between eight wheat varieties was carried out to determine the relative magnitude of components of genetic variation and heritability for important grain yield, quality and drought‐related traits. The data appeared adequate for the additive‐dominance model. The additive effects predominated for most traits, and consequently the narrow‐sense heritability was high to moderately high for flag leaf area, weight and venation, stomatal frequency and size, epidermal cell size, biomass, protein content, number of tillers, spike length, spike density, 1000‐grain weight and grain yield. These results appear promising for selecting better plants in the segregating populations with some degree of improvement for yield, quality and physiological efficiency.     

Partial antibiosis to Rhopalosiphum padi in wheat and some phytochemical correlations

The fecundity of the aphid Rhopalosiphum padi during the first ten days of reproduction was measured on five wheats at three growth stages. The wheats were of UK and Iranian origin, but also involved both spring and winter wheats as well as hexaploid and tetraploid types. Aphids which had already been reared on the respective variety for at least one generation were transferred to the experimental plants. The tetraploid Emmer showed some resistance in comparison with the hexaploid UK varieties at later growth stages, whereas the Iranian variety Moghan 2 appeared relatively resistant only at the tillering stage. The other Iranian variety, Ommid, was resistant at all growth stages, and appears to be the most resistant hexaploid wheat variety to R. padi so far identified. Correlations of aphid fecundity with plant chemistry were attempted with total phenolic compounds, hydroxamic acids and amino acids. All three of these chemical groups have previously been reported as correlated with plant resistance to cereal aphids. Even just for the results at the tillering stage, no correlation could be found for phenolics or hydroxamic acids, but a multiple regression based on the levels of alanine, histidine and threonine accounted for over 95% of the variation in aphid fecundity at all 15 data points (5 wheats × 3 growth stages). No cause or effect relationship is necessarily implied.     

Comparative genetic analysis of diploid naked wheat Triticum sinskajae and the progenitor T. monococcum accession

The inheritance of several morphological and biochemical traits was studied in diploid (2n = 2x = 14) naked wheat Triticum sinskajae. The electrophoretic pattern of storage proteins (gliadins) of T. sinskajae differed only in two components from the pattern of T. monococcum accession k-20970, in a population of which T. sinskajae had been discovered. Analysis of biochemical polymorphisms revealed a difference between T. monococcum k-20970 and T. sinskajae in a slow 6-phosphogluconate dehydrogenase region but not in the other eight enzyme systems examined. Nucleotide sequence analysis of the nuclear Acc-1 (acetyl-CoA carboxylase) gene revealed a 46-bp deletion from intron 11 in T. monococcum k-20970 but not in T. sinskajae. This difference was not regarded as species-specific in view of the intraspecific polymorphism of the Acc-1 locus in T. monococcum. A monogenic control was demonstrated for the spring growth habit of T. sinskajae, and the monogenic control of the specific T. sinskajae ear shape was verified. The T. sinskajae ear shape is controlled by a recessive gene, while the T. monococcum ear shape is controlled by a dominant gene. The T. sinskajae ear shape, nakedness, soft glume, aristate glume, and the oblique brachium of the outer glume proved to be linked. The set of E. sin-skajae diagnostic characters is determined by a single (possibly, regulatory) gene or a set of closely linked genes. The two other genes specific to T. sinskajae-awnS, determining the awnlessness, and fig, determining the nonfissile inner (flower) glume--are, respectively, 1.35 +/- 0.98 and 3.34 +/- 1.54% of crossing over away from the mom gene, which determines the T. sinskajae ear shape.