Schizaphis Graminum Rond Research Articles

Search for biocontrol agents among endophytic lipopeptide-synthesizing bacteria Bacillus spp. to protect wheat plants against Greenbug aphid (Schizaphis graminum).

Beneficial endophytic bacteria can suppress the development of insect pests through direct antagonism, with the help of metabolites, or indirectly by the induction of systemic resistance through the regulation of hormonal signaling pathways. Lipopeptides are bacterial metabolites that exhibit direct antagonistic activity against many organisms, including insects. Also, lipopeptides are able to trigger induced systemic resistance (ISR) in plants against harmful organisms, but the physiological mechanisms of their action are just beginning to be studied. In this work, we studied ten strains of bacteria isolated from the tissues of wheat and potatoes. Sequencing of the 16S rRNA gene showed that all isolates belong to the genus Bacillus and to two species, B. subtilis and B. velezensis. The genes for lipopeptide synthetase - surfactin synthetase (Bs_srf ), iturin synthetase (Bs_ituA, Bs_ituB) and fengycin synthetase (Bs_fenD) - were identified in all bacterial isolates using PCR. All strains had high aphicidal activity against the Greenbug aphid (Schizaphis graminum Rond.) due to the synthesis of lipopeptides, which was proven using lipopeptide-rich fractions (LRFs) isolated from the strains. Endophytic lipopeptide-synthesizing strains of Bacillus spp. indirectly affected the viability of aphids, the endurance of plants against aphids and triggered ISR in plants, which manifested itself in the regulation of oxidative metabolism and the accumulation of transcripts of the Pr1, Pr2, Pr3, Pr6 and Pr9 genes due to the synthesis of lipopeptides, which was proven using LRF isolated from three strains: B. subtilis 26D, B. subtilis 11VM, and B. thuringiensis B-6066. We have for the first time demonstrated the aphicidal effect of fengycin and the ability of the fengycin-synthesizing strains and isolates, B. subtilis Ttl2, Bacillus sp. Stl7 and B. thuringiensis B-6066, to regulate components of the pro-/antioxidant system of aphid-infested plants. In addition, this work is the first to demonstrate an elicitor role of fengycin in triggering a systemic resistance to S. graminum in wheat plants. We have discovered new promising strains and isolates of endophytes of the genus Bacillus, which may be included in the composition of new biocontrol agents against aphids. One of the criteria for searching for new bacteria active against phloem-feeding insects can be the presence of lipopeptide synthetase genes in the bacterial genome.

MONITORING THE NUMBER OF PHYTOPHAGES IN CROPS OF DIFFERENT VARIETIES OF WINTER WHEAT

The article presents data on the study of the influence of varieties on the dynamics of the number of phytophages in the spring-summer growing season of winter wheat in the conditions of the zone of unstable humidification of the Stavropol Territory. The research was carried out in 2020–2022 on the territory of the educational and experimental farm of the Stavropol State Agrarian University in the crops of Alekseich, Vassa and Tanya varieties. The objects of observations were the red-breasted pyavica (Oulema melanopus L.), the harmful bug turtle (Eurygaster integriceps Put.), large grass aphid (Schizaphis graminum Rond.), common grass aphid (Sitobion avenae F.), w heat t hrips ( Haplothrips tritici Kurd.), common bread sawflies (Cephus pygmaeus L .) a nd b lack ( Trachelus tabidus F.). The Vassa variety contributes to a decrease in the population of the harmful turtle bug by 45.7 % and cereal aphids by 46.4 % in the agrobiocenosis of winter wheat, this is due to two reasons: first, it has a strong wax coating on the ear, which makes it difficult for the imago and phytophagus larvae to feed; second, it is medium-early, so wax ripeness occurs earlier than that of the Alekseich variety, which prevents the normal development of the larvae of the younger pest. The Tanya variety is able to reduce the number of the harmful turtle bug by 12.8 %, due to the fact that it is medium-early and wax ripeness occurs 6–8 days earlier than the Alekseich variety, some of the younger larvae do not have time to eat. Also, this variety has a certain resistance to the red-breasted piavica, since the population of the phytophagus in all the years of observation was 25.0–35.3 % lower than in the crops of the Vassa and Alekseich varieties. Varieties Alekseich, Tanya and Vassa in the zone of unstable humidification of the Stavropol Territory do not have a significant effect on the number of populations of wheat thrips and bread sawflies.

ПОИСК ШТАММОВ ЛИПОПЕПТИД-ПРОДУЦИРУЮЩИХ ЭНДОФИТНЫХ БАКТЕРИЙ РОДА BACILLUS С РОСТ-СТИМУЛИРУЮЩИМИ И ИММУНОСТИМУЛИРУЮЩИМИ СВОЙСТВАМИ, СПОСОБНЫХ МОДУЛИРОВАТЬ УСТОЙЧИВОСТЬ РАСТЕНИЙ ПШЕНИЦЫ К ЗЛАКОВОЙ ТЛЕ SCHIZAPHIS GRAMINUM

For experiments, endophytic strains B. subtilis 26D, B. subtilis 11VM, B. thuringiensis B-6066 and two isolates of Bacillus sp. isolated from wheat leaves growing on the territory of the Republic of Bashkortostan Bacillus sp. Tas1 and Tas8.2 were selected. These strains and isolates produced lipopeptides of three families: surfactins, fengycins, and iturins. We obtained lipopeptide-rich fractions (LRF) from the cultivation medium of all strains and isolates. The aim of the work was to select growth-promoting and immunostimulating concentrations of bacterial strains and isolates and their LRFs, which are capable of modulating different types of resistance (antibiosis and endurance) of wheat plants against Greenbug aphid Schizaphis graminum Rond. Growth-promoting concentrations for bacterial suspensions were selected in the range of 1.0–2.0 μl of suspension per 1 g of seeds, and for LRF within 1.5–2.5 μg/ml. Treatment of seeds with bacterial suspensions and their LRF increased germination and elevated the growth of wet and dry biomass in test for effectiveness of biocontrol agents (GOST 12038-84). Bacteria and their LRF at growth-promoting concentrations indirectly increased plant endurance, which was expressed in leaf growth, and enhanced mortality of the pest that fed on plants treated with bacteria or LRF. All studied bacterial strains and isolates are promising for protection of wheat plants from cereal aphids.

Analysis of the count of populations and harmfulness of phytophages of agrocenoses of grain cereals of the Central ForestSteppe of Ukraine

The count of harmful entomofauna, damage to plants by phytophages and the proportion of their colonization of soft wheat (winter and spring) and common barley (spring) in the Central Forest-Steppe of Ukraine in the spring-summer period of 2004–2019 were analyzed. Such specialized pests as: leafhoppers (Macrosteles laevis Ribaut, Psammotettix alienus L., Calligypona striatella Fall.), aphids (Schizaphis graminum (Rondani), Macrosiphum (Sitobion) avenae (F.), Brachycolus (Cuernavaca) noxius Mordv., Rhopalosiphum padi (L.)), grain bugs (Eurygaster integriceps Put., Eurygaster maura L., Eurygaster austriaca Schrank, Aelia acuminata L.), wheat trips (Haplothrips tritici Kurd.), common ground beetle (Zabrus tenebrioides Goeze), аnisoplia austriaca beetle (Anisoplia austriaca Herbst, Anisoplia segetum Herbst), grain flea beetles (Phyllotreta vittula Redt., Chaetocnema hortensis Geoffr., Chaetocnema aridula Gyll.), cereal leaf beetle (Oulema melanopus (L.), Oulema lichenis Voet.), cereal flies (Oscinella frit L., Oscinella pusila Meigen, Mayetiola destructor (Say), Phorbia securis Tiensuu etc.) were the most common in agrocenoses of grain crops in a harmful entomocomplex. Polyphagous insects, namely caterpillars of gnawing scoops (Scotia segetum Schiff., Scotia exclamationis L.), also caused significant damage in cereal crops. It was revealed that a complex of sucking pests is numerous on winter wheat, represented by wheat thrips (Haplothrips tritici Kurd.), Cereal aphids (Macrosiphum (Sitobion) avenae F., Schizaphis graminum Rond.), Grain sawflies (Cephus pygmaeus L., Trachelus tabidus F.), on spring wheat grain flea beetles (Phyllotreta vittula Redt., Chaetocnema aridula Gyll.) and wheat thrips, on spring barley – grain flea beetles and cereal aphids. Under favorable conditions for overwintering, warm, moderately humid weather in spring and dry weather in summer, active colonization and an increase in the number of phytophages led to their exceeding in 2.5–5.7 times of the economic threshold of harmfulness. Under these conditions, the number of grain bugs (Eurygaster integriceps Put., Е. austriacus Schrnk., Е. maura L., Aelia acuminata L., Dolycoris baccarum L.) in some years reached 8– 15 ind./m2 , ground beetles — up to 20 ind./m2, grain beetles — up to 17 ind./m2, cereal aphids — up to 50 ind./plant.

Ecological structure of harmful entomocomplex of agrocenoses of cereal crops of the Central ForestSteppe of Ukraine

Species composition of harmful entomofauna in agrocoenosis of grain crops in Central Forest-steppe of Ukraine is specified. 54 species of insects-phytophages from 22 families and 8 orders are ascertained. In taxonomic structure of harmful entomocomplex representatives of such orders as Cоleoptera (18 species), Diptera (11), Hemiptera (8), Homoptera (8), Lepidoptera (5 species) dominated. The order of coleopterous (Coleoptera), which makes 33% in the structure of entomocomplex, was characterized with numerous species diversity among insects. The order of dipterous (Diptera) numbered 11 species from 5 families that made 20%. Representatives hemipterous (Hemiptera) and homopterous (Homoptera) orders were represented by the same number of species (8) that made 15% for each one in entomocomplex structure. Orders of hymenopterous (Hymenoptera), thysanopterous (Thysanoptera) and orthopterous (Orthoptera), which made jointly 8% in entomocomplex structure, were characterized with the least numerous specious diversity (1 family, 1–2 species). In wheat and barley agrocoenosis phytophils (hortobionts – 43 species from 18 families) dominated, portion of which made 79.6%. Geophils were represented with the less species diversity and numbered 11 species from 5 families among which geobionts (8 species from 3 families) dominated. The most numerous (dominant) species in 2004–2019 were such pests as corn-bug (Eurygaster integriceps Put.), turnip dart (Scotia segetum Schiff.), blue cereal leaf beetle (Oulema lichenis Voet.), cereal leaf beetle (Oulema melanopus L.), barley flea beetle (Phyllotreta vittula Redt.), click beetle (Agriotes sputator L.), fruit fly (Oscinella frit L.), striped leafhopper (Psammotettix striatus L.), green bug (Schizaphis graminum Rond.), corn sawfly (Cephus pygmaeus L.), wheat thrips (Haplothrips tritici Kurd.), which harmed greatly cereal crops.

Recombinant Bacillus subtilis 26DCryChS line with gene Btcry1Ia encoding Cry1Ia toxin from Bacillus thuringiensis promotes integrated wheat defense against pathogen Stagonospora nodorum Berk. and greenbug Schizaphis graminum Rond.

The novel recombinant Bacillus subtilis 26DCryChS line that contains the Bacillus thuringiensis B-5351 strain gene Btcry1Ia encoding Cry1Ia toxin is described. B. subtilis 26DCryChS line kept endophytic properties and ability to synthesize lipopeptide surfactin of B. subtilis 26D strain and acquired the capability to produce Cry1Ia protein from B. thuringiensis strain B-5351. Insecticidal activity of lipopeptide-rich fraction of cultural filtrate of B. subtilis 26D strain and B. subtilis 26DCryChS line, which was identical to commercial surfactin, against greenbug Schizaphis graminum Rond was shown for the first time. Furthermore, B. subtilis 26DCryChS as much as original B. subtilis 26D strain inhibited growth of fungal wheat pathogen Stagonospora nodorum Berk. Bas1. Insertion of the gene Btcry1Ia in genome of B. subtilis 26D strain contributed to increase of aphicidal activity of B. subtilis 26DCryChS line against S. graminum as compared with both B. thuringiensis B-5351 and B. subtilis 26D strains.Bacillus strains under investigation induced transcription of some wheat genes, which participate in systemic resistance (ISR) to S. nodorum and S. graminum. Seed treatment with B. subtilis 26DCryChS line promoted greater resistance of wheat to the pathogen and aphid than B. thuringiensis B-5351 and B. subtilis 26D strains. The recombinant B. subtilis 26DCryChS line stimulated transcriptional activity of wheat genes regulating the SA- and JA-signaling pathways.Thus, B. subtilis 26DCryChS line kept an ability of the source B. subtilis 26D strain to induce salicylate-dependent genes (Tapr1 and TaPrx) and acquired the capability to stimulate transcription of jasmonate-sensitive genes (TaPI and TaChiI). Recombinant B. subtilis 26DCryChS line could be proposed as a solution for the modern biocontrol agents development.

Induced resistance to the greenbug aphid Schizaphis graminum Rond. in species of the genus Triticum

The greenbug aphid Schizaphis graminum Rond. causes a significant loss of the grain harvest. Therefore, to improve plant resistance to aphids is one of the topical tasks. The problem of creating varieties resistant to phloem-feeding insects is quite urgent, since the mechanisms procuring the resistance of plants to insects are not fully understood. Nevertheless, modern literature describes some mechanisms associated with changes in the redox state of colonized plants. Besides, attention is being increasingly focused on the study of mechanisms that underlie inducible resistance to aphids in wheat and are regulated by hormonal signaling systems. To detect connections among the redox status, indicators of resistance (antibiosis and endurance) of wheat plants to the pest, and induction of the jasmonate (JA) and salicylate (SA) signaling pathways, we studied accessions of three species of wheat plants – Triticum aestivum L., T. monococcum., and T. timopheevii Zhuk.– infested with S. graminum greenbugs by physiological, biochemical, and molecular methods. Analysis of antibiosis and endurance showed that T. timopheevii k-58666 and T. monococcum k-39471 were resistant to S. graminum, the latter accession being the most enduring. High hydrogen peroxide contents and high peroxidase activities were detected in the resistant plants. We investigated the expression of genes encoding PR proteins, including markers and regulators of the salicylate (TaRboh, TaPAL, Tapr1, TaPrx) and jasmonate (TaPI, TaLOX, TaPrx) signaling pathways. At the early stage of infestation in the susceptible T. aestivum variety Salavat Yulaev, the expression of only jasmonate-dependent genes was activated in response to plant damage. In the resistant T. timopheevii accession k-58666, expression of only salicylate-dependent genes was activated, while the aphid reproduction was practically absent. In the resistant T. monococcum accession k-39471, expression was activated in both the salicylate-dependent and jasmonate-dependent gene groups. We assume that the oxidative burst in the resistant forms of wheat was induced via the activation of the SA signaling pathway, which was of crucial importance in the further cascade of chemical reactions leading to the development of resistance.

ИММУНОЛОГИЧЕСКАЯ ОЦЕНКА УСТОЙЧИВОСТИ ОЗИМОЙ И ЯРОВОЙ ПШЕНИЦЫ К ЭПИФИТОТИЙНО ОПАСНЫМ БОЛЕЗНЯМ В УСЛОВИЯХ ЮГО-ВОСТОКА

The factors determining the success of wheat breeding for resistance to diseases are described. The results of studies of the world collection of spring wheat and varieties of domestic breeding for resistance to Puccinia Triticina Erikss. are highlighted. The sources with a high level of resistance to brown rustand of practical interest for the selection of spring soft wheat are identified. The results of work on obtaining transgressive lines of spring wheat with different genes resistant to brown rust are presented. For the development and optimization of protective measures assessed epidemic of resistance of varieties of winter and spring wheat to the pathogen septoria S. tritici. Found that released varieties of winter and spring wheat are presented in the study differ by an epidemic of resistance to the pathogen septoria S. tritici; wheat varieties require high-intensity protective measures against the disease. The article provides information on the peculiarities of the manifestation of viral diseases on spring wheat. The study of the biological characteristics of viral diseases and insect vectors detected the most common disease - barley yellow dwarf virus (BYDV). The studies were carried out on the species composition and abundance of the Aphididae family, and the main vector of the BYDV, common cereal aphid (Schizaphis graminum Rond.) was identified. To identify donors suitable for the creation of wheat varieties resistant to the BYDV, the world’s collection of spring wheat was evaluated on a natural infectious background. The samples resistant to this disease were selected.

Strains of Bacillus spp. Regulate Wheat Resistance to Greenbug Aphid Schizaphis graminum Rond.

It has been found that the bacteria Bacillus subtilis Cohn. (strain 26 D) and Bacillus thuringiensis Berliner (strains V-6066 and V-5689) are able to suppress the vital activity of the greenbug aphid Schizaphis graminum Rond. The protective effects of the studied Bacillus spp. strains consisted of direct aphicidal activity, and they indirectly induce systemic resistance in wheat plants via the regulation of hydrogen peroxide generation, the activity of peroxidase and catalase, and an increased expression of defense-related genes, such us NADPH oxidases, PR-6, and PR-9. It has been shown that B. thuringiensis strains induced genes of the jasmonate-dependent signaling pathway, and B. subtilis strain induced genes of the salicylate-dependent signaling pathway. It has been found that the composition of the studied Bacillus spp. strains had an additive effect of wheat plant resistance to pests. These results support the use of these Bacillus spp. strains as a basis for the further development of a biopreparation against cereal aphids.

Monitoring of development resistance of aphids (Schizaphis graminum Rond.) to drugs of different chemical groups

The susceptibility of aphids to pyrethroid insecticides has been studied. The resistance index does not exceed 10. It is shown that when selecting the population by Decis Profi and Carte, the development of resistance in insects is accelerated in comparison with BI-58 New and Zolon.

Resistance of the national collection of rice varieties to phytophagous pests

The results of the field evaluation of the national collection of rice varieties, for resistance to Cricotopus silvestris Fabr., Hydrelia grisseola Fall., Ephydra macellaria Egg. & Schizaphis graminum Rond. by using an improved method of determining all types (antixenosis, antibiosis, evasion and tolerance) and adaptive resistance, are provided. Under conditions of 2011, among the 23 examined samples 3 varieties turned out to be resistant (with a score of 6) to Cricotopus silvestris Fabr., 1 to Hydrelia grisseola Fall., 2 to Ephydra macellaria Egg. In 2012, complex resistance (among 41 rice varieties) was observed in: UIR 3482, Flagman, Snezhynka, KOP-383-93 (red), which can be harnessed in a program of breeding resistant varieties. Rice samples exhibited different sensitivity to the scheme: mixed herbicide penoksulam + tsyhalofop-butyl and insecticide lambda tsyhalotryn after 10 days.

Effect of virulence genes complementary to the effective resistance genes in sorghum on fitness of the greenbug, Schizaphis graminum Rondani (Homoptera, Aphididae)

Analysis of the greenbug (Schizaphis graminum Rond.) — sorghum interaction system confirmed the hypothesis that rare insect virulence was related to reduced fitness. Greenbug clones from the Krasnodar population virulent to resistance genes Sgr5 and Sgr6 revealed lower fecundity in comparison with avirulent ones and were replaced in model populations during reproduction on a susceptible sorghum line. The main role of aphid fecundity was shown to provide higher fitness, reducing the frequency of virulent clones in natural populations.

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F3 wheat hybrid families to the bird cherry-oat aphid.

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.

Components of the greenbug (Schizaphis graminum Rond.) resistance in wheat and barley somaclonal variants

Antixenosis and antibiosis were evaluated in 3 somaclonal variants of wheat and barley with low level of resistance to greenbug (Schizaphis graminum Rond.). All somaclones possessed both components of resistance to the pest. The resistance is supposed to be under polygenic control because of its very low expressiveness and constant segregation for the trait in several generations. Simultaneous antibiosis and antixenosis changes indicated evident pleiotropic effect of minor genes for the trait. Relationships between different mechanisms for plant resistance to insects are discussed.

Different types of resistance against greenbug, Schizaphis graminum Rond, and the Russian wheat aphid, Diuraphis noxia Mordvilko, in wheat

AbstractA collection of 26 cultivars of wheat Triticum aestivum were screened for resistance against the two main aphid pests of cereals, the greenbug Schizaphis graminum Rond. and the Russian wheat aphid (RWA) Diuraphis noxia Mordvilko. Since genetic variability has been found in Argentinean populations of both aphid species, this work was aimed at determining the response of different types of resistance in wheat cultivars when infested with aphids. Antixenosis, antibiosis and tolerance were evaluated with traditional tests in controlled environmental conditions using a clone of greenbug biotype C and a clone of RWA collected on wheat. Genetic resistance was found against one or both aphid species in several wheats. Most of the highest levels of antixenosis, antibiosis and tolerance against the two aphids occurred in different cultivars; as a consequence the resistance mechanisms for both pests appear to be partly independent. Antibiosis against greenbug or RWA appears to be determined by two different sets of genes, one affecting development time and the other reducing fecundity and longevity. The antibiosis against both aphid species in terms of their development time and the intrinsic rate of population increase resulted in a partial cross effect of these aphid traits against the alternative insect species. Nonetheless, the same cultivars affected the total fertility and the longevity of both aphids. Since the highest plant performance levels and the least plant damage were recorded in different wheats, different patterns of tolerance were displayed against the greenbug and the RWA. Consequently, different genes appear to be involved in several traits of the resistance mechanisms against the two aphids. The genes that independently conferred resistance to aphids could be combined in new cultivars of wheat to broaden their genetic base of resistance against the greenbug and the RWA.

Resistance against greenbug, Schizuphis graminum Rond., and Russian wheat aphid, Diuraphis noxia Mordvilko, in tritordeum amphiploids

AbstractA collection of tritordeum amphiploids (Hordeum chilense × Triticum turgadum) and their wheat parents were screened for resistance against the two main aphid pesis of cereals, the greenhug. Schizaphis graminum Rond. and ihe Russian wheat aphid (RWA) Diuraphis naxia Mord‐vilko. Antixenosis. antibiosis and tolerance were evaluated in controlled environmental conditions using a. clone of greenbug biotypc C and a clone of RWA collected on pasta wheat. Tritordeum amphiploids pos‐sess genetic resistance against greenbug and RWA; some of the lines tested were more resistant than the parental wheat line. Four principal components explained the resistance against both aphid species. The antixenosis shown against both pests was mainly contributed by their wheat parents. The antibiosis againsl both aphid species was obviously dependent on diflerent plant traits. The highest levels of antibiosis against the two aphids occurred in different amphiploids. Different genes are involved in the antibiotic reaction against the two aphids. The Tritordeum resistance to RWA is based on anlixenosis and ant‐biosis since the tolerance trails were not independent of the other types of resistance. The level of tolerance shown to the greenbug was variable and appears to be controlled by differeni mechanisms. The tolerance to aphids shown by H. chilense is expressed in the amphiploids. but with some genomic interaction. Genes conferring resistance to aphids in H. chilensee could be incorporated into new cultivars of wheat to broaden their genetic base of resistance against greenbug and RWA.

Greenbug systemic effect on barley phosphate influx

Greenbugs ( Schizaphis graminum Rond.) cause considerable yield loss in cereals. Local feeding damage of greenbug-infested leaves includes collapsed mesophyll cells, chlorosis, alterations in photosynthesis and respiration. However, this damage cannot explain rapid changes taking place in plant metabolism (inhibition of new leaf primordia and new root differentiation, within a few hours after attack), or the early death of such plants. This study was aimed at determining whether greenbug feeding induces systemic damage to barley. The phosphate influx by roots of susceptible and tolerant barley ( Hordeum vulgare L.) plants was evaluated as an estimate of aphid systemic damage. Phosphate (P)-influx was determined at two plant growth stages, with two levels of greenbug infestation, at two different greenbug life stages. Plants grown in hydroponics in a glasshouse were infested for 0 (control), 3, 6, 12, 24, 48, and 72 h with the Argentinean biotype C greenbug. The P-influx was not significantly affected in tolerant barley plants by greenbug infestation. In contrast P-influx was significantly reduced 6 h post-infestation in the susceptible cultivar. Plants with one expanded leaf suffered a significantly greater reduction in P-influx than plants with two expanded leaves. By 48 h after infestation, the P-influx of the two-expanded-leaf treatment was similar to that of the controls, whereas P-influx in plants with one expanded leaf remained significantly less than on the controls 72 h after infestation. A larger greenbug population resulted in greater reduction in P-influx. Adult greenbugs, but not third stage nymphs, affected P-influx. In summary, the intensity of greenbug-induced systemic damage was greater when young plant stages were infested by the aphid. Reductions of P-influx may become critical under increasing natural infestation levels.

Location of genes controlling resistance to greenbug (Schizaphis graminum Rond.) in Hordeum chilense

AbstractWheat/Hordeum chilense disomic addition lines have been used to locate genes influencing resistance against greenbug (Schizaphis graminum Rond.) in specific chromosomes of H. chilense. H. chilense is a source of antixenosis, antibiosis and host tolerance to the greenbug, being resistant also to the Russian wheat aphid, the two key pests in wheat. For measuring antixenosis, the numbers of aphids per plant were recorded in a host free choice test; antibiotic resistance was determined by measuring the developmental time, the fecundity and the intrinsic rate of population increase of aphids reared on the different hosts, and host tolerance to aphids was evaluated by the leaf damage and the number of expanded leaves on the hosts after 3 weeks of infestation. The greenbugs belonged to a clone of biotype C.Plant genes with positive effects for antixenosis were located on chromosome 1Hch. Genes with positive effects for antibiosis were located on three different chromosomes and those that prolonged aphid developmental time were located on chromosomes 5Hch and 7Hch while those that reduced the total fecundity were on 4Hch. Chromosome 7Hch accounted for host tolerance to greenbug.

Selectivity and synergism of insectoacaricides by use of these preparations in mixtures for protecting agricultural crops

The comparative aspects of toxicity of phosphororganic and pyrethroid insecticides and their combinations for arthropods and warm‐blooded organisms were studied. The quantitative comparison of the coefficients of the selectivity, specific sensitivity and combined action were worked out. The most perspective mixtures were determined and the optimum ratios of their ingredients were stated. Foxim, Fluvalinat, Deltamethrin and mixture of Fluvalinat with Chlorpyriphos in ratios of 1:10 and 1:15 ‐ had more selective features for the Colorado potato beetle (Leptinotarsa decemlineata Say), the spider mite (Tetranychus urticae Koch), the spring cereal aphid (Schizaphis graminum Rond).