Russian Wheat Aphid Resistance Research Articles

PRESENT STATUS AND FUTURE PERSPECTIVES OF WHEAT (TRITICUM AESTIVUM L.) RESEARCH IN UZBEKISTAN

Wheat (Triticum spp.) is one of the premier staple foods consumed by one-third of the world’s population. Bread wheat (Triticum aestivum L.) is the only allohexaploid species with a genome formula BBAADD. Until now, from a selection point of view, a decline showed in the genetic potential of this type of wheat. However, the solution to this problem can be by developing high-yielding, disease- and pest-resistant cultivars using wheat-related species, ancient local landraces, and germplasm resources. Therefore, extensive study of the wheat gene pool using molecular tools, including identifying primary sources, is highly beneficial. For wheat improvement, breeding opportunities offer significant enhancements via genetic mapping approaches. The review focuses on the common wheat germplasm, wheat genetic approaches for genetic mapping, identification, and RWA (Russian wheat aphid) resistance, nested association mapping (NAM) population, DNA barcoding of Uzbekistan elite bread wheat cultivars, DNA marker-based screening of wheat germplasm for RWA resistance, future perspectives of wheat breeding in Uzbekistan, marker-assisted selection for abiotic stress tolerance, wheat stripe rust and its control strategies in Uzbekistan, epidemiology of the rust pathogens, pathogen characterization, and varietal resistance.

Registration of ‘USDA Fortress’ winter feed barley with multiple aphid resistance

Abstract‘USDA Fortress’ (Reg. no. CV‐375, PI 696161), a multiple aphid‐resistant, high yielding, six‐rowed, mid‐season–maturing, winter feed barley (Hordeum vulgare L.) adapted to the Southern Plains, was developed and released by USDA‐ARS in Stillwater, OK. USDA Fortress is highly resistant to Russian wheat aphid [RWA; Diuraphis noxia (Kurdjumov)] and greenbug [Shizaphis graminum (Rondani)], with seedling resistance to the new invasive pest, hedgehog grain aphid [HGA; Sipha maydis (Passerini)]. USDA Fortress has the pedigree ‘Post 90’ *4/R012. Recurrent parent Post 90 has Rsg1 resistance to greenbug, and R012 is an unadapted RWA‐resistant germplasm line selected by USDA‐ARS Stillwater from PI 10706. Post 90 and USDA Fortress rate 2 on Starks’ greenbug resistance scale of 1–9, while USDA Fortress and R012 rate a 3 on Websters Russian wheat aphid resistance scale of 1–9, where 1 is immune and 9 is dead on both scales. Over 17 location‐years, in the absence of aphids, grain yield of USDA Fortress was 19 and 12% greater than ‘Thoroughbred’ and Post 90, respectively. USDA Fortress has average test weight of 60 kg hl–1 and has stable grain yield over state‐wide variability in climatic conditions. USDA Fortress is the first multiple‐aphid resistant barley cultivar in the United States.

Fine Mapping of Russian Wheat Aphid Resistance Gene in Bread Wheat (Triticum aestivum L.)

Amaç: Bu çalışmanın amacı Rus buğday afidine dayanıklılık sağlayan Dn100695 geninin bulunduğu 7D kromozomunu SSR markörleriyle ayrıntılı bir şekilde taramak ve dayanıklılık genini çevreleyen yeni SSR markörlerini belirlemektir. 
 Materyal ve Yöntem: Basribey x IG 100695 melezinin 190 bireyinden oluşan F2 populasyonu haritalama amacıyla kullanılmıştır. Haritalama populasyonu daha önceki markörlere ilave olarak 7D kromozomunda bulunan 20 yeni SSR markörleri ile taranmıştır. Zararlının populasyondaki kloroz, kıvrılma ve afit yoğunluğu özellikleri fenotipik veriler olarak ele alınmıştır. 
 Araştırma Bulguları ve Sonuç: Çalışma sonucunda 85 polimorfik markör içerisinden 46’sı toplamda 1226.9 cM’lık bir genom bölgesini haritalandırmış ve 14 farklı bağlantı grubu oluşturmuştur. 7D kromozomu üzerinde dayanıklılık genini çevreleyen özgün bir SSR markörü (GWM121) belirlenmiş ve Dn100695 genini her iki yönden çevreleyen markörler haritalanmıştır. Ayrıca markör regresyon analizi sonucunda Rus buğday afidi dayanıklılığına katkı sağlama potansiyeli bulunan SSR markörleri de saptanmıştır.

Genome-wide association analysis of Russian wheat aphid (Diuraphis noxia) resistance in Dn4 derived wheat lines evaluated in South Africa.

Russian wheat aphid (RWA; Diuraphis noxia Kurdjumov) resistance on the 1D chromosome of wheat has been the subject of intensive research. Conversely, the deployment of the Dn4 derived RWA resistant varieties diminished in recent years due to the overcoming of the resistance it imparts in the United States of America. However, this resistance has not been deployed in South Africa despite reports that Dn4 containing genotypes exhibited varying levels of resistance against the South African RWA biotypes. It is possible that there may be certain genetic differences within breeding lines or cultivars that influence the expression of resistance. The aim of this study was to identify single nucleotide polymorphism (SNP) markers associated with resistance to South African RWA biotypes. A panel of thirty-two wheat lines were phenotyped for RWA resistance using four South African RWA biotypes and a total of 181 samples were genotyped using the Illumina 9K SNP wheat chip. A genome wide association study using 7598 polymorphic SNPs showed that the population was clustered into two distinct subpopulations. Twenty-seven marker trait associations (MTA) were identified with an average linkage disequilibrium of 0.38 at 10 Mbp. Four of these markers were highly significant and three correlated with previously reported quantitative trait loci linked to RWA resistance in wheat. Twenty putative genes were annotated using the IWGSC RefSeq, three of which are linked to plant defence responses. This study identified novel chromosomal regions that contribute to RWA resistance and contributes to unravelling the complex genetics that control RWA resistance in wheat.

Elusive Diagnostic Markers for Russian Wheat Aphid Resistance in Bread Wheat: Deliberating and Reviewing the Status Quo.

Russian wheat aphid, Diuraphis noxia (Kurdjumov), is a severe pest of wheat, Triticum aestivum L., throughout the world. Resistant cultivars are viewed as the most economical and environmentally viable control available. Studies to identify molecular markers to facilitate resistance breeding started in the 1990s, and still continue. This paper reviews and discusses the literature pertaining to the D. noxia R-genes on chromosome 7D, and markers reported to be associated with them. Individual plants with known phenotypes from a panel of South African wheat accessions are used as examples. Despite significant inputs from various research groups over many years, diagnostic markers for resistance to D. noxia remain elusive. Factors that may have impeded critical investigation, thus blurring the accumulation of a coherent body of information applicable to Dn resistance, are discussed. This review calls for a more fastidious approach to the interpretation of results, especially considering the growing evidence pointing to the complex regulation of aphid resistance response pathways in plants. Appropriate reflection on prior studies, together with emerging knowledge regarding the complexity and specificity of the D. noxia–wheat resistance interaction, should enable scientists to address the challenges of protecting wheat against this pest in future.

Accessing a Russian Wheat Aphid Resistance Gene in Bread Wheat by Long-Read Technologies.

Russian wheat aphid (RWA) ( Kurdjumov) is a serious invasive pest of small-grain cereals and many grass species. An efficient strategy to defy aphid attacks is to identify sources of natural resistance and transfer resistance genes into susceptible crop cultivars. Revealing the genes helps understand plant defense mechanisms and engineer plants with durable resistance to the pest. To date, more than 15 RWA resistance genes have been identified in wheat ( L.) but none of them has been cloned. Previously, we genetically mapped the RWA resistance gene into an interval of 0.83 cM on the short arm of chromosome 7D and spanned it with five bacterial artificial chromosome (BAC) clones. Here, we used a targeted strategy combining traditional approaches toward gene cloning (genetic mapping and sequencing of BAC clones) with novel technologies, including optical mapping and long-read nanopore sequencing. The latter, with reads spanning the entire length of a BAC insert, enabled us to assemble the whole region, a task that was not achievable with short reads. Long-read optical mapping validated the DNA sequence in the interval and revealed a difference in the locus organization between resistant and susceptible genotypes. The complete and accurate sequence of the region facilitated the identification of new markers and precise annotation of the interval, revealing six high-confidence genes. Identification of as the most likely candidate opens an avenue for its validation through functional genomics approaches.

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.

Valuable Russian wheat aphid-resistant bread wheat accessions identified using four South African Diuraphis noxia biotypes

Resistance-breaking biotypes of Diuraphis noxia have been reported in both the USA and South Africa where commercial cultivars with genetic resistance to this pest have been deployed. The need to identify novel Russian wheat aphid (RWA) resistance for deployment against new biotypes of RWA has driven the recent re-evaluation and characterisation of resistance in landraces of bread wheat from germplasm collections worldwide. Twenty-three genotypes already in use in a South African pre-breeding programme were evaluated with the extended spectrum of South African RWA biotypes, while four genotypes not yet tested with South African RWA were screened with RWASA1, RWASA2, RWASA3 and RWASA4 for the first time. Five accessions, namely PI 94355, PI 243781, PI 361836, PI 626580 and the check CItr 2401, were resistant to all four South African RWA biotypes. The previously unused accessions PI 094355 and PI 243781 will be incorporated into the programme. The sixth accession resistant to RWASA4, namely PI 366518, is susceptible to RWASA2 and RWASA3 and may possibly be unique, meriting emphasis in pre-breeding activities. The use of multiple, distinct resistance genes, including those with a moderate resistance reaction, is seen as the most responsible strategy for the stewardship of genetic resistance to RWA in bread wheat.

Genetic mapping and inheritance of Russian wheat aphid resistance gene in accession IG 100695

AbstractThe Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is an important pest of small‐grain cereals, particularly wheat, worldwide. The most efficient strategy against the RWA is to identify sources of resistance and to introduce them into susceptible wheat genotypes. This study was conducted to determine the mode of inheritance of the RWA resistance found in ICARDA accession IG 100695, to identify wheat microsatellite markers closely linked to the gene and to map the chromosomal location of the gene. Simple sequence repeat (SSR) marker scores were identified in a mapping population of 190 F2 individuals and compared, while phenotypic screening for resistance was performed in F2 : 3 families derived from a cross between ‘Basribey’ (susceptible) and IG 100695 (resistant). Phenotypic segregation of leaf chlorosis and rolling displayed the effect of a single dominant gene, temporarily denoted Dn100695, in IG 100695. Dn100695 was mapped on the short arm of chromosome 7D with four linked SSR markers, Xgwm44, Xcfd14, Xcfd46 and Xbarc126. Dn100695 and linked SSR markers may be useful for improving resistance for RWA in wheat breeding.

Field Screening of Lesotho and South African Wheat Cultivars for Russian Wheat Aphid Resistance

Russian wheat aphid (Diuraphis noxia) is an international wheat pest and was first recorded in South Africa in 1978 in the Bethlehem area in the Eastern Free State. Le-sotho lies adjacent to one of the largest wheat producing areas in South Africa, the Eastern Free State, where winter wheat and facultative types are cultivated under dry land conditions. Wheat (Triticum aestivum L.) is an important crop adapted to all agro-ecological zones of Lesotho. Russian wheat aphid may have a significant impact on wheat yield. No monitoring or pest control is being done in Lesotho and at this stage there is very little information on the Russian wheat aphid resistance of wheat culti-vars cultivated in Lesotho. In view of this it is important to monitor the distribution of Russian wheat aphid biotypes in Lesotho and determine the level of Russian wheat aphid resistance in local Lesotho wheat cultivars. Two local Lesotho wheat cultivars, Bolane and Makalaote were screened together with South African cultivars Elands, Matlabas, Senqu, PAN3379, PAN3118 and SST387, in the glasshouse against all four known biotypes that occur in South Africa. All these cultivars were also planted in 5 m plots in the field at two localities Leribe and Roma in the lowlands of Lesotho. These cultivars were screened in the field for Russian wheat aphid resistance. The predomi-nant Russian wheat aphid biotypes in these areas were also determined. The Lesotho cultivar, Bolane had resistance against RWASA2 in the glasshouse, while Makalaote did not have any Russian wheat aphid resistance in either the glasshouse or field screenings. To contribute to food security an increasing wheat yield potential is a high priority. Russian wheat aphid has been included in the list of important international cereal pests. Russian wheat aphid adapts to changing environments and taking their ecology, distribution, virulence patterns, and variability into account is important in minimizing the gap between actual and attainable yields. Current management prac-tices for winter wheat in South Africa include the use of resistant cultivars, which is the most economical management strategy for Russian wheat aphid. Introducing Russian wheat aphid resistant cultivars in Lesotho will improve overall yield and as a result food security. This will also result in lower Russian wheat aphid pest pressure in the adjacent wheat production areas in the Eastern Free State, South Africa.

Genetic Diversity for Russian Wheat Aphid Resistance as Determined by Genome‐Wide Association Mapping and Inheritance in Progeny

ABSTRACTRussian wheat aphid (RWA) [Diuraphis noxia (Mordvilko)] is an increasing problem on barley (Hordeum vulgare L.) throughout the world. Genetic resistance has been identified and used to create barley germplasm and cultivars adapted to the United States. Several mapping studies have been conducted to identify loci associated with resistance, but questions remain, particularly regarding the extent of genetic diversity among resistance sources and improved lines and cultivars. Association analysis of resistant (R) and moderately resistant (MR), unadapted accessions held in the USDA–ARS National Small Grains Germplasm Collection, adapted germplasm lines derived from these accessions, and susceptible (S) elite cultivars was conducted using 4509 single nucleotide polymorphisms (SNPs) to identify markers linked to resistance. Resistance was associated with loci on chromosomes 1H, 2H, 3H, 5H, and 7H at p‐values <0.0001, and the major 1H and 3H loci identified in previous tests were confirmed. However, the genetics of RWA resistance was shown to be complex, and it is likely that loci involved in resistance in some lines were not identified. Nevertheless, this analysis identified diversity among R lines and showed that most of the released RWA‐resistant cultivars had similar genotypes at loci associated with resistance. This analysis also identified R lines that were genetically dissimilar to the released cultivars at these loci. This information can guide parental selection for future breeding efforts designed to capture and deploy greater diversity for RWA resistance among new barley cultivars.

Saliva fractions from South African Russian wheat aphid biotypes induce differential defence responses in wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjomov, 1913), is a notorious pest that reduces yield in wheat. Nevertheless, the source of eliciting activity during RWA–wheat interaction has not been established. This paper reports on the isolation of eliciting activity in aphid saliva that is capable of inducing differential defence responses in various wheat cultivars. Aphid saliva discharged into an artificial diet by the South African RWA biotypes (RWASA1 and RWASA2) was collected and purified by C18 reversed phase and size exclusion chromatography. Intercellular injection of RWASA1, but not RWASA2, saliva fractions into wheat leaves selectively induced higher activities of defence-related enzymes (lipoxygenase, peroxidase and β-1,3-glucanase) only in the RWASA1-resistant cultivar ‘Tugela Dn1’. No defence responses were induced in the near-isogenic susceptible ‘Tugela’. Heat-treatment deactivated these fractions, suggesting their proteinaceous nature. Identification of eliciting activity in aphid saliva forms the basis for further characterisation and identification of elicitors in aphid saliva, which will help in unravelling the RWA resistance mechanism of wheat during RWA–wheat interactions.

Chromosomal genomics facilitates fine mapping of a Russian wheat aphid resistance gene.

Making use of wheat chromosomal resources, we developed 11 gene-associated markers for the region of interest, which allowed reducing gene interval and spanning it by four BAC clones. Positional gene cloning and targeted marker development in bread wheat are hampered by high complexity and polyploidy of its nuclear genome. Aiming to clone a Russian wheat aphid resistance gene Dn2401 located on wheat chromosome arm 7DS, we have developed a strategy overcoming problems due to polyploidy and enabling efficient development of gene-associated markers from the region of interest. We employed information gathered by GenomeZipper, a synteny-based tool combining sequence data of rice, Brachypodium, sorghum and barley, and took advantage of a high-density linkage map of Aegilops tauschii. To ensure genome- and locus-specificity of markers, we made use of survey sequence assemblies of isolated wheat chromosomes 7A, 7B and 7D. Despite the low level of polymorphism of the wheat D subgenome, our approach allowed us to add in an efficient and cost-effective manner 11 new gene-associated markers in the Dn2401 region and narrow down the target interval to 0.83cM. Screening 7DS-specific BAC library with the flanking markers revealed a contig of four BAC clones that span the Dn2401 region in wheat cultivar 'Chinese Spring'. With the availability of sequence assemblies and GenomeZippers for each of the wheat chromosome arms, the proposed strategy can be applied for focused marker development in any region of the wheat genome.

Oxidation of fatty acids are associated with Russian wheat aphid resistance in wheat

The oxidation of fatty acids, which is responsible for changes in lipid composition, were investigated in a comparative study using the Russian wheat aphid (RWA) (Diuraphis noxia), infested and un-infested resistant (Tugela DN) and close isogenic-susceptible (Tugela) wheat cultivars. LOX, which catalyzes the first step of the lipoxygenase pathway, was selectively induced in the infested resistant wheat. A pathogen-induced oxygenase protein was also found to be induced during the wheat-RWA interaction. The involvement of oxylipins in the RWA resistance response was confirmed by inhibition studies using indomethacin, which is known to inhibit prostanoid biosynthesis in mammalian tissue. Downstream defense reactions, e.g. LOX and POD activities, were inhibited upon indomethacin treatment. These results emphasize the importance of fatty acid oxidation as an essential process for the establishment of a successful defense response in wheat to the RWA.

Nitric oxide is an upstream signal involved in the multisignalling network during the Russian wheat aphid resistance response and its application enhances resistance

The Russian wheat aphid (RWA) is serious pest of wheat in South Africa since its discovery in 1978. Nitric oxide (NO) plays an essential role in the RWA resistance response of wheat. This study was conducted to establish whether NO acts upstream or downstream of salicylic acid (SA) during the RWA defence response and also to investigate the effect of NO application on RWA control. In addition, the involvement of peroxynitrite in the RWA resistance response of wheat was studied. Resistant and/or susceptible plants grown under controlled conditions (25 ± 2°C) were used. Using a NO donor, sodium nitroprusside (SNP), and a NO production inhibitor, sodium tungstate (NaWO4), it was proved that NO acts upstream of SA during the RWA resistance response of wheat. Furthermore, a significant decrease in RWA intrinsic increase rate (rm) and disease symptom development after SNP application emphasized the role of NO in the RWA resistance responses. High levels of peroxynitrite (by-product of NO) content in the RWA infested resistant plants and inhibition of secondary defence enzymes (β-1,3-glucanase and peroxidase) after urate (inhibitor of peroxynitrite production) application proposed the involvement of this molecule in the signalling events of the RWA resistance.

Virus-induced gene silencing suggests (1,3;1,4)-β-glucanase is a susceptibility factor in the compatible russian wheat aphid-wheat interaction.

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is a significant insect pest of wheat (Triticum aestivum L.) and has a major economic impact worldwide, especially on winter wheat in the western United States. The continuing emergence of new RWA biotypes virulent to existing resistance genes reinforces the need for more durable resistance. Studies have indicated that resistance in previously susceptible plants can be produced by knock-down of susceptibility genes or other genes involved in host plant susceptibility. Therefore, investigation into genes involved in compatible RWA-wheat interactions could be a feasible approach to achieving durable RWA resistance. The objective of this study was to test whether silencing (1,3;1,4)-β-glucanase, previously observed to be highly induced in susceptible compared with resistant wheat during aphid infestation, would confer resistance to a susceptible wheat genotype. Barley stripe mosaic virus-mediated virus-induced gene silencing was employed to test whether (1,3;1,4)-β-glucanase is involved in the susceptible reaction of 'Gamtoos-S' (GS). Controlled infestation with U.S. biotype RWA2 was done to assess aphid reproduction and host symptom development. Aphids on (1,3;1,4)-β-glucanase-silenced plants reproduced less per day and had longer prenymphipositional periods than those on control GS plants. Furthermore, the (1,3;1,4)-β-glucanase-silenced plants exhibited less chlorosis and greater dry weight compared with GS. Aphid reproduction and host plant symptom development showed linear relationships with (1,3;1,4)-β-glucanase transcript levels. Our results suggest that (1,3;1,4)-β-glucanase is required for successful infestation by the RWA and may be a susceptibility factor that could be exploited as a potential target for RWA resistance breeding.

Characterization of eight Russian wheat aphid (Hemiptera: Aphididae) biotypes using two-category resistant-susceptible plant responses.

Eight biotypes of the Russian wheat aphid, Diuraphis noxia (Kurdjumov), have been discovered in the United States since 2003. Biotypes are identified by the distinct feeding damage responses they produce on wheat carrying different Russian wheat aphid resistance genes, namely, from Dn1 to Dn9. Each Russian wheat aphid biotype has been named using plant damage criteria and virulence categories that have varied between studies. The study was initiated to compare the plant damage caused by all the eight known Russian wheat aphid biotypes, and analyze the results to determine how Russian wheat aphid virulence should be classified. Each Russian wheat aphid biotype was evaluated on 16 resistant or susceptible cereal genotypes. Plant damage criteria included leaf roll, leaf chlorosis, and plant height. The distribution of chlorosis ratings followed a bimodal pattern indicating two categories of plant responses, resistant or susceptible. Correlations were significant between chlorosis ratings and leaf roll (r(2) = 0.72) and between chlorosis ratings and plant height (r(2) = 0.48). The response of 16 cereal genotypes to feeding by eight Russian wheat aphid biotypes found RWA1, RWA2, RWA6, and RWA8 to differ in virulence, while Russian wheat aphid biotypes RWA3, RWA4, RWA5, and RWA7 produced similar virulence profiles. These biotypes have accordingly been consolidated to what is hereafter referred to as RWA3/7. Our results indicated that the five main biotypes RWA1, RWA2, RWA3/7, RWA6, and RWA8 can be identified using only four wheat genotypes containing Dn3, Dn4, Dn6, and Dn9.

Selection of reference genes for expression analysis in Diuraphis noxia (Hemiptera: Aphididae) fed on resistant and susceptible wheat plants.

The Russian wheat aphid (RWA), Diuraphis noxia Kurdjumov, is a major global pest of wheat and barley production that causes enormous economic damage. Few studies have been conducted to explore and decipher the molecular basis of RWA strategies to evade plant defense mechanisms. Gene expression studies of RWA in response to wheat genotypes carrying different RWA resistance genes have been initiated in our group; however, a secure and accurate understanding of RWA gene expression is dependent on identification of suitable reference genes. This study analyzed expression profiles of five potential reference genes selected and sequenced during RNA sequencing experiments. The expression of genes coding for actin and ribosomal protein L27 was comparatively less variable in RWA fed on different wheat hosts. Results of geNorm, NormFinder, and BestKeeper expression analyses support the use of actin and ribosomal protein L27 in RT-qPCR studies of RWA gene expression in studies involving RWA-wheat interactions.

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.

Genetic and Association Mapping Study of English Grain Aphid Resistance and Tolerance in Bread Wheat Germplasm

English grain aphid (EGA) is a destructive insect pest of wheat. To identify the loci associated with EGA resistance and tolerance, 70 bread wheat accessions mainly from central Asia were evaluated for EGA resistance and tolerance traits at two locations, and genotyped with 51 SSR markers. Totally, three accessions showed high or moderate levels resistance and 17 genotypes displayed highly or moderately tolerate to EGA. Genetic diversity of these lines was investigated also. After 97 SSR loci which evenly covered all wheat chromosomes were scanned for association, four SSR loci were significantly associated with EGA resistance and four with EGA tolerance. After association analysis was conducted with dynamic aphid densities, we found four loci Xgwm192b, Xgwm391, Xbarc98, and Xgwm613b were detected continuously at different growing stages of wheat. In addition, the loci of EGA resistance/tolerance and Russian wheat aphid resistance were compared. The results generated in this study would be helpful for utilization of the EGA resistance/tolerance germplasm, and for development of mapping populations in EGA resistance breeding programs.