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

A 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.     

Identification of wheat chromosomes involved with different types of resistance against greenbug (Schizaphis graminum, Rond.) and the Russian wheat aphid (Diuraphis noxia, Mordvilko)

Two sets of intervarietal chromosome substitution lines in the recipient,susceptible cultivar ‘Chinese Spring’ were screened to identify the wheat chromosomes involved with antixenosis, antibiosis and tolerance resistance to greenbug and Russian wheat aphid. The amphiploid ‘Synthetic’ and the cultivar ‘Hope’ were the donor parents. Antixenosis, antibiosis and tolerance were evaluated with conventional tests in controlled environmental conditions using a clone of greenbug biotype C and a clone of RWA collected on wheat. Antixenosis against greenbug was accounted for by several chromosomes in both sets of substitution lines with chromosome 2B contributing the highest level of this type of resistance. The highest levels of antixenosis against RWA were associated with the group of chromosomes 7 of the substitutions CS/Syn set and the chromosome substitutions 2B, 6A and 7D of the CS/Hope set. Antibiosis against both aphids species was accounted for by several different chromosomes. The highest levels of antibiosis for most of RWA resistance traits were recorded from the 1B substitution line of the CS/Hope set. More than one gene appears to determine antibiosis. Tolerance to both greenbug and the RWA was significantly associated with chromosomes 1A,1D, and 6D in the CS/Syn set of substitutions. These lines showed enhanced plant growth under aphid infestation. The highest levels of antixenosis, antibiosis and tolerance against the two aphid species occurred mostly in different substitution lines. Consequently, the different types of resistance for both pests seem to be partially independent. Since different genes seem to be involved in at least several traits of the resistance categories against the two aphid species, such genes could be combined in new cultivars of wheat to broaden their genetic base of resistance against the greenbug and the RWA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mapping quantitative trait loci in wheat for resistance against greenbug and Russian wheat aphid

Breeding for genetic resistance against greenbug and Russian wheat aphid (RWA) is the most effective way of controlling these widespread pests in wheat. Earlier work had shown that chromosome 7D of a synthetic hexaploid wheat, ‘Synthetic’ (T. dicoccoides × Ae. squarrosa) (AABB × DD) gave resistance when transferred into the genetic background of an aphid‐susceptible cultivar, ‘Chinese Spring’, as the recipient. To map the genes involved, a set of 103 doubled haploid recombinant substitution lines was obtained from crossing the 7D substitution line with the recipient, and used to determine the number and chromosomal location of quantitative trait loci (QTL) controlling antixenosis and antibiosis types of resistance. Antixenosis to RWA was significantly associated with marker loci Xpsr687 on 7DS, and Xgwm437 on 7DL. Antibiosis to greenbug was associated with marker loci Xpsr490, Rc3 (on 7DS), Xgwm44, Xgwm111, Xgwm437, Xgwm121 and D67 (on 7DL). Similarly, antibiosis to RWA was linked to loci Xpsr490, Rc3, Xgwm44, Xgwm437 and Xgwm121. At least two QTL in repulsion phase, one close to the centromere either on the 7DS or 7DL arms, and a second distal on 7DL could explain antibiosis to RWA and, partially, this mechanism against greenbug.     

DIBOA in wild Poaceae: Sources of resistance to the Russian wheat aphid (Diuraphis noxia) and the greenbug (Schizaphis graminum)

Hydroxamic acids are secondary metabolites typical of Poaceae that play a role in cereal resistance against pests and pathogens. The content of the hydroxamic acid aglucones DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) and DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) was evaluated in wild Poaceae belonging to the tribes Triticeae (genera Hordeum and Elymus) and Aveneae (genera Deschampsia and Phalaris). The concentration of DIBOA in seedling extracts of the wild barleys Hordeum chilense, H. brevisubulatum subsp. violaceum and H. bulbosum was negatively correlated with parameters related to performance of the cereal aphids Schizaphis graminum and Diuraphis noxia. The relevance of the results obtained for breeding programs aimed at increasing cereal resistance against aphids is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of Russian wheat aphid resistance in PI 140207 spring wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a serious, perennial pest of wheat (Triticum aestivum L.) in many areas of the world. This study was initiated to determine the inheritance of RWA resistance in PI 140207 (a RWA-resistant spring wheat) and to determine its allelic relationship with a previously reported RWA resistance gene. Crosses were made between PI 140207 and ‘Pavon’ (a RWA-susceptible spring wheat). Genetic analysis was performed on the parents, F₁, F₂, backcross (BC) population and F₂-derived F₃ families. Analyses of segregation patterns of plants in the F₁, F₂, and BC populations, and F₂-derived F₃ families indicated single dominant gene control of RWA resistance in PI 140207. Results of the allelism test indicated that the resistance gene in PI 140207, while conferring distinctly different seedling reactions to RWA feeding, is the same as Dn 1, the resistance gene in PI 137739.     

Inheritance and allelism of Russian wheat aphid resistance in several wheat lines

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused serious reduction in wheat production in 17 Western states of the United States since 1986. Inheritance of resistance to RWA in seven wheat lines and the allelism of the resistance genes in these lines with three known resistance genes Dn4, Dn5, and Dn6 were studied. The seven resistant lines were crossed to a susceptible wheat cultivar ‘Carson’ and three resistant wheats: CORWA1 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6). Seedlings of the parents, F₁, and F₂ were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21–28 days after the infestation using a 1–9 scale. The resistance level of all the F₁ hybrids was similar to that of the resistant parent, indicating dominant gene control. Only two distinctive classes were present and no intermediate types were observed in the F₂ population, suggesting qualitative, nonadditive gene action, in which the presence of any one of the dominant alleles confers complete resistance to RWA. Resistance in CI 2401 is controlled by two dominant genes. Resistance in CI 6501 and PI 94365 is governed by one dominant gene. Resistance in PI 94355 and PI 151918 may be conditioned by either one dominant gene or one dominant and one recessive gene. No conclusion can be made on how many resistance genes are in AUSVA1-F₃, since the parent population was not a pure line. Allelic analyses showed that one of resistance genes in CI 2401 and PI 151918 was the same allele as Dn4, the resistance gene in CI 6501 was the same allele as Dn6, and AUS-VA1-F₃ had one resistance gene which was the same allele as one of the resistance genes in PI 294994. One non-allelic resistance gene different from the Dn4, Dn5, and Dn6 genes in CI 2401, PI 94355, PI 94365, and PI 222668 was identified and should be very useful in diversifying gene sources in wheat breeding.     

Greenhouse evaluation of red winter wheats for resistance to the Russian wheat aphid (Diuraphis noxia,Mordvilko)

Summary The Russian wheat aphid (Diuraphis noxia, Mordvilko) (RWA) is responsible for significant economic damage to cereal crops in arid and semi-arid environments. In this research 20 red winter wheats originating from Iran were evaluated for resistance to RWA. Leaf rolling, leaf folding, and leaf chlorosis were measured using 0 to 3 scales. An overall mean damage score was calculated as the average of the three measured damage symptoms. Plants from seven central Asian accessions (PI222666, PI222668, PI225226, PI225267, PI225271, PI243630, and PI243642) had mean damage scores significantly lower (p < 0.001) than Stephens wheat (RWA susceptible) and not significantly different from Border oat (RWA resistant). These results are consistent with previous studies which found a high frequency of resistant wheats collected from the central Asian region.     

Host plant resistance in some wild wheats to the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)

A total of 259 accessions of wild Triticum species originating from different countries, along with 91 triticale (6×)× bread wheat true-breeding derivatives, two bread wheat, and three triticale cultivars were screened for resistance to the Russian wheat aphid, a serious insect pest of the wheat crop. Twenty-four entries with low damage ratings on the basis of amount of leaf rolling and leaf chlorosis were retested along with resistant and susceptible controls. On the basis of leaf roll damage ratings, eight entries including four Triticum monococcum var. boeoticum (T. boeoticum), one T. monococcum var. monococcum (T. monococcum), two T. timopheevii var. araraticum (T. araraticum), and one triticale cultivar were significantly superior to ‘Karl’ (susceptible control) wheat. Among these, four accessions — three T. boeoticum and one T. araraticum— were significantly superior to all other entries and were equal to the resistant control (PI 372129) in resistance rating based on leaf rolling and leaf chlorosis (except T. boeoticum TA 202). The leaf chlorosis damage rating of all accessions were significantly lower than that of the susceptible check.     

Mapping antixenosis genes on chromosome 6A of wheat to greenbug and to a new biotype of Russian wheat aphid

Greenbug and Russian wheat aphid (RWA) are two devastating pests of wheat. The first has a long history of new biotype emergence and recently. RWA resistance has just started to break down. Thus, it is necessary to find new sources of resistance that will broaden the genetic base against these pests in wheat. Seventy‐five doubled haploid recombinant (DHR) lines for chromosome 6A from the F₁ of the cross between “Chinese Spring’ and the “Chinese Spring (Synthetic 6A) (Triticum dicoccoides × Aegilops tauschii)” substitution line were used as a mapping population for testing resistance to greenbug biotype C and to a new strain of RWA that appeared in Argentina in 2003. A quantitative trait locus (QTL) (br antixenosis to greenbug was significantly associated with the marker loci Xgwm1009 and Xgwm1185 located in the centromere region of chromosome 6A. Another QTL which accounted for most of the antixenosis against RWA was associated with the marker loci Xgwm1291 and Xiinni1150. both located on the long arm of chromosome 6A. This is the first report of greenbug and RWA resistance genes located on chromosome 6A. It is also the first report of antixenosis against the new strain of RWA. As most of the RWA resistance genes present in released cultivars have been located in [he D‐ genome, it is highly desirable to find new sources in other genomes to combine the existing resistance genes with new sources.     

The use of low molecular weight glutenin subunits to distinguish between wheat cultivars with and without resistance to the Russian wheat aphid, Diuraphis noxia

A number of resistance sources for the Russian wheat aphid have been reported in the last few years and were used to develop resistant cultivars from current commercial cultivars in various breeding programmes. It can be diffcult to distinguish between the cultivars with and without resistance without actual infestation and so in this study we looked at low molecular weight glutenin subunits (LMW-GS) of the two groups. Distinctly different banding patterns were found for the cultivars tested and their isogenic counterparts. Although the LMW-GS and DN1 and DN5 are coded on different chromosomes, the LMW-GS are highly repeatable and banding profiles of each cultivar can be used for the identification of unknown seed.     

Genetic variability in antibiotic resistance to the greenbug Schizaphis graminum in Hordeum chilense

Hordeum chilense (Roem. et Schult), a native grass of South America, is a source of antixenotic and antibiotic resistance to the greenbug Schizaphis graminum Rondani. The genetic and environmental components of the variability in antibiotic resistance shown by H. chilense were determined by measuring the developmental time, the length of adult life, fecundity and intrinsic rate of population increase of green-bugs reared on this host. The aphids belonged to a clone of biotype C. Plants were cloned to reduce the incidence of environmental variability. Different plant characters appeared to prolong aphid developmental time and reduce the length of adult life and total fecundity. The broad sense heritability and the genetic variability of these plant characters were different. The plant character that affected aphid development appears to differ from that affecting fecundity.     

Genetic control of Russian wheat aphid (Diuraphis noxia) resistance in wheat accession PI 47545

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a major pest of cereal crops in many areas of the world, causing serious reduction in grain yield in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Incorporating genetic resistance to D. noxia into wheat cultivars is paramount to effectively reduce damage inflicted by this pest. Genetic resistance to D. noxia has been identified in wheat, barley and rye germplasm, and several resistance genes are available for use for cultivar improvement. In the United States of America, only a few Russian wheat aphid (RWA) resistant winter wheat cultivars are currently available, and these cultivars contain only one of the six known RWA resistance genes. The objective of this study was to determine the inheritance of RWA resistance in wheat accession PI 47545, using a screening method based on differences in the leaf morphology of resistant and susceptible types following insect challenge. PI 47545 was selected for study, since it displayed high levels of resistance in a white-grained wheat background, the predominant wheat class produced in the Pacific Northwest of the USA. Segregation analysis was conducted on an F₂ population developed by cross-hybridizing the susceptible soft white winter wheat cultivar ‘Daws’ to the resistant accession PI 47545. Russian wheat aphid screening data from this population indicated that the resistance in PI 47545 is controlled by a single, dominant gene (χ² = 1.72; p ≤ 0.189). This revised version was published online in August 2006 with corrections to the Cover Date.     

Monosomic analysis of Russian wheat aphid (Diuraphis noxia) resistance in Triticum aestivum line PI137739

Summary The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has become an important pest of wheat (Triticum aestivum L.) in the United States. The aphid causes a phytotoxemic reaction in wheat evidenced by local and systemic chlorosis and rolling of infested leaves. Developing resistance in wheat cultivars to D. noxia is an essential factor in controlling the damage caused by this pest. Several sources of genetic resistance to D. noxia have been identified in wheat germplasm. Monosomic analysis of the monogenic resistant T. aestivum accession PI137739 has shown that the gene (Dn1) for resistance is carried on chromosome 7D. It appears that chromosome 7B may carry a second resistance gene for D. noxia that might be a source of minor or complementary gene action for resistance.     

Resistance in wheat to a new North American–Russian wheat aphid biotype

The Russian wheat aphid (RWA), is a serious threat to wheat production worldwide. The identification of a new RWA biotype in the USA virulent to all commercially grown winter wheats poses new challenges to wheat breeders. Wheat germplasm was evaluated to identify accessions resistant to the new virulent RWA isolate (biotype 2). Eleven biotype 1‐resistant wheats and one susceptible check were challenged with RWA biotype 2. Two resistant wheat entries were identified (one highly resistant and one moderately resistant). This information is useful to wheat breeders searching for sources of resistance to the new RWA biotype to incorporate into their breeding programmes.     

A Monosomic Analysis of Russian Wheat Aphid Resistance in the Common Wheat PI 294994

Chromosome 7D of PI 294994 was indicated as carrying a single dominant gene for resistance to the Russian wheat aphid. The symbol Dn5 is proposed to designate the gene.     

A six week screening method for mechanisms of host plant resistance to Diuraphis noxia in wheat accessions

The Russian wheat aphid Diuraphis noxia (Kurdjumov) is a serious pest of wheat in South Africa. The use of D. noxia-resistant cultivars may reduce the impact of this pest on wheat production and at the same time reduce environmental risks and control costs. The mechanisms of resistance in two new sources of resistance were compared by using various methods, in order to establish a rapid and relatively accurate screening protocol. The resistant lines OSU ID 2808 and Aus 22498 were compared to the susceptible cultivars Betta and Tugela. The predominant mechanism of resistance in OSU ID 2808 was antibiosis, although a low level of antixenosis may also be present. The line Aus 22498 was primarily a tolerant type, with a moderate level of antibiosis and a low level of antixenosis. A six week screening procedure is described using the colony count technique for antibiosis, a completely random free choice experiment for antixenosis and a three week test measuring initial and final plant height, initial and final D. noxia infestation, damage rating, leaf area and dry plant mass for tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to the Russian wheat aphid in an Iranian durum wheat line

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a major economic pest of small grains in many countries. An experiment was therefore conducted to determine the inheritance of gene(s) controlling resistance to RWA in a resistant tetraploid durum wheat line. This resistant line,‘1881′, was crossed to a susceptible line, ‘Orejy‐e‐Kazeroon’, and then F₁ F₂ and BCF₁ (backcross to susceptible line) seedlings were screened in a greenhouse for RWA resistance following artificial infection. Resistance in ‘1881’ was apparently controlled by one dominant gene. Since Dnl, Dn2, dn3, Dn4 and Dn5 have been reported to be located on genome D, it was reasoned that the resistance gene in ‘1881’ is not allelic to them.     

Inheritance of resistance to Russian wheat aphid in barley

Summary The inheritance of resistance to Russian wheat aphid Diuraphis noxia (Mordvilko), in two resistant barleys, Hordeum vulgare L., ASE/2CM//B76BB and Gloria/Come, was studied in the field and in the greenhouse. The resistant genotypes were crossed with susceptible genotypes Esperanza and Shyri. Resistance reactions of F1, BC1, and F2 plants, and individual F2 plant derived F3 families indicated that resistance in each genotype was controlled by the same single dominant gene.     

Detection of Resistance to the Russian Wheat Aphid in Hexaploid Wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), poses a serious threat to wheat (Triticum aestivum L.) production in many parts of the world. This research was initiated to evaluate wheat accessions for detection of resistance to the RWA. Over 12,000 wheat cultivars and plant introductions (PIs) from the USDA-ARS National Small Grains Collection were evaluated for reaction to RWA feeding damage. Twenty-nine PIs from Iran, Afghanistan, and the former Soviet Union, of various agronomic backgrounds were identified as having moderate to high levels of RWA resistance. This information is useful to wheat breeders searching for sources of resistance to the RWA to incorporate into their breeding programmes.