No abstract

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), is one of the most devastating insect pests of wheat (Triticum spp.) and barley (Hordeum spp.) in the world. Yield losses and control costs are valued at several hundred million dollars each year. The use of D. noxia-resistant cultivars is an ecologically, economically, and biologically sound method of managing this pest. Several D. noxia resistance (Dn) genes from wheat have been used to develop cultivars resistant to D. noxia. However, a new U.S. D. noxia biotype (biotype 2) in Colorado is virulent to all known Dn genes except the Dn7 gene from rye (Secale spp.). Hence, there is an immediate need to identify and characterize unique sources of D. noxia resistance to biotypes. In this article, we report resistance to D. noxia biotype 2, identified in a selection from wheat cereal introduction (CItr) 2401, that is controlled by two dominant genes. CItr2401 has a strong antibiosis effect that is exhibited as a reduced intrinsic rate of increase of D. noxia biotype 2. CItr2401 plants also exhibit tolerance to leaf rolling and chlorosis. No antixenosis was detected in CItr2401.

Cultivated rye (Secale cereale L., 2n = 2x = 14, RR) is an important source of genes for insect and disease resistance in wheat (Triticum aestivum L., 2n = 6x = 42). Rye chromosome arm 1RS of S. cereale 'Kavkaz' originally found as a 1BL.1RS translocation, carries genes for disease resistance (e.g., Lr26, Sr31, Yr9, and Pm8), while 1RS of the S. cereale 'Amigo' translocation (1RSA) carries a single resistance gene for greenbug (Schizaphis graminum Rondani) biotypes B and C and also carries additional disease-resistance genes. The purpose of this research was to identify individual plants that were recombinant in the homologous region of.1AL.1RSV and 1AL.1RSA using both molecular and phenotypic markers. Secale cereale 'Nekota' (1AL.1RSA) and S. cereale 'Pavon 76' (1AL.1RSV) were mated and the F1 was backcrossed to 'Nekota' (1AL.1AS) to generate eighty BC1F2:3 families (i.e., ('Nekota' 1AL.1RSA x 'Pavon 76' 1AL.1RSV) x 'Nekota' 1AL.1AS). These families were genotyped using the secalin-gliadin grain storage protein banding pattern generated with polyacrylamide gel electrophoresis to discriminate 1AL.1AS/1AL.1RS heterozygotes from the 1AL.1RSA+V and 1AL.1AS homozygotes. Segregation of the secalin locus and PCR markers based on the R173 family of rye specific repeated DNA sequences demonstrated the presence of recombinant 1AL.1RSA+V families. Powdery mildew (Blumeria graminis) and greenbug resistance genes on the recombinant 1RSA+V arm were mapped in relation to the Sec-1 locus, 2 additional protein bands, 3 SSRs, and 13 RFLP markers. The resultant linkage map of 1RS spanned 82.4 cM with marker order and spacing showing reasonable agreement with previous maps of 1RS. Fifteen markers lie within a region of 29.7 cM next to the centromere, yet corresponded to just 36% of the overall map length. The map position of the RFLP marker probe mwg68 was 10.9 cM distal to the Sec-1 locus and 7.8 cM proximal to the powdery mildew resistance locus. The greenbug resistance gene was located 2.7 cM proximal to the Sec-1 locus.

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 USD A-ARS National Small Grains Gollection 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.

The Russian wheat aphid (Diuraphis noxia Mordvilko) is a serious pest of wheat (Triticum aestivum L.). To extend the range of genetic variation of resistance, attempts were undertaken to transfer near‐immunity to RWA into wheat from two Russian triticales (X. Triticosecale Wittmack) PI 386146 and PI 386156 by irradiation and by induced homologous recombination. The rye genome in the triticale lines was derived from Secale montanum Guss. Tests of resistance in early backcrosses to wheat indicated that the near‐immunity of the triticale lines was controlled by at least two loci, one of which was located on rye chromosome arm 4RLmon Centric wheat‐rye translocation 7DS.4RLmon that appeared to be compensating, was produced. To further reduce the amount of rye chromatin present, its long arm was induced to recombine with wheat chromosomes by the removal of the Ph1 locus. Among 3563 progeny screened, only two wheat‐rye recombinant chromosomes were recovered. Both appeared to be non‐compensating and were involved in multivalents in meiosis. Irradiation of PI 386156 followed by crosses and backcrosses to wheat with several generations of selection for resistance resulted in a wheat line that was found to be a disomic addition of chromosome 4Rmon–centric translocation homozygote of rye chromosome tentatively identified as 5Rmon With only one locus for resistance from the original triticale parents, the addition line of 4Rmon, centric translocation line 7DS.4RLmon and recombinant lines of 4RLmon had only moderate level of resistance to RWA. The study demonstrates that transfers of alien variation into wheat may be severely complicated by unclear genetics of the target traits, low levels of homology, and structural differences between the donor and recipient chromosomes.