Multiplex PCR effectively identifies tetraploid Triticum AABB – or AAGG-genome species

We developed a multiplex PCR DNA marker for quick and easy identification of the AAGG-genome timopheevii lineage, including Triticum timopheevii, Triticum araraticum and hexaploid Triticum zhukovskyi (AAAmAmGG), and the AABB-genome emmer wheat lineage, including Triticum durum, Triticum dicoccum and Triticum dicoccoides. Distinguishing between tetraploid AAGG- and AABB-genome wheat species based on morphology is known to be difficult. This multiplex PCR system is based on the simultaneous PCR amplification of two chloroplast regions, matK and rbcL. The matK region molecularly distinguishes the two lineages, whereas the rbcL region is a positive control amplicon. We also examined whether the simple sequence repeat is a fixed mutation within species, using genetic resources in the collection of KOMUGI, Kyoto University, which comprises accessioned species collected across diverse geographical areas. The multiplex PCR marker distinguished AAGG from AABB species with complete accuracy.

Patterns of resistance to three cereal aphids among wheats in the genus Triticum (Poaceae)

Forty-one accessions of wild and cultivated wheats belonging to 19 Triticum species were tested in the field for resistance to three species of aphids, Rhopalosiphum padi Linnaeus, Sitobion avenae Fabricius and Schizaphis graminum Rondani. Antibiotic resistance was estimated by the increase in biomass of aphids over 21 days on adult plants. Overall resistance was estimated by the plant biomass lost due to aphid infestation. All three species of aphids survived and reproduced on all wheats, and reduced spike biomass compared to uninfested controls. The level of antibiosis varied among wheat species and among accessions, with accessions from three, five and one species showing antibiosis to R. padi, S. avenae and S. graminum, respectively. Overall resistance to the three aphid species was observed in five to seven accessions per aphid species. Resistance was usually specific to one aphid species. The frequency of accessions with antibiosis or overall resistance was associated with the ploidy level of the plant species. Except for overall resistance to R. padi, resistance was highest for diploid species and lowest for hexaploid species. No consistent relationship between resistance and level of domestication was detected. Accessions of the wild wheats, Triticum boeoticum Bois, Triticum tauschii (Coss.) Schmal. and Triticum araraticum Jakubz. exhibited high levels of resistance to aphids, as did Triticum monococcum L. which is derived from T. boeoticum. Nevertheless, individual susceptible or resistant accessions occurred at all levels within the evolutionary tree of wheat.

Detection of intergenomic translocations with centromeric and noncentromeric breakpoints in Triticum araraticum: mechanism of origin and adaptive significance

Triticum araraticum Jakubz. (2n = 4x = 28, AtAtGG), a wild progenitor of the polyploid cultivated wheat T. timopheevii, shows extensive chromosome translocation polymorphism in natural populations from the Middle East and Transcaucasia. From an extensive survey, eight intergenomic translocation types were observed and their breakpoints analyzed by genomic in situ hybridization. The previously reported species-specific 6At–1G–4G cyclic translocation was found in all accessions studied. In four translocation types, the breakpoints were in interstitial regions of chromosomes and the other four arose via centric–breakage–fusion. A model is presented on the mechanism of origin and the adaptive significance of translocations with centromeric and noncentromeric breakpoints.Key words: intraspecific diversity, intergenomic translocations, Triticum araraticum.

Transfer of a gene for stem rust resistance from Triticum araraticum to hexaploid wheat

A partially dominant gene for seedling resistance to Puccinia graminis f.sp. tritici was transferred from two accessions of Triticum araraticum (PGR 6126 and PGR 6195) to hexaploid wheat by a series of backcrosses. This gene confers an intermediate level (infection type 1+ to 2) of resistance to a large number of P. graminis isolates. Because of linkage with the genes Lr13 (1.0%), Lr23 (4.7%), Lr16 (34.4%), Sr36 (21.9%) and the Sr9 (28.0%) locus, this gene is probably on the short arm of chromosome 2B. It has been assigned the symbol Sr40. No apparent deleterious quality characteristics were associated with the transfer of Sr40. This gene is being combined with the closely linked gene Lr13. This recombinant line should be useful in wheat breeding. The concurrent attempt to transfer resistance to P. recondita from T. araraticum to hexaploid wheat was not successful.Key words: Triticum aestivum, stem rust resistance, Triticum araraticum.