Ian Dundas

An elite hexaploid triticale Yukuri from Australia was used as a bridge for transferring valuable genes from Secale cereale L. into common wheat for enriching the genetic variability of cultivated wheat. Non-denaturing-fluorescence in situ hybridization (ND-FISH) identified that Yukuri was a secondary triticale with a complete set of rye chromosomes and a 6D(6A) substitution. Seed protein electrophoresis showed that Yukuri had a unique composition of glutenin subunits. A set of Yukuri-derived wheat-rye introgression lines were created from a Yukuri x wheat population, and all lines were identified by ND-FISH with multiple probes and validated by diagnostic molecular marker analysis. A total of 59 wheat-rye introgression lines including modified chromosome structural variations of wheat, and new complex recombinant chromosomes of rye were detected through ND-FISH and Oligo-FISH painting based on oligonucleotide pools derived from wheat-barley genome collinear regions. Wheat lines carrying the 1R chromosome from Yukuri displayed resistance to both stripe rust and powdery mildew, while the lines carrying the 3RL and 7RL chromosome arms showed stripe rust resistance. The chromosome 1R-derived lines were found to exhibit a significant effect on most of the dough-related parameters, and chromosome 5R was clearly associated with increased grain weight. The development of the wheat-rye cytogenetic stocks carrying disease resistances and superior agronomic traits, as well as the molecular markers and FISH probes will promote the introgression of abundant variation from rye into wheat improvement programs.

Rye 6R-derived stripe rust resistance gene Yr83 in wheat background was physically mapped to fraction length (FL) 0.87-1.00 on the long arm by non-denaturing-fluorescence in situ hybridization (ND-FISH), Oligo-FISH painting and 6R-specific PCR markers.Stripe rust resistance gene Yr83 derived from chromosome 6R of rye (Secale cereale) “Merced” has displayed high resistance to both Australian and Chinese wheat stripe rust isolates. With the aim to physically map Yr83 to a more precise region, new wheat- 6R deletion and translocation lines were produced from derived progenies of the 6R(6D) substitution line. The non-denaturing fluorescence in situ hybridization (ND-FISH) patterns of 6R were established to precisely characterize the variations of 6R in different wheat backgrounds. Comparative ND-FISH analysis localized the breakpoints of 6RL chromosomes relative to Oligo-pSc200 and Oligo-pSc119.2 rich sites in deletion lines. Molecular marker and resistance analyses confirmed that Yr83 is physically located at the fraction length (FL) 0.87-1.00 of 6RL and covers the corresponding region of 806-881 Mb in the reference genome of Lo7. Oligo-FISH painting demonstrated that the region carrying Yr83 is syntenic to the distal end of long arm of homoeologous group 7 of the Triticeae genome. The developed wheat-6R lines carrying the Yr83 gene will be useful for breeding for rust resistance.

Main conclusion A physical map of Thinopyrum intermedium chromosome 7J was constructed using translocation mapping, and a new seedling purple coleoptile gene was mapped to the bin of FL 0.35–0.63 of 7JS. Abstract Thinopyrum intermedium (2n = 6x = 42, JJJ^sJ^sStSt), a wild relative of common wheat, harbors numerous beneficial genes for wheat improvement. Previous studies showed that wheat–Th. intermedium partial amphiploid TAF46 and its derived addition line L1 had a purple coleoptile, which was derived from Th. intermedium chromosome 7J. To identify and physically map the purple coleoptile gene, 12 wheat–Th. intermedium 7J translocation lines were analyzed by sequential multicolor fluorescence in situ hybridization (mc-FISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A physical map of the 7J chromosome was constructed, consisting of eight chromosomal bins with 89 markers. Seedling evaluation of the coleoptile colors of all tested materials indicated that the purple coleoptile gene was located to the bin with a fraction length (FL) of 0.35–0.63 on chromosome 7JS. Furthermore, based on the syntenic relationships between Th. intermedium and wheat chromosomes, we developed a new chromosome 7J-specific EST-PCR marker from the chromosomal region corresponding to the purple coleoptile gene through the Triticeae multi-omics database. The approach of designing chromosome-specific markers has facilitated fine mapping of the Thinopyrum-specific purple coleoptile gene, and these translocation lines will be valuable for studying the function of the purple coleoptile gene in anthocyanin biosynthesis.

Tetraploid plants, including those induced from diploid barrel medic (Medicago truncatula Gaertn.) and the snail medic [Medicago scutellata (L.) Mill.], have the potential to increase vigor and leaf size to improve adaptation to environments with low and variable rainfall in Mediterranean climates. The growth of tetraploid lines induced from barrel medic cultivar Sultan‐SU was evaluated against the diploid parent line and a natural tetraploid snail medic cultivar Sava in field conditions in Adelaide, South Australia. In field conditions, tetraploid lines had up to 106% greater autumn biomass than Sultan‐SU, 58% larger seed weight, and a 127% increase in leaf area. In a controlled environment experiment, snail medic Sava was the only entry to show improved early season (assessed at 6 wk) shoot biomass and canopy cover under short days and low temperatures that were designed to simulate a late start to the growing season. An examination of fresh flower buds showed that the fertility and stability of induced tetraploid lines varied between lines and generations. Hardseed breakdown patterns differed among tetraploid mutant lines, with two lines having much harder seed than Sultan‐SU. Some tetraploid Medicago spp. produced greater early biomass and larger leaves than diploids. Increasing ploidy level provides plant breeders with a promising tool in the development of new cultivars better suited to future climate scenarios.

Key message A physical map of Secale cereale chromosome 6R was constructed using deletion mapping, and a new stripe rust resistance gene Yr83 was mapped to the deletion bin of FL 0.73–1.00 of 6RL. Abstract Rye (Secale cereale L., RR) possesses valuable genes for wheat improvement. In the current study, we report a resistance gene conferring stripe rust resistance effective from seedling to adult plant stages located on chromosome 6R. This chromosome was derived from triticale line T-701 and also carries highly effective resistance to the cereal cyst nematode species Heterodera avenae Woll. A wheat-rye 6R(6D) disomic substitution line exhibited high levels of seedling resistance to Australian pathotypes of the stripe rust (Puccinia striiformis f. sp. tritici; Pst) pathogen and showed an even greater resistance to the Chinese Pst pathotypes in the field. Ten chromosome 6R deletion lines and five wheat-rye 6R translocation lines were developed earlier in the attempt to transfer the nematode resistance gene to wheat and used herein to map the stripe rust resistance gene. These lines were subsequently characterized by sequential multicolor fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), mc-GISH, PCR-based landmark unique gene (PLUG), and chromosome 6R-specific length amplified fragment sequencing (SLAF-Seq) marker analyses to physically map the stripe rust resistance gene. The new stripe rust resistance locus was located in a chromosomal bin with fraction length (FL) 0.73–1.00 on 6RL and was named Yr83. A wheat-rye translocation line T6RL (#5) carrying the stripe rust resistance gene will be useful as a new germplasm in breeding for resistance.

We report transfer of a rust resistance gene named SrB, on the 6Ae#3 chromosome, to wheat by recombination with the 6Ae#1 segment carrying Sr26 and development of a linked marker.

The use of major resistance genes is a cost-effective strategy for preventing stem rust epidemics in wheat crops. The stem rust resistance gene Sr39 provides resistance to all currently known pathotypes of Puccinia graminis f. sp. tritici (Pgt) including Ug99 (TTKSK) and was introgressed together with leaf rust resistance gene Lr35 conferring adult plant resistance to P. triticina (Pt), into wheat from Aegilops speltoides. It has not been used extensively in wheat breeding because of the presumed but as yet undocumented negative agronomic effects associated with Ae. speltoides chromatin. This investigation reports the production of a set of recombinants with shortened Ae. speltoides segments through induction of homoeologous recombination between the wheat and the Ae. speltoides chromosome. Simple PCR-based DNA markers were developed for resistant and susceptible genotypes (Sr39#22r and Sr39#50s) and validated across a set of recombinant lines and wheat cultivars. These markers will facilitate the pyramiding of ameliorated sources of Sr39 with other stem rust resistance genes that are effective against the Pgt pathotype TTKSK and its variants.