Chromosomal distribution of pTa-535, pTa-86, pTa-713, 35S rDNA repetitive sequences in interspecific hexaploid hybrids of common wheat (Triticum aestivum L.) and spelt (Triticum spelta L.)

Cloning of the wheat leaf rust resistance gene Lr47 introgressed from Aegilops speltoides

Leaf rust, caused by Puccinia triticina Eriksson (Pt), is one of the most severe foliar diseases of wheat. Breeding for leaf rust resistance is a practical and sustainable method to control this devastating disease. Here, we report the identification of Lr47, a broadly effective leaf rust resistance gene introgressed into wheat from Aegilops speltoides. Lr47 encodes a coiled-coil nucleotide-binding leucine-rich repeat protein that is both necessary and sufficient to confer Pt resistance, as demonstrated by loss-of-function mutations and transgenic complementation. Lr47 introgression lines with no or reduced linkage drag are generated using the Pairing homoeologous1 mutation, and a diagnostic molecular marker for Lr47 is developed. The coiled-coil domain of the Lr47 protein is unable to induce cell death, nor does it have self-protein interaction. The cloning of Lr47 expands the number of leaf rust resistance genes that can be incorporated into multigene transgenic cassettes to control this devastating disease.

The Use of Ribosomal DNA for Comparative Cytogenetics

Fluorescence in situ hybridization (FISH) with ribosomal DNA (rDNA) sequences provides excellent chromosome markers for comparative cytogenetic analyses, especially in non-model plant species. The tandem repeat nature of a sequence and the presence of a highly conserved genic region make rDNA sequences relatively easy to isolate and clone. In this chapter, we describe the use of rDNA as markers for comparative cytogenetics studies. Traditionally, cloned probes labeled with Nick-translation have been used to detect rDNA loci. Recently, pre-labeled oligonucleotides are also employed quite frequently to detect both 35S and 5S rDNA loci. Ribosomal DNA sequences, together with other DNA probes in FISH/GISH or with fluorochromes such as CMA₃ banding or silver staining, are very useful tools in comparative analyses of plant karyotypes.

Development and Cytomolecular Identification of Monosomic Alien Addition and Substitution Lines of Triticale (×Triticosecale Wittmack) With 2Sk Chromosome Conferring Leaf Rust Resistance Derived From Aegilops kotschyi Boiss

Alien chromosome introgression has become a valuable tool to broaden the genetic variability of crop plants via chromosome engineering. This study details the procedure to obtain monosomic addition and monosomic substitution lines of the triticale carrying 2S^k chromosome from Aegilops kotchyi Boiss., which harbors Lr54 + Yr37 leaf and stripe rust-resistant gene loci, respectively. Initially, A. kotschyi × Secale cereale artificial amphiploids (2n = 6x = 42 chromosomes, UUSSRR) were crossed with triticale cv. "Sekundo" (2n = 6x = 42, AABBRR) in order to obtain fertile offspring. Cyto-molecular analyses of five subsequent backcrossing generations revealed that 2S^k chromosome was preferentially transmitted. This allowed for the selection of monosomic 2S^k addition (MA2S^k) lines of triticale. Finally, the 2S^k(2R) substitution plants were obtained by crossing MA2S^k with the nullisomic (N2R) plants of triticale. The presence of 2S^k chromosome in subsequent generations of plants was evaluated using SSR markers linked to Lr54 + Yr37 loci. Disease evaluation of the monosomic 2S^k(2R) substitution plants for the reaction to leaf and stripe rust infection were carried out under controlled conditions in a growth chamber. The results showed significant improvement of leaf rust resistance severity of monosomic substitution plants compared with control ("Sekundo"). In contrast, the introgression of the Lr54 + Yr37 loci did not lead to improvement of stripe rust resistance. In summary, the creation of monosomic addition and monosomic substitution lines of triticale is the starting point for the precise and guided transfer of Lr54 + Yr37 loci. The results showed that the developed materials could be exploited for the development of triticale varieties with resistance to leaf rust.

Cytological markers used for identification and transfer of Aegilops spp. chromatin carrying valuable genes into cultivated forms of Triticum

There are many reports describing chromosome structure, organization and evolution within goatgrasses (Aegilops spp.). Chromosome banding and fluorescence in situ hybridization techniques are main methods used to identify Aegilops Linnaeus, 1753 chromosomes. These data have essential value considering the close genetic and genomic relationship of goatgrasses with wheat (Triticumaestivum Linnaeus, 1753) and triticale (× Triticosecale Wittmack, 1899). A key question is whether those protocols are useful and effective for tracking Aegilops chromosomes or chromosome segments in genetic background of cultivated cereals. This article is a review of scientific reports describing chromosome identification methods, which were applied for development of prebreeding plant material and for transfer of desirable traits into Triticum Linnaeus, 1753 cultivated species. Moreover, this paper is a resume of the most efficient cytomolecular markers, which can be used to follow the introgression of Aegilops chromatin during the breeding process.