Development of Novel Wheat-Aegilops longissima 3Sl Translocations Conferring Powdery Mildew Resistance and Specific Molecular Markers for Chromosome 3Sl

Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease of wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3Sl#2 present in Chinese Spring (CS)-Aegilops longissima 3Sl#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3Sl#2 (3Sl#2S) by evaluating for Bgt-resistance of newly developed CS-Ae. longissima 3Sl#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3Sl#3 disomic addition line, was re-identified as an isochromosome 3Sl#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3Sl#3 (3Sl#3S). Based on transcriptome sequences of TA3575, ten novel chromosome 3SlS-specific markers were developed, of which, five could be used to distinguish between 3Sl#2S and 3Sl#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4), and the remaining five could identify both 3Sl#2S and 3Sl#3S. Besides, CL897, one of five markers specific to both 3Sl#2S and 3Sl#3S, could be used to detect Pm13 located at chromosome 3Sl#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3Sl#2S and 3Sl#3S, the CS-Ae. longissima 3Sl#2 translocation lines, and the 3SlS-specific markers developed in this study will provide new germplasm resources for powdery mildew resistance breeding and facilitate the transfer of Bgt-resistance genes into common wheat.

The unique disarticulation layer formed in the rachis of Aegilops longissima probably results from the spatial co-expression of Btr1 and Btr2

Background and Aims The brittle rachis trait is a feature of many wild grasses, particularly within the tribe Triticeae. Wild Hordeum and Triticum species form a disarticulation layer above the rachis node, resulting in the production of wedge-type dispersal units. In Aegilops longissima, only one or two of the nodes in the central portion of its rachis are brittle. In Triticeae species, the formation of a disarticulation layer above the rachis node requires the co-transcription of the two dominant and complementary genes Btr1 and Btr2. This study aims to establish whether homologues of Btr1 and/or Btr2 underlie the unusual brittle rachis phenotype observed in Ae. longissima. Methods Scanning electron microscopy was used to examine the disarticulation surfaces. Quantitative RT-PCR and RNA in situ hybridization experiments were used to identify gene expression in the immature inflorescence. Key Results Analysis based on scanning electron microscopy was able to demonstrate that the disarticulation surfaces formed in the Ae. longissima rachis are morphologically indistinguishable from those formed in the rachises of wild Hordeum and Triticum species. RNA in situ hybridization showed that in the immature Ae. longissima inflorescence, the intensity of Btr1 transcription varied from high at the rachis base to low at its apex, while that of Btr2 was limited to the nodes in the central to distal portion of the rachis. Conclusions The disarticulation pattern shown by Ae. longissima results from the limitation of Btr1 and Btr2 co-expression to nodes lying in the centre of the rachis.

Engineered Durum Wheat Germplasm with Multiple Alien Introgressions: Agronomic and Quality Performance

If genetic gains in wheat yield are to be achieved in today’s breeding, increasing the genetic variability of cultivated genotypes is an essential requisite to meet. To this aim, alien gene transfer through chromosome engineering (CE) is a validated and sound strategy. Attempts to incorporate more than one alien segment into cultivated wheat have been rare, particularly for tetraploid durum wheat. Here, we present the agronomic and quality performance of the first successful CE-mediated multiple introgression into the latter species. By assembling into 7AL, 3BS, and 1AS arms of a single genotype homoeologous segments of Thinopyrum ponticum 7el1L, Aegilops longissima 3SlS, and Triticum aestivum 1DS arms, respectively, we have stacked several valuable alien genes, comprising Lr19+Sr25+Yp (leaf and stem rust resistance and a gene increasing semolina yellowness), Pm13 (powdery mildew resistance), and Gli-D1/Glu-D3 (genes affecting gluten properties), respectively. Advanced progenies of single, double, and triple recombinants were field-tested across three years in a typical durum wheat growing area of central Italy. The results showed that not only all recombinants had normal phenotype and fertility, but also that one of the triple recombinants had the highest yield through all seasons compared with all other recombinants and control cultivars. Moreover, the multiple introgressions enhanced quality traits, including gluten characteristics and semolina yellow index. The presence of effective disease resistance genes confers additional breeding value to the novel and functional CE products, which can greatly contribute to crop security and safety.

Engineered Durum Wheat Germplasm with Multiple Alien Introgressions: Agronomic and Quality Performance

If genetic gains in wheat yield are to be achieved in today’s breeding, increasing genetic variability of cultivated genotypes is an essential requisite to meet. To this aim, alien gene transfer through chromosome engineering (CE) is a validated and sound strategy. Attempts to incorporate more than one alien segment into cultivated wheat have been rare, particularly for tetraploid durum wheat. Here we present the agronomic and quality performance of the first successful CE-mediated multiple introgression into the latter species. By assembling into 7AL, 3BS and 1AS arms of a single genotype homoeologous segments of Thinopyrum ponticum 7el1L, Aegilops longissima 3SlS, and Triticum aestivum 1DS arms, respectively, we have stacked several valuable alien genes, comprising Lr19+Sr25+Yp (leaf and stem rust resistance and a gene increasing semolina yellowness), Pm13 (powdery mildew resistance) and Gli-D1/Glu-D3 (genes affecting gluten properties), respectively. Advanced progenies of single, double and triple recombinants were field-tested across three years in a typical durum wheat growing area of Central Italy. The results showed that not only all recombinants had normal phenotype and fertility, but also that one of the triple recombinants had the highest yield through all seasons compared with all other recombinants and control cultivars. Moreover, the multiple introgressions enhanced quality traits, including gluten characteristics and semolina yellow index. Presence of effective disease resistance genes confers additional breeding value to the novel and functional CE products, which can greatly contribute to crop security and safety.

Resistance of Aegilops longissima to the Rusts of Wheat

Stem rust (caused by Puccinia graminis f. sp. tritici), leaf rust (P. triticina), and stripe rust (P. striiformis f. sp. tritici) rank among the most important diseases of wheat worldwide. The development of resistant cultivars is the preferred method of controlling rust diseases because it is environmentally benign and also cost effective. However, new virulence types often arise in pathogen populations, rendering such cultivars vulnerable to losses. The identification of new sources of resistance is key to providing long-lasting disease control against the rapidly evolving rust pathogens. Thus, the objective of this research was to evaluate the wild wheat relative Aegilops longissima for resistance to stem rust, leaf rust, and stripe rust at the seedling stage in the greenhouse. A diverse collection of 394 accessions of the species, mostly from Israel, was assembled for the study, but the total number included in any one rust evaluation ranged from 308 to 379. With respect to stem rust resistance, 18.2 and 80.8% of accessions were resistant to the widely virulent U.S. and Kenyan P. graminis f. sp. tritici races of TTTTF and TTKSK, respectively. The percentage of accessions exhibiting resistance to the U.S. P. triticina races of THBJ and BBBD was 65.9 and 52.2%, respectively. Over half (50.1%) of the Ae. longissima accessions were resistant to the U.S. P. striiformis f. sp. tritici race PSTv-37. Ten accessions (AEG-683-23, AEG-725-15, AEG-803-49, AEG-1274-20, AEG-1276-22, AEG-1471-15, AEG-1475-19, AEG-2974-0, AEG-4005-20, and AEG-8705-10) were resistant to all races of the three rust pathogens used in this study. Distinct differences in the geographic distribution of resistance and susceptibility were found in Ae. longissima accessions from Israel in response to some rust races. To P. graminis f. sp. tritici race TTKSK, populations with a very high frequency of resistance were concentrated in the central and northern part of Israel, whereas populations with a comparatively higher frequency of susceptibility were concentrated in the southern part of the country. The reverse trend was observed with respect to P. striiformis f. sp. tritici race PSTv-37. The results from this study demonstrate that Ae. longissima is a rich source of rust resistance genes for wheat improvement.