Resistance to Heterodera filipjevi and H. avenae in Winter Wheat is Conferred by Different QTL.

The coexistence of cereal cyst nematode (CCN) species Heterodera avenae and H. filipjevi, often involving multiple pathotypes, is a limiting factor for wheat production in China. Some of the known genes for resistance to CCN are not effective against both nematode species, hence complicating breeding efforts to develop CCN-resistant wheat cultivars. Here, we demonstrate that the CCN resistance in wheat cultivar Madsen to both Heterodera spp. is controlled by different genetic loci, both of which originated from Aegilops ventricosa. A new quantitative trait locus (QTL), QCre-ma7D, was identified and localized in a 3.77-Mb genomic region on chromosome arm 7DL, which confers resistance to H. filipjevi. QCre-ma2A on chromosome arm 2AS corresponds to CCN resistance gene Cre5 and confers resistance to H. avenae. This QTL is a new locus on chromosome arm 7DL and is designated Cre9. Three Kompetitive allele-specific PCR markers (BS00150072, BS00021745, and BS00154302) were developed for molecular marker-assisted selection of Cre9 and locally adapted wheat lines with resistance to both nematode species were developed. QCre-ma2A on chromosome arm 2AS corresponds to CCN resistance gene Cre5 and confers resistance to H. avenae. The identification of different loci underlying resistance to H. filipjevi and H. avenae and the development of adapted resistant entries will facilitate breeding of wheat cultivars that are resistant to these devastating nematodes in China.

Fine mapping of the wheat powdery mildew resistance gene Pm52 using comparative genomics analysis and the Chinese Spring reference genomic sequence.

KEY MESSAGE: A high-resolution genetic linkage map was constructed using the comparative genomics analysis approach and the wheat reference genome, which placed wheat powdery mildew resistance gene Pm52 in a 0.21-cM genetic interval on chromosome arm 2BL. The gene Pm52 confers resistance to powdery mildew and has been previously mapped on chromosome arm 2BL in winter wheat cultivar Liangxing 99. Because of its effectiveness against the disease, this study was initiated to finely map Pm52 using the comparative genomics analysis approach and the wheat reference genomic sequence. Based on the EST sequences that were located in the chromosome region flanking Pm52, four EST-SSR markers were developed, and another nine SSR markers were developed using the comparative genomics technology. These thirteen markers were integrated into a genetic linkage map using an F2:3 subpopulation of the Liangxing 99 × Zhongzuo 9504 cross. Pm52 was mapped within a 3.2-cM genetic interval in the subpopulation that corresponded to a ~40-Mb genomic interval on chromosome arm 2BL of the Chinese Spring reference genome. The Pm52-flanking markers Xicsl163 and Xicsl62 identified 344 recombinant individuals from 8820 F2 plants. Nine SSR markers generated from the Chinese Spring genomic interval were incorporated into a high-resolution genetic linkage map, which placed Pm52 in a 0.21-cM genetic interval corresponding to 5.6-Mb genomic region. The constructed high-resolution genetic linkage map will facilitate the map-based cloning of Pm52 and its marker-assisted selection.

PmLX66 and PmW14: New Alleles of Pm2 for Resistance to Powdery Mildew in the Chinese Winter Wheat Cultivars Liangxing 66 and Wennong 14.

Wheat powdery mildew (caused by Blumeria graminis f. sp. tritici) can be effectively managed by growing resistant cultivars. 'Liangxing 66' and 'Wennong 14' are the current winter wheat cultivars grown in northern China where powdery mildew is epidemic. Both cultivars have been demonstrated to carry single dominant genes for resistance to powdery mildew, tentatively designated PmLX66 and PmW14, on chromosome 5DS and share common linked markers with Pm2. Allelism tests were performed using a total of 15,657 plants of F2 segregating populations to determine the relationship between PmLX66, PmW14, and Pm2. All progeny from the crosses Liangxing 66 × 'Ulka/8*Chancellor' (Ulka/8*Cc), Wennong 14 × Ulka/8*Cc, and Liangxing 66 × Wennong 14 were resistant when tested with B. graminis f. sp. tritici isolate E20, indicating that PmLX66 and PmW14 are allelic to Pm2 and to each other. Liangxing 66 was resistant to 76.7% of the 60 B. graminis f. sp. tritici isolates from northern China, a slightly smaller proportion than Ulka/8*Cc (78.3%). However, Wennong 14 (85.0%) was more resistant against this set of B. graminis f. sp. tritici isolates than Ulka/8*Cc and Liangxing 66. Liangxing 66 and Wennong 14 differed from Ulka/8*Cc in respect to a number of B. graminis f. sp. tritici isolates. Based on these findings, PmLX66 and PmW14 are new alleles at the Pm2 locus.

Genetic characterization of hull color using BSR-Seq and genome re-sequencing approaches in foxtail millet.

Hull color of foxtail millet is an important indicator of certain nutritional quality parameters. An F2:6 recombinant inbred line (RIL) population developed by crossing a yellow-hulled cultivar Yugu 5 and a brown-hulled cultivar Jigu 31 was used to determine the genetic control of the hull color trait. This population segregated for yellow and brown hull colors in a ratio of 2:1, indicating that hull color is regulated by multiple genetic loci. A bulk segregant analysis-RNA sequencing (BSR-Seq) approach performed using the RNA bulks from 30 lines with brown and yellow hull colors each identified three genomic regions on chromosomes 1 (4,570,517-10,698,955 bp), 2 (40,301,380-46,168,003 bp), and 3 (44,469,860-50,532,757 bp). A new QTL for brown hull color of Jigu 31, QHC.czas1, was detected between bin markers Block43 and Block697 on chromosome 1 with the genetic linkage map constructed by re-sequencing a subset of the 147 RILs. This QTL explained a high level of phenotypic variation ranging from 28.0% to 47.0%. The corresponding genomic region of this QTL in the foxtail millet reference genome overlapped with that detected on chromosome 1 by the BSR-Seq analysis. Nineteen genes associated with biosynthesis of anthocyanin were annotated in this genomic region. Gene Si1g06530 encoding a SANT/Myb domain protein was highly expressed in developing panicles and seeds, which warrants further verification as the candidate gene for the brown color hull of Jigu 31. Moreover, several annotated genes for biosynthesis of anthocyanin were identified in the genomic regions of chromosomes 2 and 3.

Transcriptional responses of wheat and the cereal cyst nematode Heterodera avenae during their early contact stage.

Cereal cyst nematode (Heterodera avenae) is attracted to and aggregated around wheat roots to initiate infection, but this interaction between wheat and the nematode is not fully understood. The transcriptional responses of both wheat and H. avenae were examined during their early contact stage by mRNA sequencing analysis; certain numbers of the differentially expressed genes (DEGs) were validated using quantitative real-time PCR. The immobile host wheat root only had 93 DEGs (27 up-regulated and 66 down-regulated), while the mobile plant parasitic nematode reacted much more actively with 879 DEGs (867 up-regulated and 12 down-regulated). Among them, a number of wheat DEGs (mostly down-regulated) were involved in biotic stress pathways, while several putative effector genes were up-regulated in the nematode DEGs. One putative chitinase-like effector gene of H. avenae was able to suppress BAX-triggered programmed cell death in Nicotiana benthamiana. Results of these experiments demonstrated that nematode responded more actively than wheat during the contact stage of parasitism. The parasite's responses mainly involved up-regulation of genes including at least one anti-plant-defence effector gene, whereas the host responses mainly involved down-regulation of certain defence-related genes.