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Winter wheat line Tianmin 668 was crossed with susceptible cultivar Jingshuang 16 to develop 216 recombinant inbred lines (RILs) for dissecting its adult-plant resistance (APR) and all stage resistance (ASR) against powdery mildew. The RIL population was genotyped on a 16K Genotyping by Target Sequencing (GBTS) SNP array and phenotyped in six field trials and in the greenhouse. Three loci, QPmtj.caas-2BL, QPmtj.caas-2AS, and QPmtj.caas-5AL, conferring APR to powdery mildew, were detected on chromosomes 2BL, 2AS, and 5AL of Tianmin 668, respectively. The effect of resistance to powdery mildew for QPmtj.caas-2BL was greater than that of the other two loci. A Kompetitive Allele Specific PCR (KASP) marker specific for QPmtj.caas-2BL was developed and verified on 402 wheat cultivars or breeding lines. Results of virulence/avirulence patterns to 17 Blumeria graminis f. sp. tritici (Bgt) isolates, bulked segregant analysis-RNA-sequencing (BSR-Seq), and a genetic linkage mapping identified a resistance allele at locus Pm4 in Tianmin 668 based on the seedling phenotypes of the RIL population. The PCR-based DNA sequence alignment and co-segregation of the functional marker with the phenotypes of the RIL population demonstrated that Pm4d was responsible for the ASR to isolate Bgt1 in Tianmin 668. The dissection of genetic loci for APR and ASR may facilitate the application of Tianmin 668 in developing powdery mildew-resistant wheat cultivars.

Wheat powdery mildew is caused by Blumeria graminis f. sp. tritici (Bgt), a biotrophic fungal species. It is very important to mine new powdery mildew (Pm) resistance genes for developing resistant wheat cultivars to reduce the deleterious effects of the disease. This study was carried out to characterize the Pm gene in Qingxinmai, a winter wheat landrace from Xinjiang, China. Qingxinmai is resistant to many Bgt isolates collected from different wheat fields in China. F1, F2, and F2:3 generations of the cross between Qingxinmai and powdery mildew susceptible line 041133 were developed. It was confirmed that a single recessive gene, PmQ, conferred the seedling resistance to a Bgt isolate in Qingxinmai. Bulked segregant analysis-RNA-Seq (BSR-Seq) was performed on the bulked homozygous resistant and susceptible F2:3 families, which detected 57 single nucleotide polymorphism (SNP) variants that were enriched in a 40 Mb genomic interval on chromosome arm 2BL. Based on the flanking sequences of the candidate SNPs extracted from the Chinese Spring reference genome, 485 simple sequence repeat (SSR) markers were designed. Six polymorphic SSR markers, together with nine markers that were anchored on chromosome arm 2BL, were used to construct a genetic linkage map for PmQ. This gene was placed in a 1.4 cM genetic interval between markers Xicsq405 and WGGBH913 corresponding to 4.9 Mb physical region in the Chinese Spring reference genome. PmQ differed from most of the other Pm genes identified on chromosome arm 2BL based on its position and/or origin. However, this gene and Pm63 from an Iranian common wheat landrace were located in a similar genomic region, so they may be allelic.

Winter wheat cultivar Liangxing 99, which carries gene Pm52, is resistant to powdery mildew at both seedling and adult-plant stages. An F2:6 recombinant inbred line population from cross Liangxing 99 × Zhongzuo 9504 was phenotyped with Blumeria graminis f. sp. tritici isolate Bgt27 at the adult-plant stage in four field tests and the seedling stage in a greenhouse test. The analysis of bulk segregant RNA sequencing (BSR-Seq) identified a single-nucleotide polymorphism-enriched locus, Qaprpm.caas.2B, on chromosome 2BL in the same genomic interval of Pm52 associated with the all-stage resistance (ASR) and Qaprpm.caas.7A on chromosome 7AL associated with the adult-plant resistance (APR) against the disease. Qaprpm.caas.2B was detected in a 1.3 cM genetic interval between markers Xicscl726 and XicsK128 in which Pm52 was placed with a range of logarithm of odds (LOD) values from 28.1 to 34.6, and the phenotype variations explained in terms of maximum disease severity (MDS) ranged from 45 to 52%. The LOD peak of Qaprpm.caas.7A was localized in a 4.6 cM interval between markers XicsK7A8 and XicsK7A26 and explained the phenotypic variation of MDS ranging from 13 to 16%. The results of this study confirmed Pm52 for ASR and identified Qaprpm.caas.7A for APR to powdery mildew in Liangxing 99.

Wheat powdery mildew is caused by

The cereal cyst nematode (CCN) has a significant negative impact on production of wheat in China. The presence of pathotypes of both Heterodera avenae and H. filipjevi makes it necessary to identify genetic resources with a wide spectrum of resistance. Results of this study confirmed that the soft white winter wheat ‘Madsen’ was resistant to many different populations of both H. filipjevi and H. avenae in both naturally infested fields and artificial inoculation tests in China. Fewer juvenile nematodes penetrated roots of Madsen than susceptible ‘Wenmai 19’ in the early stages of the interaction between the nematodes and plant. Testing wheat cultivars in the pedigree of Madsen demonstrated that the CCN resistance of Madsen was inherited from ‘VPM1’ via the line ‘VPM1/Moisson 951’. Presence of a 2NS chromosome segment from Aegilops ventricosa was detected in Madsen using a Vrga1D-specific marker. However, it appears that gene Pm4b for resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici) was not transferred from VPM1 into Madsen because these cultivars had different reaction patterns against 20 B. graminis f. sp. tritici isolates from China. Madsen serves as an effective source of host resistance from damage caused by CCN.