A co-located QTL for seven spike architecture-related traits shows promising breeding use potential in common wheat (Triticum aestivum L.).

KEY MESSAGE: A co-located novel QTL for TFS, FPs, FMs, FFS, FFPs, KWS, and KWPs with potential of improving wheat yield was identified and validated. Spike-related traits, including fertile florets per spike (FFS), kernel weight per spike (KWS), total florets per spike (TFS), florets per spikelet (FPs), florets in the middle spikelet (FMs), fertile florets per spikelet (FFPs), and kernel weight per spikelet (KWPs), are key traits in improving wheat yield. In the present study, quantitative trait loci (QTL) for these traits evaluated under various environments were detected in a recombinant inbred line population (msf/Chuannong 16) mainly genotyped using the 16 K SNP array. Ultimately, we identified 60 QTL, but only QFFS.sau-MC-1A for FFS was a major and stably expressed QTL. It was located on chromosome arm 1AS, where loci for TFS, FPs, FMs, FFS, FFPs, KWS, and KWPs were also simultaneously co-mapped. The effect of QFFS.sau-MC-1A was further validated in three independent segregating populations using a Kompetitive Allele-Specific PCR marker. For the co-located QTL, QFFS.sau-MC-1A, the presence of a positive allele from msf was associate with increases for all traits: + 12.29% TFS, + 10.15% FPs, + 13.97% FMs, + 17.12% FFS, + 14.75% FFPs, + 22.17% KWS, and + 19.42% KWPs. Furthermore, pleiotropy analysis showed that the positive allele at QFFS.sau-MC-1A simultaneously increased the spike length, spikelet number per spike, and thousand-kernel weight. QFFS.sau-MC-1A represents a novel QTL for marker-assisted selection with the potential for improving wheat yield. Four genes, TraesCS1A03G0012700, TraesCS1A03G0015700, TraesCS1A03G0016000, and TraesCS1A03G0016300, which may affect spike development, were predicted in the physical interval harboring QFFS.sau-MC-1A. Our results will help in further fine mapping QFFS.sau-MC-1A and be useful for improving wheat yield.

A promising QTL QSns.sau-MC-3D.1 likely superior to WAPO1 for the number of spikelets per spike of wheat shows no adverse effects on yield-related traits.

KEY MESSAGE: A likely new locus QSns.sau-MC-3D.1 associated with SNS showing no negative effect on yield-related traits compared to WAPO1 was identified and validated in various genetic populations under multiple environments. The number of spikelets per spike (SNS) is one of the crucial factors determining wheat yield. Thus, improving our understanding of the genes that regulate SNS could help develop wheat varieties with higher yield. In this study, a recombinant inbred line (RIL) population (MC) containing 198 lines derived from a cross between msf and Chuannong 16 (CN16) was used to construct a genetic linkage map using the GenoBaits Wheat 16 K Panel. The genetic map contained 5,991 polymorphic SNP markers spanning 2,813.25 cM. A total of twelve QTL for SNS were detected, and two of them, i.e., QSns.sau-MC-3D.1 and QSns.sau-MC-7A, were stably expressed. QSns.sau-MC-3D.1 had high LOD values ranging from 4.99 to 11.06 and explained 9.71-16.75% of the phenotypic variation. Comparison of QSns.sau-MC-3D.1 with previously reported SNS QTL suggested that it is likely a novel one, and two kompetitive allele-specific PCR (KASP) markers were further developed. The positive effect of QSns.sau-MC-3D.1 was also validated in three biparental populations and a diverse panel containing 388 Chinese wheat accessions. Genetic analysis indicated that WHEAT ORTHOLOG OFAPO1 (WAPO1) was a candidate gene for QSns.sau-MC-7A. Pyramiding of QSns.sau-MC-3D.1 and WAP01 had a great additive effect increasing SNS by 7.10%. Correlation analysis suggested that QSns.sau-MC-3D.1 was likely independent of effective tiller number, plant height, spike length, anthesis date, and thousand kernel weight. However, the H2 haplotype of WAPO1 may affect effective tiller number and plant height. These results indicated that utilization of QSns.sau-MC-3D.1 should be given priority for wheat breeding. Geographical distribution analysis showed that the positive allele of QSns.nsau-MC-3D.1 was dominant in most wheat-producing regions of China, and it has been positively selected among modern cultivars released in China since the 1940s. Gene prediction, qRT-PCR analysis, and sequence alignment suggested that TraesCS3D03G0216800 may be the candidate gene of QSns.nsau-MC-3D.1. Taken together, these results enrich our understanding of the genetic basis of wheat SNS and will be useful for fine mapping and cloning of the gene underlying QSns.sau-MC-3D.1.

Major and stably expressed QTL for traits related to the mature wheat embryo independent of kernel size.

KEY MESSAGE: Two major and stably expressed QTL for traits related to mature wheat embryo independent of kernel size were identified and validated in a natural population that contained 171 Sichuan wheat accessions and 49 Sichuan wheat landraces. As the juvenile of a highly differentiated plant, mature wheat (Triticum aestivum L.) embryos are highly significant to agricultural production. To understand the genetic basis of traits related to wheat embryo size, the embryo of mature kernels in a recombination inbred line that contained 126 lines from four environments was measured. The genetic loci of embryo size, including embryo length (EL), embryo width (EW), embryo area (EA), embryo length/kernel length (EL/KL), embryo width/kernel width (EW/KW), and EL/EW, were identified based on a genetic linkage map constructed based on PCR markers and the Wheat 55 K single nucleotide polymorphism (SNP) array. A total of 50 quantitative trait loci (QTL) for traits related to wheat embryo size were detected. Among them, QEL.sicau-2SY-4A for EL and QEW.sicau-2SY-7B for EW were major and stably expressed and were genetically independent of KL and KW, respectively. Their effects were further verified in a natural population that contained 171 Sichuan wheat accessions and 49 Sichuan wheat landraces. Further analysis showed that TraesCS4A02G343300 and TraesCS7B02G006800 could be candidate genes for QEL.sicau-2SY-4A and QEW.sicau-2SY-7B, respectively. In addition, significant positive correlations between EL and kernel-related traits and the 1,000-grain weight were detected. Collectively, this study broadens our understanding of the genetic basis of wheat embryo size and will be helpful for the further fine-mapping of interesting loci in the future.

[Frequency and contribution of specific genetic loci transferred from wheat cultivar Mianmai 37 to its derivatives].

The development and utilization of outstanding germplasm in breeding programs can expedite breeding process. The high yielding variety Mianmai 37, grown widely in southwestern China, has been used widely in breeding programs. Comparisons between Mianmai 37 and its derivatives for yield and yield components were conducted. Simple sequence repeat (SSR) markers were used to test the frequency of specific alleles transferred from Mianmai 37 to its derivative culti-var Mianmai 367. The results indicated that the yield of the derivative cultivars was significantly higher than Mianmai 37, due to an increased grain number per spike. Favorable traits from Mianmai 37 such as resistance to stripe rust, were trans-ferred to its derivatives. At molecular level, 78.9% loci in Mianmai 367 were derived from Mianmai 37 with 75.0, 83.6 and 74.2% from A, B and D genomes, respectively. Mianmai 367 shared common loci with its parent Mianmai 37, such as re-gions Xgwm374-Xbarc167-Xbarc128-Xgwm129-Xgwm388-Xbarc101 on chromosome 2B and Xwmc446-Xwmc366- Xwmc533-Xbarc164-Xwmc418 on chromosome 3B, these regions were associated with grain number, 1000-kernel weight and resistance. The preferred transmission of alleles from Mianmai 37 to its derivatives probably can be explained by the strong selection pressures because of its favorable agronomic traits and the disease resistance.

Molecular and Cytological Identification of Wheat-Thinopyrum intermedium Partial Amphiploid Line 92048 with Resistance to Stripe Rust and Fusarium Head Blight.

Thinopyrum intermedium (2n = 6x = 42, EeEeEbEbStSt or JJJsJsStSt) contains a large number of genes that are highly adaptable to the environment and immune to a variety of wheat diseases, such as powdery mildew, rust, and yellow dwarf, making it an important gene source for the genetic improvement of common wheat. Currently, an important issue plaguing wheat production and breeding is the spread of pests and illnesses. Breeding disease-resistant wheat varieties using disease-resistant genes is currently the most effective measure to solve this problem. Moreover, alien resistance genes often have a stronger disease-resistant effect than the resistance genes found in common wheat. In this study, the wheat-Th. intermedium partial amphiploid line 92048 was developed through hybridization between Th. intermedium and common wheat. The chromosome structure and composition of 92048 were analyzed using ND-FISH and molecular marker analysis. The results showed that the chromosome composition of 92048 (Octoploid Trititrigia) was 56 = 42W + 6J + 4Js + 4St. In addition, we found that 92048 was highly resistant to a mixture of stripe rust races (CYR32, CYR33, and CYR34) during the seedling stage and fusarium head blight (FHB) in the field during the adult plant stage, suggesting that the alien or wheat chromosomes in 92048 had disease-resistant gene(s) to stripe rust and FHB. There is a high probability that the gene(s) for resistance to stripe rust and FHB are from the alien chromosomes. Therefore, 92048 shows promise as a bridge material for transferring superior genes from Th. intermedium to common wheat and improving disease resistance in common wheat.