Zhongxin Kong

Molecular genetic analysis of five spike-related traits in wheat using RIL and immortalized F2 populations

Kernel number per spike is one of the most important yield components of wheat. To map QTLs related to kernel number including spike length (SPL), spikelet number per spike (SPN), fertile spikelet number (FSPN), sterile spikelet number (SSPN) and compactness, and to characterize the inheritance modes of the QTLs and two-locus interactions, 136 recombinant inbred lines (RILs) derived from ‘Nanda2419’ x ‘Wangshuibai’ and an immortalized F2 population (IF2) generated by randomly permutated intermating of these RILs were investigated. QTL mapping made use of the previously constructed over 3300 cM linkage map of the RIL population. Three, five, two, two and six chromosome regions were identified, respectively, for their association with SPL, SPN, FSPN, SSPN, and compactness in at least two of the three environments examined. All compactness QTLs but one shared the respective intervals of QSpn.nau-5A and the SPL QTLs. Xcfd46–Xwmc702 interval on chromosome 7D was related to all traits but SSPN and had consistently the largest effects. The fact that not all the compactness QTL intervals were related to both SPL and SPN indicates that compactness is regulated by different mechanisms. Interval coincidence between QTLs of SPL and SPN and between QTLs of FSPN and SSPN was minimal. For all the traits, favorable alleles exist in both parents. Inheritance modes from additiveness to overdominance of the QTLs were revealed and two-locus interactions were detected, implying that the traits studied are under complex genetic control. The results could contribute to wheat yield improvement and better use of Wangshuibai and Nanda2419 the two special germplasms in wheat breeding program.

PmX: a recessive powdery mildew resistance gene at the Pm4 locus identified in wheat landrace Xiaohongpi.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating foliar diseases of wheat and imposes a constant challenge on wheat breeders. Xiaohongpi, a Chinese landrace of wheat (Triticum aestivum L.), shows resistance to powdery mildew during the entire growth stage in the field and under controlled conditions. The F1 plants from cross of the powdery mildew susceptible cultivar Yangmai158 with Xiaohongpi were susceptible to isolate Bgt19, the locally most prevalent Bgt isolate. In the derived F2 population and F3 progenies, the resistance segregation deviated significantly from the one-gene Mendelian ratio. However, marker analysis indicated that only one recessive gene conferred the resistance, which co-segregated with Xsts-bcd1231 that showed co-segregation with Pm4a in different studies. Allelism test indicated that this recessive resistance gene, designated as pmX, is either allelic or tightly linked to Pm4a. The pmX gene was different from Pm4 alleles in resistance spectrum. Examination of the genotype frequencies at pmX and the linked marker loci in the F2 population showed that a genetic variation favoring the transmission of Xiaohongpi alleles could be the cause of deviated segregation. Mapping of the pmX-linked markers using Chinese Spring deletion lines indicated that it resides in the 0.85–1.00 bin of chromosome 2AL.

Fine mapping TaFLW1, a major QTL controlling flag leaf width in bread wheat (Triticum aestivum L.)

AbstractIntroductionFlag leaf width (FLW) is directly related to photosynthetic capacity and yield potential in wheat. In a previous study, Qflw.nau-5A controlling FLW was detected on chromosome 5A in the interval possessing Fhb5 for type I Fusarium head blight (FHB) resistance using a recombinant inbred line population derived from Nanda2419 × Wangshuibai.Materials and methodsQflw.nau-5A near-isogenic line (NIL) with the background of Mianyang 99-323 and PH691 was developed and evaluated. FLW inheritance was investigated using two F2 populations developed from crossing the Qflw.nau-5A NILs with their recurrent parents. One hundred ten and 28 recombinants, which included 10 and 5 types of recombinants, were identified from 2816 F2 plants with Mianyang 99-323 background and 1277 F2 plants with PH691 background, respectively, and phenotyped in field trials for FLW and type I FHB resistance. Deletion bin mapping was applied to physically map Qflw.nau-5A.Results and conclusionsThe introduction of Wangshuibai Qflw.nau-5A allele reduced the FLW up to 3 mm. In the F2 populations, Qflw.nau-5A was inherited like a semi-dominant gene, and was therefore designated as TaFLW1. The FLW of the recombinant lines displayed a distinct two-peak distribution. Recombinants with wider leaves commonly have Mianyang 99-323 or PH691 chromatin in the 0.2 cM Xwmc492-Xwmc752 interval that resided in the 5AL12-0.35–0.57 deletion bin, and recombinants with narrow leaves were Wangshuibai genotype in this interval. Phenotypic recombination between FLW and type I FHB resistance was identified, implying TaFLW1 was in close linkage with Fhb5. These results should aid wheat breeders to break the linkage drag through marker-assisted selection and assist in the map-based cloning of TaFLW1.

Marker-assisted development and evaluation of near-isogenic lines for scab resistance QTLs of wheat

Fusarium head blight or scab resistance in wheat is a complex quantitative trait affected greatly by environments. Therefore, the quantitative trait loci (QTL) for scab resistance found in mapping projects require validation to be effectively utilized in breeding programs. In this study, by employing both forward and background selections with the help of molecular markers, near-isogenic lines (NILs) for scab resistance QTLs Qfh.nau-2B, Qfhs.nau-3B, Qfhi.nau-4B and Qfhi.nau-5A, three of which originating in scab resistance germplasm Wangshuibai, were developed with the elite line Miangyang 99-323 as the recurrent parent. During the process of backcross, selection was based solely on marker genotypes of the target regions, and on recipient genome recovery rate in BC2F1 and BC3F1. All the identified BC3F1 plants with the target QTL regions have more than 94% recipient genome composition (RGC), and out of four to five of them a plant with over 97% RGC were obtained in each backcross combination. Compared with Mianyang 99-323, the Qfhs.nau-3B NIL showed much better resistance to disease spread within spikes, the Qfhi.nau-4B and Qfhi.nau-5A NILs showed much better resistance to initial infection, and the Qfh.nau-2B NIL showed improvement in both types of resistance. These results were consistent with findings in the previous QTL mapping studies. Morphologically and agronomically these NILs were similar to Mianyang 99-323 except that Qfhi.nau-4B NIL was taller and had a longer spike, and Qfhi.nau-5A NIL had narrower leaves. These results demonstrated the feasibility of marker-assisted utilization of scab resistance QTLs.

Precise mapping of a quantitative trait locus interval for spike length and grain weight in bread wheat (Triticum aestivum L.)

The spike characteristics length, spikelet density and fertile floret number are related yield components and are important in cereal improvement. QSpl.nau-2D is a major quantitative trait locus controlling spike length (SPL) detected in the recombinant inbred line population developed by crossing wheat (Triticum aestivum) cultivars Nanda2419 with Wangshuibai. In this study, to validate its genetic effect and determine its precise location, QSpl.nau-2D’s near-isogenic line (NIL) was developed using Mianyang99-323 as the recurrent parent through marker-assisted selection. Field trials showed that the NIL not only had significantly longer spikes on average than the recurrent parent but also had significantly higher grain weight, but did not differ in spikelet number and kernel number per spike. In the F2 population derived from a cross of the NIL with Mianyang99-323, QSpl.nau-2D functioned like a single gene and conditioned the SPL in a partially dominant manner, and was thus designated as HL1 (for head length). To precisely map HL1, 89 recombinants, consisting of 11 genotypes, were identified in the NIL-derived F2 population of 674 plants by using markers in the Xwmc25–Xgpw4080 interval. Phenotyping these lines showed that the introduction of a 0.9-cM interval flanked by Xcfd53 and DG371 in Nanda2419 resulted in longer spikes and a higher grain weight in the NIL. The availability of markers closely linked to HL1 could facilitate its use in breeding programs.

Identification and marker-assisted transfer of a new powdery mildew resistance gene at the Pm4 locus in common wheat

Powdery mildew, a wheat (Triticum aestivum L.) foliar disease caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici, imposes a constant challenge on wheat production in areas with cool or maritime climates. This study was conducted to identify and transfer the resistance gene in the newly identified common wheat accession ‘D29’. Genetic analysis of the F2 population derived from a cross of D29 with the susceptible elite cultivar Y158 suggested a single dominant gene is responsible for the powdery mildew resistance in this germplasm. This gene was mapped to chromosome 2AL in a region flanked by microsatellite markers Xgdm93 and Xhbg327, and co-segregated with sequence-tagged site (STS) markers Xsts_bcd1231 and TaAetPR5. An allelic test indicated that the D29 gene was allelic to the Pm4 locus. To further evaluate the resistance conferred by this gene and develop new germplasms for breeding, this gene, as well as Pm4a and Pm4b, was transferred to Y158 through backcross and marker-assisted selection. In the resistance spectrum analysis, the D29 gene displayed a resistance spectrum distinguishable from the other Pm4 alleles, including Pm4a, Pm4b, and Pm4c, and thus was designated as Pm4e. The identification of new allelic variation at the Pm4 locus is important for understanding the resistance gene evolution and for breeding wheat cultivars with powdery mildew resistance.

Correction to: Fine mapping of powdery mildew resistance gene Pm4e in bread wheat (Triticum aestivum L.)

Unfortunately, the style of the units was incorrectly published (“cm” instead of “cM”) throughout the original article.