Xia Xian-chun

Mapping of Wheat Stripe Rust Resistance Gene YrZH84 with RGAP Markers and Its Application

Zhou 8425B, with an effective stripe rust resistance gene YrZH84, is a hall-mark parent line of wheat (Triticum aestivum L.) in the Yellow-Huai Rivers wheat growing region. An F2 population derived from the cross Zhou 8425B/Chinese Spring and their parents were used for polymorphism analysis employing the resistance gene-analog polymorphism (RGAP) markers and bulked segregant analysis (BSA) based on marker genotypes and phenotypes selection. An RGAP marker Xrga-1 was identified, which was tightly linked to the stripe rust resistance gene YrZH84, with a genetic distance of 0.8 cM. The fragment amplified by Xrga-1 was 343 bp. BLAST analysis indicated that the rga-1 showed 93% of identical nucleotide sequences to barley stem rust resistance gene Rpg1, and 92% to barley powdery mildew resistance gene Mla homology family. Fifty-eight cultivars from Yel-low-Huai rivers wheat growing region were genotyped by the RGAP marker Xrga-1. From the information of genotypes, pedi-grees and resistance responses, the cultivars Zhoumai 11, Zhoumai 20, Zhoumai 22, Aikang 58, 04 Zhong 36, Yuanyu 3, 05 Zhong 37, Wankang 18, and Yuzhan 10 were identified to carry the resistance gene YrZH84. These cultivars were the derivatives of Zhou 8425B. These results will greatly benefit the marker-assisted selection in wheat and cloning of the resistance gene YrZH84.

Molecular mapping of powdery mildew resistance gene in wheat cultivar Jimai 22

Wheat powdery mildew,caused by Blumeria graminis f.sp.tritici,is one of the most important diseases of wheat (Triticum aestivum L.)worldwide.Breeding resistant wheat cultivars is the most economical and effective approach to control the disease.Jimai 22,a newly released wheat cultivar with high yield,broad adaptability,and good quality,is related to broad-sprectrum resistance to the isolates of B.graminis f.sp.tritici at both seedling and adult plant stages.To map the resistance gene of Jimai 22 on wheat chromosome,we used a highly virulent isolate E20 to screen the F2 plants and F2:3 lines derived from the cross of Jimai 22/Chinese Spring.Genetic analysis indicated that Jimai 22 carried a single dominant gene for resistance to powdery mildew,designated PmJM22 tentatively.Using bulked segregant analysis(BSA)with SSR and STS markers,PmJM22 was located to chromosome 2BL.Linkage analysis indicated that the resistance gene was linked to four SSR and five EST markers,with genetic distances from 7.7(Xwmc149)to 31.3 cM(Xbarc101).Based on the origins,chromosome locations,and reaction patterns,PmJM22 is different from all the known powdery mildew resistance genes Pm6,Pm26,Pm33,and Mlzec1 on chromosome 2BL.

Genetic analysis of vegetative ground cover rate in winter wheat using digital imaging

Vegetative vigour is an important physiological trait and selection for greater seedling vigour is a goal of breeding programs,especially in rain-fed regions.This study aimed to identify the genetic variation of early vigour,determine the agronomic traits most closely associated with seedling growth,and detect the major gene-containing region of early vigour in winter wheat.Twenty-eight cultivars and advanced lines at two planting densities(240 plants m 2and 360 plants m 2)were grown in Jinan during2009–2010 and 2010–2011 cropping seasons,with randomized complete block design of three replications.Whole-genome association mapping was employed to identify the chromosome region controlling early vigour using 921 Diversity Array Technology(DArT)and 83 SSR markers.Early vigour was evaluated with vegetative ground cover rate via implementation of photographic image analysis,whereby computer analysis was used to determine percentage ground cover.Significant differences of ground cover rate between two planting densities were detected in pre-winter period,greening-up and booting stages,but not in early stem elongation stage.Ground cover rate in stem elongation stage was significantly and positively associated with maximum tiller number(r = 0.76,P 0.01),leaf area index(r = 0.74,P 0.01),spike number(r = 0.73,P 0.01),and grain yield(r = 0.73,P 0.01).Twelve gene-containing regions for vegetative ground cover rate were detected in two seasons.Most of the regions conditioning the vegetative ground cover rate were not affected by the developmental stages.Ten gene-containing regions identified were consistent with previously reported QTLs for seedling traits,grain yield and disease resistance.Three regions on 5BL,6AS,and 6BL were the same as previously reported loci for seedling traits.Therefore,there is sufficient genetic variation to increase early vigour in winter wheat,and early vigour could be quickly measured through digital image analysis.

Characterization of dense and erect panicle 1 gene (tadep1) located on common wheat group 5 chromosomes and development of allele-specific markers

Dense and erect panicle 1(OsDep1) gene is an important QTL controlling yield associated traits such as panicle length,erect type,and grain density in rice.In the present study,full-length genomic DNA sequences of TaDep1 on common wheat group 5 chromosomes were cloned by homologous cloning approach based on the sequences of rice OsDep1.TaDep1 has five exons and four introns,similar to that of rice OsDep1.The coding sequences of TaDep1-A1,TaDep1-B1,and TaDep1-D1 were 918,888,and 900 bp,encoding polypepetides of 305,295,and 299 amino acids,respectively.Five allelic variants on TaDep1-A1 locus,four on TaDep1-B1 locus,and two on TaDep1-D1 locus were identified.Three pairs of complementary dominant markers and one codominant marker were developed based on the sequence polymorphisms presented in allelic variants of TaDep1-A1 and TaDep1-B1.The codominant marker dep19,which can accurately discriminate the allelic variants of TaDep1-B1c from those of TaDep1-B1a,TaDep1-B1b,and TaDep1-B1d,was developed from a 30 bp InDel of different allelic variants at the fifth exon of TaDep1-B1.No significant association was found among the yield associated traits such as thousand-kernel weight,plant height,panicle length,spikelet number and spikelet spacing in 406 cultivars,indicating that these genes have no significant effect on the yield-related traits in current Chinese wheat cultivars.

Seedling and slow rusting resistances to leaf rust in CIMMYT wheat lines

CIMMYT wheat has played an important role in wheat breeding in China. Identification of leaf rust resistance genes in CIMMYT wheat is important for developing wheat cultivars with resistance to leaf rust in China. A total of 103 CIMMYT wheat lines and a set of 35 differential lines, mostly near-isogenic lines in the background of Thatcher with known leaf rust resistance genes were inoculated with 15 Chinese pathotypes of Puccinia triticina for postulating leaf rust resistance genes in CIMMYT wheats at the seedling stage. These genotypes were also planted in the field for characterization of slow rusting responses to leaf rust in the 2008-2009 and 2009-2010 cropping seasons. Four leaf rust resistance genes Lr26, Lr34, Lr42, and Lr47 were postu- lated in 46 genotypes through seedling test, pedigree analysis and molecular maker detection. Resistance gene Lr26 was present in nine accessions. Lr34 was identified in 28 lines. Lr42 was found in eleven lines and two lines might contain Lr47. Known resis- tance genes were not identified in the other 57 accessions and these lines were resistant to most of pathotypes tested. Forty-six genotypes showed slow leaf rusting resistance in the two cropping seasons. The results from seedling and field tests showed that CIMMYT wheats carry abundant effective seedling and adult plant resistance genes, and can be used in breeding resistant culti- vars for durable control of wheat leaf rust in China.

Characterization of Overexpressed Bx7 gene (Bx7OE) in Chinese and CIMMYT wheats by STS markers

Over-expression of the high molecular weight glutenin subunit(HMW-GS) Bx7 is highly associated with dough strength of wheat(Triticum aestivum L.) flour.A total of 163 Chinese and CIMMYT wheat cultivars and advanced lines were tested by two STS markers and RP-HPLC to understand the presence of HMW-GS gene Bx7OE.The results indicated that the markers TaBAC1215C06-F517/R964 and TaBAC1215C06-F24671/R25515 could amplify a 447 bp and a 844 bp PCR fragments,respectively,in the lines with Bx7OE,whereas no PCR products were detected in the lines without Bx7OE.Of the 163 cultivars and lines,specific PCR fragments were amplified in 11 genotypes by the two markers,indicating the presence of Bx7OE in these lines,with a frequency of 6.7%.The results obtained by RP-HPLC were consistent with those revealed by STS markers.These two STS markers could be used to detect the presence of Bx7OE gene in wheat cultivars.