Mapping Of Phytophthora Resistance Genes And QTL In Soybean

Phytophthora root rot （PRR）, caused by the soil-born oomycete pathogen Phytophthora sojae Kaufmann & Gerdemann （P. sojae）, could infect soybean plant at any growth period and bring out extensive economic losses around the world. The primary method of controlling PRR is discovery and implement resistant soybean cultivars.Screening resistance germplasms and discover new resistant genes is the foundation and key method to resistant breeding.In this study, we identify the resistance of soybean （G. max） mini core collection in China to three P. sojae isolates using hypocotyl inoculation method. The objection is to evaluate the resistance response and distribution of Phytophthora resistance germplasm in China and to provide new resistance genes pool for future breeding program. An association mapping of soybean mini core collection using 1749 single nucleotide polymorphism （SNP） markers to excavate loci associated with resistance to P. sojae isolates was carried out. A F2:3 population and a population of recombinant inbred lines（RILs） were used to do genetic analysis and linkage mapping of soybean complete resistance gene and partial resistance QTL. These results will be helpful for molecular marker assisted selection （MAS） in soybean breeding and exploration the molecular mechanism of the resistance to P. sojae.1. Characterization of Phytophthora resistance in soybean mini core collection.The 224 accessions of soybean （G. max） mini core collection were screened for resistance to three P. sojae isolates, Pm2 （lb, 2, 3c, 7）, H15 （1k, 3b, 3c, 5, 6, 7） and Pm28（1a, 1b, 1c, 1d, 1k, 2, 3b, 3c, 5, 6, 7）, adding eleven isolates used before, which are P6497, Pm14, HLJ08-35, P7071, P7063, AH, HeN08-17, PNJ1, Pmg, Pm31 and JS08-12.Most germplasm accessions have resistance to Pm 14 isolate, and the percentage ups to 56.7%, followed by isolates of P7063 （44.4%）, AH （43.4%） and HLJ08-17 （32.7%）.Isolates of Pmg and PNJ1 have the most virulent to germplasm with more than 80%susceptible accessions. Although the results imply the mini core collection were extremely susceptible to P. sojae, there are many germplasm had a range resistance spectrum of P.sojae isolates. More than 15% of accessions have resistant reactions to at least 4 isolates,among them 18 accessions show resistance to 8-11 P. sojae isolates.Sichuan, Jiangsu and Hubei provinces had the most number of resistant accessions.Germplasm from Hubei, Jiangsu, Fujian, Sichuan and Shandong provinces possessed broad spectrum resistance with resistance to more than 5 P. sojae isolates. In general, germplasm from south and huanghuaihai regions have the most diversity resistance reactions and broadest resistance spectrum than those from north and northeast regions.The soybean of mini core collection produced 135 reaction reactions with 14 P. sojae isolates. Gene postulating shows 34 germplasm may not have any resistance gene, and 22 gremplasm may contain Rps7 gene, and accession ZDD03733 may contain Rps1a+Rps3b or Rps1c+Rps3b gene combination.2. Genome-wide association mapping of resistance to Phytophthora root rot in soybean mini core collectionGenome-wide association analysis on soybean mini core collection genotyped with 1749 SNPs were associated with resistance to PRR. With population structure and kinship as covariates, adopting naive model, general linear model （GLM） and mixed linear model（MLM）, 19 SNP markers are identified significantly Phytophthora resistance associations,including 10 loci localized in previous linkage mapped gene or QTL intervals and 9 loci identified as new PRR resistance-associations.3. Linkage mapping of a Phytophthora resistance gene RpsLu4Soybean cultivar Ludou4 has different resistance reaction to P. sojae isolates as compared with a set of differentials cultivars suggesting it may carry a novel Rps gene or allele. A mapping population of F2 individuals from the cross of Ludou4 and Youchu4,which is resistant and suspect to Pm28 （1a, 1b, 1c, 1d, 1k, 2, 3b, 3c, 5, 6, 7）, was used to map the Rps gene. Through the resistant identification of parents and progeny population,PRR complete resistance in Ludou4 was controlled by a single dominant gene, named as RpsLu4. RpsLu4 was mapped on chromosome 3 （linkage group N） between SSR markers BARCSOYSSR₀3₀246 and BARCSOYSSR₀3₀305 at a distance of 0.5 and 2.6 cM,respectively. In the physical position of 4,362,217bp-5,369,472bp between the two markers,about 1Mb region, there are eight genes contain NBS-LRR domain.RpsLu4 may be a novel resistance gene or an allele of Rpsl.4. Linkage mapping of Phytophthora partial resistance QTLA population of 126 recombinant inbred lines （NJRIZM6） derived from a cross of Mong8206 and Zhengyang was used to evaluated partial resistance against P. sojae isolate P7063 （1a, 1d, 3a, 6,7）. Using composite interval mapping （CIM） in WinQTLCart software,we detected two QTLs confer Phytophthora resistance on chromosome 1 and 17 respectively, and named them qtl-01 and qtl-17. They have explained 7.9% and 8.7% of the phenotypic variance and their resistance alleles come from Zhengyang and Mong8206,respectively. The qtl-01 and qtl-17 regions overlap other known resistance gene which imply these loci confer resistance to more than one pathogen.