QTL Mapping Of Resistance Genes Of Chromosome Segment Substitution Lines To Meloidogyne Incongnita

Root knot nematode(Meloidogyne spp.)disease is one of the most devastating soil-borne plant diseases in the world.Due to its characteristics of strong adaptatility,wide host range,multiple spread methods,various species and serious damage,it is difficult to eradicate once it occurs.Root-knot nematodes occur in almost all provinces of China,especially in vegetables in protected areas.Comapred with chemical pesticides and other control methods.Disease-resistant varieties are the most economical,safe and effective control methods.Soybean is one of the important hosts of root-knot nematodes,and there are very few studies on tis resistance characteristics and resistance genes in China.Due to uniformly genetic background,the chromosomal segment substitution line(CSSLs)population can accurately identify whether it is related to traits through phenotypic detection.CSSLs population is one of the important groups to effectively recognize and identify minor or major QTLs.In this study,one soybean CSSLs population developed in Heilongjiang Province was used to screen and evaluate the disease resistance of the southern root-knot nematode M.incongnita(Mi),and 3780 SNP haplotype modules obtained from genome resequencing were used to map the quantitative trait loci(QTLs)related to the Mi resistance genes.The main results of this study are as follows:1.The phenotypic screening results of parental lines infected by Mi showed that there were significant difference between egg masses per gram of root(EM)and eggs per gram of root(EGR)among the parent lines Suinong 14 and wild type ZYD00006 through pot test(P < 0.05),there were no significant difference between galling index(GI)and reproduction factors(RF).At the inoculum with 5,000 eggs per plant,the GI,RF,EM and EGR of Suinong 14 were 3.00,0.20,3.85,653.86,and the GI,RF,EM and EGR of wild soybean ZYD00006 were 3.20,0.21,7.67,1146.76.At the inoculum with 10,000 eggs per plant,the GI,RF,EM and EGR of Suinong 14 were 3.50,0.43,15.45,3315.98,and the GI,RF,EM and EGR of wild type ZYD00006 were 3.86,0.46,37.37,5242.27,suggesting that the increase of the dose of Mi inoculum increase the disease severity.2.The phenotypic evaluation of the CSSLs population indicated that the distribution ranges of GI,RF,EM and EGR under the two inoculation doses were broader.Compared with the recurrent backcrossing parental line Suinong 14,all of CSSLs showed trangressive inheritance.When each plant was inoculated with 5000 eggs,it showed the highest superparental resistance to EGR of90.96%,and when inoculated 10000 eggs,42.94% plants displayed transgressive resistance to EGR.These results indicated that the introgression of chromosome segrement of the wild-type soybean ZYD00006 into the recurrent backcrossing parental line Suinong 14 chromosome would cause phenotypic changes.With the increase in Mi inoculation doses,the umber of the transgressive resistance lines decreased.Eleven highly resistant CSSLs(R46,R119,R152,R154,R155,R156,R158,R159,R175,R189,R190)were identifed based on the EGR.3.Combined with the results of two phenotypic screening tests,43 major QTLs were identified on 20 chromosomes by single factor nonparametric location K* detection and multiple QTL mode(MQM)mapping and 89 minor QTLs.Among the 43 major QTLs,11 of them were associated with GI,11 with RF,8 with EM,13 with EGR,.The ranges of phenotypic variance contribution among all the 132 QTLs were from 1.3% to 14.3%.Of them,65 were identified in wild type ZYD00006 and 67 were from Suinong 14.Six QTLs related to all GI,RF,EM and EGR were found at Chr5,Chr6,Chr7,Chr13,Chr16 and Chr19.Furthermore,34 QTLs associated with root weight(RW)were identified by the MQM method;of them,11 QTLs were localized in the same interval with GI,8 with RF,10 with EM,and 10 with EGR,indicating some common genes that regulate GI,RF,EM,or EGR and root weight.4.The comparison of all Mi-linked QTLs with the reported QTLs associated with the two races(race 4 and race 5)of soybean cyst nematode(Heterodera glycines)using the same CSSLs population indicated 29 common QTLs,Compared with the reported soybean Mi resistance QTLs in soybease database(www.soybase.org),a total of 13 QTLs overlapped,and five GI-related QTLs were found on chromosomes 7,10,13,14 and 18;2 RF-related QTLs were identified on chromosomes 7 and 13;3 EM-related QTLs were found on chromosomes 13,17 and 20;3 EGR related loci were located on chromosomes 7,14,and 20.In conclusion,the phenotypic screening of the CSSLs spopulation indicated a transgressive inheritance phenomenon.The identified resistant or tolerant plants are important germplasm resources for molecular resistance breeding.The results of QTL mapping demonstrated that the transgressive inheritance is caused by the combination of different loci from the two parents,which further proved that CSSLs are one of the best populations for mapping major or minor genes.The identified QTLs loci can lay a theoretical foundation for accelerating the process of molecular assisted breeding and cultivating high-quality multi-resistant soybean varieties.