Identification, Inheritance And QTL Analysis Of Resistance Of Soybean To Lamprosema Indicata (Fabricius) And Megacopta Cribraria (Fabricius)

As the public concern about food and environment safety growing steadily,to develop insect resistant or tolerant cultivars is considered the most economical way in avoiding yield losses due to insect pests.There were many insect pests limiting soybean production,specially in southern China,where a subtropical climate characterized by mild winters and long growing seasons harbored a complex of potentially important insect species that attack soybean,and sometimes,soybean plants are seriously damaged.Bean pyralid[Lamprosema indicata(Fabricius)],globular stink bug[Megacopta cribraria (Fabricius)]and common cutworm[Spodoptera litura(Fabricius)]were reported as the most important insects on soybean in southern China.A study of soybean resistant to S. litura have been done at Soybean Research Institute of Nanjing Agricultural University.To establish the method for evaluation of resistance,to screen for genetic sources with resistance and to reveal the genetic mechanism of resistance of soybeans to L.indicate and M.cribraria is of great significance in breeding for insect resistant of soybeans in southern China.The main results of the present study were as follows:1 Evaluation and identification of genetic sources resistant to L.indicata and M. cribraria in soybean(1) The results of evaluation and identification of genetic sources resistant to L. indicata:1) Damage to soybean infested by L.indicata larvae was estimated under with vs. without insecticide spray.The damage of L.indicata was mainly on seed yield rather than on seed quality.Yield losses caused by L.indicata infestation was averagely 26.27%.2) A set of resistance(damage) indices were designed and compared.Among them,rolled leave percentage was chosen to evaluate soybean resistance to L.indicata.3) The identification results of 58 varieties resistant or susceptible to leaf-feeding insect screened out from a total of 6724 domestic and foreign germplasm showed the existence of significant difference among years,observation dates and varieties in a three-year test during 2004-2006.There was also significant interaction between varieties and years and between varieties and dates. 4) After three years' tests,Jianliniumaohuang,Wujiangqingdou 3,Mianyangbaimaodou, Fengpingheidou and Anluxiaohuangdou were identified to be highly resistant and Linyicaolvdou,Morsoy,Bethol,Dare and Wan 82-178 were identified to be highly susceptible,and were suggested as the standard checks in field evaluation to compensate the fluctuations in materials and environmental conditions.5) 387 varieties were screened in 2006.Breeding lines have similar resistant frequency as land race.There was significant differential geographical distribution of resistant resources among varietal eco-regions. Materials with longer days to flowering and maturity,higher heights,semi-erect or appressed pubescence orientation might be more resistant to L.indicata and vice versa.(2) The results of evaluation and identification of genetic sources resistant to M. cribraria:1) Based on the observation of occurrence and symptoms of the insect on soybeans,a set of resistance(damage) indicators were designed and compared.Among them,the grade system according to the degree of black mildew on stem and purple spots on leaves was chosen to evaluate the resistance to M.cribraria.2) The identification results of 58 accessions showed that there existed significant difference among accessions, observation dates,and accession×date.3) A group of highly resistant accessions such as PI227687,Anluxiaohuangdou,Huaqihuangmaodou,Mianyangbaimaodou,and highly susceptible accessions such as Linyicaolvdou,Daheidou,morsoy,Huangpixiaoqingdou, Wan82-178,were screened out for breeding purposes,and was suggested as the standard checks in field evaluation.(3) Comparing results of resistance to L.indicata,M.cribraria and S.litura,the following was found:1) There existed significant positive correlation between resistance to L.indicata and that to M.cribraria,significant negative correlation between resistance to S. litura and that to M.cribraria and between resistance to S.litura and that to L.indicata.2) A group of accessions with high resistance to the three major insects,such as PI227687, Zhongdou 14,Riben,Nannong 89-30 and Wujiangqingdou 3 were screened out for breeding purposes.3) The accessions highly resistant to L.indicata and M.cribraria,such as Mianyangbaimaodou,Fengpingheidou,Jianliniumaohuang,Congyanghouzimao, Juxianqiudou A and Anluxiaohuangdou were highly susceptible to S.litura.On the contrary, the accessions highly resistant to S.litura,such as Lamar,PI171451,PI229358, Aiganhuang,Huangpixiaoqingdou and Shandongdadou were highly susceptible to L. indicata and M.cribraria.2 Inheritance of resistance to L.indicata and M.cribraria in soybean(4) Three recombinant inbred line(RIL) populations derived from susceptible by resistant crosses,i.e.NJRIKY,NJRIWT and NJRISX(derived from Kefeng No.1×Nannong 1138-2,Wan 82-178×Tongshanbopihuangdoujia and Su 88-M21×Xinyixiaoheidou,respectively) were tested in field under natural infestation.1) Rolled leave percentage evaluated in early September was chosen as the best indicator of resistance to L.indicata due to its higher genetic variation,heritability value and stability, as well as higher negative correlation with seed yield in the three populations.2) The segregation analyses were performed under major gene+polygene mixed inheritance model for the three populations.The results showed that the resistance to L.indicata was controlled by two major genes plus polygenes in the three populations with their major gene heritability being 51.0%,80.5%and 56.3%,and polygene heritability being 39.1%, 11.4%and 29.1%,respectively.(5) Two RIL populations,NJRIKY and NJRIWT were tested for their resistance to M. cribraria under natural infestation according to the degree of black mildew.The results of segregation analyses showed that the resistance to M.cribraria was controlled by three major genes and two major genes in the two populations,respectively.3 Mapping QTLs of resistance to L.indieata and M.cribraria in soybean(6) It was found that the distances of the map constructed with the software Mapmaker/Exp(3.0) were often exaggerated when large number of markers(e.g.more than 500) was involved.Two innovations were suggested in the application of Method 2 of Mapmaker/Exp(3.0) as:1) Different LOD values used for some specific linkage groups in addition to a common LOD value for the others;and 2) Multiple "order" commands each followed with multiple "ripple" commands used for ordering markers in linkage groups with a window size of 5,combined with some artificial adjustments when needed,for relatively higher likelihoods of the linkage group.(7) The results of mapping QTLs conferring resistance to L.indicata in soybean:1) The QTLs on linkage group Dla,H,C2,Dlb and O were detected often associated with resistance to L.indicata in NJRIKY during the three years;the QTLs on linkage group H, D1b and O were detected often associated with resisitance to L.indicata in NJRIWT during the three years;the QTL on linkage group Dla were detected consistently associated with resistance to L.indicata in NJRISX during the three dates in 2006.2) The resistance alleles were often from Nannong 1138-2,Tongshanbopihuangdoujia and Su 88-M21.3) The qRLP-d1a-1 on linkage group D1a in the NJRIKY population also identified in NJRISX population,is an important QTL resistant to L.indicata in soybean.4) The qRLP-h-2 on linkage group H in the NJRIKY population also identified in NJRIWT population,is another important QTL resistant to L.indicata in soybean.The qRLP-d1b-2 on linkage group D1b in the NJRIKY population was also identified in NJRIWT population.5) The fact that the QTLs was repeatedly detected in different populations,different years (environments),different dates and different indices,indicated the resistance was controlled stably by the major QTLs.Based on the results,it is inferred that the markers linked to the detected QTLs should be useful for marker-assisted selection for resistance to L.indicata in soybean.(8) The results of mapping QTLs conferring resistance to M.cribraria in soybean:1) The QTL qRMC-d1a-1 on linkage group D1a was detected consistently associated with resistnace to M.cribraria in NJRIKY during the three years,which accounted for about 7.6%-31.4%of the phenotypic variation;the QTL qRMC-c2-1 on linkage group C2 was detected during 2005-2006,which accounted for less phenotypic variation than the former one;the resistance alleles were from Nannong 1138-2.2) The QTL qRMC-h-1 on linkage group H was detected also consistently associated with resistance to M.cribraria in NJRIWT during the three years,which accounted for about 16.3%-36.2%of the phenotypic variation;the QTL qRMC-d1b-2 on linkage group D1b was detected during 2004-2005, which accounted for less phenotypic variation than the former one;the resistant alleles were from Tongshanbopi- huangdoujia.3) Therefore,basically different QTLs conferred resistance to M.cribraria in NJRIKY and NJRIWT.(9) The relationship between QTLs resistant to L.indicate and to M.cribraria in soybean:The number of QTLs resistant to M.cribraria was fewer,while important QTLs were mapped in homologous regions of linkage group.Such as,qRMC-d1a-1 and qRLP-d1a-1 were mapped between A947V and Satt482 on linkage group D1a in NJRIKY; qRMC-c2-1and qRLP-c2-1 were mapped between A748V and A397I on linkage group C2 in NJRIKY;and qRMC-h-1 and qRLP-h-2 were mapped between Satt181 and Satt434 on linkage group H in NJRIWT.(10) Gene mapping of pubescence orientation and association analysis between pubescence orientation and resistance to L.indicate:1) Association anlyisis between pubescence orientation and resistance to L.indicata and QTL/gene mapping in two recombinant inbred line populations NJRIKY and NJRISX were taken,indicating genetic association of pubescences orientation and resistance to L.indicata in soybean.2) The average rolled leave percentage reduced 27-46%in pubescence appressed and semi-appressed lines in comparision with pubescence erect line.3) The pubescence orientation gene and qRLP-d1a-1 resistant to L.indicata in the two populations were mapped in a homologous region of linkage group D1a.