Mapping Of QTLs For Mite-resistance Based On BC₂F₁, BC₃F₁ And BC₄F₁ CSSL Populations In Maize

Spider mite is one of the worldwide major pests of maize.In recent years,with the frequent occurrence of high temperature and drought,the damage by mites on maize increases year by year;generally,the loss of grain yield due to mite damages ranges from 10 to 50%,and in severe cases,exceeds 70%.So far,the research on the genetic breeding of maize mite-resistance is seriously inadequate,especially on QTL mapping for maize mite-resistance and exloiting mite-resistant genes.Therefore,QTL mapping for mite-resistance based on chromosomal substitution lines(CSSLs)in this study is very important to elucidate the molecular mechanism of maize mite-resistances and helpful for the development of marker-assisted mite-resistant breeding.In this study,the high-resistance inbred line BSSS53-B as the donor ot mite-resistant genes,three CSSL populations of BC2F1,BC3F1 and BC4F1 constructed with the genetic background of Mo17-476 highly susceptible to mites as materials by whole genome scanning with 208 SSR markers.Subsequently,QTL mapping for mite-resistances was carried out in 2016(Darta BC2F1),2017(Darta BC3F1)and 2018[Darta BC4F1(N18)and greenhouse BC4F1(Y18)].The results showed as follows:1.The total lengths of the genetic linkage groups for BC2F1,BC3F1,BC4F1(N18)and BC4F1(Y18)populations were 4436.13 cM,2351.07 cM,2236.71 cM and 2192.79 cM,respectively.2.The background recovery rates for BC3F1,BC3F1 and BC4F1 populations ranged from 34.8 to 83.0%,41.9 to 94.9%and 51.3 to 99.2%.respectively.Among the CSSLs of BC2F1(190 lines),BC3F1(215 lines)and BC4F1(464 lines),1 to 3 donor chromosomes for 86 CSSLs,1to 8 donor chromosomes for 191 CSSLs,and 1 to 9 donor chromosomes for 414 CSSLs were completely replaced by reciprocal recurrent parent chromosomes,respectively.One single segment substitution line(SSSL)was screened out from the BC4F1 population,and the length of the donor segment was 20.7 cM.3.In different CSSL populations,mite-resistance QTLs within the same marker intervals were detected.e.g.,bnlg1350-bnlg1828 on Chr8 in BC2F1 and BC4F1(N18)populations,bnlg244-umc1586 on Chr9 in BC3F1 and BC4F1(Y18)population,bnlg1828-umc1005 on Chr8 in BC4F1(N18)and BC4F1(Y18)population.4.Among the mite-resistant QTLs detected in BC2F1.BC3F1 and BC4F1 populations.the contribution rate of 19 QTLs in 9 positioning intervals varied from 5 to 10%,and the contribution rate of 6 QTLs in 3 positioning intervals exceeded 10%5.Among the mite-resistant QTLs detected here,155 QTLs mapped in 45 positioning intervals less than 10cM,in addition,83 QTLs mapped in 32 positioning intervals less than 5cM.