Mining And Utilizing A Recessive Major QTL Conferring Resistance To Maize Gibberella Stalk Rot

Corn stalk rot is one of the most devastating diseases in the world.In china,stalk rot have spread to all the corn producing areas,especially in the Yellow-Huai-Hai River region,where extreme climate occurred frequently in recent years.Stalk rot could cause substantial maize yield loss,deteriorate kernel and cause lodging which is becoming the obstacle for mechanical harvest.Although some QTLs have been explored,more resistant loci were needed to be mapped,cloned and applied.In current study,we used a RIL population containing 199 families to map QTLs conferring resistance to Gibberella stalk rot.Then,fine mapping strategy was applied for major resistant QTL-qRfg3,using constructed fine mapping population.After QTL-qRfg3 was mapped into a short interval,we explored the genetic effect of QTL-qRfg3 and backcross it to susceptible materials for resistant improvement.Main research progresses are as follows:1.A total of 1,382 high-quality and polymorphic between H127R and C7-2 SNPs were detected in the RIL population and used to construct a linkage map.The map spanned a total genetic length of 1752 cM,with an average of 1.27 cM between adjacent markers.When this map was combined with phenotypic data and BLUP value,an initial QTL map was constructed with CIM in WinQTLcart2.5.Totally,13 resistance QTLs were detected,each accounting for 3.4%to 19.4%of the total phenotypic variation.The 13 QTLs were found on all maize chromosomes except for chr.6.Among them,one major QTL,named QTL-qRfg3(located between molecular markers SNP16586 and SNP17179),was detected across all three field trials,accounting for an average of 13.9%of the total phenotypic variation.2.In 2013,two plants from each family of the RIL were crossed with susceptible line C7-2.Based on initial mapping results,families owning recombination events were selected and corresponding BC1F1 were planted in Hainan and self-pollinated to gain BC1F2 progeny.3.Using a progeny-based sequential fine-mapping strategy,the confidence interval of QTL-qRfg3 was narrowed down from 33.1Mb to 3.2Mb flanking by makers Ks6 and SSR185-3,in 2013/2014.In 2014/2015,the progeny of 21BC1F3 were used for fine-mapping,restricting QTL-qRfg3 to the interval between STS 182-70 and SNP194,with a physical distance of 670Kb.In 2015/2016 2,656 BC1F6 individuals from 22 BC1F5 narrowed QTL-qRfg3 down to an interval of 350Kb between Ks85 and STS7-5.QTL-qRfg3 was further narrowed down to 160Kb containing two candidate genes based on the B73 physical map(AGPv4),with new developed markers.Sequencing and expression analyzing was used to confirm the candidate gene.4.The genetic effect was evaluated in 2015 and 2016,demonstrating that qRfg3 is a recessive resistance locus to Gibberella stalk rot that reduced the disease severity index by?26.6%.5.The same RIL population was used to map QTLs controlling flowering time and conferring resistance to ear rot.The comparison of flowering time and RPR was conducted between NIL-H127R and NIL-C7-2 population.The results above showed that the resistance of QTL-qRfg3 may have relationship with RPR,not with flowering time and ear rot resistance.GWAS(Genome-wide association study)results indicated QTL-qRfg3 may be a rare allele.6.From 2015,QTL-qRfg3 was backcrossed to susceptible lines through MAS(marker-assisted selection)to gain resistant lines for breeding.