| Doubled haploid(DH)technology enables rapid development of homozygous lines in maize breeding programs.It is widely accepted as one of the key technologies in modern maize breeding.However,haploid genome doubling is a bottleneck for the commercialization of DH technology and is limited by haploid male fertility(HMF).Haploid male fertility rate is normally less than 10%under untreated condition.Former studies always show that HMF is highly significantly related with genetic background.Therefore,fully and deeply analysis of HMF,by exploring QTL controlling HMF,is the key point of improving HMF.In this study,the quantitative trait locus(QTL)analysis of HMF in maize is the first study to report QTL related with HMF.This study will provide effective functional markers for highthrought DH lines selection and assist help in molecular biology for large-scale appliance in DH breeding.The details are as follows:(1)Three haploid populations were comprised by lines with significant different HMF performance,Y487-1 and 4F1,which were inbred lines with high HMF,and Zheng58,which was inbred line with low HMF.Anther emergency score(AES)was identified under field conditions.Haploids with high AES(of 1)were selected.Four QTL,qhmfl,qhmf2,qhmf3,and qhmf4,controlling HMF have been identified by segregation distortion(SD)loci detection in the selected haploid population derived from Yu87-1/Zheng58.For one QTL located in bin 1.11(qhmfl),the HMF increasing allele came from inbred line Zheng58.For the other three QTL,located in bins 3.06,4.02/03,and 6.07(qhmf2,qhmf3,and qhmf4),the HMF increasing alleles were provided by Yu87-1.Three loci,qhmfl,qhmf2,and qhmf4,were also detected in the selected haploid population derived from 4F1/Zheng58.qhmf4 showed the strongest SD in the two populations.(2)In the basis of initial mapping of qhmf4,different haploid backcrossed population(HB)were established by Yu87-1 and Zheng58.By exploring 10InDel markers based on the DNA sequence of two parents,progeny test was applied for the fine mapping of qhmf4.The analysis of the 39 recombinants narrowed the qhmf4 locus down to a～1.2M kb interval flanked by markers IND1658 and IND167.Gene prediction by FEGNESH 2.6 has revealed-38 putative genes in the qhmf4 region.The gene absence of first divisionl(afd1),a maize rec8 homolog,affecting sister chromatid cohesion(SSC)is the most likely candidate gene.(3)By screening the main foreign germplasmfor HMF,GF1 with high spontaneous haploid genome doubling(SHGD),GF3 with medium SHGD,and GF5 with low SHGD were identified.Of the 1078 haploids derived from GF1/GF3,60 haploids with the best performance of male fertility and 30 male sterile haploids were selected to form the mapping population and screened by 6K SNP chip.These selected individuals with extreme phenotypic values would highly increase the statistic power of QTL detection.A total of five QTL were identified on chromosome 1,3,5,6,and 9 by X2 test(p<0.05).A composite interval mapping(CIM)was also performed with the 90 haploids,three QTL were detected on chromosome 5,6,and9.All the three QTL were detected in both methods.The QTLqshgdl,qshgd2,and qshgd3 could explain 17.53,10.11,and 8.7%of the total phenotypic variation,respectively.Except qshgd3,the source of haploid genome doubling alleles were derived from GF1.To confirm the major QTL-qshgdl,allele frequencies at the markers within the qshgdl region were tested in haploids GF1/GF5 with the best performance of male fertility,the allele frequencies showed a significantly deviate from a 1:1 ratio.Based on the analysis above all,it means that HMF might be affected by multiple QLT.(4)There are 22Chinese elite lines were selected to pollinated with normal diploid pollen to evaluated haploid female fertility(HFF).Based on haploid female fertility rate(HFFR)and average kernel number(AKN),it is found that HFF also highly affected by genetic background.The average HFFR is about 89.54,and the range is from 73.56 to 99.18%.The AKN is 15.4 and the range is from 2.67 to 59.82.The calculated broad heritability for both traits are 0.67 for HFFR and 0.86 for AKN.Under cluster analysis and multiple comparison of the 22 inbred lines,inbred line B73 has the best haploid female fertility and germplasm in Reid population performs better. |
