| Maize haploid breeding technology is a process that double haploid(DH)line is obtained by haploid chromosome doubling and applied in maize breeding after haploid production by a certain technique,which can obtain homozygous inbred lines in only two generations,and greatly shorten the breeding cycles.The haploid production,identification and doubling of chromosomes as the key steps of haploid breeding,affect the efficiency of the application of this technology.With the improvement of the haploid production frequency and enhancement of haploid identification efficiency,chromosome doubling become an important limited factor during maize haploid breeding.Most of previous researches focused on the application of chemical agents,however,some haploid plants growth would be badly affected by toxic chemicals and mechanical damage during the process of treatments and transplanting,in addition,the costs would increase a lot.Chemical agents are also harm to the health and environments,while natural doubling of haploids is regarded as the most simple,fast and efficient doubling method.The haploid male fertility restoration is a key constraints for the production of DH lines.In this study,we evaluated haploid male fertility restoration from inbred lines distributed into different heterotic groups.Two inbred lines with significantly different haploid male fertility were selected for gene mapping.The haploid male fertility of different generations of the population were evaluated.Two recombinant inbred lines with high and low stable haploid male fertility were selected to reveal the cytological mechanism of haploid male fertility.The main results as follows:1.24 elite inbred lines from 5 heterotic groups were selected,the maternal haploids were induced by in vivo inducer lines,and HMF was evaluated in three different environments.The results indicated that the haploid male fertility rate of Lancaster and Reid groups were 23.72%and 23.61%,respectively.While the haploid male fertility rate of the LuDa Red Cob group was only 7.34%;In addition,the haploids from inbred lines 4F1,K22 and C87-1 had relatively high HMF restoration ability,with the rate of 84.8,73.42,and 60.78%,respectively.2.The haploid,induced from a subset of 285 F2:3 inbred lines derived from two inbred lines Z58 and K22 with large difference in haploid male fertility,were used to QTL mapping of haploid male fertility and tassel number of branches.25 QTL were detected in two different environments,three QTL for haploid male fertility and 4 QTL for tassel number of branches were detected in both environments,respectively.To narrow down the QTL region,a backcross population with inbred line Z58 as the recurrent parent was established.Another 13 pairs of molecular markers with polymorphism were developed,the main QTL qHMF3b was located between bnlg1117 and ID3 markers,about 3.9 Mb.3.The haploid male fertility of different generations of pedigrees from inbred lines Zheng 58 and K22 were evaluated under four different environments.The results showed that the haploid male fertility rate of early generation is higher than that of late generation.The suitable growth environment were more favorable to the haploid doubling;The haploids with more than 60%of haploid male fertility rate are mainly controlled by their genotypes,while those with below 10%of HMF were affected by both factors of genotypes and environments.We found that early doubling,the first meiotic metaphase chromosomal segregation distortion,and cytoplasmic fusion could be responsible for haploid diploidization leading to HMF of No.36 haploid microsporocyte,by comparing the anther development morphology,cell ploidy and chromosome morphology at different stages of meiosis between of high frequency haploid male fertility restoration material No.36 and of low frequency haploid male fertility restoration material No.7.In particular,the pollen mother cells in the biased distribution of the first division is the key to the recovery of male fertility.This particular chromosomal behavior may be related to the regulation of specific genes in No.36.Furthermore,the ploidy analysis of leaves and PMCs of haploids and normal diploids were performed by flow cytometry,it showed that somatic cell doubling and generative cell doubling were two independent processes.It provides a valuable reference for the study of the biological mechanism of haploid male flower fertility restoration.4.A set of doubled haploid(DH)lines derived from ZD958 were evaluated in four different environments at two locations over two years,and a total of 49 quantitative trait loci(QTL)and 24 pairs of epistatic interactions related to yield and yield components were detected.Furthermore,21 QTL for six investigated phenotypic traits were detected across two different sites.Combining the results of these QTL in each environment and across both sites,three main QTL hotspots were found in chromosomal bins 2.02,2.05-2.06,and 6.05 between the simple sequence repeat(SSR)markers umc1165-bnlg1017,umc1065-umc1637,and nc012-bnlg345,respectively.The existence of three QTL hotspots associated with various traits across multiple environments could be explained by pleiotropic QTL.These genetic regions could provide targets for genetic improvement,fine mapping,and marker-assisted selection in future studies. |
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