Studies On The Genetic Basis Of Spontaneous Doubling In Maize Haploid

Doubled haploid technology has become one of the key method of modern maize breeding which including two central segments such as induction and chromosome doubling.With the advancement of maize haploid induction rate and improvement of high throughput haploid screening system,how to improve the haploid doubling rate effectively become a research puzzle in maize haploid engineering breeding in commercial scale.The haloid spontaneous chromosome doubling potential(SCD)of tassel and ear is the determining factor of spontaneous doubling rate.This study classified the genetic characteristics of SCD in tassel and ear with 13 haploid populations of each derived from a single cross between two elite inbred lines which from 22 elite inbred lines covering the 5 heterotic groups,and one of it(FAPW/BN490A)haploid population is used to QTL analysis.The main results are as follows:1.A maize haploid population derived from two elite inbred lines FAPW and BN490A was used to observe the relationship among anther extrusion,anther size and pollen sterility using t test,correlation analysis,and etc.The pollen from most haploid plants with extruded anther(81.3%)and a small number of haploid plants with unextruded anther(15.6%)is fertile.The anther of haploid plants with fertile pollen is bigger than that with sterile pollen,but the pollen fertility did not simultaneously rise with the increase of anther size in haploid plants with fertile pollen.In order to explore whether the male fertility of maize haploid is affected by genotypes,the anther extrusion and pollen fertility in three haploid populations(BN490A/BN486A,PHZ51/H33 and MT-1/H32)was investigated.Both the rate of haploid plants with extruded anther and fertile pollens are highest in FAPW/BN490A haploid population,which reached 35.7%and 72.2%,respectively,followed by BN490A/BN486A haploid population(13.0%,53.8%),PHZ51/H33 haploid population(13.0%,13.0%),and MT-1/H32 haploid population(12.0%,47.4%).Multiple comparisons indicated that both the rate of haploid plants with extruded anther and fertile pollens had significant differences between FAPW/BN490A and the remaining three haploid populations,but none among the remaining three haploid populations.2.Based on the kernel number of each ear by pollinated just with doubled pollen and firstly selfed then pollinated with doubled pollen of above 16 haploid populations,we find that the haploids have high potential of female fertility.90.58±4.05%of the haploids by pollinated just with doubled pollen in each population produced ears carrying at least one grain,and 58.94±23.57%of the haploids by pollinated with doubled pollen after selfed,both higher than it by selfed which is only 1 1.37±14.90%,equally.The plants by spontaneous doubled can become into inbred lines in next generation,while the plants pollinated with excellent inbred lines or maternal origin of F1 hybrids can be used again through crossed with inducer.The induction rate and frequency of spontaneous diploidization in secondary induced haploid lines was much higher than the first induced haploid lines,which is easier to produce haploid and DH.Besides,this way can reduce the time-consuming to develop elite inbred line which were better than the original inbred line in seven grain phenotypes,as it increases the possibility to primary more favorable alleles by multiple crosses.3.With 3072 single nucleotide polymorphism(SNP)makers integrated in Illumine DNA chip platform,we genotyped 186 progenies of FAPW/BN490A haploid population.Constructing genetic map with 812 polymorphism SNPs,we finally got a high-density genetic map with total length of 1258.2 cM and average interval of 1.9 cM.By composite interval mapping in QTL IciMapping version 2.2,16 QTL for spontaneous doubling were found in FAPW/BN490A population,which were Extrusion of Anther(qEA,3),Fertility of Ear(qFE,1)and Number of Kernel(qNK,2),and distributed on chromosomes 3,4,5,7 and 9,specifically.Each QTL can explain 5.7%to 8.9%of total phenotypic variation.The qEAl and qFE in chr3 are the same QTL which control the tassel anther exposed and whether or not the ear solid two traits simultaneously,and account for 8.2%and 7.2%of the phenotypic variation respectively.