Summaryhaploid inducer line can be transferred (DH) technology can not only shorten the breeding process but also increase genetic gain. Haploid induction and subsequent genome doubling are the two main steps required for DH technology. Haploids have been generated through the culture of immature male and female gametophytes, and through inter‐ and intraspecific via chromosome elimination. Here, we focus on haploidization via chromosome elimination, especially the recent advances in centromere‐mediated haploidization. Once haploids have been induced, genome doubling is needed to produce DH lines. This study has proposed a new strategy to improve haploid genome doubling by combing haploids and minichromosome technology. With the progress in haploid induction and genome doubling methods, DH technology can facilitate reverse breeding, cytoplasmic male sterile (CMS) line production, gene stacking and a variety of other genetic analysis.

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Genome doubling of haploids is one of the major constraints of large-scale doubled haploid (DH) technology. Improving spontaneous haploid genome doubling (SHGD) is an alternative to overcome this limitation. In this study, we aimed to construct a high-density linkage map based on genotyping by sequencing (GBS) of Single Nucleotide Polymorphism (SNPs), to detect QTL and QTL by environment (Q by E) interactions affecting SHGD, and to identify the best trait for mapping and selection of haploid male fertility (HMF). To this end, a bi-parental population of 220 F2:3 families was developed from a cross between A427 (high HMF) and CR1Ht (moderate HMF) to be used as donor. A high-density linkage map was constructed containing 4,171 SNP markers distributed over 10 chromosomes with an average distance between adjacent markers of 0.51 cM. QTL mapping for haploid fertile anther emergence (AE), pollen production (PP), tassel size (TS), and HMF, identified 27 QTL across three environments, and Q by E interactions were significant. A major QTL was identified on chromosome 5. This QTL explained over 45% of the observed variance for all traits across all environments. The introgression of this major QTL, using marker-assisted backcrossing, has great potential to overcome the need of using colchicine in DH line development.

Doubled haploid (DH) lines are used in maize (Zea mays L.) breeding to accelerate the breeding cycle and create homogenous inbred lines in as little as two seasons. These pure inbred lines allow breeders to quickly evaluate new cross combinations. There are two important steps in creating DH lines: (a) generation and selection of haploid progeny, and (b) genome doubling to create fertile, diploid inbreds. Colchicine is widely used to artificially double genomes in haploid plants, which is hazardous, expensive, and time consuming. In this study, three public inbred lines-A427, A637, and NK778-were found to have substantial haploid male fertility (HMF). A sixparent full diallel between these three HMF lines and three non-HMF lines was created and HMF was scored. Diallel analysis revealed significant general combining ability (GCA) estimates of up to 17% for HMF, as well as significant specific combining ability (SCA) effects of up to 25%. No significant reciprocal effects were found. Haploid male fertility is promising to be incorporated into elite maize breeding programs to potentially overcome the need of using colchicine treatments for genome doubling. Colchicine aided doubling success rates varying from almost 0 to 30%. Haploid male fertility has an advantage over artificial genome doubling, in terms of both increased success rates and decreased costs for DH line production.

The maize (Zea mays L.) in vivo maternal doubled haploid (DH) system is an important tool used by maize breeders and geneticists around the world. The ability to rapidly produce DH lines of maize for breeding allows breeders to quickly respond to new selection criteria based on the ever‐changing biotic and abiotic stresses that maize is subjected to across its growing area. There are two important steps in the generation of DH lines using the in vivo maternal DH system: (i) the production and identification of haploid progeny, and (ii) the doubling of genomes to create fertile, diploid inbred lines that can be used for topcross and per se evaluation. For this study, the focus is the first step, the production and identification of haploid progeny. A diallel mating between six inbred lines of maize, three highly inducible lines (CR1HT, PA91HT1, and WF9) and three lines with low inducibility (NK778, A427, and A637) was produced to study the genetic makeup of inducibility in temperate maize germplasm. A maximum estimated rate of inducibility was found in A427/A637 at 14.6%. Significant general combining ability (GCA), specific combining ability (SCA), reciprocal, environmental, and GCA × environment and SCA × environment interaction effects were found. Misclassification rates ranged from 0 to 45.2% in the 30 hybrids considered. This study supports the use of germplasm with improved inducibility for breeding to improve rates of inducibility in germplasm that has low induction rates.

Doubled haploid (DH) technology in maize takes advantage of in vivo haploid induction (HI) triggered by pollination of donors of interest with inducer genotypes. However, the ability of different donors to be induced—inducibility (IND), varies among germplasm and the underlying molecular mechanisms are still unclear. In this study, the phenotypic variation for IND in a mapping population of temperate inbred lines was evaluated to identify regions in the maize genome associated with IND. A total of 247 F2:3 families derived from a biparental cross of two elite inbred lines, A427 and CR1Ht, were grown in three different locations and Inclusive Composite Interval Mapping (ICIM) was used to identify quantitative trait loci (QTL) for IND. In total, four QTL were detected, explaining 37.4% of the phenotypic variance. No stable QTL was found across locations. The joint analysis revealed QTL × location interactions, suggesting minor QTL control IND, which are affected by the environment.