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Doubled haploid (DH) technology has changed the maize-breeding landscape in recent years. Traditionally, DH production requires the use of chemical doubling agents to induce haploid genome doubling and, subsequently, male fertility. These chemicals can be harmful to humans and the plants themselves, and typically result in a doubling rate of 10%-30%. Spontaneous genome doubling and male fertility of maize haploids, without using chemical doubling agents, have been observed to a limited extent, for nearly 70 years. Rates of spontaneous haploid genome doubling (SHGD) have ranged from less than 5% to greater than 50%. Recently, there has been increased interest to forgo chemical treatment and instead utilize this natural method of doubling. Genetic-mapping studies comprising worldwide germplasm have been conducted. Of particular interest has been the detection of large-effect quantitative trait loci (QTL) affecting SHGD. Having a single large-effect QTL with an additive nature provides flexibility for the method of introgression, such as marker-assisted backcrossing, marker-assisted gene pyramiding, and systematic design. Moreover, it allows implementation of new methodologies, such as haploid-inducer mediated genome editing (HI-edit) and promotion of alleles by genome editing. We believe the use of SHGD can further enhance the impact of DH technology in maize.

Major locus for spontaneous haploid genome doubling detected by a case-control GWAS in exotic maize germplasm Key messageA major locus for spontaneous haploid genome doubling was detected by a case-control GWAS in an exotic maize germplasm. The combination of double haploid breeding method with this locus leads to segregation distortion on genomic regions of chromosome five.

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Fertilization and kernel development are crucial for breeding and agronomic production of maize (Zea mays L.), which is prone to outcrossing. Because of this tendency, a major issue for organic corn farmers is to maintain genetic purity of their crop. One way to maintain this purity is to use a unilateral cross incompatibility system such as Ga1-s. However, lack of complete pollen exclusion has been reported in Ga1-s heterozygotes, complicating introgression of this trait into breeding germplasm. A systematic, quantitative evaluation of pollen exclusion rates in breeding lines would greatly facilitate use of this system. The purpose of this study is to quantitatively evaluate exogenous ga1 pollen exclusion of a diverse set of Ga1-s/ga1 F 1 hybrids representing the stiff stalk and nonstiff stalk heterotic groups, and the Iowa Synthetic Corn Borer population. Differences between genotypes but not heterotic groups were observed when applying exogenous ga1 pollen onto heterozygotes possessing the same Ga1-s allele, indicating there are epistatic interactions between Ga1-s and modifier loci in the ga1 parents tested.