Approaches for Haploid Detection in Maize

Doubled haploid (DH) technology, based on in vivo maternal haploid induction, is widely employed in maize breeding. This in vivo system involves haploid inducers, a male genotype capable of inducing haploids and source germplasm that serves as the donor genotype. Modern haploid inducers yield only a small percentage of haploids among many hybrid kernels, making haploid identification expensive, time-consuming and labor-intensive task. As a result, it is considered one of the most critical steps in the doubled haploid breeding. This review provides an overview of various haploid identification methods, including those based on morphological differences between haploids and diploids, biomarker-assisted selection using haploid inducers, cytogenetic, molecular markers and high throughput image-based methods. The morphological traits and their genetic basis, benefits and limitations of each biomarker system are discussed in detail. Earlier haploid selection prioritized finding clear and effective marker systems. Today, the focus has shifted to integrating multiple dependable biomarkers to enhance efficiency, while exploring opportunities for automation. Fully automated and high-throughput haploid detection is a promising advancement for the near future, with robustness and reliable accuracy as critical factors.