Maize Genomics and Genetics 2025, Vol.16, No.2, 80-88 http://cropscipublisher.com/index.php/mgg 84 4.2 Application of molecular markers Molecular marker technology has become a key tool to improve the efficiency of haploid induction. It helps locate genomic regions associated with DH production, thereby speeding up the screening process (Dwivedi et al., 2015). For example, traditional red root markers and high oil markers are now integrated into haploid induction lines, which enables DH technology to be better applied to diverse maize germplasms, such as flint maize and tropical materials, because traditional markers such as R1-nj do not perform well in these materials (Chaikam et al., 2019). In addition, some transcription factors such as ZmC1 and ZmR2 have been used to develop new haploid identification systems. They can activate anthocyanin synthesis in the embryo and aleurone layer, greatly improving the speed and accuracy of identification. The new haploid inducer line MAGIC1 combines these markers and can identify haploids nine days earlier than traditional methods with an accuracy of up to 99.1% (Chen et al., 2022). This progress reduces breeding time and cost, which is very important for large-scale production of DH lines (Chaikam et al., 2019; Chen et al., 2022). 4.3 Application of gene editing Speaking of gene editing, CRISPR/Cas9 technology has completely changed the face of haploid breeding. Through haploid induction-mediated genome editing (IMGE), scientists can use inducer lines carrying CRISPR/Cas9 to directly modify the desired agronomic traits in corn, so that homozygous improved DH lines can be obtained within two generations, avoiding the lengthy steps of traditional breeding (Wang et al., 2019). 5 Innovation of Haploid Induction Scheme 5.1 Chemical induction method In the past, chemical doubling agents were a common means to improve the efficiency of haploid induction in maize. Although effective, these chemical reagents pose considerable safety hazards to operators and plants themselves, and the common doubling rate is about 10% to 30%. In recent years, researchers have become increasingly interested in a method called spontaneous haploid genome doubling (SHGD), which does not rely on chemicals, but has an unstable success rate, ranging from less than 5% to more than 50%. The latest genetic mapping studies have discovered some key quantitative trait loci (QTLs), which are expected to improve the success rate of SHGD (Boerman et al., 2020). 5.2 Environmental optimization Environmental factors play a significant role in the success or failure of haploid induction. Conditions such as temperature, humidity, and light will significantly affect the haploid induction rate (HIR). Corn with different genetic backgrounds also responds very differently to the environment. For example, RWS and Mo-17 induction lines perform better under certain environmental conditions, while sweet corn and flint corn usually have lower induction rates (Trentin et al., 2022). Studies have found that the interaction between the induction line and the donor background is particularly important. Some donor backgrounds contain anthocyanin repressor genes, which will increase the haploid misjudgment rate and reduce HIR (Trentin et al., 2022). Therefore, it is not enough to adjust the environment alone, and the optimization plan must be customized in combination with genetic factors. By reducing the negative impact of these genetic and environmental factors, breeders can design more stable and effective haploid induction methods to maximize efficiency under a variety of conditions. 5.3 Advanced Instruments With technological advances, advanced instruments and automation technologies are revolutionizing the way haploid induction is performed. Automation technology, especially in haploid identification, has greatly simplified the process. New marker systems, such as red root markers and high oil markers, are increasingly used in induction lines, making it easier and more accurate to distinguish haploids from diploids (Chaikam et al., 2019). These new markers are particularly useful for germplasms where traditional markers such as R1-nj have failed, broadening the application range of DH technology.
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