Molecular Plant Breeding 2025, Vol.16, No.2, 146-155 http://genbreedpublisher.com/index.php/mpb 147 This study will utilize case studies to analyze how DH breeding and germplasm innovation achieve synergistic effects in disease-resistant maize breeding, exploring the integration of advanced breeding technologies. It aims to highlight the latest advancements, practical applications, and future prospects of these technologies in maize disease resistance breeding, with the hope of providing insights into the potential advantages and challenges of combining DH technology with germplasm innovation to enhance disease resistance in maize. 2 Application of Doubled Haploid Breeding in Disease-Resistant Maize Breeding 2.1 Principles and development of dh breeding technology Doubled haploid (DH) breeding technology has revolutionized maize breeding by enabling the rapid production of completely homozygous lines from heterozygous parents. This method involves the in vivo induction of maternal haploids using a male haploid inducer genotype, followed by the identification of haploids at the seed or seedling stage, chromosome doubling of haploid seedlings, and selfing of fertile doubled haploid plants (Prigge et al., 2012; Chaikam et al., 2019). The development of haploid inducers with high haploid induction rates and adaptation to different environments has facilitated the widespread adoption of DH technology, particularly in tropical regions (Prigge et al., 2011;Chaikam et al., 2019). Advances in marker systems, such as the red root marker and high oil marker, have further improved the efficiency of haploid identification (Chaikam et al., 2019). 2.2 DH induction and doubling process The DH induction process begins with the pollination of a target maize line with a haploid inducer line, which results in the production of seeds containing haploid embryos. These haploids are then identified using specific markers, such as the R1-nj marker, although alternative markers are being developed for germplasm where R1-nj is inhibited (Prigge et al., 2011; Chaikam et al., 2019). The next critical step is chromosome doubling, which can be achieved through chemical treatments or spontaneous doubling. Chemical agents, while effective, pose environmental and health risks, prompting research into spontaneous doubling methods (Boerman et al., 2020; Ren et al., 2020). Once chromosome doubling is successful, the doubled haploid plants are self-pollinated to produce homozygous seeds (Trentin et al., 2020). 2.3 Advantages of DH breeding DH breeding offers several advantages over conventional breeding methods. It significantly accelerates the breeding process by reducing the number of generations required to achieve homozygosity, thus shortening the breeding cycle and increasing genetic gain (Boerman et al., 2020; Trentin et al., 2020). This rapid production of homozygous lines enhances selection efficiency, allowing breeders to more quickly identify and propagate disease-resistant traits (Prigge et al., 2012; Chaikam et al., 2019). Additionally, DH technology facilitates the integration of genome editing techniques, such as CRISPR/Cas9, enabling the rapid generation of pure elite lines with multiple desired traits (Liu et al., 2019; Wang et al., 2019). The ability to produce homozygous lines in a single generation makes DH breeding particularly valuable for developing disease-resistant maize varieties, as it allows for the swift incorporation and fixation of resistance genes (Chaikam et al., 2019; Trentin et al., 2020). 3 Role of Germplasm Innovation in Disease-Resistant Maize Breeding 3.1 Sources and methods of germplasm innovation Germplasm innovation in maize breeding involves the strategic use of diverse genetic resources, including local germplasm, wild relatives, and exotic germplasm. Local germplasm, which is well-adapted to specific environmental conditions, provides a valuable source of genetic diversity for breeding programs. For instance, the Germplasm Enhancement of Maize (GEM) program has utilized doubled haploid (DH) breeding methods to expedite the release of lines from 300 exotic maize races, demonstrating the potential of integrating diverse genetic resources into breeding programs (Smith et al., 2008). Wild relatives of maize, such as Zea diploperennis, have been successfully used to transfer resistance genes for traits like drought tolerance and Striga hermonthica resistance into tropical maize germplasm. This approach has led to the development of new inbred lines with enhanced resistance to these stresses, showcasing the importance of wild relatives in germplasm innovation (Shaibu et al., 2021). Additionally, the incorporation of exotic
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