In vitro- and in vivo-based approaches for doubled haploid production in Zea mays L.: challenges and opportunities

Maize (Zea mays L.) is a cereal species of significant importance for global food security, animal nutrition, and agricultural economies. The enhancement of maize yield through hybrid breeding and the selection of desirable traits-such as increased vigor, resilience to biotic and abiotic stressors, and improved adaptability to diverse environmental conditions-represents a significant milestone in the field of agricultural biotechnology. Production of parental inbred lines, which is a prerequisite for hybrid breeding, can be accomplished through conventional breeding or doubled haploid (DH) techniques, the latter provides accelerated homozygosity and genetic uniformity. This review focuses on the various in vitro- and in vivo-based methods for the production of DH lines in maize, discussing their respective challenges and opportunities. Furthermore, it explores recent advancements in chromosome doubling techniques necessary for restoring fertility to haploids, which are essential for their effective integration into breeding programs. This review also aims to delineate current knowledge and future directions in maize DH technology, ultimately contributing to optimized breeding strategies for enhanced maize production.