**Abstract**

The creation of homozygous parental lines for hybrid development is one of the key components of commercial maize breeding programs. It usually takes up to 6 to 7 generations of selfing to obtain homozygous inbreds from the initial cross using the conventional pedigree method. Using doubled haploid (DH) method, concurrent fixation of all the genes covering entire chromosomes is possible within a single generation. For generation of DH lines, haploids are generated first by several means such as *in-vitro* method using tissue culture technique and *in-vivo* method using the haploid inducer (HI) lines. Of which, tissue culture-based methods have shown little promise for large-scale DH production as it needs good infrastructures and technical requirements. In contrast, inducer-based method provides more optimistic solutions for large-scale DH lines production. Due to its rapidity, DH technology is now being adopted in many countries including India for reducing the breeding cycle.

**Keywords:** doubled haploid, homozygous line, maize, and haploid inducer, inbreds

### **1. Introduction**

Maize breeding strategies rely heavily on the creation of homozygous parental lines for hybrid breeding. Using the traditional pedigree approach, it might take up to 7 generations of selfing to achieve homozygous inbreds from the first cross (**Figure 1**). In this context, because of its economic and logistical practicality, the creation of doubled haploid (DH) has received a lot of attention for varietal development in the last two decades [1]. The DH approach allows for simultaneous fixation of all genes across complete chromosomes in a single generation [2]. Haploids are initially created by a variety of methods, including an *in-vitro* way utilizing tissue culture techniques and an *in-vivo* method employing haploid inducer (HI) lines. On the other hand, Tissue culture-based approaches have not shown much promise for large-scale DH production since they necessitate adequate infrastructure and technical requirements. In contrast, because of its viability for large-scale DH line production, the inducer-based technique is deemed more hopeful and cost-effective [3]. According to the parent from which the haploids are being formed, inducer-based haploids may be divided into maternal haploid and

**Figure 1.** *Conventional breeding method for obtaining inbred lines.*

paternal haploid [1]. With the exception of their cytoplasm, the genetic constitutions of both forms of haploids are identical. Once haploids are created, their genetic constitutions can be duplicated in a single step to produce homozygous DH lines. DH technique has recently been implemented in commercial maize breeding programs in various countries because of its speed in decreasing the breeding cycle.
