Heterotic grouping (HG), also known as a heterotic pool, is defined as “a group of related or unrelated genotypes (inbred lines or populations) from the same or different populations, which display similar combining ability and heterotic response when crossed with genotypes from complementary and genetically distinct germplasm groups.” In contrast, a heterotic pattern refers to “a specific pair of two HGs, which express high heterosis and consequently high hybrid performance in their cross” (Melchinger & Gumber, 1998).

Heterotic grouping plays a crucial role in hybrid breeding by:

  • Avoiding the development and evaluation of unnecessary hybrids, saving time and resources.
  • Increasing general combining ability (GCA) variance, making early-generation test cross evaluation and selection more effective.
  • Streamlining hybrid breeding programs by guiding which parents within an HG should be crossed to develop breeding populations (BPs) and which parents from opposite HGs should be used as testers for evaluating experimental hybrids (Aslam & Zafar, 2021).

Methods of Heterotic Grouping

Different methods have been proposed for heterotic grouping, including:

  • Pedigree analysis
  • Phenotypic clustering
  • Combining ability studies
  • Marker-based genetic distance

The Advantages of Three Heterotic Groups Over Two

A three-group heterotic classification system has been shown to improve both specific and general breeding efficiency compared to a two-group system. This approach allows for better exploitation of heterotic potential by increasing the chances of producing superior hybrid combinations (Fan et al., 2018). The breeding efficiency of different heterotic grouping methods can vary under different environmental conditions, highlighting the need for adaptable breeding strategies (Badu-Apraku et al., 2015).

Continuous Improvement in Heterotic Grouping

Heterotic grouping is a continuous process where newly developed inbreds are either merged into existing HGs or used to establish new independent groups. To maintain and improve heterotic patterns, reciprocal recurrent selection (RRS) is employed. RRS enhances genetic divergence between HGs, which sustains heterotic patterns and ensures a high frequency of heterotic hybrids (Melchinger & Gumber, 1998).

Conclusion

Incorporating a three-group heterotic classification enhances breeding efficiency by optimizing hybrid performance and maintaining genetic diversity. As breeding programs continue to evolve, the selection and refinement of heterotic groups remain essential for achieving higher yields and stability in hybrid crop development.

References

  1. Aslam, M., & Zafar, S. A. (2021). Heterotic group theory: A thriving vitality in hybrid maize breeding. J. Agric. Basic Sci., 5(1), 45-61.
  2. Fan, X., Bi, Y., Zhang, Y., Jeffers, D., Yin, X., & Kang, M. (2018). Improving breeding efficiency of a hybrid maize breeding program using a three heterotic-group classification. J. Agron., 110(4), 1209-1216.
  3. Badu-Apraku, B., Annor, B., Oyekunle, M., Akinwale, R. O., Fakorede, M. A. B., Talabi, A. O., Akaogu, I. C., Melaku, G., & Fasanmade, Y. (2015). Grouping of early maturing quality protein maize inbreds based on SNP markers and combining ability under multiple environments. Field Crops Res., 183, 69-183.
  4. Melchinger, A. E., & Gumber, R. K. (1998). Overview of heterosis and heterotic groups in agronomic crops. Concepts and breeding of heterosis in crop plants, 25, 29-44.