In recent years, the development of pure lines with high levels of homozygosity in plant breeding has seen significant advancements. Traditionally, the pedigree method required a minimum of six selfing generations to achieve 99% homozygosity. However, the doubled haploid (DH) technique has emerged as the quickest method of generating 100% homozygous lines in just two generations.

DH production, being a resource-intensive process, necessitates addressing a few key issues for its effective integration in crop breeding:

  1. Whether DH-based breeding is feasible in the target crop?
  2. If yes, which filial generation is most appropriate to induce DH?
  3. What is the minimum size of DH populations to be developed?
  4. Are DH-based hybrids more productive than RIL-based hybrids?

Addressing these issues requires dependable information on the frequency of DH induction and quantitative genetic parameters, such as the presence and strength of linkage and the number of genes controlling the target trait. DH is feasible only if the frequency of DH induction is better than the probability of identifying the best homozygotes.

  • If linkage is absent, it is desirable to induce DH from F1.
  • If linkage is present, it is preferable to induce DH from either F2 or F3.
  • Since there is a narrow difference in the probability of identifying the best genotypes between F2 and F3, it is more efficient to induce DH from F2 itself.

The DH method is especially advantageous as the number of genes controlling the trait increases.

Minimum DH Population Size
The minimum DH population to be raised depends on the effective number of segregating genes to ensure there is at least a 95% probability of identifying the best recombinant genotype. For example:

  • If the effective number of genes is five, then a minimum of 95 DH plants should be raised.

Empirical Studies and Advantages
Empirical studies have demonstrated the advantages of DH over conventional RILs in crops such as maize. Researchers have suggested that DH technology should be used as a complementary tool rather than a replacement for conventional methods.

It is expected that DH technology will eventually be integrated into all economically important crops as the technology becomes more cost-effective and the frequency of DH induction improves.

REFERENCES

  1. BORDES, J., CHARMET, G., DE VAULX, R.D., LAPIERRE, A., POLLACSEK, M., BECKERT, M., AND GALLAIS, A., 2007, Doubled-haploid versus single-seed descent and S1-family variation for testcross performance in a maize population. Euphytica, 154(1): 41-51.
  2. CHOO, T.M., 1981, Doubled haploids for studying the inheritance of quantitative characters. Genetics, 99(3-4): 525-540.
  3. NEI, M., 1963, The efficiency of haploid method of plant breeding. Heredity, 18(1): 95-100.
  4. VARGAS ESCOBAR, E.A. AND GARCÍA DÁVILA, M.A., 2023, Comparison of maize performance between doubled haploids and different selfing generations in the Mexican subtropics. Acta Agronómica, 72(2): 168-175.