“Selection of Parents and Kind of Breeding Populations (F₂/BC) for Pure Line and F₁ Hybrid Breeding”

UNIVERSITY OF AGRICULTURAL SCIENCES, BANGALORE

DEPARTMENT OF GENETICS AND PLANT BREEDING

Seminar – GPB 682 (0+1)

“Selection of Parents and Kind of Breeding Populations (F₂/BC) for Pure Line and F₁ Hybrid Breeding”

Plant breeding essentially is exploitation of natural and/or deliberately generated genetic variability. In major crops, natural genetic variability has already been exploited. Therefore, breeding of major crops relies on generated genetic variability in the form of segregating (breeding) populations (BPs). Selection of the parents to create the best BP is the key to maximize the probability of isolating superior homozygous lines either for use as pure line cultivars or as parents of F₁ hybrids.

The best breeding population is the one which has high trait mean and genetic variability. High trait mean provides a head start, while high variance provides long-term scope for selection. Quantitative genetics theory has shown that mid-parental value is the best predictor of trait mean of the BPs. Along with high mean and genetic variance, the parents must be equally good, diverse, and complementary to each other². Complementarity can be tested using the test statistic Tij, which helps identify germplasm lines with the potential to contribute favourable alleles not present in a specified line or set of pure lines³.

For the ease of developing hybrid parents, there is a need to classify the working collection into different heterotic groups (HGs). HG, also called 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.” By comparison, a heterotic pattern refers to “a specific pair of two HGs, which express high heterosis and consequently high hybrid performance in their cross”⁴.

Heterotic grouping will help streamline the hybrid breeding programme by dictating which parents within a HG to cross to develop the breeding population (BP) and which parent from the opposite HG to use as a tester to evaluate experimental hybrids derived from BPs. The hybrids resulting from crossing inbred lines derived from different HGs exhibit a greater magnitude of heterosis¹. There are certain criteria to identify the best tester, which is a prerequisite for classification of breeding lines into HGs based on combining ability.

REFERENCES

1. Aslam, M. and Zafar, S. A., 2021. Heterotic group theory: A thriving vitality in hybrid maize breeding. J. Agric. Basic Sci., 5(1): 45–61.

2. Bernardo, R., 2014. Essentials of Plant Breeding, pp. 119–154.

3. Martin, S. S., Lewers, K. S., Palmer, R. G. and Hedges, B. R., 1996. A testcross procedure for selecting exotic strains to improve pure-line cultivars in predominantly self-fertilizing species. Theor. Appl. Genet., 92(1): 78–82.

4. Melchinger, A. E. and Gumber, R. K., 1998. Overview of heterosis and heterotic groups in agronomic crops. Concepts and Breeding of Heterosis in Crop Plants, 25: 29–44.