Albrecht E. Melchinger, Matthias Frisch

Theoretical and Applied Genetics; September 2023, vol. 136:203

https://doi.org/10.1007/s00122-023-04446-3

Abstract

Reciprocal recurrent genomic selection (RRGS) is a powerful tool for ensuring sustainable selection progress in hybrid breeding. For training the statistical model, one can use half-sib (HS) or full-sib (FS) families produced by inter-population crosses of candidates from the two parent populations. Our objective was to compare HS-RRGS and FS-RRGS for the cumulative selection gain (ΣΔGΣΔ�), the genetic, GCA and SCA variances (σ2Gσ�2,σ2gcaσ���2, σ2scaσ���2) of the hybrid population, and prediction accuracy (rgca����) for GCA effects across cycles. Using SNP data from maize and wheat, we simulated RRGS programs over 10 cycles, each consisting of four sub-cycles with genomic selection of Ne=20��=20 out of 950 candidates in each parent population. Scenarios differed for heritability (h2)(ℎ2) and the proportion τ=100×σ2sca:σ2G�=100×σ���2:σ�2 of traits, training set (TS) size (NTS���), and maize vs. wheat. Curves of ΣΔGΣΔ� over selection cycles showed no crossing of both methods. If τ� was high, ΣΔGΣΔ� was generally higher for FS-RRGS than HS-RRGS due to higher rgca����. In contrast, HS-RRGS was superior or on par with FS-RRGS, if τ� or h2ℎ2 and NTS��� were low. ΣΔGΣΔ� showed a steeper increase and higher selection limit for scenarios with low τ�, high h2ℎ2 and large NTS���. σ2gcaσ���2 and even more so σ2scaσ���2 decreased rapidly over cycles for both methods due to the high selection intensity and the role of the Bulmer effect for reducing σ2gcaσ���2. Since the TS for FS-RRGS can additionally be used for hybrid prediction, we recommend this method for achieving simultaneously the two major goals in hybrid breeding: population improvement and cultivar development.

See https://link.springer.com/article/10.1007/s00122-023-04446-3

Figure 1: Production of hybrids (green) for the training set using doubled-haploid lines sampled from parent populations Π_F (females, yellow) and Π_M (males, blue). Top: Half-sib reciprocal recurrent genomic selection (HS-RRGS) with N_TS/2 half-sib families in each population produced by crossing the candidates with an inbred tester from the opposite population. Bottom: Full-sib reciprocal recurrent genomic selection (FS-RRGS) with N_TS single-cross hybrids obtained from paired crosses of DH lines. DH lines in the prediction set of Π_F and Π_M are also shown.