July 30th, 2020

1. Introduction to the problem

Crop by region


Problem specification

Recycling happens very slowly which lower rates of genetic gain.

Breeding strategy component tackled


Breeders’ equation terms tackled

\(\Delta_g = (i * \sigma_g * r)/L\)


Reducing cycle time will increase the rate genetic gain.

2. Materials and methods


Treatment Description
CURRENT_F7 Current scheme, selecting parents at PYT_F7 (20), VEF_F8 (5), OF_F9 (10) using a base index.
SSD_F6 Scheme selecting parents at PYT_F6 (20), VEF_F7 (5), OF_F8 (10) using a base index.
SSD_F5 Scheme selecting parents at PYT_F5 (20), VEF_F6 (5), OF_F7 (10) using a base index.
SSD_F5_FAMILY Scheme selecting parents at PYT_F5 (20), VEF_F6 (5), OF_F7 (10) + top 20% families are selected at F2 using a base index (not parents).
SSD_F8 Scheme selecting parents at PYT_F8 (20), VEF_F9 (5), OF_F10 (10)

Simulation procedure

A 20 year burn-in period was modeled using the current breeding scheme. The burn-in was followed by a 50 year evaluation period to measure rates of genetic gain for all treatments. Genetic gain was measured by assessing changes in genetic merit in F9 lines. Genotype-by-year interaction variance was assumed to be equivalent to genetic variance (based on average correlation between locations being equal to 0.5). 20 replications done. We simulated 5 complex and 3 simple traits to be behind the genetic merit.

The current strategy and potential changes

3. Results

By year 50, the use of different recycling strategies generated:

  • Eliminating one SSD step starting PYT at F6 provides 1.26 (95% CI: 1.17,1.36) times more gain.
  • PYT at F5 provides 1.33 (95% CI: 1.26,1.41) times more gain.
  • PYT at F5 plus some family selection at F2 provides 1.74 (95% CI: 1.53,1.97) times more gain.

4. Conclusion

Deriving lines earlier to recyle at the same stages of testing increases the rate of genetic gain.

We recommend deriving lines earlier to start testing at an earlier generation and if possible apply early family selection.