September 11th, 2020
The pipeline Baseline
1. Introduction to the problem
Crop by region
IITA-Cassava WABio
Problem specification
Currently, the team uses a base index for selection. Will changing to a Smith-Hazel index improve accuracy of selection?
Breeding strategy component tackled
Crossing, Evaluation, Selection
Breeders’ equation terms tackled
r
\(\Delta_g = (i * \sigma_g * r)/L\)
Hypothesis
Use of a Smith-Hazel index will increase accuracy of selection thereby increase genetic gains
2. Materials and methods
Selection index
2. Materials and methods
Treatments
| Treatment | Description |
|---|---|
| Parents_PYT-UYT | Compared BASEINDEX and SHINDEX when parents are selected at current baseline (PYT-UYT) |
| Parents_PYT | Compared BASEINDEX and SHINDEX when parents are selected at PYT |
| Parents_CE | Compared BASEINDEX and SHINDEX when parents are selected at CE |
Simulation procedure
A 20 year burn-in period was modeled using the baseline. The burn-in was followed by a 20 year evaluation period to measure rates of genetic gain for all treatments. Genetic gain was measured by assessing changes in genetic merit at F1. Genotype-by-year interaction variance was assumed to be equivalent to genetic variance (based on average correlation between locations being equal to 0.5). 30 replications done. We used the genetic covariance among traits and weights as provided by the breeders.
3.0 What we know from the previous scenarios
Treatments 3:1 (Parents @CE, @PYT and @PYT_UYT)
The Smith-Hazel index did not have an advantage over a base index unless under very low evaluation accuracy situations
3.0 Results from the current scenarios
Treatments 3:1 (Parents @CE, parents @PYT and Parents @PYT-UYT)
The smith-hazel index has clear advantage at the CE stage where accuracy is quite low.
4. Conclusion
The Smith-Hazel index has merit over a base index in situations where the level of accuracy in the evaluation strategy is low. However, at stages where there is high accuracy to estimate breeding value, its advantages do not warrant its prioritization as an improvement plan because its contribution to genetic gains is not significantly different from the base index.