Evaluating breeding for broad versus narrow adaptation for cassava in Nigeria using stochastic simulation

Authors: BAKARE, MOSHOOD - Cornell University; KAYONDO, SIRAJ ISMAIL - International Institute Of Tropical Agriculture (IITA); KULAKOW, PETER - International Institute Of Tropical Agriculture (IITA); RABBI, ISMAIL YUSUF - International Institute Of Tropical Agriculture (IITA); Jannink, Jean-Luc

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2023
Publication Date: 12/14/2023
Citation: Bakare, M.A., Kayondo, S., Kulakow, P., Rabbi, I., Jannink, J. 2023. Evaluating breeding for broad versus narrow adaptation for cassava in Nigeria using stochastic simulation. Crop Science. Volume 64, Issue 2 pp. 603-616. https://doi.org/10.1002/csc2.21170.
DOI: https://doi.org/10.1002/csc2.21170

Interpretive Summary: This study focused on improving the process of breeding cassava plants in Nigeria. Scientists wanted to find out whether it’s better to develop cassava varieties that can grow well in many different environments or to focus on varieties that do well in specific regions. They used a computer simulation, which is like a virtual experiment, to test different breeding strategies. The study found that breeding cassava for specific regions (narrow adaptation) might be more effective than trying to create a single variety that works everywhere (broad adaptation). This is because cassava plants can behave very differently depending on where they are grown, and it's easier to make improvements when focusing on specific conditions. The findings can help farmers in Nigeria grow cassava more successfully by using varieties best suited to their local environments.

Technical Abstract: The cassava (Manihot esculenta Crantz) breeding program at the International Institute of Tropical Agriculture (IITA) has adopted genomic selection to accelerate genetic gain. The program continues to develop varieties broadly adapted across Nigeria’s diverse agroclimatic zones. However, for this purpose, genotype-by-environment interaction (GEI) presents a challenge. To decide whether broad adaptation breeding is a good strategy, we evaluated broad versus narrow adaptation strategies using stochastic simulation, assessing genetic gain, genetic variance, heritability, and selection accuracy at 0 versus realistic levels of GEI variance. To parameterize the models, we analyzed historical data from four phenotypic evaluation stages of the IITA breeding program to estimate genetic and error variances, and genetic correlations across environments. Based on these observed parameters, the genomic-enabled breeding programs exhibited higher genetic gain than the conventional program for both GEI variances. At realistic GEI variance, the narrow adaptation program showed higher genetic gain than the broad adaptation program. Across all programs, the genetic variance declined over time, though the genomic-enabled programs showed higher initial variance due to the selection of parents at earlier stages. At realistic GEI variance, an increase in genetic variance was observed in the narrow adaptation program due to its conversion of GEI between mega-environments into main genetic variance within mega-environments. This higher genetic variance led to higher heritability and selection accuracies. This study highlights the potential of genomic selection in accelerating genetic gain and suggests that dividing the IITA cassava breeding program to target more than one mega-environment should be considered.