Modified Convergent Improvement: A Breeding Method for Multiple Trait Selection

Abstract

Breeders need efficient multiple trait selection schemes that allow selection for each trait within its respective optimum environment. This report describes such a breeding procedure entitled, “modified convergent improvement,” and compares theoretical predictions of genetic gain per cycle (Δq/cycle) for the following schemes: modified convergent improvement, tandem selection in two dissimilar populations followed by a population cross (strain crossing), recurrent selection for single traits in dissimilar populations followed by a multiple population cross (multiple strain cross), and independent culling. Estimates of Δq/cycle were calculated for both additive and dominant gene action when selecting for three to six traits. Modified convergent improvement (Δq/cycle = 0.13) and independent culling (Δq/cycle 0.11) exhibited highest average Δq/cycle for traits controlled by recessive genes (P≤ 0.05). Independent culling exhibited the highest average Δq/cycle when selecting for traits controlled by dominant genes (Δq/cycle = 0.13) or by additive gene action (Δq/cycle = 0.20). Modified convergent improvement proved superior to independent culling when selecting for traits controlled by additive gene action or by recessive genes when gene frequency was low (q = 0.04−0.12). Theoretical Δq/cycle values for multiple strain cross and strain crossing were consistently lower than those obtained for either independent culling or modified convergent improvement.We propose that modified convergent improvement is a superior method for multiple trait selection when traits must be evaluated in dissimilar environments or during the initial stages of germplasm development. This procedure confers additional benefits including reducing inbreeding potential and/or disequilibrium over that observed in single population breeding procedures.