The genetics of planting density-dependent branching in chrysanthemum

Abstract The architecture of chrysanthemum plants raised for cut flowers is strongly influenced by their ability to form branches. The genetic basis of branching was revealed through a quantitative trait locus (QTL) analysis of an F 1 population generated by crossing the varieties ‘Nannong Xuefeng’ and ‘Monalisa’ grown under contrasting planting densities. Under the low planting density regime (E1), 12 additive QTLs involving seven branching-associated traits were detected, while under the high planting density regime (E2), the number of QTL detected was only eight. One of the individual QTL accounted for over 10% of the phenotypic variance. Of the 20 QTLs, only one was expressed under both high and low planting densities. A joint QTL analysis across the two environments identified two QTLs which were separately detected in E1. A set of four QTLs exhibiting additive × additive epistasis was identified, few of which had interaction with environments.