Dendranthema pacificum Nakai (Chrysanthemum pacificum Nakai; 2n = l0x = 90 chromosomes), a species native to Japan, was crossed to Dendranthema grandiflora Tzvelev (C. morifolium Ramat.; 2n = 6x = 54), the florist chrysanthemum, to develop a type with numerous small flowerheads. The first-generation hybrid was fertile, but the flowerheads were too small. In the first backcross to D. grandiflora, the desired type was obtained. The backcross (2n = 7x = 63) was very fertile, despite the odd number of genomes. D. pacificum may also be used as a source of resistance to the serpentine leaf miner (Liriomyza trifolii).
Received for publication 11 Apr. 1988. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.