Cutting of 41 chrysanthemum cultivars were evaluated for resistance to bacterial soft rot caused by Erwinia carotovora subsp. carotovora and Erwinia chrysanthemi. Cutting of the cultivars differed significantly in resistance to bacterial soft rot. Soft rot on chrysanthemum cuttings inoculated with E. chrysanthemi was more serious than that inoculated with E. carotovora subsp. carotovora in the same cultivar. Among the 41 cultivars tested, cultivar “Fen Lan Shiao Fen” was the most susceptible, while “Lung Fenq Hsiao Hung” was the least susceptible. In the in vitro test, the growth of E. carotovora subsp. carotovora and E. chrysanthemi was inhibited by several agrochemicals. Among them, streptomycin, thiophanate methyl +streptomycin, streptomycin + tetracycline, kasugamycin + copper oxychloride, cupric hydroxide and oxine-copper + copper hydroxide were more inhibitory to both Erwinia pathogen. Aforecited each agrochemical was thoroughly mixed with talc at different dilution rates, and chrysanthemum cuttings were covered with each mixture at the end. In this test, oxine-copper + copper hydroxide, kasugamycin + copper oxychloride, thiophanate methyl + streptomycin and streptomycin + tetracycline showed to be more effective in the protection of the chrysanthemum cutting from the infection of soft rot Erwinia. Root number and length of chrysanthemum were reduced by the treatments of thiophanate methyl + streptomycin or streptomycin + tetracycline, but not oxine-copper + copper hydroxide or kasugamycin + copper.

Key words: chrysanthemum, Erwinia, soft rot, resistance, chemical control.