Effects of acibenzolar-S-methyl on the suppression of Fusarium wilt of cyclamen

Acibenzolar-S-methyl (ASM; Actigard 50 WP®, Syngenta Inc.) was evaluated for its ability to suppress Fusarium wilt of cyclamen in the greenhouse. The effect of applying increasing rates of ASM to cyclamen seedlings grown in potting mix infested with Fusarium oxysporum f. sp. cyclaminis resulted in a negative relationship between estimates of disease progress values (area-under-the-disease-progress-curve, AUDPC) and ASM rate. Disease symptoms were still evident in most plants, but some ASM-treated plants remained asymptomatic for the entire period. Dry mass of plants grown in infested potting mix were proportionally increased as ASM concentrations increased. In the absence of the pathogen, however, increasing rates of ASM resulted in linear reductions in dry mass. Flower number and quality were not affected by ASM rate. When seedlings were sprayed with 50 μg a.i. ASM ml−1 and then grown in potting mix infested with increasing densities of F. oxysporum f. sp. cyclaminis, disease progress was significantly less than untreated seedlings, but there was variation among repetitions of the experiment. Dry mass was similarly greater than untreated seedlings. The major benefit of ASM was that it delayed the onset of wilt symptoms in most plants for up to 3 weeks and kept a few plants completely asymptomatic. Although applications resulted in no visible phytotoxicity on the leaves, the decline in dry mass may suggest some level of inhibition due to ASM. ASM may still be a useful component of an integrated disease management program for Fusarium wilt of cyclamen.