Studies on Resistance of Phoma asparagi Sacc. to Benzimidazole Fungicides

The sensitivity of Phoma asparagi Sacc. from diseased asparagus of different areas in Fujian to thiophanate methyl was tested during 1989 to 1991. The results showed that strains from Changle and Putian possess high resistance to thiophanate methyl. Mycelia of these resistant strains can grow on PSA medium with 2000 ug/mL thiophanate methyl and the MIC value was hardly measured. Mycelia of the sensitive strains from Putian and Fuzhou, however, failed to grow on the PSA containg 10 ug/mL thiophanate methyl. In the area of Hunan in Changle County where asparagus has been cultivated for more than ten years and thiophanate methyl was used frequently, the ratio of resistant strains was as high as 100% in the field. The thiophanate methyl-resistance of strain F1 can be maintained at least 14 generations by the means of incubation on the biocide-free PSA medium. The cross resistance of two strains F1, L2 was found among benzimidazole fungicides, such as thiophanate methy 1, carbendazim and thiabendazole. However, these resistant strains are identical to sensitive strains, and all sensitive to Procymidone and guazatine.