Occurrence of strobilurin-resistant strains of Mycovellosiella nattrassii, causal fungus of leaf mold of eggplants.

Seventy isolates of Mycovellosiella nattrassii, collected from eggplants in Kochi Prefecture, Japan, were tested for sensitivity to strobilurin fungicides in 2000. The frequency distribution of minimum inhibitory concentrations of azoxystrobin against mycelial growth had two distinct peaks at 3.13ppm and over 1600ppm, considered to be sensitive and resistant, respectively. Isolates resistant to azoxystrobin had cross resistance to kresoxim-methyl. The EC50 of azoxystrobin and kresoxim-methyl for mycelial growth and the inhibitory rate of conidial germination by azoxystrobin were also clearly distinguishable between resistant and sensitive strains. Control efficacy of these two fungicides was very low against resistant strains in an inoculation test.