Monitoring sensitivity of field isolates of Pyricularia oryzae to isoprothiolane, IBP [iprobenfos] and EDDP [edifenphos] from 1993-96
1999
Hirooka, T. (Nihon Nohyaku Co. Ltd., Osaka (Japan)) | Uchigurohane, T. | Nishiguchi, T.
From 1993-96, the sensitivity to isoprothiolane in field isolates of Pyricularia oryzae was monitored using EC50 values for mycelial growth on agar medium. Sensitivity to organophosphorus tiolate (PTL) fungicides, IBP and EDDP, was also monitored as EC50 values, because mutants resistant to PTL fungicides (in vitro mutants) obtained by in vitro selection showed resistance to isoprothiolane. EC5O values of isoprothiolane and IBP were compared with those obtained from 1977-83. The sensitivity to isoprothiolane apparently fell into one group that was as sensitive as the sensitive stock isolates in each monitoring period. From 1977-83, the sensitivity to IBP was recognized as two groups: One was sensitive, and the other was the moderately resistant (MR) isolates which consisted of a less resistant cluster at a high incidence and a more resistant one at a low incidence. From 1993-96, the sensitivity of isolates belonging to the less IBP-resistant MR cluster increased, but those in the more resistant MR cluster were unchanged. From 1993-96, the sensitivity to EDDP was near that of the sensitive stock isolates. No highly resistant isolates like the in vitro mutants were found in the field isolates at both monitoring periods. The difference in the resistance level of IBP-MR isolates and their sensitivity to isoprothiolane and EDDP was not correlated. Preventive foliar applications revealed that IBP-sensitive and MR isolates were sensitive to isoprothiolane and EDDP both at their practical doses and at half the practical doses. These results suggest that IBP-MR isolates in fields do not show cross-resistance to isoprothiolane and EDDP
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