Development of rapid in vitro assays and current status of fungicide sensitivity in the pecan scab pathogen Fusicladium effusum

Abstract

Isolates of F. effusum from three baseline orchards in Georgia were tested for sensitivity using a mycelial growth assay in microtiter plates. The 50% effective dose (EC50) values were estimated for azoxystrobin, dodine, fentin hydroxide, and propiconazole. The role of alternative oxidase inhibitors salicylhydroxamic acid and propyl gallate in quinone outside inhibitor assays also was evaluated. Both chemicals were found to be toxic to F. effusum and therefore were not used in the assays. A more rapid assay was developed based on conidial germination and micro-colony growth. Isolates of F. effusum from 35 commercial orchards were profiled using the new assay and in vitro resistance to fentin hydroxide, dodine, thiophanate-methyl, propiconazole, and azoxystrobin was detected in 20, 4, 6, 21, and 19 of the 35 orchards respectively. Taxonomy of F. effusum in the family Venturiaceae was supported based on the sequenced cytochrome b gene.