Cyanide-insensitive Respiration of Phytopathogenic Fungi Demonstrated by Antifungal Joint Action of Respiration Inhibitors

Abstract

A survey was conducted for involvement of cyanide-insensitive respiration of phytopathogenic fungi by testing a joint fungitoxic action between salicylhydroxamic acid (SHAM) as an inhibitor of the cyanide-insensitive pathway and the inhibitors of cytochrome pathway of respiratory chain such as methoxyacrylate derivatives or antimycin A. Remarkable synergism in fungitoxic action was shown in Botrytis cinerea, Monilinia fructicola and Pyricularia oryzae. The synergism may result from the induction of the alternative pathway by the latter inhibitors and the inhibitionof the induced alternative pathway by SHAM. To confirm the induction of the alternative pathway, effects of SHAM on oxygen consumption by hyphal cells of three fungi were tested by pretreating with methoxyacrylate or potassium cyanide. These results confirmed the induction of cyanide-insensitive respiration by the pretreatment with methoxyacrylate or potassium cyanide as expected from the joint fungitoxic action. The synergism in fungitoxic action was also observed in Cochliobolus miyabeanus, though it was less remarkable. In Rhizoctonia solani, the synergism was observed with methoxyacrylates but hardly with antimycin A, so that cyanide-insensitive respiration was induced with the methoxyacrylates but hardly with antimycin A in Rhizoctonia solani. In Gibberella fujikuroi, Pythium sp. and Valsa ceratosperma the synergism was not necessarily clear. A phytopathogenic bacterium, Xanthomonas campestris pv. citri and a yeast, Saccharomyces cerevisiae did not show any synergism in joint antimicrobial action of the above inhibitors.

Sensitivity of Venturia inaequalis to trifloxystrobin

“…Induction of the alternative respiration (cyanide‐resistant respiration) by antifungal joint action of respiration inhibitors was recently reported by Watanabe et al 9 and Hayashi et al 10 Experiments with SHAM and antimycin A indicate that alternative respiration plays an important role in the germination of resistant conidia of V inaequalis . However, in the mycelial growth stage, alternative respiration does not seem to play a major role for the mode of resistance 5.…”

Characterization of a Split Respiratory Pathway in the Wheat “Take-all” Fungus, Gaeumannomyces graminis var.tritici

“…It was also anticipated that the data would provide information as to the possible induction of the alternative respiratory pathway following inhibition of the primary cytochrome pathway. Inhibitor doses were selected with reference to previous studies with other fungi (2,13,20) and reflect concentrations in excess to that required for 100% inhibition of their respective target sites.…”

“…A recent report, based on whole cell sensitivity studies to the alternative oxidase inhibitor, salicylhydroxamic acid (SHAM), 1 inferred that the alternative oxidase may be more extensively distributed among pathogenic fungal species than had previously been reported (13), but remains to be conclusively demonstrated.…”

Modulators of membrane drug transporters potentiate the activity of the DMI fungicide oxpoconazole against Botrytis cinerea

“…The synergism has been ascribed to inhibition of phosphoramidate metabolism by a phosphorothiolate 3. The fungitoxic activity of mitochondrial bc 1 complex inhibitors such as metominostrobin (Qo site inhibitor), and antimycin A (Qi site inhibitor) can be synergized in Botrytis cinerea Pers, Cochliobolus miyabeanus (Ito & Kuribay) Drechsler ex Dastur, Monilinia fructicola (Winter) Honey, and P oryzae by salicylhydroxamic acid that inhibits the cyanide‐insensitive respiration pathway 4. Mixtures of stereoisomers of the sterol biosynthesis inhibitors cyproconazole or tebuconazole also display synergism 5.…”