Study of Inhibitory Effects and Action Mechanism of the Novel Fungicide Pyrimorph against Phytophthora capsici

Abstract

The antifungal activity of the novel fungicide pyrimorph, (E)-3-[(2-chloropyridine-4-y1)-3-(4-tert-butylpheny1)acryloyl]morpholin, against Phytophthora capsici was investigated in vitro. Pyrimorph inhibited different stages in the life cycle of P. capsici including mycelial growth, sporangium production, zoospore release, and cystospore germination with EC(50) values of 1.84, 0.17, 4.92, and 0.09 microg mL(-1), respectively. The effect of pyrimorph on mycelial growth was reduced by the addition of different concentrations of ATP, which suggested that the action mechanism of pyrimorph was connected with impairment of the energy generation system. Meanwhile, pyrimorph exhibited certain inhibition on metabolic approaches of Embden-Meyerhof-Parnas (EMP), tricarboxylic acid cycle (TCA), and hexosemonophosphate (HMP) by measuring the oxygen consumption of pyrimorph combining with three representative inhibitors to the metabolic approaches. The results indicated that pyrimorph could inhibit the approach of HMP significantly. Morphological and ultrastructural studies showed that pyrimorph caused excessive septation and swelling of hyphae, distortion and disruption of most vacuoles, thickening and development a multilayer cell wall, and accumulation of dense bodies. These results suggested pyrimorph exhibited multiple modes of action including impairment of the energy generation system and effect on cell wall biosynthesis directly or indirectly.

Resistance to the Novel Fungicide Pyrimorph in Phytophthora capsici: Risk Assessment and Detection of Point Mutations in CesA3 That Confer Resistance

“…This indicates that pyrimorph might also bind to some unknown protein in addition to CesA3 in P. capsici . It is also consistent with the finding that pyrimorph has multiple modes of action including impairment of the energy generation system and impairment of cell wall biosynthesis [23].…”

“…It exhibits excellent activity against Rhizoctonia solani and some oomycetes such as Phytophthora infestans , Pseudoperonospora cubensis, Peronophythora litchii , and P. capsici [21]–[24]. In sensitive oomycetes, pyrimorph strongly inhibits various asexual stages including mycelial growth, sporangium production, and cystospore germination [23], [24]. Pyrimorph is currently registered in China for the control of Phytophthora blight of pepper ( Capsicum annuum L.) and tomato ( Lycopersicum esculentum Mill) late blight (http://www.chinapesticide.gov.cn).…”

“…Inhibition of P. capsici by pyrimorph might result from multiple modes of action including the impairment of the energy generation system and direct or indirect impairment of cell wall biosynthesis [23]. The mechanism of action for pyrimoph might be similar to that for carboxylic acid amide (CAA) fungicides because CAA-resistant laboratory mutants of P. capsici were also resistant to pyrimorph [26].…”

Studies on Inhibition of Respiratory Cytochrome bc1 Complex by the Fungicide Pyrimorph Suggest a Novel Inhibitory Mechanism

“…In the current study, we followed up on the previous observation that pyrimorph may act on the cellular respiratory chain of pathogenic fungi [20]. We showed that pyrimorph is able to suppress the respiratory chain function at 4 μM concentration by inhibiting the activity of Complex III in isolated mitochondria of P. capsici mycelia (Table 1).…”

“…One CAA member, mandipropamid, was shown to target the pathway of cell wall synthesis by inhibiting the CesA3 cellulose synthases [19]. However, treatment of fungal pathogens with pyrimorph appeared to affect multiple cellular pathways, including, but not limited to, those of cellular energy metabolism and cell wall biosynthesis, either directly or indirectly [20]. Indeed, a recent report has correlated the pyrimorph resistance phenotype in P. capsici with mutations in the CesA3 gene [21].…”