Study of inhibitory effects and action mechanism of the novel fungicide pyrimorph against Phytophthora capsici.

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.