Activity of A Novel Succinate Dehydrogenase Inhibitor Fungicide Pydiflumetofen Against Fusarium fujikuroi causing Rice Bakanae Disease.

New fungicides are tools to manage fungal diseases and overcome emerging resistance in fungal pathogens. In this study, a total of 121 Fusarium fujikuroi isolates were collected from various geographical regions of China and their sensitivity to a novel succinate dehydrogenase inhibitor (SDHI) fungicide 'pydiflumetofen' was evaluated. The 50% effective concentration (EC50) value of pydiflumetofen for mycelial growth suppression ranged from 0.0101 to 0.1012 µg/ml and for conidial germination inhibition ranged from 0.0051 to 0.1082 µg/ml. Pydiflumetofen-treated hyphae showed contortion and increased branching, cell membrane permeability, and glycerol content significantly. The result of electron microscope transmission indicated that pydiflumetofen damaged the mycelial cell wall and the cell membrane, and almost broke up the cells, which increased the intracellular plasma leakage. There was no cross-resistance between pydiflumetofen and the widely used fungicides such as carbendazim, prochloraz, and phenamacril. Pydiflumetofen was found safe to seeds and rice seedlings of four rice cultivars, used up to 400 µg/ml. Seed treatment significantly decreased the rate of diseased plants in the greenhouse as well as in field trials in 2017 and 2018. Pydiflumetofen showed superb results against the rice bakanae disease (RBD), when used at 10 or 20 g a.i./100 kg of treated seeds, providing over 90% control efficacy (the maximum control efficacy was up to 97%), which was significantly higher than that of 25% phenamacril (SC) at 10 g or carbendazim at 100 g. Pydiflumetofen is highly effective against F. fujikuroi growth and sporulation as well as RBD in the field.

[Mineral nutrition niche of rice sheath blight fungus].

By using the principles and methods of niche, this paper studied the mineral nutrition niche of rice sheath blight fungus. The results showed that the mineral nutrition niche breadth of the fungus at rice tillering, booting, heading, and waxing stages was 0.2710, 0.3865, 0.4252 and 0.4817, respectively, i.e., increased with rice growth, but still comparatively narrower, indicating that rice sheath blight fungus only utilized smaller parts of mineral nutrients at various growth stages of rice. The fungus always gave priority to occupy the nutrition niches where Mg, Zn and Si contents were lower, suggesting that Mg, Zn and Si contents had close relations to the resistance of rice against rice sheath blight.

[Microclimatic niche of rice sheath blight fungus].

By using the principles and methods of niche, the microclimatic niche of rice sheath blight fungus was analyzed. The results showed that the integrative effect of ecological factors light intensity, air temperature, and humidity was higher than the effect of each of the factors, and the combination of light intensity and air temperature had higher effect than the other combinations of the three factors. At the tillering, booting, heading, and waxing stages of rice, the microclimatic niche breadth of the fungus was 0.3112, 0.4012, 0.4326, and 0.7365, respectively, i.e., increased with rice growth, and the microclimatic niche occupied by the fungus was mainly with the low light intensity, low air temperature and high humidity as the prior microclimate type.