Journal of Pesticide Science

Homology modeling of plant 4-hydroxyphenylpyruvate dioxygenase (4-HPPD) was carried out using structural information on the Pseudomonas fluorescens enzyme as a template. A three-dimensional structural model of the barley enzyme was investigated in detail to compare its catalytic pocket with that of the Pseudomonas enzyme. Striking conservation of the catalytic pocket provided a rational basis for designing potent 4-HPPD inhibitors by the in silico docking of compounds and model/template enzymes.

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Synthesis and characterization of anti-rice blast activity of pyrazole derivatives was described. Structure-activity relationship study indicated that a carboxyl group at 5-position of 1-methyl-1H-pyrazole played an important role in the activity and that a halogen atom such as a chlorine or bromine at 3-position enhanced the activity. Among the derivatives, 3-chloro-1-methyl-1H-pyrazole-5-carboxylic acid (CMPA) exhibited the highest anti-rice blast activity with the ED₈₀ (80% effective dose, the concentration needed for 80% inhibition of disease development) of 0.05 mg/pot. CMPA did not have any significant effects on the hyphal growth, spore germination, and appressorium formation of Pyricularia oryzae, suggesting that CMPA induces systemic acquired resistance in rice plants.

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A rapid gas chromatographic method for determining organophosphorus pesticide residues in allium such as onion and welsh onion containing high levels of sulfur-matrices was studied. A sample was extracted with acetonitrile and the acetonitrile layer separated by salting-out. The extract was cleaned up with gel permeation chromatography, and then with a tandem silica-gel/PSA mini-column. The test solution was subjected to gas chromatography with a pulsed flame photometric detector. Organophosphorus pesticide residues in such sulfur-rich matrices were determined without any serious interfering peaks on the chromatograms by diluting the extracts 8-fold (0.25 g/ml of sample). No additional pretreatment to deactivate enzymes which caused interference was necessary. The rate of recovery of 36 organophosphorus pesticides from fortified onion and welsh onion ranged from 61 to 105% with the RSD usually < 10% for five experiments. The detection limits of these pesticides were good (0.002-0.01 mg/kg) for monitoring organophosphorus pesticide residues in agricultural products including allium, except for degradable trichlorfon. The method was applied to onion and welsh onion to demonstrate its use in routine analysis.

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The effects of ethephon spraying on the growth development, flower bud stage and leaf color were studied in a summer-to-autumn-flowering chrysanthemum (Dendranthema grandiflorum (Ramat.) Kitamura) under open field conditions. The growth of all cultivars was slow until the last ethephon spraying stage, but that from the involucre formation stage to the floret formation stage was fast and growth before flowering was slow again. Leaf segments grew after rosette formation at high positions under a schedule of three 200 mg/l ethephon sprayings with 1000 mg/l for strong inhibition of flower bud differentiation. The plant height overtook that achieved with three 200 mg/l ethephon sprayings in ‘Seiun’ and ‘Summer-yellow’ cultivars. First growth using ethephon sprays with pinching was slower that without pinching. Leaf color of flowers treated with ethephon sprays and pinching was more inhibited than that without pinching in all cultivars. Our results showed that, ethephon spraying inhibited early flower bud differentiation, growth of stems and change of leaf color to dark green, however, the stem length was longer than controls because the growth of stems is fast in summer-to-autumn-flowering chrysanthemum.

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