Potential resistance of tricin in rice against brown planthopper Nilaparvata lugens (Stål)

The aerial parts of resistant rice plant (IR36) was immersed in 85% ethanol at room temperature, and ethanol-soluble extracts were prepared. Different solvents including petroleum ether, ethyl acetate, absolute ethanol, and water were then used to separate the ethanol-soluble extracts and different solvent fractions were obtained. These fractions were tested for their effects on the mortality rate of the brown planthopper nymphae (BPH). The results indicated that EtOAc fractions had significant effects on the mortality of brown planthopper nymphae after the third day of treatment. EtOAc fractions of resistant rice plants (IR36) were separated using column chromatography over silica gel and 5,7,4′ -trihydroxy-3′,5′-dimethoxyflavone (tricin) was isolated. After the BPH were allowed to feed on diets containing tricin for 15 days, it was found that the weight of honeydew of the nymphae showed a decrease as tricin concentrations in the diets increased. The mortality rate of the nymphae increased with increasing tricin concentration. The corrected mortality rate was 58.21% for the 3rd instar nymphae and 31.75% for the 4th instar nymphae, respectively, at 500 μg/ml concentration. In addition, tricin (500 μg/ml) significantly inhibited oviposition behavior and feeding of the brown planthopper females in choice tests when spread on susceptible rice plant (TN1).