Nitrogen and plant growth regulator affect plant detoxification metabolism and tritrophic interactions among Triticum aestivum, Sitobion avenae and Aphelinus asychis

Abstract

The application of nitrogen fertilizers and plant growth regulators (PGRs) are common agronomic practices in wheat production. To investigate the influence of these two factors on a wheat banker plant system and the associated tri-trophic interactions, we exogenously applied 0, 50, 150 or 250 mg/L indole-3-acetic acid (IAA) on wheat seedlings culti-vated in Hoagland Nutrient Solutions spiked with 0, 640, 1280 or 1920 mg/L NH₄NO₃, and examined performance and biochemical response mechanisms of plants and insects. Results indicated that the application of 1280 mg/L NH₄NO₃ coupled with 150 mg/L IAA increased leaf area of wheat seedlings significantly. In addition to the lower water content, more photosynthetic pigments and higher activity of polyphenol oxidase (PPO), peroxidase (POD) and catalase (CAT) were also detected within this treatment. However, wheat plants with the greatest leaf area did not produce heavier Sitobion avenae. Aphids feeding on seedlings applied with 1920 mg/L NH₄NO₃ coupled with 0 or 50 mg/L IAA treatments showed larger body weight difference, more trehalose and relatively higher activity of detoxification and metabolic enzymes. Moreover, not only did this treatment support the largest aphids, but also medium weight aphids produced the largest para-sitoids Aphelinus asychis, which were produced from seedlings with 1280 mg/L NH₄NO₃ and 250 mg/L IAA, 1920 mg/L NH₄NO₃ and 50 mg/L IAA and 640 mg/L NH₄NO₃ and 50 mg/L IAA. This study provided baseline data for regulating the application of nitrogen and PGRs for optimization of banker plant systems. Moreover, the manipulation of growth conditions of wheat must be considered when comparing different approaches to Integrated Pest Management.