Effect of foliar application of Silicic acid on biological parameters of Lipaphis erysimi (Kaltenbach) and activity of plant defensive enzymes in rapeseed

Silicic acid (SA) is an important source of silicon (Si) that induces resistance in plants against insect pests. The present study aimed to investigate the impact of foliar spray of SA on the biological parameters of aphid, Lipaphis erysimi and the activity of defensive enzymes in rapeseed (Brassica napus L.). The first experiment evaluated the biological parameters of L. erysimi with two treatments viz., foliar application of 0.4% SA and a control. The results indicated that the foliar spray of 0.4% SA in rapeseed significantly reduced the nymphal period, adult longevity and fecundity of L. erysimi compared to the control. In the 0.4% SA- treated rapeseed, the nymphal period, adult longevity and fecundity of L. erysimi were 7.00 days, 7.96 days and 23.52 nymphs/ female, respectively, while in the control, these were 7.92 days, 8.80 days and 26.04 nymphs/ female, respectively. Furthermore, the foliar application of 0.4% SA significantly enhanced the Si content (0.31%) in rapeseed compared to control (0.16%). The second experiment aimed to investigate the activity of plant defensive enzymes in rapeseed with four treatments: 0.4% SA alone, aphid alone, 0.4% SA + aphid and a control. The results revealed no significant changes in the activity of defense related enzymes such as peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia- lyase (PAL) in the treatments of 0.4% SA alone and the control. However, a significant increase in enzyme activities were observed in both the 0.4% SA + aphid and aphid alone treatments. Notably, the 0.4% SA + aphid exhibited higher levels of plant defensive enzymes activity compared to the aphid alone treatment, suggesting the role of Si in enhancing the defensive responses in rapeseed against L. erysimi. Additionally, this study established a significant negative correlation between Si content and biological parameters of L. erysimi.