Tanja Mucha-Pelzer

Response of glucosinolate and flavonoid contents and composition of Brassica rapa ssp. chinensis (L.) Hanelt to silica formulations used as insecticides.

Silica-based substances have increased in popularity in recent years as alternative insecticides in horticultural crop protection. However, no research has been conducted into the influence of silica on plant biochemistry. Formulations (Fossil Shield 90.0s, AE R974, AL-06-109, Surround) were applied electrostatically on pak choi. Plants were harvested on two dates to measure immediate (first) and decelerated (second) influence, as well as recovery following the removal of silica formulations. The predominant individual glucosinolate (GS) in pak choi Black Behi was 1-methoxy-3-indolylmethyl GS. A significant increase in total glucosinolate contents in all treatments was measured from the first to second harvest. During the first harvest, no changes in glucosinolate levels in plants were found in any of the treatments. After a 48 h recovery period, two substances showed decreased amounts for indole GS compared to the control. Flavonoids (kaempferol and isorhamnetin) decreased from the first to second harvest. Kaempferol in particular decreased in treated plants from the first to second harvest date. The shading of leaves by silica mainly caused the decrease in secondary metabolites in treated plants. Treatments with silica formulations as an alternative insecticide cause shifts in the composition and contents of bioactive secondary metabolites in Brassica rapa spp. chinensis plants and should, therefore, be used with care to control insects.