The physiological response of Phalaenopsis × hybridum ‘Innocence’ to biotic stress caused by Pseudococcus longispinus feeding was investigated. The condition of the cytoplasmic membranes expressed by a value of electrolyte outflow (E_L) and TBARS and the activity of antioxidative system enzymes: catalase and peroxidase, and the amount of non-enzymatic antioxidant – proline, were determined. The changes in all the analyzed physiological parameters depended on the duration of the pest feeding. The outflow of electrolytes, TBARS content and catalase activity was the highest in the first period of the experiment (after 24-hour of mealybug feeding). Significant increase of peroxidase activity and proline content was noted after 7 days of insects feeding. The values of all analyzed parameters (except E_L) demonstrated a decreasing tendency after 14 days of P. longispinus feeding. The observed reaction of P. hybridum ‘Innocence’ testifies to mechanisms triggered with the aim of neutralizing the effects of biotic stress and enabling the normal functioning of the cells in the orchid plants colonized by longtailed mealybug.

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