Seed Soaking Using Methanol Kalanchoe pinnata Leaf Extracts Induces Rice Resistance against Bacterial Leaf Blight

Bacterial leaf blight (Xanthomonas oryzae pv. oryzae) is a significant rice disease. Aqueous crude extracts of Kalanchoe pinnata were shown to induce rice resistance against the disease. This study aims at testing the disease-reducing effects of K. pinnata leaf extracts using the liquid–liquid extraction method with three different solvents (dichloromethane, methanol, and water). This serves as a basis to select appropriate extracts for effective disease control. Three concentrations (1, 1.5, and 2%) of each extract were tested using seed soaking. The extracts did not show adverse effects on seed germination and seedling growth. Methanol extracts showed significantly different effects compared to those of the untreated control. The involvement of induced resistance in the disease reduction was shown through activities of the four defense-related and antioxidant enzymes, i.e., peroxidase (POX), catalase (CAT), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL). Using 1% methanol extract, activities of POX and CAT involved in hydrogen peroxide production in rice tissues increased 1–4 days after pathogen inoculation (DAI) and remained at high levels until 6 DAI. Activities of PPO and PAL involved in resistance signaling pathways significantly increased after pathogen inoculation. Activities of the four enzymes generally increased after pathogen inoculation and reached higher levels with extract applications.