SEED SOAKING COMBINED WITH FOLIAR SPRAYING USING AQUEOUS Kalanchoe pinnata LEAF EXTRACTS INDUCES RICE RESISTANCE AGAINST BACTERIAL LEAF BLIGHT (Xanthomonas oryzae pv. oryzae)

Abstract

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae is an important rice disease. This paper presents the disease-reducing effects of aqueous Kalanchoe pinnata leaf extracts using seed soaking combined with foliar spraying and the involvement of induced resistance in the observed disease reduction. The extracts were prepared by the liquid-liquid extraction method. Three application methods using three extract concentrations (1, 1.5 and 2%) were tested under greenhouse conditions. The application methods included (1) seed soaking + foliar spraying 14 days before inoculation (DBI), (2) seed soaking + foliar spraying 7 DBI and (3) seed soaking + foliar spraying 14 and 7 DBI. The disease was assessed through lesion lengths at 7, 14 and 21 days after inoculation (DAI). Seed soaking combined with foliar spraying at 14 DBI using 1.5% extract maintained the disease-reducing effect until 21 DAI. Induced resistance involved in the observed disease reduction through activities of the four defense-related and/or antioxidant enzymes, i.e., peroxidase (POX), catalase (CAT), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL). Indeed, activities of these enzymes increased with the presence of either pathogen inoculation or extract application and reached higher levels with the presence of both pathogen inoculation and extract application (seed soaking combined with foliar spraying).