Effects of seed soaking and foliar spraying of Kalanchoe pinnata aqueous leaf extracts against rice bacterial leaf blight

Abstract

This study aims at evaluating the disease-reducing effects against rice bacterial leaf blight (Xanthomonas oryzae pv. oryzae). Under greenhouse conditions, the activities of the four enzymes [peroxidase (POX), catalase (CAT), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL)] after application of Kalanchoe pinnata aqueous leaf extracts using the combination of seed soaking and foliar spraying were studied. Overall, two extract concentrations [1 and 2% (w/v)] applied as seed soaking combined with the five extract concentrations [1, 2, 3, 4 and 5% (w/v)] applied as foliar spraying were tested. Three application methods were furthermore used for foliar spraying (7 days before pathogen inoculation (DBI), 14 DBI and their combination). Results showed the effects increased with the increase of extract concentrations and durations from application time points prior to pathogen inoculation. The combination of foliar spraying at 7 and 14 DBI provided stronger protection compared to single sprays. The effects involved induced resistance. Indeed, the activities of POX and CAT increased until 4 days after inoculation (DAI) and remained until 7 DAI, while those of PPO and PAL increased similarly then decreased until 7 DAI. Activities of these enzymes increased after pathogen inoculation and reached higher levels with extract applications.