Control of black spot disease caused by Alternaria alternata on jujube (Ziziphus jujuba Mill. cv. Dongzao) using HarpinXoo protein

Abstract

SummaryCurrently, no adequate control measures exist for the fungal disease, black spot (Alternaria alternata (Fr.) Keissler) on ‘Dongzao’ jujube (Ziziphus jujuba Mill. cv. Dongzao). Black spot is an important factor limiting jujube fruit yield under certain conditions. In this study, three concentrations (10, 20, or 30 µg ml–1) of the HarpinXoo protein, or water (negative control), were sprayed onto ‘Dongzao’ jujube trees to control black spot disease. Following HarpinXoo protein treatment, its effects on the control of black spot disease were determined, and the levels of a defence-related substance [i.e., salicylic acid (SA)], and the activities of peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) were measured. The incidence of black spot disease was significantly decreased, compared with water-treated control, fruit by ≤ 88.4%. After 2 d, SA levels, and POD, PPO, and PAL activities in HarpinXoo-treated fruit were clearly higher than those in control fruit. After fruit had been stored for 45 d at 0ºC, SA levels, and POD and PPO activities showed no differences between the HarpinXoo treatments and the controls, but PAL activities in HarpinXoo-treated fruit were lower than those in the controls. The most appropriate concentration of HarpinXoo protein to control black spot disease was 20 µg a.i. ml–1. These results suggest that the HarpinXoo protein induced systemic acquired resistance in ‘Dongzao’ jujube trees and may offer a worthwhile strategy for disease control.