Effects of Combined Application of Potassium Silicate and Salicylic Acid on the Defense Response of Hydroponically Grown Tomato Plants to Ralstonia solanacearum Infection

Ni-Hao Jiang,Shi-Han Zhang

doi:10.3390/su13073750

Abstract

Bacterial wilt, caused by soilborne pathogenic bacterium Ralstonia solanacearum, is a serious and widespread disease that affects global tomato production. Both silicon (Si) and salicylic acid (SA) play important roles in enhancing tomato resistance against bacterial wilt, however, their combined effects on the defense responses of infected tomato plants remain unknown. Hence, the combined effects of Si and SA on physiological and biochemical parameters of R. solanacearum-infected tomato plants were investigated. The combination treatment of Si and SA significantly decreased disease incidences, lipoxygenase (LOX) activity and ethylene (ET) production. The combined treatments were more prominent in improving the morphological traits of root systems, such as root length, root surface area, average root diameter and root volume. The activities of polyphenol oxidase (PPO) and peroxidase (POD) and the concentrations of total soluble phenolics (TSPs) and lignin-thioglycolic acid (LTGA) derivatives were significantly increased in the plants with combined treatments. Si in combination with SA could significantly enhance neutral invertase (NI) and acid invertases (AI) activities in the leaves of tomato plants at 3 days post-infection (dpi) compared with application of Si alone. Three defense-related genes, PAL, POD and pathogenesis-related protein 1 (PR1), were significantly induced in Si+SA treatment at 7 dpi when compared with individual application of Si or SA. The expression level of salicylic acid-binding protein 2 (SABP2) was significantly higher for combination treatment when compared with treatment of Si or SA alone. The possible mechanisms involved in the synergistic effects of Si and SA on the control of tomato bacterial wilt were proposed. This study indicates that under hypertonic conditions, the combined application of 2.0 mM potassium silicate (K2SiO3) and 0.5 mM SA had a synergistic effect on the control of tomato bacterial wilt.

Highlights

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops in the world [1]
Si- and/or salicylic acid (SA)-treated susceptible tomato plants were inoculated with R. solanacearum to assess the protective effect of combined application of Si and SA, and the disease development was evaluated daily for 7 days
The bacterial number was measured in different tissues at 1, 3 and 7 dpi, and no significant difference was observed for a bacterial number between Si-treated plants and controls (Figure 2a)

Summary

Introduction

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops in the world [1]. Bacterial wilt, which is caused by the soilborne pathogenic bacterium. Ralstonia solanacearum, is a serious and widespread disease that affects tomato production throughout the world [2,3,4]. Bacterial wilt is managed with synthetic fungicides and by breeding resistant cultivars [6,7,8,9]. Breeding for stable and durable bacterial wilt resistance is a daunting task due to the high degree of genetic diversity and pathogenic variability of R. solanacearum [6,7,8]. Application of chemical agents has been the main strategy for bacterial wilt control, but it may have negative environmental consequences and/or pose risk to humans [6,7,8]. An environment-friendly alternative strategy for bacterial wilt management needs to be developed

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