Abstract
Tomato bacterial wilt (BW) caused by Ralstonia solanacearum seriously restricts tomato production and no effective control measures are available. A microbial restoration substrate (MRS) had been proved to be effective control of tomato BW in a greenhouse cultivation. In this study, MRS was combined with an avirulent Ralstonia solanacearum (aRS) strain to control the disease under an open field condition. In the two consecutive year (2017 and 2018) trials, the combined use of aRS and MRS resulted in better disease control compared with either aRS or MRS alone. Moreover, the combined treatment was more effective than expected and suggesting a synergistic control effect. Compared with control (CK, non-aRS or MRS), the application of aRS and MRS treatments alone or in combination could all promote plant growth, increase root activity and yield (e.g. the yield for the treatment of aRS + MRS increased by 463.64% in 2017). Soil nutrients, including soil organic carbon, total nitrogen, total phosphorus and total potassium contents were also significantly increased by the application of aRS and MRS treatments alone or in combination (P < 0.05). The application of MRS or in combination with aRS changed the soil from acidic to neutral, which is one of the key factors for controlling BW. The soil enzymatic activities were notably influenced by the combined use of aRS and MRS, which increased urease (87.37% in 2017 and 60.89% in 2018), catalase (93.67% in 2017 and 279.37% in 2018) and alkaline phosphatase activities (193.77% in 2017 and 455.73% in 2018). These results suggest that the combination of MRS and aRS could effectively control tomato BW and thus represents a promising new tool to control this disease.
Highlights
The tomato (Solanum Lycopersicum L.) is one of the world’s main vegetable crops, and it is cultivated worldwide for fresh vegetable consumption or for processing[1]
Based on previous studies under greenhouse cultivation, we further investigated a combination of the biocontrol agent R. solanacearum FJAT-1458 with the soil amendment microbial restoration substrate (MRS) in control of tomato bacterial wilt (BW) under open field cultivation
The results showed that disease incidence was negatively correlated with soil pH and with soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), TK and the exchangeable calcium contents, with correlation coefficients of −0.54, −0.62, −0.42, −0.71, −0.84 and −012, respectively (Table 5), which indicated that high soil pH and high SOC, TN, TP, TK and exchangeable calcium contents are beneficial for plant health
Summary
The tomato (Solanum Lycopersicum L.) is one of the world’s main vegetable crops, and it is cultivated worldwide for fresh vegetable consumption or for processing[1]. Biocontrol emerges as an environmentally friendly strategy and popular method to suppress tomato BW disease[8,9], and several biocontrol agents have been isolated from the rhizosphere soil or plant tissues, such as Bacillus spp.[10], Streptomyces spp.[11] and avirulent mutants of R. solanacearum[12,13,14], which have shown antagonistic effects against pathogenic R. solanacearum. A type of microbial restoration substrate (MRS) was used to amend 7-year continuous cropping tomato soil under a greenhouse cultivation and proved to be effective in reducing the severity of BW22. Based on previous studies under greenhouse cultivation, we further investigated a combination of the biocontrol agent R. solanacearum FJAT-1458 with the soil amendment MRS in control of tomato BW under open field cultivation. The objectives of this study were (i) to evaluate the potential biocontrol abilities of the avirulent strain FJAT-1458 in combination with the microbial restoration substrate against BW, and (ii) to investigate their mode of action and effect on properties of tomato rhizosphere soils
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