Purpose

Continuous cropping of tomato (Solanum lycopersicum Mill.) causes soil degradation, accumulating Ralstonia solanacearum that induce Ralstonia wilt notably in plastic shed soils. Arbuscular mycorrhizal (AM) fungi play a crucial role in protecting hosts against such soil-borne pathogens, but comprehensive understanding of the soil–plant defense systems upon mycorrhization is not clear yet, especially at the later period of fruit production. The aim of this study was to investigate the underlining mechanisms in both soil and plant.

Materials and methods

A 10-week greenhouse pot experiment with four treatments, including control and inoculation with Funneliformis caledonium (Fc), R. solanacearum (Rs), and both strains (Rs + Fc), was carried out on a sterilized soil. Pots with two tomato plants each were randomly arranged with six replicates per treatment. The wilt severity; the tissue biomass and nutrient content; the root mycorrhizal colonization and total phenolic compounds; the leaf peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) activities; and soil AM fungi and R. solanacearum abundances, soil pH, organic C and nutrient concentrations, and phosphatase activity were all tested. Both redundancy analysis (RDA) and structural equation modeling (SEM) were performed to illustrate plant overall performance among treatments and to elucidate the major influencing pathways of AM fungi.

Results and discussion

The additional inoculation with F. caledonium resulted in significant decreases of soil R. solanacearum abundance and Olsen-P concentration, as well as increases of soil pH, organic C concentration, and phosphatase activity, as compared to the soil only inoculated with R. solanacearum. Mycorrhizal inoculation also increased root total phenolic compound content, and leaf POD and PPO activities, but reduced shoot/root K ratio in plants under the attack of R. solanacearum, thereby alleviating Ralstonia wilt severity by 65.7% and yield loss by 46.5%. The RDA and SEM results revealed significant variation in plant overall performance among treatments, and the contribution of AM fungi in suppressing tomato Ralstonia wilt and yield damage particularly via ameliorating soil quality and alleviating plant metabolic pressure.

Conclusions

This study verified the bio-protection of AM fungi in both soil and plant systems against tomato Ralstonia wilt. Mycorrhization shifted the soil environment and suppressed soil R. solanacearum population, and also modulated plant nutrient translocation, increased phenolic compounds synthetization, and activated defense enzymes. Through establishing the integrated defense systems in both rhizosphere and plant, AM fungi alleviated the severity of Ralstonia disease and ameliorated yield damage in tomato.

中文翻译：

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丛枝菌根真菌通过建立土壤-植物综合防御系统抑制番茄 (Solanum lycopersicum Mill.) Ralstonia 枯萎病

目的

番茄的连作（番茄磨。）导致土壤退化，积累青枯雷尔氏菌诱导青枯萎特别是在塑料大棚的土壤。丛枝菌根 (AM) 真菌在保护宿主免受此类土壤传播病原体的侵害方面起着至关重要的作用，但对菌根形成后土壤-植物防御系统的全面了解尚不清楚，尤其是在水果生产后期。本研究的目的是研究土壤和植物中的重要机制。

材料和方法

在无菌土壤上进行为期 10 周的温室盆栽试验，包括对照和接种Funneliformis caledonium ( Fc )、R. solanacearum ( Rs ) 和两种菌株 ( Rs  +  Fc )。每个有两个番茄植株的盆被随机排列，每个处理六个重复。枯萎的严重程度；组织生物量和营养成分；根菌根定植和总酚类化合物；叶过氧化物酶 (POD)、多酚氧化酶 (PPO) 和苯丙氨酸解氨酶 (PAL) 活性；和土壤 AM 真菌和青枯菌丰度、土壤 pH 值、有机碳和养分浓度以及磷酸酶活性都进行了测试。进行冗余分析 (RDA) 和结构方程模型 (SEM) 以说明处理之间的植物整体性能并阐明 AM 真菌的主要影响途径。

结果和讨论

与仅接种青枯菌的土壤相比，额外接种F. caledonium导致土壤青枯菌丰度和 Olsen-P 浓度显着降低，以及土壤 pH、有机碳浓度和磷酸酶活性增加. 菌根接种也的攻击下增加的根总酚化合物的含量，和叶POD和PPO活性，但降低的枝条/根K比值在植物青枯菌，从而减轻青枯萎严重性由65.7％，产率损失46.5％。RDA 和 SEM 结果揭示了处理间植物整体性能的显着差异，以及 AM 真菌对抑制番茄的贡献Ralstonia枯萎和产量损害，特别是通过改善土壤质量和减轻植物代谢压力。

结论

这项研究验证了土壤和植物系统AM真菌的生物保护，防止番茄青枯病枯萎。菌根作用改变了土壤环境并抑制了土壤青枯菌种群，还调节了植物养分转运、增加酚类化合物合成和激活防御酶。通过在根际和植物中建立综合防御系统，AM 真菌减轻了Ralstonia病害的严重程度并改善了番茄产量损失。