Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici has severely threatened sustainable greenhouse tomato production. However, the effects of nutrient enrichment due to excessive fertilization on Fusarium wilt remain unclear. This study aimed to investigate the relationships among soil nutrient enrichment, microbial community structure, and the occurrence of Fusarium wilt under greenhouse conditions. This study used chemical analysis and microbiological techniques to analyze rhizosphere soil samples from greenhouse tomato production areas with varying degrees of Fusarium wilt. The results showed that, as compared with the Health group, the rhizosphere soil of Disease group has a significant nutrient enrichment, which significantly influences bacterial diversity and structure. Particularly when soil NO₃⁻–N content exceeds 170.43 mg kg⁻¹, there was a significant reduction in the relative abundance of key biocontrol bacteria such as Bacillus and Lysinibacillus. This reduction indirectly contributes to an increase in Fusarium oxysporum abundance, subsequently elevating the likelihood of pathogen infection. Furthermore, the Disease group also exhibited a simplified co-occurrence network with a 22.37% reduction in competitive interactions between bacteria and fungi. These changes might collectively increase the risk of tomato Fusarium wilt infection. Meanwhile, the relative abundance of bacteria carrying antibiotic resistance genes significantly increased in the Disease group, which also reduced soil resistance. Together, the results presented here not only uncover the effect of long-term excessive fertilization on the occurrence of Fusarium wilt but also advance our understanding of the interactions among soil nutrient management and microbial communities in the tomato rhizosphere, which provides a scientific basis for formulating strategies to prevent soil-borne diseases in greenhouse tomatoes.

Polyethylene (PE) microplastics (MPs) from residual mulch films are prevalent in peanut-cultivated soils, yet their specific effects on peanut nodulation remain unclear. This study investigated the impacts of PE-MPs at concentrations of 0.2%, 0.6%, and 1.0% on peanut nodulation. Results indicated that PE-MPs significantly reduced peanut nodule number. Transcriptome analysis revealed that all three concentrations of PE-MPs down-regulated nodulation-related flavonoids, promoted lignin deposition in cell walls, disrupted antioxidant system, and enhanced the accumulation of antimicrobial substances, collectively impairing peanut nodulation efficiency. These findings indicate that PE-MPs substantially compromise the symbiosis between peanut and rhizobia, and provide insights into their interference with plant–beneficial microbe interactions in contaminated soils.

Introduction: In the symbiotic interaction between legumes and rhizobia, the induction of peanut super-nodulation by Type II Bradyrhizobium strains represents a relatively unusual phenomenon, yet the underlying regulatory mechanisms remain largely unclear. Methods: This study investigated the roles of both nod genes and chromosomal genes of the Type II strain B. guangxiense CCBAU 53363 ^T (II-53363) in regulating peanut nodulation. Results: First, all Type II strains harbor identical plasmid-borne nod genes, which are distinct from their Type I homologs. Knockout and complementation of nodB and nodC genes resulted in the loss and restoration, respectively, of the nodulation phenotype in II-53363. Second, through Tn 5 transposon insertion along with targeted gene knockout and complementation, we identified seven chromosomal genes that positively regulate peanut super-nodulation. Disruption of these genes affected the metabolic capacity and EPS production of strain II-53363. Nevertheless, given their absence in some Type II strains and their high sequence similarity to Type I homologs, these chromosomal genes are likely to play an indirect role. Discussion: This study demonstrates that the plasmid-borne nod genes in Type II bradyrhizobia strains are essential for peanut nodulation, although their specific contribution to super-nodulation remains to be demonstrated. Furthermore, it reveals the indirect roles of multiple chromosomal genes in regulating peanut super-nodulation.

Legume–rhizobium symbiosis represents a crucial biological nitrogen fixation system. The AP2/ERF transcription factor ERN1 plays a vital role in nodulation of model legumes; however, its function in peanut (Arachis hypogaea), a typical crack-entry infection legume, remains unclear. To explore this, we performed transcriptome sequencing of peanut roots at 3 days post-inoculation (dpi) with rhizobium. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that differentially expressed genes (DEGs) were mainly enriched in DNA-binding transcription factor activity, plant–pathogen interaction, and plant hormone signal transduction pathways. The most strongly up-regulated gene was AhERN1, which was highly expressed in peanut roots and nodules. Subcellular localization indicated that AhERN1 was a nuclear-localized protein, and yeast transcriptional activation assays confirmed that AhERN1 functions as a transcriptional activator relying on its C-terminal domain. Furthermore, hairy root overexpression of AhERN1 significantly increased the number of peanut nodules. Collectively, these results reveal that AhERN1 acts as a positive regulator to promote rhizobium-induced nodule development in peanut, providing new insights into the regulatory mechanism of nodulation in dalbergoid legumes.