The purpose of this study was to investigate the mechanism and efficacy of Lvnonglin ^®41 compound microbial fertilizer in mitigating black pepper continuous cropping obstacles from the perspectives of soil nutrients, microbial community structure and diversity, so as to provide technical strategies for the industrial cultivation of black pepper in Hainan. Field experiments were conducted on a plot with a history of severe black pepper Fusarium wilt. Four treatments were designed: water control (CK), Lvnonglin^® 41 compound microbial fertilizer (LNL41), compound microorganisms (CM), and bacterial fertilizer nutrient substrate (NS). The incidence of Fusarium wilt in the rhizosphere, plant growth and soil nutrients were measured. Using 16S rDNA sequencing technology, the differences in the occurrence of black pepper Fusarium wilt and the bacterial community structure in the rhizosphere soil under LNL41 application were explored. The results showed that compared with CK, all treatments exhibited certain effects, with the LNL41 treatment being the most effective. Soil nutrient indicators in the LNL41 and CM treatments were significantly higher than those in CK. The increases in chlorophyll content, spike length and 1000-grain weight under LNL41, CM and NS treatments reached 26.12%-67.87%, 6.20%-18.33% and 1.48%-6.44%, respectively. The incidence rates at different growth stages in the LNL41 treatment were 2.67%-15.67%, with control efficacies of 81.64%-90.06%. The Ace and Chao1 indices of rhizosphere soil bacteria increased by 12.82%-20.28% and 12.89%-18.78%, respectively, and the Shannon diversity index increased by 1.05%-3.53%, while the Simpson index showed no significant difference among treatments. At the order level, Chitinophagales, Rhizobiales and Burkholderiales were the dominant bacterial orders. At the genus level, Gaiella, P3OB 42, Lactobacillus, Pseudolabrys and Terrimonas were the dominant bacterial genera. The abundances of the common dominant genus Bacillus and Candidatus Omnitrophus were similar across treatments. Linear discriminant analysis (LEfSe) results indicated the presence of six indicator bacterial taxa in the LNL41 treatment. Ellin6067 and Tepidisphaera showed significant or highly significant positive correlations with soil pH, organic matter, available potassium, ammonium nitrogen and available phosphorus. Network analysis further revealed that the LNL41 treatment enhanced the complexity and stability of the soil bacterial co-occurrence network. Bugbase functional prediction demonstrated that the abundance of stress tolerant functional groups in the LNL41 treatment increased by 5.38 percentage points, while it decreased by 10.43 and 7.25 percentage points in the CM and NS treatments, respectively. LNL41 significantly improved the ratio of soil nutrients, thereby enhancing the structure and functional characteristics of the soil bacterial community, stimulating bacterial stress tolerance functions, promoting black pepper growth, and reducing the incidence of Fusarium wilt.

In this study, Cymbopogon winterianus was used as the experimental material, and the DNA sequence of C. winterianus was sequenced using the Illumina NovaSeq 6000 sequencing platform. The sequencing data were assembled with GetOrganelle v1.7.7.0 software to construct the chloroplast genome. Referring to the known chloroplast genome of C. flexuosus, the chloroplast genome of C. winterianus was annotated, and the genomic characteristics were analyzed and a phylogenetic tree was constructed. The chloroplast genome of C. winterianus was 139 823 bp in length, with a typical circular quadripartite structure. The GC content was 38.45%, and the AT content was 61.55%. It included a large single-copy region (LSC) with a length of 82 214 bp, a pair of inverted repeat regions (IR) with a length of 21 368 bp, and a small single-copy region (SSC) of 14 873 bp. A total of 130 genes were annotated in the chloroplast genome of C. winterianus (including 85 mRNA genes, 37 tRNA genes, and 8 rRNA genes). In addition, among the annotated genes, there were 16 double-copy genes, accounting for 12.31%, including 7 tRNA genes, 4 self-replication genes, 4 rRNA genes, 2 protein genes with unknown functions, and 1 NADH dehydrogenase subunit gene. A total of 144 SSR loci were detected in the chloroplast genome of C. winterianus, with mononucleotide repeats being absolutely dominant, mainly A/T. After comparing the boundaries of the inverted repeat sequences of four Cymbopogon species, it was found that C. flexuosus, C. pospischilii, and C. winterianus exhibited extremely high homology in gene structure and species. Among them, the ndhH gene was located in the small single-copy region (SSC), and the ndhF gene was located in the boundary region between the SSC and IRb. However, C. winterianus had an additional rps3 gene in the LSC region compared with C. flexuosus and C. pospischilii. Phylogenetic tree analysis showed that C. winterianus had the closest genetic relationship with C. pospischilii and C. citratus (MK593547.1). This study completed the assembly and annotation of the complete chloroplast genome of C. winterianus, analyzed the characteristics of the chloroplast genome of C. winterianus, and preliminarily explored the phylogenetic position of C. winterianus within the genus Cymbopogon. It would lay a good foundation for the phylogenetic, genetic diversity, and genomic studies of Cymbopogon plants, as well as for the discovery and utilization of important functional genes.