Comparative analysis on microbial communities between rhizosphere soils of wilt diseased and healthy papaya

【Objective】Papaya is a tropical fruit with significant potential for further development. However, in recent years, severe outbreak of papaya wilt disease has led to crop failure and severely restricted the development of the papaya industry. This study explores the effects of papaya wilt disease on the diversity and structure of fungal and bacterial populations in the rhizosphere soil of the plants. 【Methods】During the high incidence period of papaya wilt disease from April to May, at the Guangxi Innovation Base for Papaya Germplasm Resources Protection in Nanning, plants with severe wilt disease and healthy plants in the fields of papaya variety Suizhonghong were used as materials. The rhizosphere soil samples collected from healthy plants were labeled as Heath (HS), and those from the diseased plants as (Disease) DS. Five-point sampling method was used for sampling in the affected areas,with one plant taken from each point. The rhizosphere soil of the five affected plants was pooled into one sample and labeled as one replicate. A total of three replicates were taken and labeled as DS 1 to DS 3. Using the same method, three samples of the rhizosphere soil were taken from healthy plants and labelled as HS 1 to HS 3. The obtained samples were stored at -80 ℃. The structure and abundance of fungi and bacteria in the rhizosphere soil samples were determined with high-throughput sequencing of 16S rRNA and ITS. FLASH software was used to concatenate the double ended sequences, and Vsearch software used for mosaic sequence filtering. Clean tags with sequence similarity greater than 97% were designated as OTUs. Species annotation was performed using Blast software to compare and analyze the OUT sequences with RDP databases. Based on the annotation results, top 20 species in terms of relative abundance were selected at the phylum and genus classification levels for each group, bar charts were constructed to analyze the Alpha, Beta, and LeFSe diversity index of OTUs.【Results】The fungal community diversity, species abundance, and evenness in HS samples were higher than the DS ones. The bacterial community diversity, species abundance, and evenness in DS were higher than HS. The results indicates that at the fungal phylum level, the most dominant phyla for HS and DS were Ascomycota. The relative abundance of Chytridiomycota in HS was higher than DS, at 0.48% and 0.04%, respectively. Abundance of Glomeromycota in DS was higher than HS, at 0.59% and 0.09%, respectively. The dominant phyla for both HS and DS in bacteria were Proteobacteria, with a relative abundance of 42.68% in DS and 37.98% in HS. Actinobacteria ranked the second in relative abundance, which was 28.03% in HS and 24.44% in DS. The phylum Acidobacteria ranked the third in relative abundance, being 13.46% in HS and 10.51% in DS. The phyla Latescibacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Nitrospirae in DS were lower than in HS, while the phyla Deinococcus Thermus, Proteobacteria, Candidatus_Saccharibacteria, Chloroflexi, Firmicutes, and Parcubactercandidate- divisionWPS-2 were lower in DS. At the fungal genus level, the dominant genus in HS was Agaricomycetes_unclassified, with a relative abundance of 21.34%, while its relative abundance in DS was only 0.01%. The relative abundances of Pseudogymnnosus, Rhizopycnis, Trechispora, Eurotiomycetes_unclassified, Davidiella, Basidiomycota_uncassified, and Humicola in HS were higher than DS. The dominant genus in DS was Conocybe, with a relative abundance of 18.51%, in contrast to 0.24% in HS. The relative abundances of Cryptococcus, Sphaerobolus, Leucoagaricus, and Gymnopilus were higher in DS than in HS. The relative abundance of Actinomycetales_unclassified bacteria was the highest (7.52% ) in HS, while that of Chujaibacter genus was the highest (7.00%) in DS. The relative abundance of Actinomycetales_unclassified, Gp3, Gaiella, Gp1, Thermomonosporaceae_unclassified, Flavobacterium in DS were lower than HS. The relative abundance of Chujaibacter Bacteria_unclassified, Saccharibacteria genera incertae sedis, Acidimicrobiales unclassified, Thiobacillus, Steroidobacter in DS were significantly higher than HS.【Conclusion】In summary, Agaricomycetes_unclassified, Actinomycetales unclassified, Pseudo Gymnoscus and Thielavia were enriched in HS; Conocybe, Cryptococcus, Chujaibacter and other bacterial genera were significantly enriched in DS. The papaya wilt pathogen changed the structure and stability of the microbial community in the rhizosphere soil, increased bacterial diversity, and reduced fungal richness. The beneficial bacteria in the microbial community exert their advantages to resist the pathogen of papaya wilt disease, while pathogenic bacteria participate in the process of decomposing diseased plants, ultimately leading to the death of the entire plant. The influence of these microbial changes on the incidence of papaya wilt disease and on healthy plant development remains to be fully elucidated through further isolation, purification, identification, and culture of relevant bacterial strains. This research provides a theoretical basis for the occurrence mechanism of papaya wilt disease and the search for effective biocontrol agents for papaya wilt disease.