RESUMEN
Rehmannia glutinosa, a perennial herbaceous species, belongs to the family Scrophularia-ceae. As a staple medicinal material, its tuberous roots are highly valued in traditional Chinese medicine. However, R. glutinosa suffers from serious consecutive monoculture problems in production, which leads to a decline in both productivity and quality. Phyllosphere bacteria, the most abundant component of phyllosphere microorganisms, play crucial roles in plant growth and health. Characterization of phyllosphere bacteria could provide new insights into the mechanisms of consecutive monoculture problems and their control measures. Meanwhile, the varied taxa could be served as an important indicator of consecutive monoculture problems. The barcoded pyrosequencing of 16S rDNA genes combined with a culture-dependent approach was applied to characterize the shifts of bacterial community structure and diversity in the phyllosphere under consecutive monoculture of R. glutinosa. The results showed that consecutive monoculture clearly affected bacterial community structure in the phyllosphere. The phyllosphere bacterial communities of the two-year monocultured (TY) and the diseased plants (DP) were more similar, and different from the one-year monocultured (OY). The evenness, Shannon and Simpson diversity indices were significantly lower in TY and DP than in OY. Species annotation showed that bacterial community in R. glutinosa phyllosphere mainly consisted of Proteobacteria (91.2%), Firmicutes (5.1%) and Actinobacteria (3.7%). There was no significant difference in the number of detected bacterial taxa. However, Proteobacteria was significantly increased while Firmicutes and Actinobacteria were significantly decreased under consecutive monoculture. At the genus level, the relative abundances of genera Exiguobacterium, Bacillus and Arthrobacter, potentially beneficial microorganisms, were significantly higher in OY than that in TY and DP, but it was opposite for the genus Pseudomonas. The results from the culture-dependent approach and pathogenicity test showed that Pseudomonas plecoglossicida D9, widely isolated from the diseased leaves, was highly pathogenic to leaves. In conclusion, R. glutinosa monoculture resulted in distinct phyllosphere bacterial community variation with the accumulation of pathogen loads at the expense of beneficial microorganisms, which could contribute to the occurrence of leaf disease symptoms,and aggravate R. glutinosa replant disease in a monoculture regime.
Asunto(s)
Rehmannia , Bacterias , ADN Ribosómico , Raíces de Plantas , PseudomonasRESUMEN
Pseudostellaria heterophylla is a perennial herbaceous plant in the family Caryophyllaceae. The tuberous roots of P. heterophylla are highly valued in traditional Chinese medicine and have a high market demand. However, extended monoculture of P. heterophylla results in a significant decline in the biomass and quality, and escalates disease and pest problems. Therefore, it is important to understand the underlying mechanism and biocontrol methods for consecutive monoculture problems. With "Zheshen 2" as an experimental material, the changes in the contents of main nutrients in soil, phenolic acids and specific microbes under monoculture and different amendments were analyzed by using high performance liquid chromatography (HPLC) and qPCR. The results showed that consecutive monoculture of P. heterophylla led to a decrease in yield by 43.5% while the microbial fertilizer treatment and the paddy-upland rotation could relieve the consecutive monoculture problems. Available nitrogen, available phosphorus, available potassium and total potassium were significantly higher in the consecutively monocultured soils than in the newly planted soils. But consecutive monoculture resulted in soil acidification. HPLC analysis showed that conse-cutive monoculture of this plant did not lead to a consistent accumulation of soil phenolic acids. At middle stage of root expansion and at harvest stage, most of phenolic acids were even higher in the newly planted soils than in the consecutively monocultured soils. Furthermore, qPCR analysis showed that the amounts of three specific pathogens identified previously (i.e. Fusarium oxysporum, Talaromyces helicus, Kosakonia sacchari) were significantly higher in the consecutively monocultured soils than in the newly planted soils. However, the microbial fertilizer treatment and the paddy-upland rotation resulted in a significant decline in the population of these specific pathogens and improved the soil environment. In conclusion, the consecutive monoculture problems of P. heterophylla may be due to the rapid proliferation of host-specific pathogens, rather than the deficiency of soil nutrients and the autotoxicity of allelochemicals in root exudates. The results in this study could provide the theoretical basis to explore the underlying mechanism of replanting disease of P. heterophylla and its biocontrol strategies.