Abstract
BackgroundBlack shank, caused by the oomycete pathogen Phytophthora nicotianae, is responsible for huge economic losses worldwide. Research has focused on biocontrol to prevent disease and to minimize the use of synthetic fungicides.MethodsWe explored and compared the efficacy of suppressive microflora cultured from soil and roots on the growth of P. nicotianae for controlling the incidence of black shank.ResultsWe found that 31 microfloral communities, enriched from 40 root samples but only 18 microfloral communities from soil samples, were antagonistic to P. nicotianae. In the field experiment, the root functional microflora (RFM) showed a greater suppressiveness of black shank than the soil functional microflora (SFM), while both RFM and SFM altered diversity, composition, structure, and interaction of soil bacterial communities during plant growth. Although the inoculation of RFM onto roots significantly (p < 0.05) decreased microbial diversity, molecular ecological network analysis indicated more possible interactions among soil microbes, while an opposite trend was observed with SFM inoculation. Linear regression analysis revealed that diversity indices were negatively correlated with suppression on the black shank, suggesting that specific taxa (e.g., OTU_322 and OTU_6478) could colonize and be active during plant growth at the expense of microbial diversity. In addition, 18 functional strains, isolated and screened from 3 RMF (12 strains) and 3 SMF (6 strains), were identified as bacterial genera Acinetobacter (12), Enterobacter (1), Bacillus (1), Stenotrophomonas (2), and Citrobacter (2). Spearman’s ranked correlation tests revealed that relative abundances of some OTUs affiliated with genera Acinetobacter, Enterobacter, and Bacillus were significantly (p < 0.05) and positively correlated with the level of disease suppression.ConclusionMicrofloral communities or key functional species isolated from plant roots might be more effective in controlling black shank than those from soil, and they may be developed for disease control.
Highlights
Black shank, caused by the oomycete pathogen Phytophthora nicotianae, is one of the primary diseases of Nicotiana tabacum, and a global concern resulting in huge economic losses (Lucas, 1975)
The antagonism results showed that some microfloral community enrichments could inhibit the growth of P. nicotianae HD1 (Supplementary Table suppression levels were -32.1% (S1)), including 10 Soil of disease plant (DP_S), 8 Soil of healthy plant (HP_S), Root of disease plant (DP_R), and Root of healthy plant (HP_R)
We found that root functional microflora (RFM) had a greater effect on the diversity, composition, and structure of soil bacterial communities during plant growth, and were more effective in controlling black shank compared to SFM, and RFM inoculated more functional strains, which may be more successful in colonizing on plant roots or soil environment, and strengthened the interaction among soil microbial communities
Summary
Black shank, caused by the oomycete pathogen Phytophthora nicotianae, is one of the primary diseases of Nicotiana tabacum, and a global concern resulting in huge economic losses (Lucas, 1975). The traditional approaches to control N. tabacum diseases generally include synthetic fungicides (You et al, 2016), soil removal and replacement, crop rotation (Niu et al, 2017), and/or disease-resistant varieties (Deb et al, 2018). Many disadvantages have been found during the use of those traditional approaches, such as the emergence of fungicide-resistant populations, disruption of local ecosystems, large labor requirements, and threats to human health. It is urgent to develop effective and environmentally friendly methods to control N. tabacum diseases. Black shank, caused by the oomycete pathogen Phytophthora nicotianae, is responsible for huge economic losses worldwide. Research has focused on biocontrol to prevent disease and to minimize the use of synthetic fungicides
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