Root Exudates Dominate the Colonization of Pathogen and Plant Growth-Promoting Rhizobacteria

The biocontrol potentials of rhizospheric bacterium Bacillus velezensis K0T24 against mulberry bacterial wilt disease

Mulberry bacterial wilt disease, caused by Ralstonia pseudosolanacearum, is a devastating soil-borne disease in the silk-mulberry-related industry. In this study, through high-throughput sequencing, we compared the rhizosphere bacterial composition of the mulberry-resistant cultivar (K10) and susceptible cultivar (G12), confirming Bacillus as a genus-level biomarker for K10. Next, twelve Bacillus spp. isolates, derived from the rhizosphere of K10, were screened for their antagonistic activity against R. pseudosolanacearum. The isolate showing strong antagonism was identified as B. velezensis K0T24 and selected for further analysis. The fermentation supernatant of B. velezensis K0T24 significantly inhibited the growth of R. pseudosolanacearum (82.47%) and the expression of its pathogenic genes. Using B. velezensis K0T24 in mulberry seedlings also increased defense enzyme activities and achieved a control efficacy of up to 55.17% against mulberry bacterial wilt disease. Collectively, our findings demonstrate the potential of B. velezensis K0T24 in suppressing mulberry bacterial wilt disease.

Linking plant functional genes to rhizosphere microbes: a review

The importance of rhizomicrobiome in plant development, nutrition acquisition and stress tolerance is unquestionable. Relevant plant genes corresponding to the above functions also regulate rhizomicrobiome construction. Deciphering the molecular regulatory network of plant-microbe interactions could substantially contribute to improving crop yield and quality. Here, the plant gene-related nutrient uptake, biotic and abiotic stress resistance, which may influence the composition and function of microbial communities, are discussed in this review. In turn, the influence of microbes on the expression of functional plant genes, and thereby plant growth and immunity, is also reviewed. Moreover, we have specifically paid attention to techniques and methods used to link plant functional genes and rhizomicrobiome. Finally, we propose to further explore the molecular mechanisms and signalling pathways of microbe-host gene interactions, which could potentially be used for managing plant health in agricultural systems.

Appraisal of biofilm forming bacteria in developing buffalo dung-based bioformulation coupled to promote yield of Foeniculum vulgare Mill

Chemical fertilizers impart deleterious effects on crop productivity and its nutrients which is a serious concern among agriculturist. Current research focuses on the commercial preparation of an eco-friendly and cost-effective bioformulation using buffalo dung slurry and beneficial plant growth-promoting (PGP) and biofilm forming strains. 40 strains were isolated from buffalo dung showing PGP activities. Among them, 03 strains were further selected to sequence by 16S rRNA technology and identified as Pseudomonas aeruginosa BUFF12, Proteus mirabilis BUFF14, Enterobacter xiangfangensis BUFF38. The strains were used for consortium preparation on the basis of increase in PGP activity. The consortium of strains increases in vitro PGP attributes at different percentage, i.e., 22% increase in IAA production, 10% increase in siderophore production, 5% increase in P- solubilization, 8% increase in K- solubilization, and 11% increase in S-oxidation. Three carrier materials, i.e., molasses of sugarcane, rice gruel, and buffalo dung slurry, were chosen to conduct the study. Among them, dung slurry proved to be an effective supportive material on the basis of their physico-chemical analysis and viability of strains for long-term storage. It maintained the population mixture of strains (9.4 × 108 cfu/ml) for 120 DAI followed by molasses (9.1 × 108 cfu/ml) and rice gruel (7.9 × 108 cfu/ml). These beneficial strains were further applied in field for crop productivity and slurry-based formulation with mixture of strains exhibited incredible plant growth after definite interval of time. Chemotactic activity proved these strains as strong root colonizers which was confirmed by Field Emission Scanning Electron Microscopy (FE-SEM). This research disseminates a successful technology to develop an eco-friendly bioformulation of buffalo dung slurry augmenting the crop growth in an eco-friendly manner leading to sustainable agriculture.

Differences in Microbial Communities Stimulated by Malic Acid Have the Potential to Improve Nutrient Absorption and Fruit Quality of Grapes

Malic acid is a component of the rhizosphere exudate and is vital for crop growth. However, little information is available about the effects of external applications of malic acid on the nutrient absorption and quality of grape fruit, and few studies have been performed on the relationship between the changes in the rhizosphere microbial community and nutrient absorption and fruit quality of grapes after adding malic acid. Here, the LM (low concentration of malic acid) and HM (high concentration of malic acid) treatments comprised 5% and 10% malic acid (the ratio of acid to the total weight of the fertilizer) combined with NPK fertilizer, respectively. Applying malic acid changed the grape rhizosphere microbial community structure and community-level physiological profile (CLPP) significantly, and HM had a positive effect on the utilization of substrates. The microbial community structure in the rhizosphere of the grapes with added malic acid was closely related to the CLPP. The N and P content in the leaves and fruits increased after applying malic acid compared to the control, while K content in the fruits increased significantly. In addition, malic acid significantly reduced the weight per fruit, significantly increased soluble sugar content (SSC) and vitamin C content of the fruit, and significantly improved the fruit sugar-acid ratio and grape tasting score. Moreover, the principal component analysis and grape nutrient and fruit quality scores showed that grape nutrients and fruit quality were significantly affected by malic acid and ranked as 5% malic acid > 10% malic acid > control. Pearson's correlation heatmap of microbial composition, nutrient absorption and fruit quality of the grapes showed that the grape microbial community was closely related to grape nutrients and fruit quality. Adding malic acid was positively correlated to Planococcaceae, Bacillaceae, Woeseiaceae and Rhodobacteraceae. Furthermore, Planococcaceae, Bacillaceae, Woeseiaceae and Rhodobacteraceae were closely related to grape nutrient absorption and fruit quality. Bacillaceae and Woeseiaceae were positively correlated with total soluble sugar, while Planococcaceae and Rhodobacteraceae were positively correlated with titratable acid. Hence, Bacillaceae and Woeseiaceae were the key bacteria that played a major role in grape fruit quality and nutrient absorption after applying malic acid water-soluble fertilizer.

Identification of the metabolites regulated in soybean-Rhizobia symbiosis through solid phase microextraction coupled with LC-MS

Legumes provide one of the uniquely nutrient-rich food sources to the population and are one of the primary field crops that play significant roles in agricultural sustainability. Inoculation with Bradyrhizobium japonicum is necessary for the high yield of leguminous crops, i.e. soybean. Nodulation of soybean by Bradyrhizobium japonicum is a complex process that is essential for cultivation of these legumes and external stress factors, such as draught and soil acidity, that influence the nodulation and crop yield. Alterations in the nodule metabolites are known to identify the type of stress that mitigates nodulation and lowers crop yield. Current techniques aimed at understanding the metabolic activities in the symbiont, such as in the case of metabolic regulations in varying nodule growth phases, rely on exhaustive techniques based on the removal of nodules or other plant tissue. Aiming to capture a more in-depth, accurate profile of this system without quenching the metabolic activity in the nodules, or removing the nodules, a workflow was prepared for the metabolite sampling through in vivo solid phase microextraction in thin film format (TF-SPME). This technique was followed by LC-QTOF-MS instrumental analysis with subsequent metabolite annotation and reference standard validation. Our approach is unique in terms of eliminating the effects that arise due to analyte partition coefficients. We show that the symbiont undergoes metabolic regulations throughout the cultivation period, displaying the efficacy of TF-SPME as a non-exhaustive sampling method that can be used as a tool to investigate the metabolic alterations in nodules. These alterations would potentially fingerprint the environmental effects on soybean yield.

The impact of sewage sludge on the fungal communities in the rhizosphere and roots of barley and on barley yield

Current problems with sewage sludge (SS) disposal could be solved by application to agricultural land considering its fertilizer properties and ability to improve soil condition. However, SS may contain heavy metals as well as pathogenic microorganisms. In this study, molecular analysis of partial 18S rRNA gene was used to study the impact of SS application into the soil on the genetic diversity of fungal communities, especially arbuscular mycorrhizal fungi in the rhizosphere and roots of barley. These samples were collected on three dates from the control soil without SS and from the soil with the addition of SS at the concentrations of 5 and 15 t ha-1. Fungal alpha diversity in the rhizosphere of barley was affected by SS differently than in barley roots. In addition, principal component analysis and cluster analysis revealed that fungal communities were strongly influenced by the SS addition into the soil, sample type, and the sampling date. This approach was complemented by an evaluation of the basic parameters of barley production and the response of these parameters to the presence of SS in the soil. The plant height increased with increasing SS concentration and the thousand seed weight significantly increased at the concentration of 5 t ha-1 SS but significantly decreased in 15 t ha-1.