Inoculation of Bacillus megaterium strain A14 alleviates cadmium accumulation in peanut: effects and underlying mechanisms

Biochar-immobilized Bacillus megaterium enhances Cd immobilization in soil and promotes Brassica chinensis growth

Phosphate solubilizing bacteria (PSB) has been considered an environmental-friendly phosphate fertilizer without cadmium (Cd) input into soils, but its possibility of Cd fixation in soil needs to be explored. Since direct inoculation results in a rapid decline of the population and activity, we immobilized Bacillus megaterium with maize straw biochar (B-PSB) and investigated its feasibility in remediating Cd-contaminated soil. Pot experiments showed that the application of B-PSB significantly ameliorated the growth of Brassica chinensis under Cd stress, with a fresh weight increased by 59.08% compared to the Cd-control. B-PSB reduced Cd accumulation in Brassica chinensis by 61.69%, and promoted the uptake of P and N by 134.97% and 98.71% respectively. Microbial community analysis showed B-PSB recruited more plant growth-promoting bacteria in near-rhizosphere soil, which provides a favorable microenvironment for both PSB and crops. Column leaching experiments verified that B-PSB achieved the dissolution of stable P while fixing Cd. Batch tests further revealed that biochar served as a successful carrier facilitating the growth of B. megaterium and Cd immobilization. Given the widespread Cd contamination in agricultural soils, our results indicate that B-PSB is a promising soil amendment to secure food safety.

Preinoculation with Endophytic fungus Phomopsis liquidambaris reduced rice bakanae disease caused by Fusarium proliferatum via enhanced plant resistance

AIMS

This study evaluated the control effect of the endophytic fungus Phomopsis liquidambaris B3 against rice bakanae disease (RBD) caused by Fusarium proliferatum and the disease control result of different inoculation times of beneficial micro-organisms.

METHODS AND RESULTS

Rice seedlings preinoculated, coinoculated and noninoculated with B3 were exposed to F. proliferatum stress and grown under controlled conditions. Greenhouse experimental results showed that rice preinoculation with B3 significantly reduced rice bakanae disease by 21.45%, inhibited the colonization of F. proliferatum, increased defence-related enzyme activities, upregulated the expression of defence genes and promoted plant photosynthesis. However, bakanae disease in rice coinoculation with B3 increased by 11.45%, resulted in excessive reactive oxygen species (ROS) bursts and plant cell death.

CONCLUSIONS

Preinoculation with the endophytic fungus P. liquidambaris B3 significantly reduced rice bakanae disease by triggering the SA-dependent defence pathways of plants, and promoted plant growth. However, coinoculatiton with P. liquidambaris B3 activated excessive defence responses, resulting in plants cell death and aggravation of bakanae disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicated that P. liquidambaris B3 was an effective method for agricultural control against rice bakanae disease caused by F. proliferatum, and provides an experimental basis for the development of sustainable endophytic fungal resources to effectively control plant diseases caused by pathogenic fungi, and suggests that precise application of beneficial micro-organisms may be become a key factor in farmland crop disease management.

Role of Nodulation-Enhancing Rhizobacteria in the Promotion of Medicago sativa Development in Nutrient-Poor Soils

Legumes are usually used as cover crops to improve soil quality due to the biological nitrogen fixation that occurs due to the interaction of legumes and rhizobia. This symbiosis can be used to recover degraded soils using legumes as pioneer plants. In this work, we screened for bacteria that improve the legume–rhizobia interaction in nutrient-poor soils. Fourteen phosphate solubilizer-strains were isolated, showing at least three out of the five tested plant growth promoting properties. Furthermore, cellulase, protease, pectinase, and chitinase activities were detected in three of the isolated strains. Pseudomonas sp. L1, Chryseobacterium soli L2, and Priestia megaterium L3 were selected to inoculate seeds and plants of Medicago sativa using a nutrient-poor soil as substrate under greenhouse conditions. The effects of the three bacteria individually and in consortium showed more vigorous plants with increased numbers of nodules and a higher nitrogen content than non-inoculated plants. Moreover, bacterial inoculation increased plants’ antioxidant activities and improved their development in nutrient-poor soils, suggesting an important role in the stress mechanisms of plants. In conclusion, the selected strains are nodulation-enhancing rhizobacteria that improve leguminous plants growth and nodulation in nutrient-poor soils and could be used by sustainable agriculture to promote plants’ development in degraded soils.