Application of Serratia marcescens RZ-21 significantly enhances peanut yield and remediates continuously cropped peanut soil.

BACKGROUND: Continuous cropping practices cause a severe decline in peanut yield. The aim of this study was to investigate the remediation effect of Serratia marcescens on continuously cropped peanut soil. A pot experiment was conducted under natural conditions to determine peanut agronomic indices, soil microorganism characteristics, soil enzyme activities and antagonism ability to typical pathogens at different growth stages. Four treatments were applied to red soil as follows: an active fermentation liquor of S. marcescens (RZ-21), an equivalent sterilized fermentation liquor (M), an equivalent fermentation medium (P) and distilled water (CK). RESULTS: S. marcescens significantly inhibited the two typical plant pathogens Fusarium oxysporum A1 and Ralstonia solanacearum B1 and reduced their populations in rhizosphere soil. The RZ-21 treatment significantly increased peanut yield, vine dry weight, root nodules and taproot length by 62.3, 33, 72 and 61.4% respectively, followed by the M treatment. The P treatment also increased root nodules and root length slightly. RZ-21 also enhanced the activities of soil urease, sucrase and hydrogen peroxidase at various stages. In addition, RZ-21 and M treatments increased the average population of soil bacteria and decreased the average population of fungi in the three critical peanut growth stages, except for M in the case of the fungal population at flowering, thus balancing the structure of the soil microorganism community. CONCLUSION: This is the first report of S. marcescens being applied to continuously cropped peanut soil. The results suggest that S. marcescens RZ-21 has the potential to improve the soil environment and agricultural products and thus allow the development of sustainable management practices.

Decomposition of silicate minerals by Bacillus mucilaginosus in liquid culture.

The extraction of K(+) and SiO(2 )from silicate minerals by Bacillus mucilaginosus in liquid culture was studied in incubation experiments. B. mucilaginosus was found to dissolve soil minerals and mica and simultaneously release K(+) and SiO(2) from the crystal lattices. In contrast, the bacterium did not dissolve feldspar. B. mucilaginosus also produced organic acids and polysaccharides during growth. The polysaccharides strongly adsorbed the organic acids and attached to the surface of the mineral, resulting in an area of high concentration of organic acids near the mineral. The polysaccharides also adsorbed SiO(2) and this affected the equilibrium between the mineral and fluid phases and led to the reaction toward SiO(2 )and K(+) solubilization. These two processes led to the decomposition of silicate minerals by the bacterium.

[Correlation between inhibition activity of endophytic fungus from Euphorbia pekinensis and its host].

To develop endophytic fungi resources from medicinal plants, this paper studied the correlation between endophytic fungus Fusariium sp. ES from Euphorbia pekinensis and its host through analyzing the inhibition activity of this pathogen. An endophytic strain S12 (Alternaria sp.) from Sapium sebiferum was used as contrast. The results showed that E5 had an inhibitory effect on the host, while S12 and E. pekinensis extract didn't have it. The inhibition activity of E5 could be stimulated by the extract of host leaf, and its inhibitory effect could only be found when it was cultured with enough oxygen. The inhibition activity was affected by pH, temperature, and ultra-violet. These characters of endophytic fungus E5 showed a good correlation with its host, and this correlation was mutualism.