Chitosan nanoparticles as a rice growth promoter: evaluation of biological activity.

The agriculture sector is the building block of an economy with more than 60% of the world population depending on it for livelihood. Among the many crops, rice is the most important income source. It is the staple food for more than half of the world population. In spite of its huge demand, rice production has been dwindling due to various constraints. Chitosan nanoparticles (ChNP) are an excellent choice for agricultural applications owing to its non-toxic, biodegradable nature. Chitosan is an interesting polymer and is then partially or fully deacetylated chitin. In the present study, the effectiveness of ChNP as a growth promoter in improving the yield and biological activity of rice has been analyzed. 1 mg/ml of ChNP was applied as a seed, soil, foliar and combination treatments and the growth and yield parameters were measured to understand the best mode of application. The combination treatment of seed, soil and the foliar application was found to be most efficient. The cellular uptake of ChNP was also studied to deduce the mechanism of action. The soil toxicity of ChNP was studied prior to application and was found to be non-toxic.

Characterization of the major antifungal extrolite from rice endophyte Lysinibacillus sphaericus against Rhizoctonia solani.

Sheath blight of rice caused by Rhizoctonia solani is regarded as one of the most widely distributed diseases of rice, and is one of the major production constraints for rice in India and most rice-growing countries of Asia. Biological control of plant diseases using antagonistic bacteria is now considered as a promising alternative to the use of hazardous chemical fungicides or bactericides. Several bacterial endophytes have been reported to support growth and improve the health of the plants and therefore, may be important as biocontrol agents. In the present study, putative antifungal metabolites were extracted from rice foliage endophyte Lysinibacillus sphaericus KJ872548 by solvent extraction methods and purified using HPTLC techniques. Separated bands were subjected to assess the in vitro antagonistic activity toward rice sheath blight pathogen Rhizoctonia solani using a dual culture method. Partially purified active fraction B2 obtained from HPTLC analysis showed the highest percentage of inhibition (76.9%). GC MS and FTIR analyses of B2 revealed the compound as1, 2-Benzenedicarboxylic acid butyl 2-Ethylhexyl ester, a strong antifungal volatile organic compound. Light microscopic analysis of the fungal mycelium from the dual culture plate of both culture filtrate and 1, 2-Benzenedicarboxylic acid butyl 2-Ethylhexyl ester disclosed strong mycolytic activity as evident by mycelial distractions and shrinkage. This is the first report on antifungal production by endophytic Lysinibacillus sphaericus against R. solani, the rice sheath blight pathogen. The findings of this study biologically prospect the endophyte L. sphaericus as an inexpensive broad spectrum bioagent for eco-friendly, economic and sustainable agriculture.

Bioprospecting endophytic diazotrophic Lysinibacillus sphaericus as biocontrol agents of rice sheath blight disease.

The present study tried to explore the possible in vitro biocontrol mechanisms of Lysinibacillus sphaericus, a diazotrophic endophyte from rice against the rice sheath blight pathogen Rhizoctonia solani. The in vivo biocontrol potential of the isolate and the induction of systemic resistance under greenhouse conditions have also been experimented employing different treatments with positive control carbendazim, the chemical fungicide. The endophytic isolate showed 100% growth inhibition of the fungal pathogen via volatile organic compound production and was positive for the production of siderophores, biosurfactants, HCN, and ammonia. Under greenhouse conditions, foliar and soil application of L. sphaericus significantly decreased the percentage of disease incidence. All bacterized treatments are superior to chemical fungicide treatment. Application of L. sphaericus in single and combination treatments induces systemic resistance as evident from the significant accumulation of defense enzymes such as peroxides, polyphenol oxides and phenylalanine ammonia in addition to the increase of phenolic compounds. The results biologically prospect endophytic diazotroph L. sphaericus as a potent plant growth promoter with excellent biocontrol efficiency.

Growth enhancement of rice (Oryza sativa) by phosphate solubilizing Gluconacetobacter sp. (MTCC 8368) and Burkholderia sp. (MTCC 8369) under greenhouse conditions.

Two indigenous rhizospheric phosphate solubilizing isolates PSB 12 identified as Gluconacetobacter sp. (MTCC 8368) and PSB 73 identified as Burkholderia sp. (MTCC 8369) were examined for their growth enhancement potential of rice (Jyothi PTB 39) under pot culture assays. The results showed significant impact on microbial count and PSB population, phosphatase and dehydrogenase activity, available phosphorous in the soil, plant nutrient uptake and yield parameters. Gluconacetobacter sp. + RP60 treatment (30.96 µg PNP g-1 soil) retained highest phosphatase activity whereas Gluconacetobacter sp. + Burkholderia sp. + RP60 treatment recorded maximum dehydrogenase activity (38.88 µg TPF g-1 soil) after 60 days of treatment. The treatments Burkholderia sp. + RP60 and Gluconacetobacter sp. + RP60 produced comparable amount of P and these treatments were statistically at par throughout the growth period. Highest nutrient uptake and yield was noted in Gluconacetobacter sp. + Burkholderia sp. + RP60 treatment. A positive synergistic interaction between strains of Gluconacetobacter sp. and Burkholderia sp. has been noticed for their plant growth promotion activity. These strains could be of potential to develop as biofertilizers after testing their performance under field conditions either alone or as components of integrated nutrient management systems.