Antifungal potential of Azotobacter species and its metabolites against Fusarium verticillioides and biodegradation of fumonisin.

AIMS: In the study, seven Plant Growth Promoting Rhizobacteria (PGPR) Azotobacter species were screened against three strains of Fusarium verticillioides to test its antifungal activity. Azotobacter strains were tested for the degradation of fumonisin produced by F. verticillioides. Secondary metabolites were isolated and characterized from the Azotobacter strains for the first time. METHODS AND RESULTS: Potential seven Azotobacter species antifungal activity was tested following the dual culture assay against three strains of Fusarium verticillioides namely FVM-42, FVM-86 and MTCC156 estimating the substantial zone of inhibition. Azotobacter species AZT-31 and AZT-50 strains significantly inhibited the growth of F. verticillioides recording drastic growth enhancement of maize under in-vitro conditions by calculating the infection incidence, vigour index and germination percentage. As confirmation, dereplication studies were conducted for the reconfirmation of Azotobacter strains by isolating from rhizoplane. Azotobacter strains played a key role in the degradation of fumonisin produced by F. verticillioides reporting 98% degradation at 2 h of incubation with the pathogen. Furthermore, in the study first time, we have tried to isolate and characterize the secondary metabolites from the Azotobacter strains exhibiting six compounds from the species AZT-31 (2) and AZT-50 (4). Preliminary in-vitro experiments were carried out using the compounds extracted to check the reduction of infection incidence (90%) and increase in germination percentage upto 50 to 70% when compared to the test pathogen. CONCLUSION: Azotobacter strains referred as PGPR on influencing the growth of plant by producing certain substances that act as stimulators on inhibiting the growth of the pathogen. SIGNIFICANCE AND IMPACT OF THE STUDY: The future perspective would be the production of an active combination of carboxamide compound and Azotobacter species for preventively controlling the phytopathogenic fungi of plants and crops and also towards the treatment of seeds.

Antifungal Potential of Azotobacter salinestris Strain Azt 31 against Phytopathogenic Fusarium spp. Associated with Cereals.

Antifungal efficacy of Azotobacter salinestris against trichothecene-producing Fusarium spp. was investigated in maize, sorghum, and wheat. The three cereals were subjected to four treatments as control (T1), Fusarium alone (T2), combination of Fusarium and A. salinestris treatment (T3), and only A. salinestris (T4). All the treatments were evaluated for total mass of seedlings, root and shoot length, seed germination, and vigor index (VI), and extent of rhizoplane colonization by A. salinestris was investigated. Further, greenhouse studies were conducted to learn the efficacy of A. salinestris in vivo conditions. Antifungal efficacy was tested by the dual-culture method which resulted in significant reduction in Fusarium growth. Infection by Fusarium was reduced up to 50% in treated cereals such as maize, sorghum, and wheat, and there was also significant increase in seedling mass in the three hosts. Maize showed the highest VI (1859.715), followed by sorghum (1470.84), and wheat (2804.123) with A. salinestris treatment. In addition, seed germination was enhanced to 76% in maize, 69% in sorghum, and 68% in wheat, respectively. Efficacy of rhizoplane colonization showed successful isolation of A. salinestris with high CFU rate, and furthermore, significant colonization inhibition by Fusarium spp. was observed. In the greenhouse conditions, on the 45th day of the experimental set-up, the highest shoot length/root length recorded in maize was 155.70/70.0 cm, in sorghum 165.90/48.0 cm, and in wheat 77.85/56.0 cm, and the maximum root mass recorded was 17.53 g in maize, 4.52 g in sorghum, and 1.90 g in wheat. Our present study showed that seed treatment by A. salinestris, may be used as an alternate biocontrol method against Fusarium infection in maize, sorghum, and wheat.

Antifungal activity of Azotobacter nigricans against trichothecene-producing Fusarium species associated with cereals.

Antifungal efficacy of Azotobacter nigricans on Fusarium infection, total seedlings mass, root and shoot length, and seed germination in maize, sorghum, and wheat were investigated. Antifungal efficacy of A. nigricans against Fusarium sporotrichioides, Fusarium graminearum, Fusarium poae and Fusarium equiseti showed a significant reduction in growth and Fusarium infection incidence (up to 50%) in all the three treated cereals. However, challenge inoculation of Fusarium spp. to the three cereals showed 100% infection incidence. Total mass of the maize seedlings increased two fold by A. nigricans treatment; however, only a slight increase was observed in sorghum and wheat seedlings. The highest vigour index recorded in maize was 1321 against Fusarium crookwellense, 1616.71 against Fusarium sporotrichioides in sorghum, and 1584.8 against Fusarium acuminatum in wheat treated with A. nigricans. Highest germination incidence of 64% was in maize, 67% in sorghum, and 56% in wheat treated with A. nigricans.

Pesticide tolerant Azotobacter isolates from paddy growing areas of northern Karnataka, India.

A total of 14 Azotobacter strains were isolated from different paddy cultivating soils with pH ranging from 6.5 to 9.5 by using serial dilution agar plate method. The strains were Gram negative, rod shaped, cyst forming and developed brown to black colored colonies, which were glistening, smooth, slimy on Ashby's agar plates. Biochemically they were positive for biochemical tests namely, indole production, citrate, catalase, carbohydrate fermentation and Voges-Proskauer test. Further, sequence analysis of PCR amplicons obtained from these cultures revealed the presence of five different Azotobacter species viz., Azotobacter vinelandii, Azotobacter salinestris, Azotobacter sp., Azotobacter nigricans subsp. nigricans and Azotobacter tropicalis. Phylogenetically these strains were grouped into two distinct clusters. These strains were tested for their ability to grow on a media containing four different pesticides such as pendimethalin, glyphosate, chloropyrifos and phorate, which are commonly used for the paddy. Out of 14 strains tested, 13 strains were able to grow on a media containing herbicides such as pendimethalin, glyphosate and insecticides like chloropyrifos and phorate. However, five Azotobacter strains were able to grow at higher concentration of 5% pesticides, without affecting their growth rate. Further, the effect of pesticides on the indole acetic acid (IAA) production by Azotobacter strains was also estimated. Azotobacter-16 strain was found to produce 34.4 µg ml(-l) of IAA in a media supplemented with 1,000 mg of tryptophan and 5% of pendimethalin. Present study reveals that species of Azotobacter are able to grow and survive in the presence of pesticides and no significant effects were observed on the metabolic activities of Azotobacter species.