Screening of azotobacter isolates for PGP properties and antifungal activity

Abstract

Among 50 bacterial isolates obtained from maize rhizosphere, 13 isolates belonged to the genus Azotobacter. Isolates were biochemically characterized and estimated for pH and halo tolerance ability and antibiotic resistance. According to characterization, the six representative isolates were selected and further screened in vitro for plant growth promoting properties: production of indole-3-acetic acid (IAA), siderophores, hydrogen cyanide (HCN), exopolysaccharides, phosphate solubilization and antifungal activity (vs. Helminthosporium sp., Macrophomina sp., Fusarium sp.). Beside HCN production, PGP properties were detected for all isolates except Azt 7 . All isolates produced IAA in the medium without L-tryptophan and the amount of produced IAA increased with concentration of precursor in medium. The highest amount of IAA was produced by isolates Azt 4 (37.69 and 45.86 µg ml -1 ) and Azt 5 (29.44 and 50.38 µg ml -1 ) in the medium with addition of L-tryptophan (2.5 and 5 mM). The isolates showed the highest antifungal activity against Helminthosporium sp. and the smallest antagonistic effect on Macrophomina sp. Radial Growth Inhibition (RGI) obtained by the confrontation of isolates with tested phytopathogenic fungi, ranged from 10 to 48%.

Među 50 izolata bakterija iz rizosfere kukuruza, 13 izolata pripadali su rodu Azotobacter. Izolati su biohemijski karakterisani i ispitana je tolerantnost prema reakciji sredine, koncentraciji soli i rezistentnost na antibiotike. Nakon karakterizacije, odabrano je šest reprezentativnih izolata za dalja ispitivanja PGP svojstava: produkcije indol-3-sirćetne kiseline (IAA), siderofora, cijanovodonične kiseline, egzopolisaharida, fosfosolubilizacije i antifungalne aktivnosti (prema Helminthosporium sp., Macrophomina sp., Fusarium sp.). Osim produkcije HCN, PGP svojstva utvrđena su za sve izolate osim Azt 7 . Najveću količinu IAA produkovali su izolati Azt 4 (37,69 i 45,86 µg ml -1 ) i Azt 5 (29,44 i 50,38 µg ml -1 ) u podlozi sa dodatkom L-tryptophan-a (2,5 i 5 mM). Izolati su ispoljili najveću antifungalnu aktivnost prema Helminthosporium sp., a najmanji antagonostički efekat prema Macrophomina sp. Procenat inhibicije rasta (RGI) dobijen suočavanjem izolata sa ispitivanim fitopatogenim gljivama kretao se od 10 do 48%.