Biostimulatory Potential of Microorganisms from Rosemary (Rosmarinus officinalis L.) Rhizospheric Soil

Summary The objective of the present paper was to isolate microorganisms (Pseudomonas sp., Bacillus sp. and Azotobacter sp.) from the rhizospheric soil of rosemary (Rosmarinus officinalis L.) and investigate their biostimulatory (plant growth-promoting – PGP) and biocontrol potential. The bacteria isolated from the rhizosphere of rosemary included 15 bacteria of the genus Pseudomonas, 20 of the genus Bacillus, and 11 of the genus Azotobacter. Based on the morphological characteristics of colonies and cells, representative isolates of each genus were chosen (marked as Pseudomonas sp. P42, P43, P44; for Bacillus isolates B83, B84, B85, B92, B93; and for Azotobacter isolates A15 and A16) for different physiological and biochemical examination. The study included in vitro screening of the bacterial isolates for their PGP and biocontrol properties. Pseudomonas isolates showed the ability to live at low temperature (10ºC) and high pH (9), and to use different sources of carbon. All Pseudomonas isolates produced lipase, siderophore, hydrogen cyanide, and utilized organic and inorganic phosphorus, while only isolate P42 produced amylase, pectinase and cellulase. Only Bacillus isolates could grow at 45 ºC (all Bacillus isolates), pH 5 (isolates B83), and on a medium containing NaCl 5 and 7% (all isolates). Isolates denoted as B83 and B93 produced lipase, amylase, and pectinase. All isolates had the ability to solubilize phosphate, produce siderophores (except B85) and hydrogen cyanide, while only two isolates (B84 and B85) produced IAA. Azotobacter isolates had the optimal growth at 37ºC and minimal growth on a medium with pH 6 and 9. All Azotobacter isolates used all carbohydrates as a source of carbon and produced lipase, amylase, and hydrogen cyanide. The best result in suppressing the growth of pathogenic fungi Fusarium oxysporum was achieved by using isolate B92. Application of isolate B83 led to the greatest growth suppression of Sclerotinium sclerotiorum.