Abstract
The characterized 10 Streptomyces isolates were previously selected by their abilities to solubilize phosphates. To investigate whether these isolates represent multifaceted plant growth-promoting rhizobacteria (PGPR), their potassium-solubilizing, auxin-producing and inhibitory activities were determined. The 10 Streptomyces spp. yielded a variable biomass in the presence of insoluble orthoclase as the sole potassium (K) source, indicating that they were able to extract different amounts of K from this source for their own growth. Three strains (AZ, AYD and DE2) released soluble K from insoluble orthoclase in large amounts into the culture broth. The production levels ranged from 125.4 mg/L to 216.6 mg/L after 5 days of culture. Only two strains, Streptomyces enissocaesilis (BYC) and S. tunisiensis (AI), released a larger amount of soluble K from orthoclase and yielded much more biomass. This indicated that the rate of K released from this insoluble orthoclase exceeded its consumption rate for bacterial growth and that some strains solubilized K more efficiently than others. The results also suggest that the K solubilization process of AZ, AYD and DE2 strains, the most efficient K-solubilizing strains, involves a slight acidification of the medium. Furthermore, these 10 Streptomyces spp. were able to secrete indole acetic acid (IAA) in broth medium and ranged from 7.9 ± 0.1 µg/mL to 122.3 ± 0.1 µg/mL. The results of the antibiosis test proved the potential of the 10 tested strains to limit the growth of fungi and bacteria. In dual culture, S. bellus (AYD) had highest inhibitory effect against the three identified fungal causal agents of root rot of sugar beet: Fusarium equiseti and two F. fujikuroi at 55, 43 and 36%, respectively. Streptomyces enissocaesilis (BYC), S. bellus (AYD) and S. saprophyticus (DE2) exhibited higher multifaceted PGPR with their potassium-solubilizing, auxin-producing and inhibitory activities, which could be expected to lead to effectiveness in field trials of sugar beet.
Highlights
One of the most commonly cultivated plants used in the sugar industry is sugar beet (Beta vulgaris L.)
Ten selected Actinomycete strains used in this study were isolated from three different sugar beet rhizospheres that were previously selected for their abilities to solubilize insoluble phosphate forms using the SMM medium and to produce siderophores [40]: AYD, AZ, AV and BX related to Streptomyces bellus; BYC: Streptomyces enissocaesilis; AI: Streptomyces tunisiensis; BP: Streptomyces coerulescens; CYM: Streptomyces cyaneofuscatus; DE1: Streptomyces bellus and DE2: Streptomyces saprophyticus
This indicated that the strains were able to assimilate variable amounts of potassium from these insoluble K sources, with a different efficiency, and use it for their own growth
Summary
One of the most commonly cultivated plants used in the sugar industry is sugar beet (Beta vulgaris L.). In Morocco, sugar beet occupies an area of. 57,171 hectares with a production of 3.7 million tons in 2019 [3]. Microorganisms 2021, 9, 1429 region (east of Casablanca), located in a vast agricultural plain in Morocco, represents 26%. Of the national production with an area of 15,000 hectares [4], and contributes 20.5% and. 21.2% to the national area and production of sugar beet in Morocco, respectively [5]. Sugar beet requires balanced fertilization by the three macronutrients, nitrogen (N), phosphorus (P) and potassium (K). Potassium is one of the most important elements for sugar beet nutrition and plays a significant role in enzyme activation, charge balance, osmoregulation and reduction in the negative effects of drought stress [6,7]. Hanafy et al [9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
