Influence of PGPR on growth, essential oil and nutrients uptake of sweet Basil Kourosh ordookhani, Shahram Sharafzadeh, Mahdi Zare.
Sweet Basil (Ocimum basilicum L.), is a culinary herb of major importance. Most culinary and ornamental basils are cultivars of the species Ocimum basilicum, but other species are also grown and there are many hybrids between species. The genus of Ocimum, of the family Lamiaceae (Labiatae), include at least 60 species and numerous varieties . Ocimum spp. contain a wide range of essential oils rich in phenolic compounds and a wide array of other natural products including polyphenols such as flavonoids and anthocyanins . Leaves and flowering parts of O. basilicum are traditionally used as antispasmodic, aromatic, carminative, digestive, galactogogue, stomachic, and tonic agents [3,4]. Fresh basil is used as an ingredient in various dishes and food preparations, especially in the Mediterranean cuisine. Due to its antimicrobial [5,6] and insecticidal  activity and very pleasant aroma, basil essential oil is widely used in the food, pharmaceutical, cosmetic, and aromatherapy industries.
Sweet basil is a widely grown aromatic crop cultivated either for production of essential oil, dry leaves for the fresh market, or as an ornamental [8,9]. Within this species, there is a significant variation in phenotype and chemotype in terms of oil content and oil composition [9-11]. Today, utilization of biofertilizers such as plant growth promoting rhizobacteria (PGPR) has become a feasible production practice. PGPR can enhance plant growth, nitrogen fixation, hormone production, plant nutrition and also control of plant diseases. Different PGPR including associative bacteria such as Azospirillum, Bacillus, Pseudomonas and Enterobacter have been used for their beneficial effects on plant growth [12,13]. Many marketable biofertilizers are mainly based on plant growth promoting rhizobacteria (PGPR) that exert beneficial effects on plant development often related to the increment of nutrient availability to host plant .
The objective of this work is to determine the effect of inoculating Ocimum basilicum root with PGPR (Pseudomonas putida strain 41, Azotobacter chroococcum and Azosprillum lipoferum) on growth and essential oil yield.
Materials and methods
Applied PGPR contained Pseudomonas putida strain 41, Azotobacter chroococcum strain 5 and A. lipoferum strain OF. To provide microbial inoculants, PGPR were inoculated in nutrient broth medium. Each bacterium was then removed at the end of logarithmic growth phase, and was asepticcally transferred to plastic containers containing sterile perlite and was then mixed well. PGPR concentration was adjusted to 1x108 (CFU/gr) in all inoculants.
Growth condition and plant materials:
This study was conducted in experimental glasshouse of Islamic Azad University, Firoozabad Branch (28[degrees]35' N, 52[degrees]40' E; 1327 m above sea level).
Ocimum basilicum L. seeds were inoculated and sown in a soil field, mixed with waterworn sand and peat (1/3, v/v each of them), in pots containing 7 kg of the mentioned (mixed) soil. Seven PGPR treatments were considered (Pseudomonas putida, Azotobacter chroococcum, A. lipoferum, P. putida + A. chroococcum,P. putida + A. lipoferum, A. chroococcum + A. lipoferum and P. putida + A. chroococcum + A. lipoferum). A non-inoculated treatment was set as control and N fertilizer was added to all the treatments according to the soil test. Shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, shoot height, N,P,K content were determined at full bloom stage. Isolation of essential oils was performed using hydrodistillation of 20 g sample of dried shoots by using a Clevenger-type apparatus over 4 hours. The oils were dried over sodium sulphate and the yields of the essential oils (w/w) were calculated. The physicochemical properties of the soil were also determined (Table 1).
Experiment was conducted based on a randomized complete block design (RCBD) with four replications. Three pots were assigned for a replicate. Means were compared with Duncan's new multiple range test (DNMRT) in SAS software for windows.
Results and discussion
The results showed that the PGPR have the capacity to enhance Ocimum basilicum growth. Data explained significantly differences between applied PGPR treatments on shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, shoot height, N,P,K content and essential oil yield (Table 2). Maximum Root wet weight (3.96 g/plant), N content (4.72%) and essential oil (0.82%) were observed in the Pseudomonas + Azotobacter + Azosprillum treatment which was significantly different when compared to other treatments (Fig. 3, Fig. 6 and Fig. 7).
Maximum shoot fresh weight (61 g/plant), shoot dry weight (8.47 g/plant) and root dry weight (0.87 g/plant) were found in the Pseudomonas + Azotobacter + Azosprillum treatment which which was significantly different when compared to other treatments except Azotobacter + Azosprillum treatment (Fig. 1, Fig. 2 and Fig. 4). Minimum of all factors were observed in the control treatment which had differed significantly from other treatments.
Other reports showed beneficial effect of PGPR on plant growth. Increased nutrient uptake by plants inoculated with plant-growth promoting bacteria has been attributed to the production of plant growth regulators at the root interface, which stimulated root development and resulted in better absorption of water and nutrients from the soil [15,17]. PGPR can improve plant growth, plant nutrition, root growth pattern, plant competitiveness and responses to external stress factors. Many microorganisms in the soil are able to solubilize 'unavailable' forms of K-bearing minerals, such as micas, illite and orthoclases, by excreting organic acids which either directly dissolve rock K or chelate silicon ions to bring the K into solution [18,21]. Bacterial inoculation also significantly increased nutrient contents by plants. Already reported increased N content of Adhatoda vasica plants inoculated with different strains of A. chroococcum . Researches reported better response of Ocimum basilicum plants inoculated with consortia of G. fasciculatum, P. fluorescens and Bacillus megaterium .
The results indicated, in the PGPR treatments, all factors were higher in the Pseudomonas + Azotobacter + Azosprillum and Azotobacter + Azosprillum treatments, which stated a positive synergistic interactions between them whereas found an antagonistic interactions between usage of Pseudomonas + Azotobacter and Pseudomonas + Azosprillum treatment on Ocimum basilicum growth compared to the other PGPR treatments. A few studies in the literature comparing the efficacy of combinations of beneficial rhizobacteria to single strain inoculation showed that mixed inoculate can lead to a competitive process by which plant growth may be reduced [24,25]. Abbass showed that Azotobacter has positive effects on plant growth . Synergistic effects of combined inoculation of PGPRs have also been reported in various crops, for examples tomato , potato , rice  and sugar beet and barley .
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This research was supported by Islamic Azad University, Firoozabad Branch, Iran. I would like to thank Dr. Hassan Zare Neirizi for his help.
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Islamic Azad University, Firoozabad Branch, Iran
Kourosh Ordookhani, Shahram Sharafzadeh, Mahdi Zare: Influence of PGPR on Growth, Essential Oil and Nutrients Uptake of Sweet Basil
Kourosh ordookhani, Islamic Azad University, Firoozabad Branch, Iran E-mail: firstname.lastname@example.org Tel:+989179114470 Fax: +987116277937.
Table 1: physicochemical properties of soil used Parameter value Electrical conductivity ([dsm.sup.-1]) 0.83 PH of Saturated soil solution 7.43 Clay (%) 14 Silt (%) 32 Sand (%) 54 Nitrogen (%) 0.037 Organic carbon (%) 0.41 Phosphorous (ppm) 7 Potassium (ppm) 292 Iron (ppm) 4.11 Zinc (ppm) 1.02 Table 2: Variance analysis of shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, shoot height, N,P,K content and essential oil yield in sweet basil SOV Degree of Shoot height Shoot fresh Shoot dry Freedom (df) (cm) weight weight (gr/plant) (gr/plant) Block 3 35.28 ns 5.37 ns 0.208 ns Treatments 7 326.64 ** 263.33 ** 5.36 ** C.V% 8.29 5.42 6.22 SOV Root fresh Root dry N (%) P (%) weight weight (gr/plant) (gr/plant) Block 0.068 ns 0.0031 ns 0067 ns 0.00006 NS Treatments 2.06 ** 0.075 ** 1.26 ** 0.012 ** C.V% 7.52 6.69 5.9 5.54 SOV K (%) Essential oil yield (%) Block 0.0087 NS 0.00005 ns Treatments 1.41 ** 0.059 ** C.V% 7.27 3.47 Ns, ** are levels of significance (not significant, p<0.01 respectively) Sov: sources of varition
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|Title Annotation:||Original Article; plant growth promoting rhizobacteria|
|Author:||Ordookhani, Kourosh; Sharafzadeh, Shahram; Zare, Mahdi|
|Publication:||Advances in Environmental Biology|
|Date:||Mar 1, 2011|
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