Inoculation Effect of Some Liquid Inocula of Enterobacter cloacae on Oil and Fatty Acids Percentages, and Nutritional Indices of Rapeseed (Brassica napus L.)

Background and Objectives: Biofertilizers play major role in sustainable agriculture. Biofertilizers are inoculants containing useful microorganisms which are used in solid, liquid and/or encapsulated formulations. Different materials can be used as liquid carriers. Increasing inoculant longevity by using different materials is the main purpose in production of liquid inocula. These additives are carbon-based and reduce environmental stresses. In this study the effectiveness of liquid inocula of Enterobacter cloacae S16-3 on oil content, fatty acids and nutrient uptake of rapeseed in a sterile sandy loam soil were evaluated. Nine liquid inocula of S16-3 (F1-F9) were prepared using different amounts of materials including glycerol, polyethylene glycol (PEG), trehalose, carboxymethylcellulose (CMC), Arabic gum (AG), polyvinylpyrrolidone (PVP), glucose and starch, in different combinations. Then, the effect of liquid inocula on growth of rapeseed (Brassica napus L.) cultivar hyola 308 was investigated.
Methodology: The experiment was carried out in greenhouse condition based on completely randomized design (CRD) with three replications. The factors were including 9 liquid inocula (F1-F9), in all these treatments, 70% of NPK was added to the soil in each pot, since we assumed that S16-3 is able to supply only 30% of these elements, one control treatment without adding any bacteria and fertilizer (negative control), and two positive controls (using NPK equal to 70% and 100% of fertilizer recommendation). Germinated seedlings of rapeseed were planted and inoculated with inocula in each pot. Except for NPK elements, other micronutrients were provided based on soil test; however, in the case of nitrogen, phosphorus and potassium elements that were the main objective of this experiment, no chemical fertilizer and bacteria were used in negative control treatment. In positive control (100NPK), based on the soil test and previous experiments, 100% of the recommended amount of fertilizer, equivalent (56.5 mg N/kg soil, from Urea source), (13 mg P/kg soil, from triple superphosphate source) and (31.3 mg K/kg soil, from potassium sulfate source) were used, moreover, for other positive control treatment (70NPK), 70% of the above values in pot culture were added to the pots. During the growth period, irrigation was performed with sterile water and the moisture content of the pots was maintained by weighing in a moisture range (0.7 - 0.8 FC). In pot culture, characteristics such as dry weight of roots, shoots and seed, seed oil percentage and fatty acids, uptake of nitrogen, phosphorus, potassium, iron, zinc, manganese and calcium in the root and shoot were measured.
Findings: The results obtained from the greenhouse experiments showed that the dry weight of roots, shoots and seed, seed oil percentage and fatty acids, uptake of nitrogen, phosphorus, potassium, iron, zinc, manganese and calcium in the root and shoot of rapeseed (Brassica napus L.) cultivar hyola 308 were significantly influenced by the presence of E. cloacae bacteria (in the form of nine inocula) and 100NPK and 70NPK treatments. The highest percentage of seed oil (47.02%) and the highest amount of oleic acid (53.1%) was obtained by F9 (glycerol, glucose, AG, PEG) treatment, and oil quality was affected by bacterial inoculation. the highest amount of saturated fatty acids, such as stearic acid (4.5%) and palmitic acid (5.6%) was measured in without inoculation treatment (negative control). Nutrition analysis in dry tissue of plant showed that 100NPK treatment had the highest N, K, Fe, Zn and Ca uptake in the plant, and among liquid inocula treatments (F1-F9), the highest uptake of these elements belonged to the F5 (AG, starch, PEG). The highest amount of total P in F1 treatment (glycerol, trehalose, CMC) and F4 (trehalose, AG, PEG) and highest Mn absorbed in the plant were obtained in F5 treatment.
Conclusion: In most measured indices, the effects of liquid inocula had higher performance than without inoculation treatment (negative control). From the nutritional point of view, F5 (AG, starch, PEG) liquid inoculant were better than the other inocula. F9 treatment had a significant effect on quantitative and qualitative characteristics of rapeseed oil. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .