عنوان مقاله [English]
The relationship between arbuscular mycorrhizal fungi (AMF) and their associated bacteria has great importance for sustainable agriculture especially in the case of highly mycorrhizal plants such as flax seed. Bio-fertilizers use in sustainable agricultural systems is important in production and enables plants to absorb more water from soil and improves plant nutrient uptake and photosynthesis. The alleviating effect of the AMF symbiosis in response to drought generally relies on the uptake and transport of water and on an improved uptake of nutrients. The cooperation of bacteria and mycorrhizal is probably due to specific attributes of micro-organisms that make the mother plants more tolerant to drought stress .The interacting effects of mycorrhizal colonization and phosphate solubilizing bacterial (PSB) inoculation on plant vegetative growth and crop yield have been studied previously. But, the impact of these above micro-organisms on the plant reproduction and the actual (quality) crop yield has received much less attention. Thus the main aim of this study was to evaluate the effects of AMF species, PSB and their interactions on the quality of harvested flax seeds.
Materials and Methods
A 2-year field experiment was conducted at the Urmia University, Urmia city, located at North-West of Iran during the years 2014 and 2015. The experimental design was factorial (three factors) based on a randomized complete block with three replications. The treatments were included two AMF species (Funneliformis mosseae, Rhizophagus intraradices and non-mycorrhizal control), PSB (Pseudomonas putida P13 and non-inoculated control) and three irrigation regimes (irrigation after 60, 120 and 180 mm of evaporation from Class A pan). Seeds were sown into a loamy soil at a depth of 2 cm in plots. Mycorrhizal inoculum was placed in the planting rows below the seeds. For bacterial treatments, the seeds were inoculated with bacterial suspension of Pseudomonas putida strain P13 before being immediately planted. At the end of the growing season, when the plants had produced mature seeds, samples were taken. Seed factors included germination percentage, nutrient percentage (N, P and K), mucilage percent, swelling factor, electrical conductivity and potassium leakage (parameters as a result of damage to seed cell membranes) were measured. Finally, data was analyzed using SAS 9.1 and means were compared by Student Newman Keul’s test at 5% level of probability.
Results and Discussion
Combined ANOVA of 2-yr data showed a significant interaction effect of irrigation regimes multiply by bacteria and mycorrhiza on the final germination percent, mucilage content, swelling factor, swelling rate per gram mucilage, seed nutrients (nitrogen, phosphorus and potassium), and potassium leakage, and significant interaction of year multiply by irrigation regimes and mycorrhiza on the electrical conductivity in flax seeds. Results indicated that with increasing irrigation interval from 60 to 120 mm of evaporation in control (non-inoculated) plants, phosphorus percent, potassium percent, mucilage percent, swelling factor and swelling rate per gram mucilage, and potassium leakage were in high level. These above traits decreased with increasing in severe stress up to 180 mm of evaporation. With increasing drought stress in flax plants (from irrigation after 60 to 180 mm evaporation), protein content and final germination percentage and rate of harvested seeds were decreased. Mycorrhizal and bacterial inoculation of flax plants, especially dual inoculation, compensated a part of drought-induced seed protein reduction. In all irrigation regimes, the highest percentage of phosphorus, potassium, mucilage and swelling factor were observed in dual inoculated plants due to synergistic effect of mycorrhiza and PSB. This synergistic effect led to reducing cell membrane damages that indicated the vigorous seeds. But a downward trend of seeds germination percentage harvested from inoculated plants, related to higher mucilage volume and its negative correlation with seed germination.
A mixture of AMF and bacteria improved the results more than they were for the non-inoculated control plants. The development of multi-functional microbial inoculants seems to be a promising method to increase the positive effects of micro-organisms. In this study, the participation of micro-organisms contributed to a higher quality and vigor of flax seeds. Assessment the effects of plant-beneficial micro-organisms (Pseudomonas putida and two mycorrhizal species, alone or/and in combination) on the quality of flax seeds obtained from plants grown in the field, showed the beneficiary of dual colonization.