Changes in agro-morphological traits of flax (Linum usitatissimum L.) under plant growth promoting bacteria effect and drought stress

Introduction The importance of oilseeds for human and livestock in terms of providing energy, has special value among agricultural products. Due to the shortage of oilseeds cultivation in Iran, billions of dollars spend to import oilseeds and crude oil to the country, annually. Flax (Linum usitatissimum L) is used for its oil and fiber in several industries. Flaxseed obtains bioactive compounds and components including linolenic acid, lignans, omega-3, and other essential compounds. In many parts of the world, drought is the main factor which limits flax yield. Reductions in grain yield, physiological traits, oil yield and percentage were reported in many oilseeds crops under drought stress. The use of bacteria as priming, cause plants tolerance to environmental stresses. Plant growth promoting bacteria increase crops yield by regulating hormonal and nutritional levels, resistance to plant pathogens, solubilizing of elements and other mechanisms. Since water deficit is one of the main limiting factors of crops production in Iran, on the other hand, the cultivation and production of oilseeds in Iran is low, therefore, this research was carried out in order to investigating the effect of plant growth promoting bacteria on production of flax under water deficit conditions. Material and Methods This experiment was conducted in the research farm of Shahrekord University in 2013-2014 in split-plot based on randomized complete block design with three replications. The experimental factors were irrigation in three levels (100, 75 and 50 % of plant’s water requirement) and plant growth promoting bacteria in seven levels (No inoculation and inoculation by six bacteria including Bacillus sp strain1, Bacillus sp strain2, Bacillus amyloliquefaciens, Azotobacter Chroococcum, Pseudomonas putida and Azospirillium lipoferum). Before stress applying, flooding irrigation was done one day apart. Stress was applied 14 days after planting date, based on plant's water requirement. Stress was carried out base on 75 and 50% plant’s water requirement. At flowering stage, number of flower heads per plant measured. Plant height, number of capsules per plant, number of seeds per capsule and 1000 grain weight were measured at harvesting stage. After oil extraction, oil percentage was calculated. The results of variance analysis was done by using of SAS software, comparison of means by LSD and the interactions of mean comparison by using slicing method. Results and Discussion Main effects of irrigation levels and bacterial treatments on all traits were significant. Interaction effect of investigated factors on plant height, number of stem and flower heads per plant, number of capsules per plant, 1000 grain weight, biological yield, grain yield and grain oil percentage were significant while its effect on number of grain per capsules was not. The highest grain yield and grain oil percentage was obtained in 100 % of plant’s water requirement. These treatments had increasing of 88% and 28% in comparison with 50 % of plant’s water requirement, respectively. Within each three irrigation levels, the bacterial treatments had the maximum amount of measured traits compare to control treatment. The effect of Bacillus sp strain1, Bacillus amyloliquefaciens and Azotobacter Chroococcum in most of the investigated traits were more pronounced. Bacillus sp strain1 had the highest grain yield and grain oil percentage in three irrigation levels. Conclusions According to the results, , the amount of measured traits decreased by increasing drought stress levels, however, bacterial treatments reduced the effects of stress in comparision with control treatment. Among bacterial treatments, Bacillus sp strain1, Bacillus amyloliquefaciens and Azotobacter were more effective on reduction effects of stress. Also the highest grain yield, biological yield, and oil percentage were found in these bacterial treatments. Probably these microorganisms, especially Bacillus species, have increased plant production due to their phosphate solubilizing ability, IAA, cytokinin and ACC-deaminase enzyme production and better absorption of nutrients.