Effect of Bio-Priming with Plant Growth Promoting Bacteria on Growth and Biochemical Characteristics, Phenol, Flavonoid, Vitamin C and Nitrate in Lettuce (Lactuca sativa L.) Rabicon Cultivar in Different Growth Substrates

Organic amendments not only promote soil quality but also indirectly facilitate the establishment of bacteria. A greenhouse experiment was conducted to investigate the effects of organic substrates and plant growth promoting rhizobacteria inoculation on morphological characteristics of lettuce (Lactuca sativa L. Cv Rabicon.) in a factorial arrangement based on completely randomized design with four replications. Experimental treatments included organic fertilizers (vermicompost 20% v/v, spent mushroom 10% v/v and soil) and seed priming with promoting growth regulating bacteria (Pseudomonas putida P10, Pseudomonas fluorescence R159 and R150 and non-inoculated). At the end of growth stage, morphological traits (plant height, leaf number, crown diameter, leaf area, root length and volume, shoot fresh and dry weight), photosynthesis pigments (chlorophyll a, b, total and carotenoid), vitamin C, phenol, flavonoid and nitrate concentration were measured. The results indicated that the simple effects of substrate and bacterial strains inoculation were significant on traits including plant height, crown diameter, leaf area, root length and volume, shoot dry and fresh weights, chlorophyll a, b, total and carotenoid, vitamin C, phenol and flavonoid. Interaction of both factors had significant effects on leaf area, root length and volume, chlorophyll a and phenol. However, plants treated with vermicompost and Pseudomonas fluorescence R159 had higher values for both fresh and dry weight, phenol content and chlorophyll. Although some traits were higher in plants treated with compost and Pseudomonas putida P10 or vermicompost and Pseudomonas putida P10, but finally it seems that Pseudomonas fluorescence R159 has played a higher role in the final quantity and quality of lettuce.