Effects of vermicompost and biofertilizers on essential oil composition of lemon balm (Melissa officinalis L.) under drought stress

Effects of vermicompost and plant growth promoting biofertilizers on the essential oil composition of lemon balm (Melissa officinalis L.) were studied under different irrigation conditions. The study was conducted in a split-split plot experiment based on a randomized complete block design with three replications, at Research Institute of Forests and Rangelands.Treatments included irrigation in two levels (100 and 60% FC drought stress), vermicompost in three levels (0, 5 and 10t/ha) and plant growth promoting biofertilizers in four levels (Pseudomonas fluorescence, Azotobacter Azospirillum, Azotobacter Azospirillum P. fluorescence, and the control). The essential oil components including citronellal, geraniol, neral, β-caryophyllene and methyl citronellat were studied. The interaction of irrigation × vermicompost showed significant effect on citronellal at P≤0.01 and on geraniol and methyl citronellat at P≤0.05. Mean comparison of irrigation indicated that the highest and lowest citronellal, geraniol, neral and β-caryophyllene, were obtained for drought stress and normal irrigation (100% FC), respectively. The highest and lowest methyl citronellat were recorded for the normal irrigation and drought stress (60% FC), respectively. Mean comparison of the effect of vermicompost showed that the highest (47.7%) and lowest (45%) citronellal were obtained for 10 t/ha vermicompost and control treatments, respectively. Application of 5 t/ha vermicompost resulted in the highest β-caryophyllene (6%). Mean comparison of the biofertilizers indicated that Azotobacter Azospirillum P. fluorescence had the highest citronellal (47.2%) and β-caryophyllene (5.9%); the lowest citronellal (45.6%) and β-caryophyllene (5.1%) were achieved in the control. Drought stress increased the essential oil compounds. Vermicompost just affected the citronellal. In addition, PGPR had a positive effect only on citronellal and β-caryophyllene.