Study of beet bagasse effect on biochemical characteristics, photosynthetic pigments and antioxidant activity of leaf extracts of peppermint (Mentha piperita L.) under drought stress conditions

To study the effects of drought stress and soil application of beet bagasse on biochemical characteristics, photosynthetic pigments content and antioxidant activity of peppermint (Mentha piperita L.) leaf, a pot experiment was conducted in 2015 at Ferdowsi University of Mashhad. The experiment was carried out as a factorial experiment based on completely randomized design with four treatments of drought stress (30, 50, 70 and 90% of field capacity) and three levels of soil application of beet bagasse (0, 10, 20% by volume) in 3 replications. The results showed that the highest amounts of chlorophyll a, chlorophyll index, ratio of chlorophyll a/b, carotenoid and relative water content were obtained in 90% stress of field capacity and 20% application of beet bagasse, so that increasing stress levels reduced the aforementioned characteristics. Furthermore, the application of bagasse created significant changes in the above characteristics. The highest contents of chlorophyll b, total chlorophyll, antioxidant activity and electrolyte leakage were obtained in 30% drought stress of field capacity and without use of sugar beet bagasse treatment, so that was equal to 47/19, 49/48 mg/kg fresh weight, 91/2% and 75/93%, respectively. Application of beet bagasse at this level of drought stress caused a significant reduction in these traits. Based on the results obtained, it is clear that application of beet bagasse in the medium due to high water absorption and retention, improves biochemical traits and photosynthetic pigments in the peppermint.