Physiological and biochemical performance of lettuce (Lactuca sativa L.) seeds treated with essential oils used to control phytopathogens

Abstract

This work aimed to evaluate the physiological and biochemical performance of lettuce (Lactuca sativa L.) seeds treated with essential oils (EOs) of citronella (Cymbopogon sp.), guaçatonga (Casearia sylvestris Sw.), melaleuca (Melaleuca sp. L.), patchouli (Pogostemon sp. Benth), and pitangueira (Eugenia uniflora L.). The experimental design was completely randomized in double factorials (5 oils × 4 doses) at different doses (10, 20, 30, and 40 μL), with an additional treatment that served as growth control (without EOs, 0 μL). In other words, the experimental design entails 5 oils × 4 doses + 1 control, with 4 replicates of 100 Grand Rapid lettuce seeds without industrial chemical treatment. The response variables were: first germination count (FGC, %), last germination count (LGC, %), germination rate (GR), normal seedlings (NS, %), abnormal seedlings (AS, %), aerial part length (APL, cm), fresh mass (mf, g), total soluble proteins content (mg•g-1), and enzyme activities of β-1,3-glucanase (UA•mg-1) and phenylalanine ammonia-lyase (PAL, UA•mg-1). The lettuce plant proved to be a good reference plant for evaluations related to physiological and biochemical performance when treated with EOs. However, although treatment of lettuce seeds with EOs did not cause undesirable damages, it positively altered the physiological parameters APL and mf. All EOs affected the total proteins content and enzyme activities of PAL and β-1,3-glucanase. Therefore, EOs demonstrated the potential to activate the plant's defense mechanism to control phytopathogens. More specifically, 10 μL of citronella EO activated two plant defense mechanisms: PAL and β-1,3-glucanase activities. In addition, EOs of melaleuca (10 and 40 μL) and patchouli (20 and 30 μL) also activated PAL enzyme activity.