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.

Óleo essencial de guaçatonga no controle alternativo de fungos causadores do mofo cinzento e alternarioses

“…A guaçatonga (Casearia sylvestris), também conhecida como erva-de-bugre ou cafezinho-do-mato, está entre as espécies vegetais brasileiras de uso medicinal, indicada para várias enfermidades humanas, e tem despertado grande interesse no ramo de fitoquímicos (FERREIRA et al, 2011). Na agricultura, a guaçatonga demonstrou ter efeito inseticida sobre o ácaro rajado Tetranychus urticae que ataca várias culturas (BECKER, 2008), além de reduzir o crescimento in vitro dos fungos deterioradores de madeira Trametes villosa, Ganoderma australe e Pycnoporus sanguineus (BENTO et al, 2016), apresentando também potencial como indutor de mecanismos de defesa das plantas (STENGER et al, 2021;VISMARA et al, 2022). Embora os resultados de estudos utilizando os extratos e o óleo essencial da planta sejam promissores, pesquisas para uso no controle de fitopatógenos ainda são raros.…”