Effects of plant extracts and sodium hypochlorite on lettuce germination and inhibition of Cercospora longissima in vitro

Abstract

Abstract Vegetables that are propagated by seeds are considered to be commercially and nutritionally valuable. However, there is a need to overcome the present challenge of developing alternative technologies for organic horticulture. This paper evaluates the potential use of the aqueous extracts of clove, cinnamon, and coriander and the sodium hypochlorite in the germination of lettuce (Lactuca sativa) seeds and in the control of Cercospora disease. Two experimental groups were thus designed: 1) the effects of the different aqueous extracts on germination and initial development of lettuce seeds were observed and; 2) the effects of these extracts on the mycelial growth of the fungus Cercospora longissima (isolated from lettuce plants) were evaluated. The treatments used in the first group were control (with water only), 5% (v/v) sodium hypochlorite (NaOCl) and 5% (w/v) aqueous extracts of clove, cinnamon, and coriander. The pretreatment of seeds was performed just before placing them for germination by immersing in these solutions. In the second set of the experiment, the inhibition of mycelial growth of the Cercospora longissima, isolated from lettuce plants presenting cercosporiosis symptoms, was evaluated. In the seeds treated with clove and cinnamon extracts, the germination speed index was negatively affected, while those treated with coriander extract showed an increase in the fresh mass of the aerial part and in the number of leaves of lettuce seedlings. In the second experimental group, it was observed that the growth of Cercospora longissima was inhibited completely by the cinnamon extract and by sodium hypochlorite.