Efficacy of essential oils in the management of soft rot caused by Pectobacterium aroidearum in lettuce

Lettuce is susceptible to several diseases, especially soft rot caused by bacteria of the genus Pectobacterium. Due to the adaptability of this pathogen and the lack of disease control registered for the crop, the objective of this work was to evaluate the effects of essential oils in the management of soft rot caused by P. aroidearum in lettuce. The study was developed at the Universidade do Estado da Bahia, Juazeiro, BA, Brazil, and the essential oils (EOs) of orange, bergamot, lemongrass, palmarosa, citronella, cloves, tea tree, rosemary, sage, and ginger were used in concentrations of 0.25; 0.5; 0.75 and 1.0% to assess the in vitro growth inhibition of the bacterium. Subsequently, the curative effects of the disease were evaluated by applying the EOs that obtained the best results in vitro in lettuce plants of the susceptible variety “Mônica”. The treatments were applied, via spraying, 12 hours after inoculation using the bite method with bacterial suspension. The best in vivo treatment was selected to assess its preventive and curative activity, as well as to find the ideal concentration for reducing epidemiological variables and chromatographic characterization. The EOs of palmarosa, sage, citronella, lemongrass, and cloves (0.25%), and that of sage (0.75%), inhibited bacterial growth in vitro. The EO of salvia showed the best results in vivo, inhibiting the growth of the disease in concentrations of 0.50 and 0.75%, so it was selected for the preventive and curative control tests alone. The preventive treatment was not efficient for the management of soft rot in lettuce, however, from the regression analysis, a concentration of 0.64% of the salvia EO was found as a potential for curative control of this bacteriosis, as it reduces the incidence and severity of the disease. Linalyl acetate and linalool were found in higher concentrations in the chromatographic analysis. These components, probably, conferred the bactericidal capacity of the EO of sage, being potential for the use in the control of P. aroidearum in lettuce.

Chromatographic characterization of juice in fruits of different Japanese quince (Chaenomeles japonica L.) genotypes cultivated in Sweden

The juice in fruits of 19 genotypes of Japanese quince (Chaenomeles japonica), representing plant breeding material, was characterised using high performance liquid chromatography. The juice was extracted by halving and squeezing the fruit. Samples of Japanese quince juice were always analysed fresh. The main compounds found were sugars: glucose (131-1056 mg 100 ml-1), fructose (351-2515 mg 100 ml-1) and sorbitol (10-367 mg 100 ml-1); organic acids: malic acid (2.27-4.84 g 100 ml-1) and quinic acid (0.50-2.50 g 100 ml-1); amino acids: aspartic acid (0.8-10.7 mg 100 ml-1), asparagine (0.2-36.3 mg 100 ml-1) and glutamic acid (6.2-17.7 mg 100 ml-1); the cation potassium (145-214 mg 100 ml-1) and the anion fluoride (21-122 mg 100 ml-1). These results on composition suggest that Japanese quince may be an interesting raw material source of valuable substances and its juice an ingredient for the food industry. A principal components analysis separated the Japanese quince genotypes, thus indicating a clear difference in the chemical composition of the juice.