The effect of oils and plant extracts was evaluated for controlling soft rot in lettuce and assessed the influence of these products in physico-chemical characteristics of this vegetable. In the in vitro tests, filter paper discs were soaked in eleven essential oils (0.0, 0.25, 0.50, 0.75 and 1%) and twenty plant extracts (10, 40, 70 and 100%) being deposited on a culture medium containing Pectobacterium carotovorum subsp. carotovorum (strain Pcc A1). The zones of inhibition were measured after 24 and 48 h of incubation. In the greenhouse, plants of cv. Veneranda were treated with eleven oils (0.5 and 1%), twenty extracts (10%) and Mycoshield® (3 g L-1) and after 72 h were inoculated with Pcc A1. We evaluated the disease severity with an interval of six hours until 48 h, and the area under the disease progress curve (AUDPC) was calculated. In a similar experiment plants treated with Corymbia citriodora oil, seven plant extracts and Mycoshield® were analyzed for soluble solids, vitamin C, acidity and pH. Strain Pcc A1 was not inhibited in vitro. Two oils (C. citriodora and C. sinensis) and seven extracts (Parkinsonia aculeata, Chamaecrista cytisoides, Sida galherensis, Polygala violaceae, C. desvauxii and Pityrocarpa moniliformis) significantly reduced disease severity in comparison to control, without differing from Mycoshield®. On the other hand AACPD was reduced by eight oils and ten extracts. It is worth to notice that severity and AUDPC were reduced by eucalyptus oil at 0.5% (3.6, 83.35) and by the extract of S. galherensis (3.5, 88.25) with the same efficiency as Mycoshield® when compared to control (7.5, 132.3). The levels of vitamin C, acidity and pH were not altered in leaves of lettuce treated with eucalyptus oil and extracts of P. aculeata and C. cytisoides.
Lactuca sativa; Pectobacterium carotovorum subsp. carotovorum; alternative control
