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Abstract
More than 51 isolates of bacteria were obtained from leaves, crushed leaves and rhizosphere of lettuce plants. The bacteria isolates were purified and assayed against Cercospora lactucae-sativae on PDA plate by dual culture technique. Four isolates showed zone of inhibition against the pathogens. The antagonistic bacteria isolate LBF02 showed the highest percentage of growth inhibits against C. lactucae-sativae leaf spots with 80.82% inhibition, compared with the control. Based on morphological and biochemical tests, isolate LBF02 was identified as belonging to the Bacillus subtilis group. The LBF02 isolate was chosen for the formulation development. The formulation contained 40 ml of cell suspension, 89 g of rice flour, 1 ml of vegetable oil and 10 g of sucrose. The biocontrol of leaf spot diseases was tested by using a formulation applied in greenhouse experiments. The result showed that spraying 1 hour before or after the pathogen inoculation on lettuce plants was more effective in suppressing leaf spot disease than simply pathogen inoculation alone. Moreover, the antagonistic bacteria in formulation have the ability to survive for more than 6 months under storage at room temperature and survive for up to 15 days on lettuce leaves.
Highlights
Lettuce (Lactuca sativa L.) is the most popular leafy salad vegetable in Thailand
Favorable results were found by Korsten & Jager (1995) who demonstrated the efficiency of Bacillus subtilis, Bacillus cereus and Bacillus licheniformis in hibiting effectively avocado post-harvest pathogens Colletotrichum gloeosporioides, Phomopsis perseae, Drechslera setariae, Pestalotiopsis versicolor and Fusarium solani
The antagonistic bacteria LBF02 isolated showed the highest percentage of inhibition against C. lactucae-sativae
Summary
Lettuce (Lactuca sativa L.) is the most popular leafy salad vegetable in Thailand. But, the vegetable is susceptible to leaf spot disease caused by Cercospora lactucae-sativae; this is disease that has important economic implications around the world and normally, this disease has been a major damage-causing one in Thailand (To-Anun et al, 2011). In the year 2004, due to an attack of just the Cercospora longissima comm losses of up to 68% were reported in the specific conditions (Gomes et al, 2004). All these antagonistic bacteria that have been isolated from the soil surrounding the plants and from the plant surfaces (Weller, 1988; Kim et al, 1997; Sindhu et al, 2002; Todorova & Kozhuharova, 2010) are active under the general mechanism of competitive exclusion or reduction of growth by other microorganisms, which is the interference process of the pathogens. The formulations were applied by spraying on the plant leaves in the greenhouse experiments and fields
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