Growth Inhibitors of Lettuce Seedlings from Curvibacter sp. GA75-1

The microbial strain GA75-1, which exhibited growth inhibitory activity on lettuce seedlings, was selected out of more than five hundred bacterial colonies by pot experiment for isolation and identification of plant growth retardants. The strain was identified as Curvibacter sp. by the nucleotide sequence of the 16S rRNA gene. The culture broth was consecutively partitioned with dichloromethane, ethyl acetate, and butanol. The bioassay-guided fractionation of butanol extract led to the isolation of compound 1 and 2 which inhibited 56.8 and 54.1% of lettuce root elongation and 22.5 and 47.3% of shoot growth at 50 mg L-¹, respectively. From ¹H NMR and EI-MS spectra, 1 and 2 were identified as uracil and 4-methoxybenzoic acid, respectively. The concentrations of uracil and 4-methoxybenzoic acid required for 50% inhibition of root were 48.4 and 49.1 mg L-¹ and of shoot were greater than 100.0 and 51.3 mg L-¹, respectively. Uracil derivatives are one of very well-known herbicide groups; however, this is the first report on the herbicidal effect of uracil itself on lettuce. In addition, 4-methoxybenzoic acid is firstly isolated from the genus C. lanceolatus as an inhibitor of lettuce seedling growth. C. lanceolatus containing the above compounds is expected to be useful as the lodging-preventer and/or biotic herbicide.