Lettuce germination

Four bioassays a) 120h lettuce germination test (Lactuca sativa) b) 48h acute crustacean test (Ceriodaphnia dubia) c) 96h acute amphipod test (Hyalella azteca) Waters collected from wells dug in an urban landfill, sediments collected in an adjacent river... 

Komal et (Ref. 53) found gc-ms evidence of the sesquiterpenes 6 sellnene (54), methyl farnesate, farnesyl acetate (55), and farnesol (56) present In an Inhibitory fraction Isolated from water nutgrass (Cyperus serotinus ). This fraction at 300 ppm Inhibited lettuce germination and also Inhibited growth of lettuce and rice seedlings as well as nutgrass Itself. The authors conclude that the sesquiterpenes are responsible for the observed allelopathlc effects. 

In addition to the sesquiterpene lactones, two chromenes, Eupa-toriochromene (I) and Encecalin (II) (14) have been isolated from yellow starthistle and have been shown to have some effects on germination and growth of lettuce. 

Encecalin (I) causes a dwarfing of lettuce shoots at concentrations from lOppm and up. On the other hand, eupatoriochromene (II) causes very little dwarfing of the seedling but does inhibit germination of lettuce at lOOppm and above. The concentration of these two chro-raenes in yellow starthistle may indeed allow for some effect to be exerted on the surrounding plant community. 

The dlterpene lactone 17-acetoxyacanthoaustralide (25) has minor effects, showing promotion of clover (112%), cucumber (109%) and Palmer amaranth (111%) and inhibition of carrot germination (91%). The flavonoid artemetin (26) at 0.05 mM concentrations slightly affects onion (93%), oat (91%) and promotes seed germinations In carrot (116%) and Palmer amaranth (113%). In closing, it is noteworthy to point out that lettuce and cress are not significantly affected by all ten sesquiterpene lactones as well as the dlterpene (25) and artemetin (26). 

The most concentrated (1 16, w/w) extract inhibited only lettuce, tomato, and ryegrass. The osmolarity of the solution was 40.3 mOsm, insufficient to affect germination of most seeds (2). 

Dilution to 1 20 eliminated inhibition in onion, oat, ryegrass, red clover, and cheatgrass. Further dilution to 1 40 limited inhibition to lettuce, carrot, and Palmer amaranth. At this concentration lovegrass germination was promoted. The addition of 0.1%... 

Table VIII. Effect of Ragweed Organic Solvent Extracts on Lettuce and Carrot Germination...

Experiments using a matrix of four levels of ferulic acid and four levels of moisture stress demonstrated that the combined action was additive under more stressful levels of the individual factors than in the previous tests. Duke et al. (23) tested the germination of lettuce seeds treated with phenolic acids (1 mM) at water potentials (D-mannitol) of 0, -0.2, -0.4, and -0.6 MPa. The combined action of low water potential and exposure to phenolic acids resulted in an additive detriment to germination, and the authors concluded from probit analysis that the mechanism of action from these sources was similar. Whatever their mechanisms, moisture stress and phenolic acids appear to work together in limiting growth of plants. 

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