An experiment on the effects of compounds on various plants to show an inhibitory effect on lettuce seed germination and seedling growth.

Firstly, I would like to share some background information on Allelopathy which is the effects that a living plant can have an other organisms such as microorganisms as-well as other surrounding plants. It can influence the growth and reproduction for example in other organisms.

The effects is caused by secondary metabolites which are organic compounds.
To discover more on the allelopathic effects we carried out this experiment to examine and understand more on allelopathy.

Materials used:

• Various plant materials were used in this experiment such as walnut, garlic and daffodil leaves.
•  3 Petri dishes
• Para-film
• Mortar and pestle
• 4 15ml screw capped tubes
• Lettuce seeds

Image of lettuce seeds also known as Lactuca sativa.

Method:

• 2 g of daffodil leaves, walnuts and garlic were weighed and the material was grind-ed by the mortar and pestle separately.
• After the plant material was turned it to a fine powder it was placed in to 15ml screw capped tube, it was labelled and then 10ml of water was added at 37 degrees Celsius.
• The tube was mixed well and it was left for 10 minutes, after it was centrifuged.
• This process was repeating with the walnut and garlic.
• 1 Petri dish was labelled as the control and the following 3 Petri dishes were labelled garlic, walnut and leaves.
• A filter was placed in every Petri dish,distilled water was then applied to the filter paper of the control.
• The corresponding tubes were added to the filters in the Petri dishes.
• 40 lettuce seeds were placed on each filter paper and then the Petri dishes were wrapped with para-film and then they were placed in an incubator.

Results:

The following Petri dish shows the control with the lettuce seeds germinated.In the control the lettuce seeds germinated 100%. the seedlings are healthy with no discoloring and no inhibition occurred.

This Petri shows lettuce seeds with garlic. Unexpectedly there was growth in the lettuce seeds where this should not occur, as garlic contains an inhibitory compound that inhibits the growth of seeds. As garlic produces an alkaloid and the main alkaloid in garlic is allicin.

The following Petri dish shows lettuce seeds with walnuts. Growth is present. Although the walnut produces juglone it inhibits the growth of surrounding plants. There was around 60 % germination. There appears to be inhibition. The black walnut tree produces a compound known as juglone which occurs naturally and it is toxic to surrounding plants.

This dish contains lettuce seeds with daffodil leaves. You can see the allelopathic effects shows greatly in this dish. There is around 50% germination but there is little growth in the shoots showing the inhibition effects of the alkaloid.

Conclusion: 

The control grew under the right conditions as distilled water was added to the lettuce seeds.

The daffodil leaves, walnuts and garlic all contain alkaloids which inhibits anything to grow which in this case its the lettuce seeds. Germination may occur but inhibition occurs also,so  the seeds will not grow to its full potential as it would under the right conditions.