Neighbours From Hell!

This is a report on an experiment done in a botany lab in which our class examined how certain plants can have varying effects on living plants that may be present nearby in a phenomenon known Allelopathy, this is where plants are capable of producing secondary metabolites which aren't of critical importance to the plants own survival but instead can have negative effects on the growth, survival, and reproduction of other nearby plants which come into contact with them, in a way they can be considered the noisy neighbours who make life hard for plants growing nearby, this is not done out spitefulness on the plants part however it is simply that plants that produce these compounds have been favored and evolved to act in this intolerable way towards nearby plants as it is of benefit in instances where this forms a land barrier around that plant by making that soils around it tough to grow on for other plants and thus it has a much better supply of nutrients in the soil which are often in limited supply by eliminating the competition of other plants, in much the same way a business would prefer to have a monopoly than a open market, greedy plants...

Materials Used

For this allelopathy experiment we used the following

• Parafilm
• Mortar and Pestle
• 3 Petri Dishes
• 15ml screw cap tubes 
• 2g of Walnut
• 2g of Garlic
• 2g of Daffodil
• Lettuce seeds

So we chose to examine 3 separate plant species (walnut, Garlic and Daffodil) to see if they induced this allelopathic effect on germinating lettuce seeds

Procedure-

1. We Selected and weighed out 2g of walnut, garlic and daffodil plant tissue and ground up the various plant tissues up separately in a mortar and pestle.

2. Once the material was ground up to a fine powder, it was placed into a 15ml screw capped centrifuge tube and carefully labelled with the name of the plant.

3. 10ml of water was added at about 37°C.

4. It was then mixed thoroughly and left for about 10 minutes.

5. The tubes were then Centrifuged.

6. We then Carefully labelled the lid of a Petri dish as a control and then labelled a further 3 Petri dishes with the names of the plant materials being extracted.

7.  A piece of filter paper was placed in the base of each of the Petri dishes.

8. We wet the filter paper disc of the control dish with distilled water.

9. Wet the filter paper dish of the three other dishes with the extract corresponding to their label.

10. 40 lettuce seeds were placed on each filter paper taking care that the seeds do not touch and that there is sufficient space between each.

11. We carefully wrapped Parafilm around each dish to prevent drying out and contamination and place them in an incubator. Leave there for 7 days.

12. We retrieved the plates and recorded the observations relating to lettuce seed germination and growth. we then observed the lettuce seeds for any signs of growth/promotion or inhibition and if the seeds were healthy and finally if the seeds were discoloured.

13. We Measured the length of the different plant regions of each germinated seedlings ; the cotyledon, shoot and root length.

Results

When treated with the walnut, garlic and daffodil each of these had their own separate allelopathic effects on the growth and health of the lettuce in varying degrees of potency, inhibition of growth occurred in all but the control seeds.

•   .    walnut exhibited a allelopathic effect of germination being inhibited by half in the lettuce seeds than compared to that of the control, walnuts are known to secrete juglone which acts as a toxic phenolic compound that when present in soil can inhibit seedling growth in other plant species, this feature has obvious benefits to success of the walnut species.

•     While daffodil didn’t inhibit germination as much as both the walnut and garlic it did have a pronounced effect on the health of the seedlings which did manage to germinate, they typically had profoundly shortened root and shoot lengths with discolouration of the lettuce plants pigmentation also occurring, these effects in the wild would have a detrimental impact on the survival of the seedlings coming into contact with the allelopathic compounds present in the daffodil which are known to be inhibitory to growth (Anti-mitotic) in effect.

•    .  The Garlic had the greatest and most potent allelopathic effect on growth of all the plants materials tested, it had a complete inhibition on germination of the lettuce seeds, the allelopathic compound in effect is allicin which also functions in the soil as an anti pathogenic compound.