Effects of Allium Sativum (Garlic) on Seed Germination

Allelopathy, is a vast concept in biology. We will be observing the effects of allelopathy on radish seed growth. A phenomenon that effects the survival, growth and reproduction of organisms other then ones self. This is a product of the biochemical’s produced from another organism, called allelopathy. In nature, allelopathy is used as a defense mechanism against competing plant organisms, predatory animals and such. We would generally see this phenomenon in such organisms as plants, bacteria and fungi, algae and coral (1a).

The term allelopathy, comes from Greek origin, meaning mutual suffering (2). While over the years the term has developed and come to mean more then simple toxic interactions between various plant organisms competing for food, water and light. It developed a broader meaning, of any and all interaction of organisms between one another (3). It is obvious that there can be many different types of interactions between organisms, such as symbiotic, mutualistic or parasitic. Although when allelopathy is referred to, the meaning is to the biochemical effects on secondary metabolites (1b). Secondary metabolites are metabolic processes effecting growth, development and reproduction.

Allium Sativum is a plant organism found in nature, and commonly referred to as wild garlic. It is very common and can grow in many climates and environments, such as deserts, beaches and even forests. Garlic can be used in cooking, medicines in many different ways. When garlic is minced or crushed it can produce volatile chemicals. The volatile chemicals found in garlic are; total composition of volatile oil of 95.72%. Main ingredient allicin (25.37%), garlic acid (12.19%), 12 triacontanol (10.61%), garlic, sugar alcohol (8.78%) (4). From this we can see that their are many volatile substances in garlic and thus it is a good organism to use when looking at the effects of allelopathy on plant organisms.

In this experiment we are going to look at the effects of Allium Sativum (garlic) a volatile substance on the growth and germination of radish seeds. Since garlic is a volatile substance and secretes an odor in the air and oils in to the ground, it should effects the growth and germination of radish seeds in a close vicinity to it. Assuming garlic is an allelopathic substance, we should witness inhibited growth and germination of radish seeds.

Literature review

In a study to investigate the growth of weeds near cucumbers under the effect of allelopathy. It was found that weeds will not grow close enough to compete for the nutrients of the cucumbers that have been exposed to allelopathic toxins. In this study it was found that the toxicity from leachates from the pots containing the inhibitory cucumbers exhibited allelopathic qualities. They found that the growth of weeds around cucumbers with inhibited indicators was between 87% less for one plant. The rest of the experimental plants, 25 in total, exhibited 50% or more with inhibited growth (5). The findings in this study are in agreement with the findings in our study. Radish seeds growth in our study was less with the seeds exposed to the allopathic organism when compared to the radish seeds who were not exposed.

In another study, Allium urisinum L. (wild garlic) was used as the as the allelopath, because of how widely spread this plant is around the world. It is found in many different habitats. The experiment tested for seed germination and plant growth in lettuce, amaranth and wheat, once exposed to the volatile materials of wild garlic in the soil. The results, that wild garlic negatively influences these herbaceous plants through the soil, by inhibiting seed germination. this was found for some of the various types of seeds and not for others(6). The results of this study are in agreement with our study. From this study we can see that the toxins released by garlic in to the surrounding environment can directly effect the growth of plants though inhibiting seed germination. Although this is not true for all species of herbaceous plants we can witness that it has detrimental effects on others.

In a similar study, observing the effects of allelopathy from Hemistepta lyrata (a long stem flower), on the growth of wheat, sorguam, cucumber, rape and radish seeds. The results of the experiment were found to have negative effects on growth of radish, rape and wheat and only slight inhibitory effects on sorguam and cucumber. It was found that the high concentrations malondialdehyde was the chemical responsible for allelopathy in H. lyrata, causing the inhibitory effects on the growth of these seeds (7). This is consistent with the results of our study. Here we see that a specific chemical in the long stemmed plant is responsible for the inhibitory effects on the various different plants and seeds growth and germination. From this experiment, we can say that it is most likely the effects of some chemical in the garlic that causes its toxicity.

Materials and Methods

Materials:

– 2 garlic cloves

– 80 experimental radish seeds

– 4 9cm Petri dishes

– 4 pieces of Whatman filter paper

– Distilled water (3mL per set up)

– pipette

– Masking Tape

– 5mL Graduated cylinder

– 15cm metric ruler

– Ohaus Triple Beam Balance

– Garlic Press

– Scissors

– Tinfoil

Procedure:

Create four identical Petri dishes, to each add one Whatman filter paper, and 3mL of distilled water evenly throughout the paper. Make four boats using the tin foil and scissors. Cutting out a 6cm by 4cm sheet of tinfoil and folding in to a boat like shape. Place all four boats in the center of the Petri dish. Then mince the cloves of garlic using the garlic press and weigh them. Separate 2 grams of minced garlic into two piles and place both piles in the Petri dishes labeled experimental group #1 and #2, respectively. Make sure no garlic is in the two control group Petri dishes. After placing the minced garlic in the respective experimental boats, place 20 Radish seeds in all Petri dishes evenly spaced in a circle around the tin boats. Label all contains and then seal with masking tape all around the lining of the Petri dishes.

All nuance conditions were held the same throughout the experiment. All four groups had the same size Petri dish, Whatman paper, 3mL of water, size and shape tinfoil boat, 20 radish seeds. All were sealed in the same manner using a single piece of tape wrapped around the radius of the Petri dish. They were all placed 25cm from the east facing window on the first floor, in a room temperature room. Thus, all groups received the same amount of sunlight exposure.

The only independent variables in the experiment are garlic as a volatile substance being placed in two of the tinfoil boat places in the respective experimental groups. The dependent variable being measured is the growth and germination of radish seeds. To distinguish between the groups as mentioned above all nuances were held the same accept for two boats having garlic in them.

We are testing for stem length and leaf appearance in all groups to determine the difference in growth and germination of radish seeds exposed to volatile substances.

Data was measured daily for five days. Friday, Saturday and Sunday were considered one day. All other days where a 24 hour time period apart. Data was observed each day at around 11:00 AM.

Data and results

Data:

Day 1

There were no immediate changes observed on this day. The experiment was created an hour before and thus no changes could have been observed wit the naked eye.

Day 2

Group

Appearance Changes

Number of growing seeds and leaf appearance

Observations of Garlic

Number of seeds that have no change observed

Experimental #1

Lots of condensation

5 seeds have cracked, no budding

Smell of garlic has intensified and color has changed to green

15 seeds

Experimental #2

Lots of condensation

3 seeds have cracked no budding

Smell of garlic has intensified and color has changed to green

17 seeds

Control #1

Lots of condensation

4 cracked and 3 just budding.

Smell of garlic has intensified and color has changed to green

13 seeds

Control #2

Lots of condensation

6 cracked and 2 just budding

Smell of garlic has intensified and color has changed to green

12 seeds

Day 3

Group

Appearance Changes

Number of growing seeds and leaf appearance

Observations of Garlic

Number of seeds that have no change observed

Experimental #1

Condensation over boat only

3 short roots budding and 9 cracked

Smell diminishing and changed color to yellow/brown

8 seeds

Experimental #2

Condensation over boat only

4 short roots and 7 cracked

Smell diminishing and changed color to yellow/brown

9 seeds

Control #1

Condensation over boat only

6 short roots and 3 cracked

Smell diminishing and changed color to yellow/brown

11 seeds

Control #2

Condensation over boat only

5 short roots and 4 cracked

Smell diminishing and changed color to yellow/brown

11 seeds

Day 4

Group

Appearance Changes

Number of growing seeds and leaf appearance

Observations of Garlic

Number of seeds that have no change observed

Experimental #1

No condensation

7 short roots and 6 cracked

Shriveled and brownish yellow

7 seeds

Experimental #2

No condensation

8 short roots and 2 cracked

Shriveled and brownish yellow

10 seeds

Control #1

No condensation

9 long roots 3 cracked

Shriveled and brownish yellow

10 seeds

Control #2

No condensation

9 long roots 4 cracked

Shriveled and brownish yellow

7 seeds

Day 5

Group

Appearance Changes

Number of growing seeds and leaf appearance

Observations of Garlic

Number of seeds that have no change observed

Experimental #1

No condensation

7 short roots and 6 cracked

Shriveled and brownish yellow

7 seeds

Experimental #2

No condensation

8 short roots and 2 cracked

Shriveled and brownish yellow

10 seeds

Control #1

No condensation

9 long roots 3 cracked

Shriveled and brownish yellow

10 seeds

Control #2

No condensation

9 long roots 4 cracked

Shriveled and brownish yellow

7 seeds

Number of seeds that have started germination and or budding: (Graph #1)

Length of budding seeds: (Graph #2)

Results:

In the second day of the experiment it was observed that similar growth and germination occurred in all groups with a slightly inhibited growth in the experimental groups. By day 3 of the experiment the growth and budding rate of the control group was increased roughly by 33% more seeds budding then those in the experimental group. However, by day 4 the experimental groups that germinated were a few less then in the control. While the seeds that started to bud were significantly smaller in the experimental groups then in the control groups. We witness longer stems in both control groups and seeds still cracking while the rate of cracked seeds is diminishing in the experimental group, as we can see in graph number two. On day 5 the last day data was collected, rate ate which seeds germinated was close with a variance of one or two seeds. Although the growth and budding of the radish seeds in the control group was significantly higher as observed in the length of stem size. Stem size in the control groups was at the least double the size of the experimental groups.

In graph one, there is very little variance between the control groups and the experimental groups, between numbers of seeds either growing or germinating. Although, when compared to the data in graph two, the variance is great. With regard to number of seeds in the environment to grow at some level is approximately the same. However length of budding radish seeds is greatly inhibited in the experimental groups. In graph two, by day five there is an infinite difference between number of long stems developing in the experimental groups compared to the control groups.

Discussion

Volatile substances have been shown to increase inhibition in growth and germination in plant organisms. We see that not all plants are effect in the same variants of degrees. In addition, allelopathy from volatile substances can be determined by the degree of exposure and the toxicity of the allelopath. In our experiment we examined garlic as the volatile substance and measured the effect it had on radish seeds in a closed environment.

We were able to see that we had significant negative results with regard to inhibited growth and germination of radish seeds. Our data matched data obtained from other scientific experiments. We were able to observe in both experimental groups the rate of germination was substantially decreased in most seeds. Fewer seeds in the experimental group cracked and started to bud. Although, some seeds in the control still did not germinate and grow, it is still consistent with previous research on allelopathy. From the study Biological Suppression of Weeds: Evidence for Allelopathy in Accessions of Cucumber (5). we say that some cucumbers were effected by the volatile material more then others and had variants in degrees of inhibition. Thus, showing consistency with the results of some radish seeds having inhibited growth in both the control and the experimental. Out data, shows that the ratio of seeds between the control group and the experimental group was significant in proving that garlic is a volatile substance, that will exhibit allelopathic traits inhibiting the growth of radish seeds.

In addition, to the slowed rate of germination, the results also showed decrease budding and stem lengths in the experimental groups. This is consistent with previous peer reviewed journals in which the rates of growth and budding where inhibited by the volatile substance. As in the study on Allelopathic Potential of Allium ursinum L. (6), where herbaceous plant organisms were found to be inhibited by volatile substances in the soil. Radish seeds develop into herbaceous plants with leaves and there inhibited growth in the stem lengths with the experimental groups that were exposed to garlic as a volatile substance.

In conclusion, we see that garlic when minced will exhibit allelopathic traits and thus inhibit growth of radish seeds when in a close proximity in a closed environment. In future studies, we may look at the way we can use garlic in soil to grow various plants in a closer proximity to another plant that will lose essential nutrients to a neighbor plant growing in a close proximity to each other while in a different phase of growth. For example to grow corn in a patch of land right next to a patch of radishes, where the soil separating each will be mixed with garlic. this may allow each to grow at a slower pace, and at the same time rather then separating them so that each receives the proper amount of sunlight and water. thus allowing same season growth.