Effect of phytotoxicity of allelopathic extracts on growth of various plant species

How does the effect of the extracts of allelopathic plant on the growth of leguminous plants, measured in terms of percentage germination depends on the type of the allelopathic plant chosen- Ocimum tenuiflorum (Tulsi) and Azadirachta indica (Neem) and the type of plant taken-Vigna radiata, Vigna unguiculate, Cicer arietinum, Cicer arietinum L, Pisum sativum?

On a tour of a plant nursery the manager was talking about weed removal from plants. He mentioned the concept of plant allelopathy in passing and it happened to catch my attention. When I went home I decided to do some further research on the topic and found out that a lot of common plants are allelopathic in nature. What i didn’t understand is why this is not a developed technique. To understand the real world relevance of the allelopathic properties of plants i decided to experiment with the resources readily available to me. In environmental sciences in the 9th grade we studied the economic structure of india briefly wherein i found out that most indians stick to a diet of basic legumes. Seeing that my house had multiple variations of leguminous seeds it was evident that this study would be relevant if it had a positive outcome.

Legumes, or pulses, are flowering plants in the Leguminosae family, (Fabaceae, Leguminosae, or Papilionaceae, commonly known as legume, pea, or bean Family, in the Order of Fabales, is a Family, the third largest land plant Family in terms of number of Species). Legumes have often been associated with poverty throughout history. In cultures where a portion of the population can obtain protein from animal sources, beans are seen as food only fit for peasants; the “poor man’s meat”. Eating beans is a cheap way of maintaining important nutritional requirements, but is also accompanied with a negative stigma associated with the lower class; those that could not afford meat had to depend on beans. Food security, lowering the risk of climate change and meeting the increasing demand for energy will increasingly be critical challenges in the years to come. Producing sustainably is therefore becoming central in agriculture and food systems. Legume crops could play an important role in this context by delivering multiple services in line with sustainability principles. In addition to serving as fundamental, worldwide source of high-quality food and feed, legumes contribute to reduce the emission of greenhouse gases, as they release 5–7 times less GHG per unit area (Wong and Ng)compared with other crops; allow the sequestration of carbon in soils with values estimated from 7.21 g kg⁻¹ DM, 23.6 versus 21.8 g C kg⁻¹ year (Genomics in Leguminous Plant-Nutrition Research | Frontiers Research Topic); and induce a saving of fossil energy inputs in the system thanks to N fertilizer reduction, corresponding to 277 kg ha⁻¹ of CO₂ per year (Farkas and Mohácsi-Farkas)

Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms. These biochemicals are known as allelochemicals and have beneficial or detrimental effects on target organisms (Latif et al.) Plant allelopathy is one of the modes of interaction between receptor and donor plants and may exert either positive effects (e.g., for agricultural management, such as weed control, crop protection, or crop re-establishment) or negative effects (e.g., autotoxicity, soil sickness, or biological invasion). To ensure sustainable agricultural development, it is important to exploit cultivation systems that take advantage of the stimulatory/inhibitory influence of allelopathic plants to regulate plant growth and development and to avoid allelopathic autotoxicity. Allelochemicals can potentially be used as growth regulators, herbicides, insecticides, and antimicrobial crop protection products (Genomics in Leguminous Plant-Nutrition Research | Frontiers Research Topic).

This section refers to a study- “Phytotoxic Activity of Ocimum tenuiflorumExtracts on Germination and Seedling Growth of Different Plant Species” (Islam and Kato-Noguchi) by A. K. M. Mominul Islam1 and Hisashi Kato-Noguchi published in “The Scientific World Journal”. An investigation was carried out to study the effect of methanolic extract of O.tenuiflorum on various seeds – cress, alfalfa, lettuce, Italian ryegrass and barnyard grass. A bioassay of germination percentage was measured as an index to understand the effect on germination. It was observed that increasing the concentration of the extract taken has reduced the germination percentage especially in terms of seedling growth. Though the result in case of barnyard grass was different. A positive impact of the extract on germination percentage was observed in case of barnyard grass unlike the other species taken.

Percentage germination – the % of seeds that have germinated after 48 hours.

Formula used: Percentage germination = \(\frac{Number\ of\ seed\ germinated}{total\ number\ of\ seeds\ taken} × 100\)

• The seeds grown in either the Ocimum tenuiflorum solution or the Azadirachta indica solution will show slower growth than the seeds grown in water.

• The experiment uses 50 plastic containers which are a hazard to the environment thus making this experiment environmentally unsustainable. If the plastic containers are cleaned and upcycled for home usage instead, this issue can be taken care of.
• Seeds that are used are used up in compost so that their usage is not a waste.

• Heat resistant gloves: worn during the boiling of water in order to prevent any injuries or burns from the heat.
• Lab coat: worn while boiling water in order to prevent any scope of spillage which might cause skin burns.

• Pick out O. tenuiflorum leaves from a plant
• Clean out 1 container
• Place 1 container on a top pan balance
• Tare the weight of the container
• Add whole leaves of approximately the same sizes 1 by 1
• Keep adding leaves till the sum of their weight is 10g
• Grind the leaves into fine pieces using a blender along with 100ml of water
• Transfer the pasty outcome to a heat safe container with a lid
• Boil 500ml of water
• Add the water to the container with the leaves
• Cover the container with a lid and leave it out for 24 hours
• Using a fine thread, soft, muslin cloth as a filter drain out all the liquid from the mixture
• Leave the cloth with the leaves in it hovering over the container for 2 hours to make sure maximum liquid is drained out.
• Set the acquired extract aside till the final set up.
• Do steps 1-to-14 for the A.indica leaf

• Get a fresh roll of clean white cotton sheet
• Count 55 containers of the identical dimensions and kind
• Place 1 container on a top pan balance
• Tare the weight of the container
• Add thin cotton sheets of approximately the same dimensions 1 by 1
• Keep adding cotton until the weight is 5g
• Repeat steps 1-to-6 for the remaining 54 containers.

• Bring freshly bought packets of each kind of seed
• Pick out 5 large containers
• Count 165 seeds of each kind
• Keep all 5 sets of 165 counted seeds in each of the 5 containers
• Fill all containers with enough water to submerge the seeds fully
• Leave the seeds in the water for 2 hours
• Using a sieve drain out the water from all containers and leave the seeds to dry under the fan for 5 hours

• Layout the containers in two -5×5 grids in two sets as indicated in the diagram below.

• Count 15 seeds of one kind and scatter in one container.
• Repeat for all the containers in the coloumn.
• Each coloumn will be a different seed.
• Add 30 cc of Ocimum tenuiflorum extract to 5/5 rows of the first grid containers.
• Add 30 cc of Azadirachta indica solution to 5/5 rows of the second grid of containers.
• Place a separate row of 5 unique seed containers in the same order.
• Add 30 cc of water to these 5 containers.
• Leave the containers at room temperature by an open window, in direct sunlight.
• After 2 days (48.00 hours), count the number of seeds that has germinated.

Mean number of seeds = \(\frac{Trial-1\ +\ Trial-2\ +\ Trial-3\ +\ Trial-4\ +\ Trial\ 5}{5}\)

The mean has been expressed up to two decimal places and not rounded off to get a more accurate result for the percentage germination.

Standard deviation (SD) = \(\frac{\sum^{i=5}_{i=1}(trial\ value-mean\ value)^2}{5}\)