Introduction:
Invasion of weeds is one of the major factors in the reduction of yield of agricultural crops in the field conditions. Use of allelopathic plants is one of the methods of weeds control. So far, numerous laboratory and farm methods have been designed to evaluate the allelopathy in various plants. Recently, there have been advances in allelopathy knowledge through the advent of innovative techniques and suitable bioassays. Researchers have shown that numerous problems could be solved in allelopathy investigations by the implementation of such techniques. The old methods have been replaced with new methods such as the Sandwich method by which allelopathic properties of various plants could be evaluated during the shortest time and using the minimum amount of plant sample.
Materials and methods:
Considering that there is significant evidence of the presence of allelopathic compounds in invasive weeds as well as medicinal plants, therefore, in the current research, the main focus was on these two groups of plants for the selection. In this research, the allelopathic activity of 57 plant species (60 samples including leaf, stem, seed, rhizome, flower, gum) of 18 families was investigated using the Sandwich method. In this method, plant samples were first dried at 40 degrees Celsius and then weighed in three replicates with amounts of 10 and 50 mg. Special containers with 6 well were used for cultivation. The diameter of each well was 3 cm. In one row of the wells, 10 mg and 50 mg of plant sample powder were placed in the other row. Then 5 ml of 0.5% agar solution was added to the samples and after the agar cooled and coagulated, another 5 ml of agar solution was added to each well. In this way, the plant sample was placed between two layers of agar. Then, in each well, 5 seeds of lettuce (Lactuca sativa) variety Great Lakes 366 were planted vertically on the agar surface. This variety of lettuce has been selected as an indicator due to its high sensitivity to metabolites. Then the containers were sealed and placed in an incubator with a temperature of 25 degrees Celsius in the dark conditions. After 3 days, the percentage of seed germination was checked by measuring the length of lettuce radicle and hypocotyl. To make it easier to compare plants, data clustering was performed using Minitab software.
Results and discusion:
Using this method, 59 plant samples were placed into 10 distinct clusters. The similarity of plants in each cluster was 85%. The findings revealed that the leaf residues of Anethum graveolens and a Cynara cardunculus clustered together based on their allelopathic activity, demonstrating the most significant growth-inhibitory effect at a concentration of 10 mg of the plant sample. The average percentage of inhibition of radicle and hypocotyl growth of lettuce seedlings caused by these two plants was reported to be 94.95 and 87.65 percent, respectively. Also, 13 plants including leaves of Chenopodium album, Prangos ferulacea, Lepidium draba, Petroselinum crispum, Dianthus barbatus, Convolvulus arvensis, Narcissus tazetta, Heracleum persicum, Onosma dichroantha, Stellaria media, Brassica cretica, Ipomoea purpurea and Apium graveolense Seeds were placed in one cluster. This group also had significant growth inhibitory effects. Although their inhibitory effects were always less than Anethum graveolens and a Cynara cardunculus. The average percentage of radicle and hypocotyl growth inhibition in these plants with 10 mg of dry plant sample was 79.76 and 62.27, respectively. This study demonstrated that both the leaf residue of Hypericum perforatum and Hypericum scabrum significantly enhanced the growth of lettuce seedlings. Even minimal amounts (10 mg of the dried plant sample) resulted in a remarkable increase in radicle growth by 14.65% and hypocotyl growth by 45.15%. Additionally, at a mount of 50 mg, Pistacia lentiscus gum demonstrated exceptional efficacy, enhancing radicle growth by an impressive 90%. Among the plants studied in this study, Cupressus sempervirens leaf residues had an inhibitory effect on radicle growth but stimulated hypocotyl growth. Centaurea behen leaf residues only produced a growth-stimulating effect (43.3%) on hypocotyl growth at amount of 10 mg, and in other cases, they showed allelopathic effects in the form of growth inhibition.
Conclusion:
This study confirms the reliability of the sandwich method for identifying allelopathic plants and assessing their properties. It efficiently evaluates a variety of plants with fewer samples and time. The results suggest that plant residues could be used in organic farming to control weeds. Further research is necessary to identify the specific allelopathic compounds involved.
Acknowledgement:
The authors of this article would like to thank Mr. Mohammad Reza Joharchi, a faculty member of the Herbarium of Ferdowsi University of Mashhad, for his sincere cooperation in identifying the plants used in this study from a botanical perspective, confirming the Persian names, and matching them with scientific names. |
