Introduction

It is widely known that weeds have special concern on agricultural production as they compete crops for the water and nutrients (Możdżeń and Repka, 2014; Al-Harbi, 2017; Glab et al., 2017; Oliwa et al., 2017). Hence, this has negative impact on economic value and production of the crop yield. (Navas, 1991). The weeds are of importance in agriculture and crop production for their harmful effect which is known as allelopathy. The term “allelopathy” is the ecological interference of the weeds through chemical compounds released from them which eventually inhibit the crop germination and growth. These allelochemicals differ from weed species to another (Zimdahl, 2007; Glab et al., 2017). In the last few decades, there is a growing interest to among ecologist to apply examine the allelopathy potential of wild plant species on specific weed species.  Many field experiments have shown that allelopathic substances affect plants (Lawrence, 1991, Inderjit and Dakshini, 1994; Tanveer et al., 2014; Możdżeń and Repka, 2014; Oliwa et al., 2017). Allelopathy is defined as the direct or indirect harmful of one plant on another by releasing of some chemical compounds in the environment (Ashrafi et al., 2008). In fact, allelochemicals are the secondary metabolites that have a remarkable potential as natural pesticides and as growth control (Chon et al., 2005). Allelopathy plays a very important role in natural ecosystem and its management (Inderjit et al., 2005; Glab et al., 2017). Allelochemicals found in any part of the plant, but the greatest amounts are often located in the roots and leaves (Inderjit and Dakshini, 1994; Oliwa et al., 2017).

murale is a widespread harmful weed grows in more than 25 crop species and tree orchards in more than 57 countries  (Lazarides et al., 1997), and it is affects cultivated plants and native plants (Al-Harbi, 2017). Weeds are considered that a major constraint and important problems to agriculture production for all world (Al-Harbi, 2017). In agricultural ecosystems there are many technologies to control weeds by producing chemicals from plant parts of different species (Naseem et al., 2009; Glab et al., 2017). There is a current worldwide demand for environmentally safe for modern weed control methods on the allelopathic potential of some plant species (Al-Harbi, 2017; Glab et al., 2017). Therefore, weeds have been identified as very important factor in crop quality reduction, so weed control is crucial. Mechanical, chemical and biological methods are the major factors in weed management, allelopathic properties of plants is an alternative way of improving weed management. (Tanveer et al., 2014; Motamedi, 2016; Glab et al., 2017; Oliwa et al., 2017) R. epapposum is a perennial plant in the genus Rhanterium belonging to the Asteraceae family. It is native to that Arabian Peninsula, in Saudi Arabia it grows widely in several areas.

Epapposum is a perennial plant in the genus Rhanterium belonging to the Asteraceae family. It is native to that Arabian Peninsula, in Saudi Arabia it grows widely in several areas.

It is a bushy shrub approximately 75 cm height. S. imbricate is a species of the genus Salsola and in the Cheanobodum family. Also, it is a bushy shrub approximately 85cm height.

Recent research work done on allelopathic potential of wheat highlighted a variety of studies which includes natural herbicides derived from allelochemicals could be used to control several weeds (Al-Sherif et al., 2013). The present study was carried out to determine the allelopathic effects of R. epapposum and S. imbricata aqueous extracts obtained from leaves, and their uses as control on seed germination and growth of two weed species Portulaca oleracea and Chenopodium murale.

Materials and Methods

Collection of Plant Materials

The experiment was carried out at Biology laboratory in University College of Tayma, Tabuk University. Leaf samples of selected plants (R. epapposum and S. imbricata) were collected from several locations in Tayma region during the spring (April 2017). The collected samples were cleaned and dried at room temperature 23 ± 2ºC, then shredded into small pieces and grounded into fine powder by electrical grinder and stored in paper bags until use. The seeds of C. murald and P. oleracea were collected and cleaned by the distilled water and  their surface were sterilized with 3% sodium hypochlorite for 4 min to avoid the effects of fungal contamination, and then dried and stored in paper bags until use.

Preparation of Extract

Leaves extract was obtained by soaking 100 g of fine powder in 1000 ml of distilled water at room temperature (23 ± 2ºC) for 48 hours with occasional shaking. The mixture of the extract was filtered twice by two layers of cotton to prevent any plant particulate material from being in the extracts. The extract were saved in the refrigerator at 5ºC until used, the different concentrations (0%, 20%, 40%, and 60%) were made from the stock solution of the extract in addition to the control (distilled water). The concentrations (0, 20, 40 and 60%) were obtained by adding distilled water to the leaves solution. For instance, the 0% control had no leaves extract, while the 20% concentration means of 20% leaf extract and 80% distilled water.

Germination of seeds

To study the allelopathic effect of aqueous extract of R. epapposum and S. imbricata leaf aqueous extract on germination and root, shoot length growth of C. murale and P. oleracea was conducted in four treatments and three replications of both extracts for each of the selected weed species. Twenty seeds of each weed species (C.mural and P.oleracea) were placed in 12 cm diameter Petri-dishes lined with three discs of Whatman No.1 filter paper for control and test, and a 12 ml of the aqueous extract from each concentration were added to each Petri-dish. After three days, germination and root and shoot lengths of the tested species were measured. The measurements were repeated for three times for three days until the end of the experiment (approximately after 15 days).

Calculations

Germination percentage (GP)

The Reduction percentage in root and shoot Length (RP)

Results

The present study revealed that the concentration of the plant extract is an important factor in the allelopathy effect on the P. oleracea and C. murale. All parameters (germination %, shoot length and root length) showed significant differences in their means regardless the extracts used (i.e. R. epapposum and S. imbricata). The results of One-way ANOVA of the parameters means are shown in Table 1.

Table 1: Results of One-way ANOVA showing the effect of extracts concentrations (R. epapposum and S. imbricata) on the germination percentage and shoot and root lengths of P. oleracea and C. murale.

The present study found that there was no significant effect of the plant extract species on the three parameters measured of the targeted plant species. For example, the percentage of germination of P. oleracea exposed to either extract (R. epapposum or S. imbricata) showed no significant difference (t=-0.221, P=0.827). 

Seed Germination

Based on the results of this study the aqueous extracts of R. epapposum and S. imbricata had an inhibitory effect on seed germination of C. murale and P. oleracea at both concentrations, but in P. oleracea seed germination inhibitory effect of R. epapposum extract higher than S. imbricata extract specially concentration of 60%, and in C.mural seed germination inhibitory effect  of R. epapposum  extract higher than S. imbricata extract in all concentrations 20%, 40% and 60% (Table 1).

Table 2: Allelopathic effect of different concentrations of R. epapposum and S .imbricata aqueous extracts on germination percentage of  P. oleracea and C.murale.

Root and Shoot Length

The study showed that aqueous extracts of R. epapposum and S. imbricata had an inhibitory effect on shoot and root length of C. murale and P. eoleracea at both concentrations, but in C. murale shoot and root lengths inhibitory effect  of R. epapposum  extract higher than S.imbricata extract especially concentration of 40% and 60%, generally C.murale shoot and root length more sensitive than P. oleracea  in all concentrations of R. epapposum and S. imbricata aqueous extracts (Tables 2 and 3).

The results showed that the reduction percentages of C. murale root and shoot length under the different concentrations of R. epapposum and S. imbricata aqueous extract is higher than the reduction percentages of P. oleracea root and shoot length under the different concentrations of R. epapposum and S. imbricata aqueous extract (Fig. 1 and 2).

Table 3: Allelopathic effect of different concentrations of R. epapposum and S. imbricata aqueous extracts on Shoot length (cm) and Root length (cm) of C. mural.

Figure 1: Reduction percentages of C. mural root and shoot length under the different concentrations of R. epapposum and S. imbricata aqueous extract. Click here to View figure

Table 4: Allelopathic effect of different concentrations of R. epapposum and S. imbricata aqueous extracts on shoot length (cm) and root length (cm) of P. oleracea.

Figure 2: Reduction percentages of P. oleracea root and shoot length under the different concentrations of R. epapposum and S. imbricata aqueous extract. Click here to View figure

Discussion

The present study aims to examine the effects of the leaf aqueous extracts of Rhanterium epapposum and Salsola imbricata at different concentrations (20%, 40%, and 60%) on the germination and shoot and root lengths of two weed species;  Portulaca oleracea  and Chenopodium murale. Results proved that the inhibitory effect of seed germination and shoot and root lengths of the studied species was largely dependent on the concentration of R. epapposum and S.imbricata leaf extracts. It is acceptable fact that the allelpathic effect of growth inhibition of plant aqueous extracts is proportionally increased with the concentrations. Several studies had found that the inhibitory or stimulatory effect of allelochemicals is notably dependent on their concentrations (Purvis et al., 1985; Sinha et al., 2004; Swain et al., 2005). The involvement of chemical compounds in the allelopathy is evident, hence the higher concentration of these chemical compounds result in more significant effect on the target plant species. According to Tantiado and Saylo (1993), it is difficult to isolate the effect of a single chemical compound and accuse it for growth inhibition effect as the allelopathy process is complicated. Furthermore, this process may involve other ecological influences on the microbial and chemical nature of the soil (Kaur et al., 2009; Weidenhamer et al., 2009).

The allelopathic effect of the two plants in the present study showed remarkable variation of their effect on the germination and shoot and root lengths. This is evident as the seed germination can be inhibited by other allelopathy effect usually between 5-10%. However, this inhibition can increase with higher concentrations of the plant extracts. The allelopathic chemicals have the potential to damaging the seeds structure which results in changing the growth rate (Coder, 1999). The quality of germination of plant species under unfavourable conditions can be indicated by two interacted parameters; number of germinated seeds and how fast the germination is (Tanveer et al., 2014).

In this study, application of the germination percentage is good indicator for the allelopathy effect. This is in agreement with previous studies (e.g. Bewley et al., 2012). Many studies emphasized that germination bioassays are potential indicators to assess the influence of one or more chemical compounds either in laboratory of field (Tanveer et al., 2014). The process of seed germination is more difficult than we thought. It involves various biochemical, physiological and morphological changes in appropriate sequence (Bewley et al., 2012). If any of these changes are interrupted this will eventually results in hindering proper germination and growth and this can be through presence/absence of certain chemical substances.

It is recommended that the extracts of these two plant species; R. epapposum and S. imbricate can be applied in the field to control the invasive weed species which is responsible for remarkable loss of the yield in the agricultural production scale. Further studies in this context are needed to better understand the mechanisms behind the inhibitory/stimulatory effect of plants extracts on weeds species. This includes investigating the chemical constitution of the plant extracts to determine any synergetic effect of these chemicals and their potential in changing the biochemical and physiological structure of the seeds/plants.

Conflict of Interests

There is no conflict of interests.

Acknowledgments

The author would like to thank financial support  for this study from Deanship of Scientific Research, University of Tabuk, Saudi Arabia, grant no. (S – 0067 – 1439).

Funding Source

The financial support  for this study from Deanship of Scientific Research, University of Tabuk, Saudi Arabia, grant no. (S – 0067 – 1439).

References

1.  Repka P. M. Allelopathic influence of aqueous extracts from the leaves of Morus alba L. on seed germination and seedling growth of Cucumis sativus L. and Sinapsis alba L. Modern Phytomorphology. 2014;5:93-99.
2. Harbi A. Diversity and taxonomic composition of weeds in olive orchards in Tabuk Region, Saudi Arabia. Arid Ecosystems. 2017;7:203-208.
   CrossRef
3. Głąb., Sowiński  J., Bough  R., Dayan F. E. Allelopathic Potential of Sorghum (Sorghum bicolor (L.) Moench) in Weed Control: A Comprehensive Review. Advances in Agronomy. 2017;145:43-95.
   CrossRef
4. Oliwa., Możdżeń  K., Rut  G., Rzepka  A. The influence of alcoholic extract from leaves of Helianthus annuus L. on germination and growth of Sinapis alba L. Modern Phytomorphology. 2017;11:91-97.
5. Navas L. Using plant population biology in weed research a strategy to improve weed management. Weed Research. 1991;31:171-179.
   CrossRef
6. Zimdahl L. Fundamentals of weed science, 3ed edn. Academic press. 2013;129-175.
7. Lawrence J. G., Colwell A., Sexton O. J. The ecological impact of allelopathy in Ailanthus altissima (Simaroubaceae). American Journal of Botany. 1991;48:948-958.
   CrossRef
8. Inderjit.,Dakshini.  Allelopathic effect of Pluchea lanceolata (Asteraceae) on characteristics of four soils and tomato and mustard growth. American Journal of Botany. 1994;8:799-804.
   CrossRef
9. Tanveer., Safdar  M. E., Tariq  M. A., Yasin  M., Noorka  I. R. Allelopathic inhibition of germination and seedling vigor of some selected crops by achyranthes aspera L. Herbologia. 2014;14:213-225.
   CrossRef
10. Ashrafi., Sadeghi  S., Mashhadi  H., Hassan  M. Allelopathic effects of sunflower (Helianthus annuus) on germination and growth of wild barley (Hordeum spontaneum). Journal of Agricultural Technology. 2008;4:219-229.
11. Chon U., Jang  H. G., Kim D. K., Kim  Y. M., Boo H. O., Kim  Y. J.  Allelopathic potential in lettuce (Lactuca sativa L.) plants. Scientia Horticulturae. 2005;106:309-317.
    CrossRef
12. Inderjit .,Weston  A., Duke  S. O. Challenges, achievements and opportunities in allelopathy research. Journal of Plant Interactions. 2005;1:69-81.
    CrossRef
13. Lazarides., Cowley  K., Hohnen  P. CSIRO handbook of Australian weeds. CSIRO publishing. 1997.
14. Naseem., Aslam  M., Ansar  M., Azhar M. Allelopathic effects of sunflower water extract on weed control and wheat productivity. Pakistan Journal of Weed Science. 2009;15:107-116.
15. Motamedi., Karimmojeni  H., Sini  F. G. Evaluation of allelopathic potential of safflower genotypes (Carthamus tinctorius L.). Journal of Plant Protection Research. 2016;56:364-371.
    CrossRef
16. Purvis., Jessop  R., Lovett  J. Selective regulation of germination and growth of annual weeds by crop residues. Weed Research. 1985;25:415-421.
    CrossRef
17. Sinha K., Samar  J. S. Allelopathic effects of Xanthium strumarium on Parthenium hysterophorus. Indian Journal of Plant Physiology. 2004;9:313-315.
18. Swain., Pandey  P., Paroha  S., Singh  M., Yaduraju  N. Effects of Physalis minima on Parthenium hysterophorus. Allelopathy Journal. 2005;15:275-283.
19. Tantiado G., Saylo  M. C. Allelopathic potential of selected grasses (Family Poaceae) on the germination of Lettuce seeds (Lactuca sativa). Aquaculture. 1993;112:39-45.
20. Kaur., Kaur  R., Kaur  S., Baldwin  I. T. Taking ecological function seriously: soil microbial communities can obviate allelopathic effects of released metabolites. PloS one. 2009;4:e4700.
21. Weidenhamer D., Boes  P. D., Wilcox  D. S. Solid-phase root zone extraction (SPRE) a new methodology for measurement of allelochemical dynamics in soil. Plant and Soil. 2009;322:177-186.
    CrossRef
22. Coder D., Warnell  D.  Potential allelopathy in different tree species. University of Georgia, Cooperative Extension Service, Forest Resources. 1999.
23. Bewley  J. D., Bradford  K., Hilhorst  H.  Seeds: physiology of development, germination and dormancy, 3ed edn. Springer Science & Business Media. 2012.