Iranian Journal of Seed Research

Extended Abstract
Introduction: The weed invasion is one of the main yield-reducing factors in crops. They are potent competitors on vital resources which limits the availability of the resources for crops. Allelopathy is one of the weeds' abilities that commonly with inhibitory influences, affects plant communities' behavior. Therefore, the evaluation of these compounds' effects is important on crop plants. Also, the identification of allelopathic plants and their bioactive compounds can be a suitable approach to weed management. Thus, the aim of this study was the evaluation of the allelopathic potential of C. falcate on germination indices of wheat seeds and the mode of action of the extract on some enzyme activities. Furthermore, secondary metabolites in methanolic root extract were identified and reported.
Materials and methods: Germination and seedling experiments of Triticum aestivum var. Sardary seeds were tested by 0, 5%, 10%, 15%, and 20% concentrations of C. falcata root extracts based on CRD with four replications at the research laboratory of Maragheh University during 2018-19. Also, the influence of the extract was studied on enzyme activities of alpha-amylase, catalase, peroxidase, superoxide dismutase, and polyphenol oxidase. Furthermore, chemical compounds of the root methanolic extract identified by GC/MS instruments.
Results: Germination percentage and germination rate decreased significantly with the increase in the concentration of the extract, and germination stopped at concentrations above 15%. The results of seedling growth showed severe inhibitory effects of the extract on radicle and shoot organs of wheat seedlings that associated with reducing of the lengths and weights of the organs, and consequently, the vigor of seedling declined. The extract significantly reduced the activity of alpha-amylase, however, the activities of antioxidant enzymes first increased at low and medium concentrations but at high concentrations, the activities declined. The phytochemical analysis identified 62 compounds in the root of this plant that Octadecatrienal, Dihydro-4H-pyrazolo [3, 4-d] pyrimidin-4-one, Hexadecanoic acid, Hexadecanoic acid, 2-hydroxy-1 (hydroxymethyl) ethyl ester, Isopropyl isothiocyanate, and Cyclohexanone could be effective compounds on seed germination.

Conclusion: C. falcata had a very strong inhibitory effect on the seed viability and seed vigor of the wheat seeds. According to the results, the mode of action of the allelopathic compounds is induced by induction of oxidative stress and inhibition of seed reserves remobilization during germination. The high sensitivity of alpha-amylase activity to allelochemicals was detected in this experiment. The decrease in the activity of all studied enzymes at high concentrations of C. falcata root extract was also significant. Stearic acid and palmitic acid derivatives accounted for about 30% of the compounds, which are very likely to interfere with the activity of the enzymes.

 Highlights:

1. Allelopathy effects of C. falcata root extract on germination indices of wheat were studied.
2. Chemical compounds identified were in methanol extract of the plant roots of C. falcate.
3. Oxidative stress is induced by the allelochemicals of C. falcata.

Extended abstract
Introduction: In agricultural systems, several environmental stresses can remarkably alter the growth, physiological, and biochemical responses of plants under stress. One of these factors is the biochemical reactions between plants along with the production of secondary compounds. Allelochemicals mainly have defence and cell wall ligninization roles in plants and do not directly play a role in the growth processes of plants. Thus, an experiment was carried out to evaluate the effect of allelopathic stress of Hypericum perforatum on the germination, physiological, biochemical, and antioxidant activity characteristics of green pea, the benchmark plant sensitive to allelochemicals.
Materials and methods: The treatments included different concentrations of H. perforatum at 11 levels (i.e., 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of the aqueous extract). This research was carried out as a completely randomized design with three replications at the weed science laboratory of Gonbad Kavous University in 2023.
Results: The results of this study showed that one of the factors influencing the physiological, and biochemical characteristics of green pea is the concentration of the H. perforatum extract. In most cases, the percentage and rate of green pea germination, radicle and plumule length, and dry weight of radicle and plumule decreased with increased concentration of aqueous extract compared to the control, so that the greatest reduction in these characteristics was observed in 100% of H. perforatum extract. In contrast, the content of compatible osmolytes such as proline and soluble sugars, phenolic and flavonoid compounds, and antioxidant activity of green pea roots and plumules increased significantly in all studied treatments, with the highest increase in these characteristics observed at the concentration of 100% of H. perforatum aqueous extract. In general, the decrease in the dry weight of green pea seedlings due to the increase in the concentration of the aqueous extract of H. perforatum, despite the relative increase in the content of physiological and biochemical traits, indicates the high intensity of allelopathic stress of H. perforatum extract and their insufficiency, which leads to cytotoxicity against oxidative stress.
Conclusion: Considering the heterotoxicity effect of H. perforatum on green pea sensitive to allelochemicals and its distribution in gardens, barren lands, and wheat and corn fields, the possible effect of their residues in the next planting and even in case of presence in mixed cultivation should be considered.

Highlights:

1. Aqueous extract obtained from the H. perforatum drastically reduces the germination and seedling growth of green peas.
2. The difference in the effect of the aqueous extract of H. perforatum on green pea, the benchmark plant sensitive to allelochemicals, depends on their concentration threshold.
3. The high intensity of allelopathic stress of H. perforatum extract and insufficient non-enzymatic antioxidants lead to oxidative stress.

Extended abstract
Introduction: Chemical compounds in plants include primary or secondary compounds. The allelopathic compounds are mainly of the secondary type, which are released by ways such as leaching, decomposition of plant residues, volatilization, and root exudation. Plants with allelopathic properties have a negative or even positive effect on the germination and growth of other plants by releasing substances in their surroundings. These effects depend on the type of organ, concentration, plant growth location, physiological maturity, etc.
Materials and Methods: An experiment was conducted to evaluate the allelopathic potential of wild barley (Hordeum spontaneum) weed on some germination, morphophysiological, and biochemical characteristics of a reference plant sensitive to allelochemicals, cress (Lepidium sativum), in 2021. This experiment was conducted in the form of a completely randomized design with three replications. The treatments included different concentrations of H. spontaneum aqueous extract at 11 levels (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%).
Results: The results showed that different concentrations of H. spontaneum aqueous extract had a significant decreasing effect on the percentage and rate of seed germination, radicle and shoot length, seedling length vigor index, radicle and shoot dry weight, as well as photosynthetic pigments (i.e., chlorophyll a, b, total, and carotenoids) of cress. Their effectiveness was dependent on the concentration threshold of the aqueous extract. In contrast, the content of proline amino acid , soluble sugars, ion leakage, catalase activity, guaiacol peroxidase enzymes, the concentration of malondialdehyde, and phenolic compounds showed an increasing trend compared with the control. In most cases, the highest increase in these compounds was obtained at the 100% aqueous extract concentration of H. spontaneum. This indicates the oxidative stress and high cytotoxicity caused by harmful compounds present in the aqueous extract of H. spontaneum.
Conclusions: According to the results of this experiment, it can be decucted that the aqueous extract of H. spontaneum, due to its allelopathic properties, prevented germination and seedling growth of L. sativum. Therefore, according to the proof of the harmful effect of H. spontaneum and its high biomass, it may be possible to introduce the bioactive compounds present in this plant for the production of environmentally friendly herbicides or even the potential to produce new formulations of synthetic herbicides in case its positive effect on other species is proven.

Highlights:

1. The difference in the effect of different concentrations of Hordeum spontaneum weed aqueous extract on germination and seedling growth of a reference plant sensitive to the allelochemicals, Lepidium sativum, is related to their concentration threshold.
2. The significant decrease in germination characteristics and photosynthetic pigments of L. sativum indicates the intensity of oxidative stress caused by the harmful compounds in the aqueous extract of H. spontaneum.
3. The allelopathic characteristics of H. spontaneum weed can be a suitable candidate for the production of biological herbicides.