# Allepolatible Interactions between Seeds of _Portulaca oleraea_ L. and Crop Species
## 1 Introduction  
Weeds are a threat in all cropping systems. These undesirable plants decrease input efficiency, interfere with agricultural practices, impair the quality of plant products, deplete resources such as soil nutrients, moisture, and space allocated to crop plants, and ultimately cause heavy losses in plant production [1]. It has been estimated that the economic damage of weeds is more than 100 billion dollars worldwide [2]. Therefore, eradicating or decreasing the harmful effects of weeds on crop plants is the main target of weed management.  
Allepolathy is a natural process that can be considered as a tool for biological weed control in agriculture [3, 4]. According to the International Allepolathy Society, allepolpathy is defined as any process in which the secondary metabolites produced by plants affect the growth and development of biological systems [5]. Approximately 100,000 secondarymetabolites have been identified to date in plants [6]. A smaller number of these are described as bioactive allelochemicals and are generally classified as members of specific chemical families that include phenolics, terpenoids, glycosteroids, and alkaloids [7]. These compounds are present in various concentrations in many plant parts, including leaves, stems, roots, flowers, seeds, rhizomes, pollen, bark, and buds [8], and are released through root exudates, leaching, volatilization, and decomposition of plant residues [9; 10].  
Several researchers have reported that some plant growth inhibitors from allelopathic plants can inhibit weed growth [11]. Consequently, allelopathic plants and allelochemicals can also be applied in the biological and non-synthetic chemical control of weeds; thus, introducing a new generation of environmentally friendly weed inhibitors and reducing the costs of crop productivity [12; 13].  
Purslane (_Portulaca oleraca_ L.) is a summer annual C4 weed from the Portulacaceae family and is a very troublesome weed worldwide. This weed has been ranked as the 9 th worst weed in the world, recorded in 45 crops in 81 countries [14]. It can severely decrease the yield of plants such as wheat (_Triticum aestivum_ L.), maize (_Zea mays_ L.), tomato (_Solanum Lyopersicum_ L.), and other vegetables [14]. This weed species has been identified as an allelopathic plant containing terpen [15], tannins [16], saponins [17], alkaloids [18], phenolic acids, and flavonoids [19; 20]. [PERSON] et al. [21] indicated that leaves and roots of _P. oleraca_ had detrimental effects on the germination and growth of _Allium cpa_ L., _Brassica oleracea_ L., _Raphanus oleraca_ L., and _S. Lyopersicum_. In addition, leaf and root aqueous extracts of _P. oleracea_ adversely affected the activities of antioxidant enzymes and photosynthetic pigments of _Cucurbitta pepo_ L. So far, no study has reported the allelopathic effect of _P. oleracea_ seeds on seed germination and seedling growth of other species. For this reason, the aim of the present study was to investigate the allelopathic effect of _P. oleracea_ on seed germination and growth of _Phaseous vulgaris_ L., _A. cpa_, _Beta vulgaris_ L., _Vicia faba_ L., and _Pisum sativum_ L.