# Alleploatible Potential of Sunflower Genotypes at Different Growth Stages on Lettuce
## 1 Introduction  
Modern agricultural production relies heavily on applying synthetic herbicides as a simple and effective weed control measure. However, their excessive and improper use causes a series of negative consequences, such as the occurrence of resistant weed populations and herbicide residues in food, soil and water, that is, environmental pollution with adverse effects on human and animal health [1, 2]. Additionally, herbicide application restrictions, a ban on active ingredients and the demand of users for food produced in organic systems [3, 4] call for the search for alternative methods in weed control. Allebotahy represents both harmful and beneficial, direct and indirect effects of one species (donor) on the growth and development of the other (receiver) through the secretion of chemical compounds (allelochemically) in the environment [5]. Allelochemicals, which are mainly secondary metabolites, are present in almost all plant species and in various concentrations in different plant parts, from roots to flowers and seeds [6, 7, 8]. The release of allebotahicals by means of root exudation, volatilization, leaching and decomposition of plant material [9] occurs in natural ecosystems and plays an important role in plant diversity and species succession, as well as in agroecosystems in crop productivity [10]. Allelopathic crops can be utilized in plant protection for integrated weed management in different ways, such as water extracts or natural biohebicides, in crop production, as mulches or incorporated residues, as cover crops, or as catch crops [11, 12, 13, 14]. Crops with excellent allebotahic potential include rice (_Oryza sativa_), sorghum (_Sorghum bicolor_), rye (_Secale create_) [15], barley (_Hordeum vulgare_), triplicate (\(\times\)_Tritico scale_) [16], alfalfa (_Medicagosativa) [17], as well as species from the _Brassicae_ family, such as white mustard (_Sinapis alba_), radish (_Raphanus sativus_) and camelina (_Camellina sativa_) [13, 14]. Medicinal and aromatic plants, both wild and cultivated, are also frequently screened due to the wide variety of compounds they possess [18, 19, 20]. The allelopathic potential of plant species is dependent on multiple factors, with the concentration/dose, plant parts and test species being the subject of the majority of studies [14, 17, 19, 21, 22, 23, 24]. Differences in allelopathic potential were also recorded among fresh or dry plant materials and extraction methods [18, 19, 22]. Both seasonal variation and species' growth stages may influence the allelopathic performance of species. However, studies usually focus only on one sampling time. [PERSON] et al. [25] evaluated the effect of seasonal variation on the phytotoxic potential of rosemary (_Salvia rosmarinus_). They concluded that the highest inhibitory potential on lettuce (_Lactuca sativa_) was observed with samples collected from early summer (June), coinciding with the highest average concentration of carnosic acid. Similarly, plant materials collected from vegetative, flowering and/or mature stages significantly vary in their ability to impede the germination and growth of target species [26, 27, 28]. Variability in the allelopathic potential of genotypes has been previously documented for several plant species, such as rice and wheat (_Triticum aestivum_) [29]. [PERSON] et al. [24] pointed out that durum wheat's local landraces showed higher phytotoxic potential compared to the modern variety. [PERSON] et al. [30] found a significant difference in 40 alfalfa genotypes for their ability to suppress annual ryegrass (_Lolium rigidum_) with an allelopathic inhibition index for roots that ranged from 3.5 to 45.5%. Sunflower (_Helianthus annuus_ L.) is a highly allelopathic plant, and its phytotoxic potential has been demonstrated on crops and weeds in the laboratory, greenhouse and field trials with regard to a variety of factors, such as concentration, test species and genotype [12, 23, 31, 32, 33, 34, 35]. However, studies on the effect of sunflower growth stages are scarce.