Weeds can limit the reproductive and survival traits of cultivated plants either directly or indirectly. Direct effects involve factors such as light, nutrients, water, and space, while indirect effects primarily involve allelopathy. Seed germination is one of the most crucial stages in the life cycle of all plants. Allelopathic effects are one of the significant factors influencing seed germination. Allelopathy occurs through allelochemicals, which are biochemical substances released by one plant that affect the growth of other plants. This study aimed to observe allelopathic effects and determine which weed species have a greater impact on the germination of a selected crop plant. Samples of Amaranthus retroflexus L., Sinapis arvensis L., and Diplotaxis tenuifolia (L.) DC were collected, dried, and ground into small pieces, which were then mixed in distilled water for 24 hours. The mixture was centrifuged, filtered using Whatman filter paper, and the extracts were obtained. The extracts were prepared at concentrations of 12.5%, 25%, 50%, and 100%.These extracts were applied at 6 ml per petri dish containing 10 lettuce seeds each. The petri dishes were kept in an incubator for 6 days at 18°C, with 70% humidity, and under a 16-hour light and 8-hour dark cycle. The effects of the various weed extracts on seed germination count and seedling length were observed and compared with control samples.The results indicated that Amaranthus retroflexus did not have a critical level of allelopathic effect, while Diplotaxis tenuifolia and Sinapis arvensis exhibited significant allelopathic abilities that were of critical importance.
Kosdak et al. (Tue,) studied this question.