Screening Phytotoxic Compounds against Dodder Seedlings

A screening of the 25 compounds (1–25) described in Figure 1 was performed to identify phytotoxic activity against the growth of C. campestris seedlings. The germination of C. campestris seeds is inhibited by a thick seed coat that preserves seedbank viability in agricultural fields over time [2 (link)]. To promote C. campestris germination, the hard seed coat was eliminated by scarification with sulfuric acid for 45 min [36 ], followed by thorough rinses with sterile distilled water. Then, twenty scarified C. campestris seeds were placed using tweezers onto 5 cm-diameter filter paper discs inside 5.5 cm-diameter Petri dishes. All compounds were dissolved in dimethyl sulfoxide and then diluted to 1, 0.5, and 0.25 mM in MES 0.3 mM (2-(N-Morpholino) ethanesulfonic acid) (Sigma M-8250). The final concentration of dimethyl sulfoxide in all treatments was 1%. This was conducted for all compounds except for compounds 3, 4, and 5, which were purchased in liquid form and dissolved directly into MES but supplemented with 1% of dimethyl sulfoxide to allow comparisons. Triplicate aliquots of 1 mL of each treatment were applied to filter paper discs containing the scarified C. campestris seeds. Triplicate aliquots of treatment only containing 1% of dimethyl sulfoxide and MES were used as a control. Treated C. campestris seeds were incubated in the dark at 23 °C for 5 days. The seedling length was measured in each of the five randomly chosen C. campestris seedlings for each of the three replicate filter paper discs per treatment. Seedling growth for each treatment was calculated in relation to the seedling growth of the corresponding control. In addition, notes were taken for each C. campestris seedling regarding whether the root apex had developed dark coloration. The percentage of seedlings that developed the darkening of root apices was calculated in each triplicated petri dish for each treatment.