Screening of Some Cotton Varieties for Allelopathic Potential on Clover Broomrape Germination

Research on the chemical basis of allelopathy has often been hindered by the complexity of plant and soil matrices, making it difficult to track active compounds. Well-designed bioassays under controlled environments can be useful in evaluating the allelopathic potential of plants. This paper describes two experiments about the allelopathic potential of cotton (Gossypium hirsutum L.). In the first experiment, root exudates were collected from six common cotton (G. hirsutum L. and G. barbadense L.) varieties grown hydroponically. The cotton (donor plant) root exudates were tested on clover broomrape (Orobanche minor Smith), to determine which variety had the highest allelopathic potential. In the second experiment, the allelopathic potential of 22 soon-to-be-released cotton varieties was evaluated for clover broomrape using rhizosphere soil and extracts from different plant parts. The results indicated that methanol was a more suitable reagent than distilled water for extracting germination stimulants from cotton plants. There was a significant positive correlation between the rates of clover broomrape germination in the rhizosphere soil treatments and those in the stem extract (r = 0.6018, P < 0.05) and the leaf extract treatments (r = 0.5540, P < 0.05). There was also a significant positive correlation between germination rates in the root extract treatments and the stem extract treatments (r = 0.7237, P < 0.05). In conclusion, the allelopathic potential of cotton can be assayed by observing the germination of clover broom rape seeds treated with cotton stem extracts.