Allelopathic Potential and Allelochemicals in Different Intercrops for Weed Management in Rainfed Cotton

Allelochemicals released by plants serve as the primary defence by targeting the establishment of weeds and other plants. In this study, 12 different intercrops were assessed over five seasons for total phenol and terpenoid content. A detailed analysis on allelochemi-cals produced was also done using gas chromatog-raphy–mass spectrometry (GC–MS) to correlate with their weed suppression efficiency. Total phenol con-tent of intercrops ranged from 6.5 to 17.6 mg g^–1 tissue dry wt, with the highest value in carom followed by sorghum, sunnhemp and marigold. Total terpenoid content of leaf extracts of the intercrops varied from 14.5 to 35.9 μg g^–1 tissue dry wt, wherein pearl millet had maximum terpenoid content (35.9 μg g^–1 tissue dry wt) followed by sunnhemp and sesame. Analysis using GC–MS indicated the presence of some unique as well as common allelochemicals in the experimental intercrops. To correlate the abundance of these allelo-chemicals released from intercrops with their weed suppression competence, relative neighbour effect (RNE) value was determined for each intercrop. Posi-tive RNE values for sunnhemp, pearl millet and sesame indicate their efficiency in effectively reducing weed population than the other intercrops. Thus, in-tercrops with high phenolic, terpenoid and other alle-lochemicals specific to sunnhemp, pearl millet and sesame can be correlated well with weed suppression as perceptible from their RNE values.