Allelopathic inhibition of seedling emergence in dicotyledonous crops by <i>Cucumis</i> bio-nematicide

Abstract

Crop yield reduction is proportional to the initial nematode numbers at planting. Thus, nematicidal seed dressing is important in the management of plant-parasitic nematodes. When used as postemergent bio-nematicide, crude extracts of ground Cucumis myriocarpus fruits consistently suppress numbers of the southern root-knot nematode (Meloidogyne incognita). This study was initiated to determine suitability of crude extracts of ground C. myriocarpus fruits as a pre-emergent bionematicide on 10 cultivars of different dicotyledonous crops. In each trial, ten levels of crude extracts of C. myriocarpus fruits viz. 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00 and 2.25 g, were arranged in a randomised complete block design (RCBD), with five replicates, under greenhouse conditions. Successful seedling emergence was recorded. Seedling emergence percentage had significant (P ≤ 0.01) negative quadratic relationship with concentrations of crude extracts, with the concentration of crude extracts of C. myriocarpus explaining more than 90% to the total treatment variation in mean seedling emergence of all tested crops. In conclusion, crude extracts of ground C. myriocarpus fruits are not suitable for use as pre-emergent bio-nematicide for seed dressing in the 10 tested crops.

Key words: Allelochemicals, allelopathy, auto-allelopathy, concentration-dependent, cucurbitacin A, crude extracts, synthetic nematicides.