Based on the minimum duration of exposure, the effect of aqueous plant extract of Croton bonplandianum on seed germination and seedling growth of Triticum aestivum and Brassica campestris was established. Allelopathic activity of the extract increased with increasing duration of presoaking, being more in wheat than in mustard. There is an increasing evidence that several allelopathic compounds inhibit the growth of affected plants through a direct or indirect effect on the rate of photosynthesis. Chlorophyll content and Hill activity of both the crops decreased upon treatment with the inhibitor solution. Soil dressing with leaf-extract seriously affected the target crops. Plant height, root length, number of leaves as well as fruit output and fresh weight are the parameters that were affected more.

Allelopathy describes the reciprocal harmful biochemical interactions that are believed to occur in nature between all classes of plants including microorganisms (Rice, 1984). Substances potentially involved in allelopathy are liberated from plants by (a) abscission and litter fall; (b) leaching of foliage by rain; (c) volatilization by foliage; and (d) root exudation. Biochemical substances involved in allelopathic interaction have been termed allelochemicals and are secondary metabolites widely distributed in plants. Allelopathic potential of several weeds on crop plants have been reported (Schreiber, 1967; Einhellig and Rasmussen, 1975; Shaukat et al., 1985; Putnam and Weston, 1986; Inderjit, 2002; and Oussama, 2003) so far due to the presence of phenolic acid, terpenes, terpenoides, glycosides, alkaloids and flavonoids. In West Bengal, Croton bonplandianum grows vigorously as a noxious weed in various types of habitats like canal bank, riverside, waste places among human dwelling, open and shaded roadside, railway track, swamps, dried or ploughed agricultural field and saline soil of sea coast. Datta and Sinha (1975) studied the inhibition of seed germination and seedling growth of six weedy associate of this unwanted weed. They also indicated that the phytotoxin or inhibitor residing in the leaves of Croton bonplandianum serve as a deterrent to the growth of other plants with which the species is commonly associated. It is very likely that the same toxin(s) would affect many crop plants. Taking this viewpoint into account, a study was conducted with the leaf leachate of this toxic weed to ascertain its inhibitory effect on mature growth parameters of wheat and mustard.

Healthy leaves of Croton bonplandianum were collected from agricultural field of Habra, North 24-Parganas, West Bengal. 20 g of washed and air-dried leaves were crushed, soaked in 100 mL distilled water for 24 h and filtered through Whatman No.1 filter paper. This filtrate served as the stock inhibitor solution of 1:5 concentration from which other concentrations like 1:10, 1:20 and 1:40 were prepared by way of dilution. Surface-sterilized 20 seeds (2% sodium hypochlorite for 2 min) each of wheat and mustard were soaked separately in these concentrations for 3, 6, 12, 24, 36, 48, 64 and 72 h. After the required time period, seeds were washed thoroughly (30 s) and allowed to germinate in 9 cm diameter sterile petridishes containing two layers of Whatman No.1 filter paper and 10 mL of water. Seeds receiving 0 h exposure to test extract served as control. There were four replica per treatment. All the dishes were kept at room temperature (24 ± 3 °C). Visible roots approximately 1 mm. in length were taken as the index of germination. The results were expressed as percentage of corresponding control.

Life Sciences Journal, Allelopathic Effects, Croton Bonplandianum Baill, Seed Germination, Chlorophyll Molecules, Mustard Plants, Chlorophyll Degradation, Chlorophyll Biosynthesis, Soil Treatments, Seed Production, Root Exudation.