The basic approach of allelopathic research in agriculture deals with the screening capacity of weeds in suppressing the growth of crops in different aspects. In the present study, fresh aqueous shoot extracts of Chenopodium murale and Cassia tora, two common obnoxious weeds, were used to determine their allelopathic potential on seed germination and seedling growth of mustard (Brassica nigra L.). The rate of germination reduced considerably with 1:5 concentration of the extracts. In both the cases, root lengths were inhibited more than the hypocotyl lengths, as compared to control. The inhibitory effect was a function of the concentration gradient (1:20, 1: 10 and 1:5), and the greatest inhibition observed was under the high concentration application. Similar effects were observed in the case of enzyme assays. Activities of catalase and ?-amylase were more affected than that of the peroxidase in treated seedlings. Pretreatment of seeds with GA3 could not prevent the inhibition of seed germination and seedling growth when transferred to shoot extracts of the experimental weeds. The shoot extract of C. tora was more inhibitory than C. murale regarding their allelopathic effect on mustard.

There is always a competition between field crops and surrounding weeds of available resources. In addition to this competition, some weeds also interact with the crops through the production and release of allelochemicals present in all its parts (Putnam and Tang, 1986). The concentration of these chemicals vary from one part to another depending on the age of the plant. Allelochemicals may be selective in their action or plants may be selective in their response. Rizvi and Rizvi (1986) considered allelopathy as both harmful and beneficial interaction between the plants, and such interactions play a prominent role in ecology and evolution of plant community. The chemical mechanism of plant interference is characterized by a reduction in emergence or growth of some target species in the vicinity. Though recent studies have revealed the phytotoxic effect of phenolic compounds in plants, the role of other chemicals cannot be ruled out. The root and the shoot extract of Chenopodium murale reduced the growth of many weeds and crops (El-Khatib et al., 2004; Alam and Shaikh, 2007). Aqueous leaf extracts of Cassia tora produced inhibitory allelopathic effect on many weeds (Gupta and Yadav, 2007; and Chin et al., 2001).

C. murale and C. tora, two noxious weeds, both considered as pest in agroecosystems, are found to grow rapidly and densely surrounding the crop fields of West Bengal, India. Assuming that water soluble materials of these two weeds may be released from the plant tissue and exert allelochemic effects on neighboring species, a study was initiated to determine their effect on mustard.

Life Sciences Journal, Milk Production Systems in Bure District, Amhara National Regional State, Milk Development, Marketing Systems, Agricultural Products, Feeding Systems, Calf Rearing, Milk Feeding, Bucket Feeding, Partial Suckling, Dietary Treatments, Veterinary Services.