الفهرس 
ِAcknowledgementOnly 14 pages are availabe for public view
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Abstract
Weeds constitute a serious global problem influencing the I agriculture and overall crops productivity. Weeds interfere with the field | crops in two ways, competition for the limited resources and also I through allelopathy. Allelopathy is the concept for the general
phenomenon of chemical plant interaction. Allelopathy implies both I promotion and inhibition also; direct and indirect influence mediated
through natural synthesized chemicals namely allelochemicals.
The present study investigated the allelopathic activity of the weed [species of Beni-Suef governorate; particularly weeds grown associated
to important field crops and Citrus orchards within the study area. Beni-Suef is one of Egyptian governorates that locates on the river Nile and characterizes by the presence of cultivated lands on both sides of the Nile.
Ninety seven weed species were collected from the crop fields and orchards within the study area. Weeds belong to Graminae, leguminosae and compositae families are most abundant in fields. These are large families containing of large number of plant species.
The allelopathic potential of weed plants was demonstrated in a laboratory bioassay (Sandwich Method), and then biochemical analysis was done for assessment of Phenolic compounds that produced by these weeds and may play an essential role of their allelopathic activity. Some weed species which found to have the greatest allelopathic potential were analyzed by high performance liquid chromatography HPLC for identification of possible allelochemicals in order to get insight of the effective compounds within each plant. Various studies are conducted in
allelopathy to find out plant species with high allelopathic activity, identify allelochemicals, study dynamics and modes of action of allelochemicals.
The results show the variability of the allelopathic activity of all studied weed species. Since, they exhibited allelopathic potential (stimulatory or inhibitory) against lettuce {Lactuca sativa) at various degrees. However, the strongest allelopathic inhibitory activity were obvious in five weed species, Anagalis arvensis, Chenopodium ambrosioides, Medicago polymorpha, Melilotus indicus and Trigonella hamosa. In terms of inhibition percentage these five species were strongly suppressive to lettuce growth (both radicle and hypocotyl) and in both 10 and 50 mg leaf treatment and the inhibition pronounced more in holes containing 50 mg dry leaf litter due .to the increment of |allelochemicals content. Moreover, some species show significant suppressive capability but less remarkable than the aforementioned weeds.
The studied species leaf materials were subjected to biochemical analysis for determination of their phenolic content. Phenolic compounds are secondary metabolites involved in plant defense mechanisms and among the most ubiquitous putative allelochemicals in allelopathy literature. Results revealed variability of the total phenolic content of studied species. v$
HPLC analysis of the most allelopathically active weed species [(mentioned above) show the presence of a number of phenolic scompounds and phenolic acids such as ferulic, p-coumaric, salicylic, p-hydroxybenzoic acids which are previously documented as potent allelochemicals. In addition Melilotus indicus and Trigonella hamo s
contain high concentration of coumarin. Coumarin and its derivatives are exist in many plants and commonly known for their medical importance I and also known as anti-insecticide.
The present study was conducted to seek for the potentiality of weed species against the economically important crops, hoping to provide the allelopathic literature with useful information. Much efforts I made, and still continuing, aiming for the efficient use of allelopathy for I weed management.