الفهرس 
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Abstract
Both crops and weeds produce phytotoxins that could be allelochemicals providing an advantage in plant-plant competition. The knowledge of chemical relationships between plants may help in the development of new herbicides. If we mimic nature, we could get new compounds with different sites of action.
Beta vulgaris L var. Cicla (chard) is one of the most harmful weeds in Egypt with important effects on Triticum vulgare. This species shows autotoxicity being a source of allelopathic residues and potential natural herbicides. Indeed, residues of chard in wheat crop that shows strong allelopathic properties brings important agronomic impacts such as the reduction in weed biomass and the increase in wheat yield and soil improvement at green house stage.
The allelopathic potential of Beta vulgaris L. var. Cicla (chard) mature air dried whole plant was evaluated under controlled laboratory and green house conditions using both wheat and chard as experimental plants; wheat grains were germinated and grown in a mixture with chard seeds. Furthermore, chard seeds were germinated and grown separately to confirm its autotoxicity which was indicated from preliminary test. Qualitative and qualitative analysis of phenolic aglycone by HPLC revealed the presence of eight phenolic compounds. The (+) camphor and shikimic acids were the most dominant, while coumarin acid and protocatechuic acid were detected in lesser amounts.
Under laboratory conditions, during period of wheat and chard
germination some growth characteristics were affected as a result of
SUMMARY
treatment with different concentrations of aqueous whole chard plant for * 10 days of exposure. The results obtained for germination and growth characteristic can be summarized follows:
A- Lower concentrations 0.25 and 1% (w/v) stimulated the germination (percentage and speed) of W+C, while C+W and C germination was stimulated at 0.25% and inhibited at 1%. This difference in the response may relate to the sensitivity of each species to the applied aqueous extract. Higher concentrations inhibited and delayed the germination of W+C, C+W and C plants with respective to controls, indicating that chard show autotoxic behaviour at allelopathic concentrations ranged from 1 to 12% (w/v).
B- The reduction in growth parameters (especially, fresh and dry weights) of wheat and chard plant seedlings increased as the concentration of applied allelochemicals increased above 0.25 and 1% respectively, indicating the interference of these allelopathic substances with water uptake and biochemical processes involved in the biomass yield. The high and low values of fresh/dry weight ratio induced by the lowest and highest concentrations of allelochemicals respectively, might be due to the stronger interference of allelopathic substances in water uptake than in the biochemical reactions involved in biomass yield.
C- Thestimulation or reduction in the accumulation of total soluble nitrogen and phosphorus as well as total soluble carbohydrates and nucleic acids (DNA and RNA), which coincided with the estimated amylase activity ^evel, caused with the concentration (0.25 and 1%) or (4, 8, and 12%) and (0.25%) or (1, 4, 8, and 12%) of aqueous whole chard plant extract treatment for wheat and chard respectively. Whereas the
SJJMMA
treatment induced a reduction in the phenolic aglycone which v associated with the increase in phenolic glycosides, relative to the cont samples. An opposite pattern of changes with an obvious inhibitory eff was observed in plants exposed to the higher levels of allelochemic Kind the inhibition was concentration independent.
D- Germination and growth parameters values were more in C tr C+W under control treatment, this could be explained by assuming tl germinating wheat allelochemicals interfere with C+W germination addition to allelochemicals of aqueous chard extract.
In green house pot experiment, incorporation of whole chard pk residues into soil, at the rate 1, 2 and 4% (w/w) induced a stimulate effect on measured parameters in both root and shoot of wheat plai throughout the two growth periods. Chard residue can overcome t harmful effects of chard on wheat, as indicated by the improvement wheat length, biomass and yield production. On the other hand, wh< chard plant residue produced reduction in all growth prameters of cht under the application of the same allelopathic concentrations. T obtained data also indicated that the growth parameters were more in
treatment induced a reduction in the phenolic aglycone which was associated with the increase in phenolic glycosides, relative to the control samples. An opposite pattern of changes with an obvious inhibitory effect was observed in plants exposed to the higher levels of allelochemicals and the inhibition was concentration independent.
D- Germination and growth parameters values were more in C than C+W under control treatment, this could be explained by assuming that germinating wheat allelochemicals interfere with C+W germination in addition to allelochemicals of aqueous chard extract.
In green house pot experiment, incorporation of whole chard plant residues into soil, at the rate 1, 2 and 4% (w/w) induced a stimulatory effect on measured parameters in both root and shoot of wheat plants throughout the two growth periods. Chard residue can overcome the harmful effects of chard on wheat, as indicated by the improvement of wheat length, biomass and yield production. On the other hand, whole chard plant residue produced reduction in all growth prameters of chard under the application of the same allelopathic concentrations. The obtained data also indicated that the growth parameters were more in C than C+W at treatment control may due to wheat allelochemicals’ negative effect on chard growth.