الفهرس 
Allelopathic effectsOnly 14 pages are availabe for public view
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Abstract
Allelopathy, the direct or indirect effect of one plant on another through the production of chemical compounds that escape into the environment, occurs widely in natural plant communities and is postulated to be one mechanism by which weeds interfere with crop growth. The most obvious and probably the most significant. consequence of allelopathy is the control and modification of population densities explaining vegetation patterns in plant .; . communities. Laboratory, pot and field experiments were conducted at laboratories and Experimental Farm of the Faculty of Agriculture, Tanta University at Kafi El-Sheikh, Egypt. I. LABORATORY EXPERIMENTS Allelopathic influence of sunflower stems aqueous extracts on seed germination and seedling growth of wheat and some wheat-weeds Laboratory experiments were conducted to determine the allelopathic influence of sunflower stem extracts (1:20 and 1:10 w/v) with different concentrations (0, 25, 50,75 and 100% VN) on wheat and ryegrass (Lolium temulentum, L.), canary grass (Phalaris minor, Retz.), wildoats (Avena fatua, L.) and common vetch (Vicia sativa, L.). I. Germination I.A.1. Germination percent : The allelophathic effects of the aqueous extracts of sunflower stems on germination of wheat, rye grass (Lolium temulentum, L.), canary grass (Phalaris minor, Retz.), wildoats (Avena fatua, L.) and common vetch (Vicia sativa, L.) were concentration dependent and species specific. The aqueous extracts of sunflower stems with various concentrations had no significant effect on final germination percent of wheat seed. However, it inhibited seed germination of all test weed species and delayed its initiation as the concentration of the two extracts increased. I.A.2. Indices of germination rate : Germination speed and mean germination time indices were calculated from daily count of germinated seeds for each test species to determinate the rate of germination. variation in concentration of the two extracts caused a significant difference in the two indices of all test species. Dilution of the two sunflower stem extracts progressively increased germination speed index of all test species. The inverse was true in mean germination time index. There is an apparent difference in species response to various concentrations of the two extracts. Generally, increasing extract concentration delayed seed germination and increased the time required for complete seed germination. I.B.1. Shoot and root length : The concentration 25% of the two extracts had relatively no or little effect on shoot and root length of wheat and test wheat-weed seedlings. However, increasing extract concentration greater than 25% caused a marked reduction in shoot and root length of seedlings for all test species in most cases. I.B.2. Seedling fresh weight : The extract 1:20 (wlv) at concentration 25% slightly stimulated seedling growth (fresh weight) of the grass species, wheat, ryegrass, canary grass and wildoats seedlings. However, increasing extract concentration from 50 to 100% in the two extracts decreased this trait for all test species. I.B.3. Seedling dry weight : Unlike fiesh weight, dry weight did not show significantly inhibition or stimulation at various concentration of the two sunflower extracts in all test species, except canary grass grown in the extract-2, whereas dry weight reduced at the concentration 100%. 11. POT EXPERIMENTS : (Allelopathic influence of chopped sunflower stems on wehat and two wheat-weeds). Pot experiments were conducted to determine the allelopathic influence of chopped-sunflower stems (mixed with soil at levels 0,2,4,6,8 and 10% wlw) on germination, growth and grain yield of wheat as well as germination and growth of two wheat-weeds (canary grass and wildoats)