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Abstract SUMMARY The novel plant protectants based on natural products especially which prepared from allelopathic plants is one of the most important approaches to find alternatives of chemical herbicides. Such approach is expected to play an important role in preventing the adverse effects of the chemical herbicides. So, the aim of the present study is to evaluate the herbicidal activity allelopathic plant extracts namely Sorghum bicolor L and Oryza sativa L on wheat and wheat weeds (wild oat, canary grass) under local conditions. The biocidal activity of the tested extracts was compared with two of the most common herbicides i.e. diclofop- methyl and clodinafoppropargyl used on wheat. Also, residues of the tested herbicides in wheat plant and soil were determined. Evaluation the herbicidal and phytotoxic effects of the tested materials were carried out under laboratory, green house and semi field conditions, and the following parameters were measured: 1- Germination percentage of wheat 2- Seedling shoots and root length 3- Dry weight of treated wheat, wild oat and canary grass 4- Chlorophyll content 5- Plant height 6- Plant numbers in experimental plots 7- Spike length and spike weight of treated wheat The obtained results could be summarized as follows: I-Herbicidal activity and phytotoxic effects of the prepared extracts and conventional herbicides on wheat and associated weeds 1- Germination percentage Aqueous and methanolic extracts of sorghum and rice straw at 10&20% were completely suppressed germination of wild oat and canary grass. However, the concentration of 5% from both indicated less inhibition in 93 SUMMARY Amira, S. Mahmoud, M.Sc., 2016 germination of the two tested weeds, wheat the germination percentage ranged 5± 0.8 – 51.3 ±1.73. On the other hand, the effect of all extracts on wheat as compared with control and the two chemical herbicides was variable based on the concentration. Some concentrations such as sorghum methanolic extract at concentration of 10 and 20% showed 0% germination percentage. On the contrary sorghum aqueous extract at concentration 20% caused an increase in germination percentage 75 ±1.4 in control to 90 ±2.6. 2-Seedling shoots and root length All tested aqueous extracts of both sorghum and rice straw had no negative effect on seedling shoot and root length of wheat. However, the tested methanolic extracts as well as chemical herbicides significantly decreased seedling shoot and root length. On the other hand all tested treatments completely suppressed seedling shoot and root length of wild oat and canary grass compared with the control. With exception of 5% aqueous extract of sorghum showed (1.94 ±0.8 and 1.54 ±0.9 cm) and (4.94 ±0.8 and 3 ±0.4 cm) for wild oat and canary grass, whereas they were (2.38 ±0.8 and 1.75 ±1.3) and (6.04 ±0.3 and 2.7 ±0.5) in control, respectively. 3-Dry weight (under laboratory, green house and semi field conditions) 3.1- In Laboratory. The maximum reductions in dry weight (100%) of wheat were obtained with 20% aqueous and methanolic extract of sorghum. Whereas, the reduction caused by each of diclofop- methyl and clodinafop- propargyl were 4.1 and 16.6 %, respectively. Regarding wild oat all tested extracts significantly reduced the dry weight of the weed. The heights reductions (100%) were observed for all concentrations of the methanolic extracts, 10 and 20% aqueous extracts. whereas, maximum inhibition in the dry weight of canary grass (100%) was obtained for concentrations of 10& 20% rice straw extracts and 20% methanolic extract of sorghum. 94 SUMMARY Amira, S. Mahmoud, M.Sc., 2016 3.2- In Green House All treatments including tested extracts had no significant different effect on dry weight of wheat than control. Regarding wild oat the highly reductions of dry weight were observed with diclofop- methyl then clodinafop- propargyl by 43 and 27.2 %, respectively. Lower % reductions were recorded by tested extracts. However, the highest % reduction was recorded against canary grass by the two tested herbicides as well as the highly concentrated extracts at 10 and 20 %. 3.3-In Semi Field The two tested herbicides caused an increase in dry weight of wheat ranged 12.39- 36.32 %. Extracts of sorghum and rice straw at concentrations of 10 and 20 % caused the same trend or lightly reduction ranged 1.28- 11.54%. The concentration at 5% caused higher reduction of the dry weight ranged 7.69- 22.22%. Reduction in dry weight of wild oat was observed with all treatments. The maximum reduction was recorded with sorghum methanolic extract at 20% (31.42 %) and diclofop-methyl treatment (30.97%). Other extracts caused variable percentage of reduction based on the concentration. Dry weight of canary grass was reduced in all treatments. Diclofop-methyl gave maximum reduction (53.85%) and was followed by clodinafoppropargyl (37.12%) and 20% aqueous extract of sorghum (37.46%). 4- Chlorophyll percentage 4.1- In Green House All tested extracts and herbicides have no negative effect on chlorophyll contents of wheat leaves compared to the untreated plants (control). Regarding wild oat all treatments caused observed reduction in chlorophyll content based on type of treatment. Methanolic extracts at 20% indicated decrease in such content reach to 31.8 and 31.4, respectively. Whereas, diclofop- methyl and clodinafop-propargyl showed reduction at 28.2 and 30. The same trend of the effect of the tested herbicides and extracts on the chlorophyll content was observed on canary grass. 95 SUMMARY Amira, S. Mahmoud, M.Sc., 2016 4.2-In Semi Field All tested extracts and herbicides have no negative effect on chlorophyll contents of wheat leaves after three successive applications. However the chlorophyll content of wild oat after the 3 application was reduced to reach 24.5 as a result of treatment with diclofop –methyl and was followed by clodinafop- propargyl and 20% of tested extracts. On the other hand chlorophyll content of canary grass was significantly decreased by all treatments as compared to control. 5- Plant height 5.1- In Green House All tested extracts had no negative effect on plant height of wheat compared to the untreated plants. However, plant height of wild oat was significantly affected by all treatments. There is reduce in plant height depending on the type of herbicide and concentration of the tested extracts. Regarding canary grass of plant height showed non- significant effect between concentrations of tested extracts at 5 and 10%. However, treatments at 20% concentration as well as the two tested herbicides caused similar results in reduction the plant height. 5.2-In Semi field All tested extracts and herbicides have no negative effect on chlorophyll contents of wheat leaves compared to the untreated plants. However, aqueous extract of sorghum recorded similar results which obtained with the diclofop- methyl and clodinafop- propargyl on reduction plant height. Aqueous extract of rice straw with the two tested herbicides showed the same trend against canary grass. 6- Plant Number (under Semi Field Conditions) All extracts at the different concentrations as well as the two tested herbicides caused reduction in plant number of wild oat. Some of extracts recorded similar effect of diclofop- methyl and clodinafoppropargyl such as the methanolic extracts of rice straw at 5and 20%. 96 SUMMARY Amira, S. Mahmoud, M.Sc., 2016 Regarding the canary grass, only the methanolic rice straw at 20% caused similar results of the two tested herbicides. 7- Spike length and spike weight of treated in wheat Data concerning spike length and spike weight of treated wheat with the two tested herbicides and extracts especially at 20% concentration showed now negative effect on the two parameters of crop productively under green house or in semi field conditions. II- Herbicides residues in wheat plants and soil 1. The dissipation of diclofop-methyl residues on wheat leaves and soil The initial residues of diclofop-methyl on leaves were 5.24 μg a.i/ gm and reached 3.95 μg a.i/ gm at 7 days after application. However, no residues were detected after 14 days of application on wheat leaves. On the other hand, the higher level of residues was recorded in soil samples at two week and four week of spraying, showing 0.44 and 0.14 μg a.i/ gm respectively. 2. The dissipation of clodinafop-propargyl residues on wheat leaves and soil The clodinafop-propargyl was rapidly degraded in the wheat leaves and soil samples. Where, the residues of the treated herbicide were not detected in all successive intervals of soil and leaves samples except after 3 h of application on leaves which reached 0.078 μg a.i/ gm. |