الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
In attempt to enhance the germination of three important weeds infested the fields of agricultural crops in Egypt, several laboratory and wire house experiments were conducted in Weed Research Central Laboratory, Agriculture Research Center (ARC), Giza, Egypt. Laboratory experiments were conducted twice in sterilized glass Petri dishes for great wild oat and redroot pigweed, while laboratory and wire house experiments were conducted on common cocklebur. Generally, the experiments involved the estimation of germination and growth traits of obtainable seedling as affected by different concentrations of gibberellic acid and potassium nitrate for great wild oat and redroot pigweed, in addition to thiourea for wild oat. The experiments of common cocklebur included the stimulating effect of some chemicals compared to water and dry fruits/seeds.
The most significant findings obtained from different experiments can be summarized as follow:
1. Avena sterilis L.
1.1. Effect of GA3 on seed germination and seedling growth
All tested concentrations of gibberellic acid caused increases in germination percentage higher than the control. Application of GA3 at a rate of 200 mg L‒1 along with 150 and 250 mg L‒1 showed the maximum germination percentages.
Furthermore, GA3 at a rate of 200 mg L‒1 along with 150 and 250 mg L‒1 treatments showed the highest increases in radicle length, plumule length and seedling dry weight, surpassing the other treatments, except 1000 mg L‒1 GA3 treatments for radicle length, plumule length and seedling dry weight GA3 treatments for radicle length. GA3 at a rate of 200 mg L-1 recorded the maximum germination % (100 %), and the highest values of seedling growth traits.
1.2. Effect of KNO3 on seed germination and seedling growth
All tested concentrations of potassium nitrate caused significant increases in germination percentage higher than the control treatment. Potassium nitrate (KNO3) at a rate of 500, 750 or 1000 mg L‒1 (for radicle length and plumule length), in addition to 200 and 250 mg L‒1 (for radicle length) recorded the highest values. Non-significant (p≥0.05) response was obtained in seedling dry weight owing to the different KNO3 concentrations.
1.3. Effect of thiourea on seed germination and seedling growth
All tested thiourea concentrations caused increases in germination percentage as well as the investigated growth traits higher than the control treatment, except 150 and 200 mg L-1 in which the increase did not reach the significant level (p ≥ 0.05).
The highest values in all studied traits were recorded with the highest thiourea concentration (1000 mg L-1).
2. Amaranthus retroflexus L.
2.1. Effect of GA3 on seed germination and seedling growth
The maximum values of germination percentage were recorded with application of GA3 at rates of 250, 500 and 750 mg L‒1 surpassing the control (0 mg L‒1) and the high concentration (1000 mg L‒1).
2.2. Effect of KNO3 on seed germination and seedling growth
Data of the effect of KNO3 on A. retroflexus L. revealed that there were no significant (p≥0.05) variations among different KNO3 concentrations on germination percentage, plumule length and seedling dry weight. Unlike, radicle length significantly responded to KNO3 levels producing the higher values with 250 and 500 mg L‒1 of KNO3.
3. Xanthium strumarium L.
3.1. Effect soaking fruits in some chemicals reagents on germination and seedling growth at different intervals
The increases in germination % owing to application of thiourea, GA3, and KNO3 amounted to 26.9, 21.5 and 26.9%, respectively, compared to the dry fruits. Germination % did not significantly differ along the various intervals.
GA3 was the effective treatment for increasing the seedling root length statistically leveled with KNO3. The increases in root length due to such two treatments were 53.5 and 31.2%, respectively, compared to the dry fruits.
KNO3 was the effective treatment for increasing the seedling shoot length statistically leveled with thiourea. The increases in root length due to such two treatments were 93.1 and 69.5%, respectively, compared to the dry fruits.
Neither chemicals nor intervals remarkably influenced seedling dry of Xanthium strumarium L. seedlings.
3.2. Effect of soaking upper and lower seeds in water and some chemicals reagents on germination and seedling growth
Regardless the location of seed, soaking X. strumarium seeds in chemicals or not (dry seeds) showed higher germination than soaking seeds in water. Moreover, the germination of lower seed was higher than that of upper one by about 46.4%.
The interaction revealed that all used chemicals and dry seed showed higher germinability for both lower and upper seed than water soaking, except thiourea for upper seeds.
GA3 and KNO3 showed the longest seedling root surpassing the other treatments. The increases in root length with soaking in GA3 and KNO3 amounted to 74.6 and 46.1%, respectively, compared to soaking in water. Root length emerged from lower seed was longer than that of emerged from upper seed by 1.17 time. The lowest root length values were recorded with water soaking for upper and lower seeds and with soaking in thiourea or KNO3 for upper seed.
Upper and lower seeds soaked in GA3 as well as dry lower seed or lower seed soaked in thiourea or KNO3 showed similar root length.
Shoot length of X. strumarium upper seed was as similar as shoot length of lower seed. Dry seed and seeds soaked in different chemicals produced shoot length higher than water-soaked seed
Except upper or lower seed soaked in water and upper seed soaked in thiourea, all other interactions showed the highest similar statistical values.
Dry weight of upper seed was as similar as dry weight of lower seed. Dry seed and seeds soaked in different chemicals produced seedling dry weight higher than water-soaked seed. The lower dry seed or lower seeds soaked in thiourea or GA3 exhibited the maximum seedling dry weight.
3.3. Effect of soaking the fruits in water for different times on germination and seedling growth was grown under wire house conditions
Germination and all seedlings growth traits significantly influenced by the period length of soaking fruits in water. All soaking periods surpassed the control (no soaking) for reducing the germination percentages.
Soaking X. strumarium L. fruits for 36 or 48 h completely inhibited germination %, root length, shoot length and seedling dry weight.
3.4. Effect of soaking the fruits in water for different times under light conditions on germination and seedling growth
Results showed that seed germination of X. strumarium L. significantly (p≤0.05) influenced by the period length of soaking fruits in water under light conditions, while radicle length, plumule length and seedling dry weight did not affect (p≥0.05).
The maximum reductions in germination percentage were recorded with soaking the fruits for 48 or 36 h lower the control (no soaking) by about 66.7 and 41.7%, respectively.
3.5. Effect of soaking the fruits in water for different times under dark conditions on germination and seedling growth
Germination %, radicle length, plumule length and seedling dry of X. strumarium L. significantly (p≤0.05) influenced by the period length of soaking fruits in water under dark conditions. In this respect, without fruits soaking treatment showed the maximum germination and all seedling growth traits significantly equaling soaking for 12 h (in germination %); soaking for 12, 24 and 36 (in radicle length) as well as 12 and 24 h (in plumule length and seedling dry).
The calculated reductions in germination percentages exhibited that soaking X. strumarium L. fruits in water in dark for 48, 36 and 24 h caused approximately 90.0, 70.0 and 60.0% reductions compared to no soaking treatment.
It is interesting to note that soaking X. strumarium L. fruits in water in dark for 48 h achieved reductions in radicle length, plumule length and seedling dry amounted to 75.3, 80.0 and 75.8%, respectively, compared to the control (no soaking).