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Abstract
V SUMMARY AND CONCLUSION
Two experiments were conducted during the winter seasons of (2007,2008) and (2008,2009), to investigate the effects of seed priming on pepper ,tomato and sweet corn seed (1) germination in the laboratory under different stress conditions(salinity and low temperature), (2) seedling growth under green house conditions.
Pepper( Capsicum annuum l.) cv. local, tomato( Lycopersicon esculentum l.) cv. Castle rock and sweet corn(Zea mays l.) cv…Merecure. Seeds soaked in water and different osmotic solutions were studied under stress conditions (salinity and low temperature). The study was conducted in the laboratory and green house conditionsof the Department of Horticulture, Faculty of Agriculture, Suez Canal University, Ismalia In the first experiment, 8 seed priming agents were tested plus a check (control without priming). Priming agents used were (1) PEG 6000, (2) KNO3, (3) KH2PO4, (4) CaCl2, (5) NaCl, (6) MgSO4, (7) KCl, or (8) mannitol under salinity (control, 1500, 3000 and 4500 ppm). All priming solutions were prepared at the same osmotic potential of -1.0 Mega Pascal (MPa). Seeds were then subjected to either standard laboratory germination tests or emergence tests in trays.
Under laboratory conditions. The following data were recorded:
1. Seed germination measurements: germination percentage (GP), mean time to germination in days (MGT), coefficient of velocity of germination, germination performance index (GPI), time to reach 50% germination (T50), and uniformity of germination.
2. Seedling growth parameters, including seedling length, fresh and dry weights.
3. Enzymatic activity, i.e., amylase and peroxidase activities.
In the tray germination experiment, the following data were recorded:
1. Emergence percentage (EP).
2. Mean time to emergence in days (MET).
3. Number of leaves per seedling.
4. Growth rate (mm/day).
5. Leaf production per week.
6. Seedling fresh and dry weights.
The second experiment studied the effects of salinity and low temperature on seedling traits. Five seed priming(control,PEG,KNO3,NaCl and CaCl2) with four salinity levels (0,1500, 3000 and 4500 ppm ),low temperature( 10,15,20,25°c) . After priming, seeds were sowed in rolled filter paper and in the trays under green house conditions. A 4 X 9 and 4 X 5 factorial experiment in a randomized complete block design was used in laboratory and green house, respectively and the following data were recorded:
1. Seed germination measurements: germination percentage (GP), mean time to germination in days (MGT), coefficient of velocity, germination performance index (GPI), time to reach 50% germination (T50), and uniformity of germination.
2. Seedling growth parameters including seedling length, fresh and dry weight.
RESULTS
First Experiment
A. Laboratory Germination
1. In both years, all priming agents increased pepper germination percentage significantly over the control treatment. PEG and KNO3 were the most effective treatments.
2. PEG and KNO3 were the most effective priming agents in decreasing or reducing mean germination time.
3. Coefficient of velocity responded significantly to seed priming treatments and PEG, KNO3 and mannitol were better than other treatments.
4. PEG, KNO3 and mannitol significantly increased pepper germination performance index over other treatments.
5. Time in days required to 50% germination and uniformity were significantly reduced by seed priming agents. PEG, KNO3 and mannitol were the most effective treatments.
6. Seedling characteristics of seedling length, seedling fresh weight and seedling dry weight were significantly increased over the control by priming treatments. Primed pepper seeds recorded the highest value in seedling length. KH2PO4 -priming was most effective in increasing seedling fresh weight. KH2PO4, mannitol, MgSO4 and KNO3 gave the best results in increasing pepper seedling dry weight.
7. All seed priming treatments except KH2PO4 in the first season and KCl in the second season increased amylase activity. KNO3 was the best treatment in increasing amylase activity.
8. Most treatments exhibited incremental increases in peroxidase activity. KH2PO4 was the most effective treatment, whereas NaCl depressed it.
B. Tray Germination
1. PEG and KNO3 were the most effective treatments and significantly increased emergence percentage and decreased mean time to emergence of pepper seedlings.
2. Priming pepper seeds in mannitol solution was most effective in increasing seedling leaf number, followed by KNO3 and Na2SO4.
3. Pepper seedling leaf production per week responded differently to different priming agents. K2HPO4, NaCl and MgSO4 did not affect it, while mannitol, KNO3, KCl and PEG significantly increased it. Mannitol was the most effective.
4. Priming pepper seeds in K2HPO4 was the best treatment in increasing seedling growth rate.
5. Priming pepper seeds in PEG or KNO3 was the most effective in increasing both seedling fresh and dry weights.
Second Experiment
1. Priming pepper seeds in PEG or KNO3 were most effective in increasing germination percentage.
2. The best interaction treatment in improving germination percentage was priming in PEG, combined with salinity at level 1500 ppm.
3. PEG was the most effective priming treatment in decreasing mean germination time in the first season, while KNO3 and mannitol were the best treatments in the second season.
4. The best interaction in decreasing mean germination time, increasing coefficient of velocity, and germination performance index was priming pepper and tomato seeds in PEG with 1500 ppm salinity.
5. Priming pepper seeds in PEG, KNO3 or mannitol was the most effective in increasing coefficient of velocity and germination performance index.
6. PEG was the most effective priming agent in decreasing T50 and uniformity in days.
7. The best interaction of treatments in reducing T50 and uniformity in days priming in PEG and at 20 and 25°C.
8. KNO3 –priming of seeds was the most effective in increasing seedling length and fresh and dry weights.
CONCLUSION
Under the conditions of these experiments, it may be concluded that:
1. Seed priming agents have promotional effects on pepper ,tomato seed germination and seedling establishment.
2. Using PEG or KNO3 as priming agents give the best germination behavior and seedling growth.
3. Salinity with primed pepper,tomato seeds can maintain the benefits acquired by seed priming, especially if priming solutions used are PEG, KNO3 or mannitol. Some harmful effects appear if KCl is used as priming agent, so its use should be avoided.
FURTHER STUDIES NEEDED
More studies should be conducted to:
1. Investigate the effects of seed priming on germination behavior under stress conditions of low temperature, high temperature, or salinity.
2. Study the anatomical, physiological and molecular aspects associated with seed priming.
3. Investigate the effects of seed priming on vegetative growth, flowering behavior and yield of vegetable crops.
GENERAL EVALUATION
Seed priming can create and open new research and crop production windows in seed technology under Egyptian conditions.