Only 14 pages are availabe for public view
It is well known that hydro and osmo-priming treatments of pre-sowing seeds are one of the most important factors that affecting the breakdown of seed dormancy and increase germination behavior, growth and yield as well as increase plant tolerance versus unfavorable conditions such as water deficit as well as soil and water irrigation salinity. Therefore, the present investigation was carried out to study the effect of some hydro and osmo-priming agents including soaking astor bean seeds in tap water, humic acid (HA,1 and 3% w/w), saline solution (4000 and 8000 ppm) and polyethylene glycol (PEG, 8 bar) were tested for tolerance of water irrigation salinity (2000 and 4000 ppm). The best treatments were applied in a field under saline soil conditions. Therefore, the results will be discussed under the following topics:
1. Laboratory experiments.
2. Field pot experiment.
3. Field experiments.
1. Laboratory experiments
This experiment was conducted to evaluate the effect of pre-sowing castor bean seeds inhydro and osmo-priming solutions to enhance their germination percentage. The castor bean seeds were soaked in each of tap water, HA 1 and 3% (w/w), saline solution (4000 and 8000 ppm) using Straganov solution and polyethylene glycol (PEG, 8 bar) using PEG8000 for 4 days as well as un-soaked seeds as control treatment.
Data indicated that germination of un-soaked castor bean seeds were failed after 4 days and slightly increased up to15% after 14 days of germination. Hydro priming initiated the seeds to absorb water and initiate metabolic enzymes that led to enhance the hydrolysis of complex compounds stored in the seeds. Therefore, the germination percentage was gradually and markedly increased from 5% after 4 days of germination up to 30% after 14 days. pre-soaking seeds in 4000 or 8000 ppm saline solution or PEG 8 bar increased germination percentage reaching their maximal values of 75, 70 and 72%, respectively after 14 days with insignificant differences between them. from the above mentioned data, it could be concluded that soaking castor bean seeds in HA 3% was the best favorable treatment that enhance the germination value to its maximal value of 87%.
Therefore, the response of castor bean seeds primed in 3% HA to water salinity was evaluated.Data indicated that germination percentage remarkably increased up to100% after 14 days as a result of irrigation with tap water. Increasing water salinity to 1000, 1500, 2000 or 2500 ppm decreased significantly the germination percentage at every stage of germination exhibiting 86, 85, 82 and 85% after 14 days, respectively with insignificant discrepancy between them. As the water irrigation salinity increased up to 3000, 4000 and 5000 ppm the germination percentage was markedly declined reaching 70, 51 and 50% for the above respective water salinity.
2. Field pot experiment
The castor bean seeds were soaked in some osmo-priming solutions i.e., water, HA 3%, PEG 8 bar and 8000 ppm saline solution for four days followed by water washing and air drying. The seeds were sown in polyethylene bags and irrigated with tap water. At 21 days old the seedlings were transplanted to plastic pots in the field to evaluate their response to water irrigation salinity of 2000 and 4000 ppm in comparison to tap water as a control treatment. Plant samples were taken to analysis periodically after 41, 55 and 70-days old from transplanting.
2. 1. Effect of osmo-priming treatments
The data of SPAD readings as indication of total chlorophyll leaves number/plant and plant height was determined periodically after 41, 55 and 70 days old from sowing. Data indicated that soaking seeds in each of tap water, HA 3% or PEG 8 bar had slight effect on SPAD readings. Mean- while, soaking castor bean seeds in 8000 ppm saline solution inhibited the chlorophyll biosysythesis and significantly reduced the SPAD readings to its minimal value.
The data of leaves number/plant showed remarkable effect as a result of pre-sowing treatment in HA 3% exhibiting 5.0 leaves/plant. Pre-soaking in each of tap water and PEG being in the second order recording 4.5 and 4.2 leaves/plant, respectively with statistically slight differences between them. Whereas, pre-soaking seeds in 8000 ppm saline solution restricted the differentiation of leaves that reduced them to its minimum value of 2.5 leaves/plant. The priming seeds were not affected SPAD readings and differentiation of leaves, but also affected markedly on enlargement, deviation of stem cells that reflected markedly on plant height. revealed that soaking seeds in HA 3% obtained the significant tallest plants followed by soaking in tap water. The lowest values were found by soaking seeds in each of PEG 8 bar or saline solution 8000 ppm.
Advancing the plant growth period to 55-days old, the SPAD readings were at their maximal levels due to priming seeds in tap water or HA 3% (51.1 and 51.0, respectively). Priming seeds in PEG 8 bar or in saline solution 8000 ppm were in the second and third order. Priming seeds in tap water, HA 3% or PEG 8 bar showed statistically a stable number of leaves/plant being 3.6 to 4.6 leaves/plant. Meanwhile, soaking seeds in saline solution reduced significantly number of leaves/plant to only 2.3 leaves/plant. The significant tallest plants was found due to pre-sowing castor bean seeds in HA 3% exhibiting 30.8 cm. Soaking seeds in each of tap water or PEG 8 bar statistically had the same plant height. Soaking seeds in saline solution 8000 ppm enhanced germination percentage but restricted the growth and elongation of plant height to its minimal.
As the plants aged to 70-days old, the pre-soaking seeds in tap water or HA 3% had slight effect on SPAD readings and leaves number/plant followed in descending order with PEG 8 bar and 8000 ppm saline solution. Pre-sowing seeds in HA 3% had a significant favorable effect on plant height and enhance the plant height in comparable to pre-soaking seeds in tap water or PEG 8 bar, while salt priming in 8000 ppm saline solution inhibited the plant elongation.
The dry matter of tillers, leaves and whole plant were estimated at 70- days old to differentiate between mitigation treatments and their effect on accumulation of biochemical components in plant parts. Data elucidate that priming seeds in HA 3% obtained the best treatment on accumulation of dry matter in tillers, leaves and subsequently the whole plant that overcome the other studied mitigation treatments followed by PEG 8 bar and hydro-priming. The lowest dry tillers, leaves and whole plant were obtained by salt priming in 8000 ppm saline solution.
2.2. Effect of water irrigation salinity
The effect of priming seeds on the response of castor plant to tolerate water irrigation salinity during early growth at different plant ages was evaluated during the present investigation. Data revealed that water salinity affected substantially on some growth parameters including SPAD readings, leaves number/plant and plant height.
At 41-day old the SPAD readings were gradually increased versus increasing water salinity till 4000 ppm for water salinity. These results are true at 41 and 55-days old. On the contrary, the number of leaves/plant at 41, 55 and 70-days old was markedly decreased versus increasing water irrigation salinity. The plant height of seedlings irrigated with tap water was markedly the tallest plants followed by irrigation with 2000 and 4000 ppm.
from the aforementioned data, it could be concluded that increase water salinity affected negatively and substantially some plant growth parameters at early growth stages. It was also found that the studied growth parameters were increased versus advancing the plant age. These increases were in negative relationship with increasing water irrigation salinity, i.e., from tap water up to 2000 and 4000 ppm.
At the end of the growth period, i.e., at 70-days old, the dry weight of tillers, leaves and whole plant were determined. The results indicated that the accumulation of dry weight in plant parts was markedly decreased by increasing water irrigation salinity. It was decreased by about 50% by increasing water salinity up to 4000 ppm in comparison to that irrigated with tap water.
2.3. Effect of the interaction between priming treatments and water irrigation salinity
The effect of the interaction between mitigation treatments by pre-soaking seeds in tap water, HA 3%, PEG 8 bar, 8000 ppm saline solution and water irrigation salinity was studied during growth at 41- days old, 55-days old and 70- days old. It was generally cleared that, the castor bean plants exhibited different sensitivity to water salinity in case of SPAD readings, leaves number/plant and plant height. It was also found that seed osmo-priming in 3% HA reflected a better response of plants to tolerate the increase of water salinity than hydro-priming or osmo-priming using PEG 8 bar or 8000 ppm saline solution. One exception was noticed for SPAD readings; it was generally in positive relationship with increasing water irrigation salinity.
At the end of early growth stages, i.e., 70 days old, the weight of tillers, leaves and whole plant dry weight were determined. The results revealed a favorable effect of osmo-priming seeds in 3% HA before sowing on each of the studied parameters that overcome the other hydro-or osmo-priming mitigation treatments. Also, the dry weight of plant parts was reduced to a large extent versus increasing water irrigation salinity reaching their minimal values by irrigating plants using 4000 ppm water salinity.
3. Field experiments
Two field experiments were carried out in 2011 and 2012 growing seasons to evaluate the response of some mitigation treatments on growth and yield of castor bean plants under saline soil conditions. At harvest of yield components were estimated including plant height, number of branches/plant, leaves number/plant, dry leaves and total plant dry weight. Data indicated that hydro-priming of seeds before sowing obtained castor plants characterized by plant height 93.0 cm, branches number/plant 7.3, leaves number/plant 76.4, dry weight of leaves 100.2 g/plant, dry weight of tillers 189.3 g/plant and total plant dry weight 289.5 g/plant. Mitigation castor seeds in HA 3% before sowing was significantly improved the above respective yield components by rate of 9.1, 34.2, 9.4, 10.1, 26.5 and 20.5%. Whereas, mitigation treatment of seeds in PEG 8 bar slightly reduced the yield component parameters in comparison to priming in HA3%, but still overcome those of seed hydro-priming.
from the above mentioned mitigation treatments of castor seeds in HA 3% and PEG 8 bar, it could be concluded that osmo-priming castor bean seeds before sowing initiate the germination percentage and plant establishment. This observation reflected significantly on studied growth parameters. On the other side, the uses of the above two osmo-priming agents help the plants to tolerate the negative effects of soil salinity and also tolerate the plants versus physiological drought.
Opposite phenomenon was found in case of osmo-priming castor bean seeds in 8000 ppm saline solution. While, this treatment increased germination percentage (Table 1 and Fig 1), the growth characters were generally restricted resulting in reducing plant height by rate of 8.6%, number of branches/plant by 21.9%, differentiation of leaves by 7.3%, biosynthesis and accumulation of biological components in leaves by 7.3%, dry weight of leaves/plant by 7.8%, dry weight of tillers/plant by 9.9% and whole plant dry weight by 9.2% in comparable to control hydro-primed seeds.
3.2. Yield parameters
The increase of yield components of castor plant as a result of mitigation treatments of seeds before sowing by soaking either in HA 3% or PEG 8 bar reflected significantly on seed and biological yields per plant. The increase in seed yield was by 21.2% and13.5%; biological yield by 20.8 and 20.4% for the above respective parameters. Meanwhile, salt priming declined seed yield/plant by 27.2% and biological yield/plant by 9.2%.
The data indicated that the increase in seed yield/plant as a result of pre-soaking seeds in water or HA 3% was corresponded by increase the biological yield being approximately by the same rate of hydro-priming exhibiting harvest index with statistically no significant discrepancy ranging between 68.6 to 68.8%. Osmo-priming in PEG 8 bar or salt priming obtained harvest index in the second and third order being 64.6 and 57.3%, respectively. These findings indicated clearly that the negative effect of PEG 8 bar or salt-priming seeds in 8000 ppm saline solution reflected not only on growth of castor plant but also on seed and biological yields, which subsequently reduced the biological yield and significantly decreased harvest index. Concerning the 100-seed weight, data reveal that it was slightly affected by mitigation treatments ranging between 30.5 to 31.8g. This finding indicated clearly that the studied priming treatments had negligible effect on translocation and accumulation of dry matter in seeds during seed filling period. from the above aforementioned data, it was concluded that the osmo-priming castor bean seeds in either 3% HA or PEG 8 bar for four days before sowing were the most promising osmo-priming treatments that rising the yield and yield components of castor plants.
The results indicated that the seed and crude oil yields/fad were in positive relationship with seed yield/plant. Instantly, the seed and crude oil yields/fad were in descending order with mitigation treatments using HA 3%, PEG 8 bar and hydro-priming exhibiting 870.0, 837.6, 820.8 kg seed yield/fad for seed yield; 399.3, 386.1 and 371.8 kg crude oil/fad, respectively. One exception was monitored for priming in 8000 ppm saline solution that decreased seed and crude oil yield from820.8 and 371.8 and kg/fad due to hydro-priming to 752.0 and 339.2 kg crude oil/fad as a result of salt priming, respectively These decreases were by 8.4 and 8.8% for the above aforementioned parameters as compared to hydro-priming. This finding indicated clearly that pre-sowing salt priming was not adapted to apply as mitigation treatment to tolerate the adverse effects of soil salinity.
3.3. Seed quality
At harvest, castor bean seeds were subjected to chemical analysis of crude protein, total carbohydrates and crude oil content. Data elucidate that the chemical analysis of castor bean seeds were slightly differed versus studied mitigation treatments. Instantly, the seed crude protein percentage ranged between 27.5 to 28.9%; total carbohydrates between 21.5 to 22.7% and crude oil between 45.3 to 46.1%. The extracted oil was used to determine its chemical constituents, i.e., iodine and saponification values. Data cleared that hydro-; osmo- and salt-priming had a slight effect on iodine value ranging between 80.5 to 81.7 and saponification value between 185.1 to 186.4.