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0Faculty of Agriculture, Ain Shams University Annals of Agricultural Science
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Original Article
Response of some varieties of canola plant (Brassica napus L.) cultivated in a newly reclaimed desert to plant growth promoting rhizobacteria and mineral nitrogen fertilizer
M.A. El-Howeity *, M.M. Asfour
Environmental Studies & Research Institute (ESRI), Minufiya University, Sadat City, Egypt
Received 10 April 2012; accepted 23 April 2012 Available online 25 October 2012
KEYWORDS
Canola varieties; Plant growth promoting rhizobacteria;
Nitrogen fertilization; CO2-evolution; Dehydrogenase; Sandy soil
Abstract A field experiment was conducted on a sandy loam soil (newly reclaimed desert), during two successive seasons, to evaluate the effect of plant growth promoting rhizobacteria (PGPR), i.e. Azotobacter chroococcum, Azospirillum brasilense and Paenibacillus polymyxa were added with 30 kg N per fadden (as NH4NO3), in comparison with 30 or 60 kg N only, on yield and its components of canola plants, as well as on the microbial activities in soil, namely CO2 evolution and dehydrogenase activity. A number of canola varieties were tested, i.e. Sedo, Duplo, Serw-4, Pactol and Drakkar.
The obtained results showed that the variety Serw-4 was the best as it recorded the highest values, for most of the studied parameters, i.e. the obtained values of seed yield/plant and seed yield/hectare were (53.11 g and 3034.57 kg) and (56.20 g and 3211.28 kg), in both cultivation seasons, respectively. Results also, indicated that application of PGPR significantly increased both measures of seed yield. However, plant inoculation with Azospirillum brasilense + 30 kg N/fed. (T2) showed the highest increases of both seed yield/plant and seed yield/hectare (37.85 g and 2147.05 kg) and (37.92 g and 2235.33 kg), in both seasons, respectively, as compared with the other bacterial agents or the un-inoculated plants that amended with 30 kg N/fed. However, the highest values obtained with 60 kg N/fed., for seed yield/pant and seed yield/hectare, were (50.96 g and 2934.73 kg) and (50.52 fcsw and 2886.77 kg), in both seasons respectively. Addition of any of the PGPR significantly improved microbial activities in the rhizosphere soil of canola plants, represented by dehydrogenase activity and CO2 evolution. The results gained showed that the Serw-4 variety with 60 kg N/fed. scored the highest values among the other tested varieties, i.e. (73.70 g and 4211.24 kg) and
Corresponding author. E-mail address: journalaaru@yahoo.com (M.A. El-Howeity). Peer review under responsibility of Faculty of Agriculture, Ain-Shams University.
0570-1783 © 2012 Faculty of Agriculture, Ain Shams University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aoas.2012.08.006
(76.33 g and 4361.70 kg), in both seasons, respectively. Response of the other examined varieties to the experimental treatments revealed the order: Serw4 > Duplo > Sedo > Drakkar > Pactol. © 2012 Faculty of Agriculture, Ain Shams University. Production and hosting by Elsevier B.V. All rights
reserved.
1. Introduction
Beneficial plant-microbe interactions in the rhizosphere are determinants of plant health and soil fertility (Jeffreys et al., 2003). In the era of sustainable agricultural production, the interactions in the rhizosphere play a pivotal role in transformation, mobilization, solubilization, etc. from a limited nutrient pool in the soil and subsequent uptake of essential plant nutrients by the crop plants to realize full genetic potential of the crop. Soil microorganisms are very important in the bio-geochemical cycles of both inorganic and organic nutrients in the soil and in the maintenance of soil health and quality (Jeffreys et al., 2003). Thus, the need of the hour is to enhance the efficiency of the meager amount of external inputs by employing the best combinations of beneficial microbes for sustainable agricultural production. Soil-plant-microbe interactions are complex and there are many ways in which the outcome can influence the plant health and productivity (Kennedy et al., 2004). Plant growth promoting rhizobacteria (PGPR) comprise a diverse group of rhizosphere-colonizing bacteria and diazotrophic microorganisms, when grown in association with a plant, stimulate growth of the host. PGPR can affect plant growth and development indirectly or directly (Glick, 1995; Vessey, 2003). In indirect promotion, the bacteria decrease or eliminate certain deleterious effects of a pathogenic organism through various mechanisms, including induction of host resistance to the pathogen (Van Loon and Glick, 2004; Van Loon, 2007). In direct promotion, the bacteria may provide the host plant with synthesized compounds, facilitate uptake of nutrients; fix atmospheric nitrogen; solubilize minerals such as phosphorus; produce siderophores, which sol-ubilize and sequester iron, synthesize phytohormones, including auxin, cytokinins, and gibberellins, which enhance various stages of plant growth, or synthesize enzymes that modulate plant growth and development (Lucy et al., 2004; Gray and Smith, 2005).
Canola plants (Brassica napus L.) is an important oil crop that ranks only behind soybean and palm oil in global production (Francois, 1994). Once considered a specialty for Canada, it is now a global crop. Many other countries including the United States, Australia and those in Europe also grow canola. However, Canada and the United States account for most of the global production. In Egypt canola has a bright future to contribute in reducing oil deficiency gap between production and consumption of edible oil. Growing canola oil crop in less fertile and/or salt affected soils may become successful if it could produce a relatively high economic yield with low level of inputs mainly nitrogen fertilizer.
The present study aims at declaring the influence of using PGPR, i.e. Azotobacter chroococcum, Azospirillum brasilense, and Paenibacillus polymyxa on growth, yield and some yield components of some varieties of canola, as well as the overall microbial activities in soil, represented by CO2 evolution rate (soil respiration) and dehydrogenase activity under the conditions of newly reclaimed desert in Egypt.
2. Materials and methods
2.1. Microorganisms (PGPR) used
Cultures of each of Azotobacter chroococcum, Azospirillum brasilense, and Paenibacillus polymyxa were kindly obtained from the Biofertilizers Production Unit, Agric. Microbiology Dept., Soils, Water and Environ. Res. Inst.(SWERI) Agric. Res. Center (ARC), Giza, Egypt.
2.2. Preparation of bacterial inocula
Each of the bacterial agents, mentioned above, was pre-cul-tured on the recommended media (Hegazi and Niemeia, 1979; Dobereiner, 1978; Dowson, 1957, respectively). The bacterial strains were grown in nutrient broth liquid media for 2 days at 30 0C. Cultures were then centrfugated at 1000 rpm for 30 min. at 10 0C. The sediment was re-suspended in 5 ml sterilized 0.8% KCl (w/v). Each bacterial suspension was again shacked for 5 min. These materials were considered as inocula.
2.3. Agricultural practices
A field experiment was carried out during two successive seasons of 2008/2009 and 2009/2010 on a newly reclaimed desert, at the farm of the Environmental Studies and Research Institute, Minufiya University, Sadat City, Minufiya Governorate, Egypt, to evaluate the effect of inoculation with the above mentioned PGPR plus a half dose of nitrogen fertilizer on growth of some canola varieties (Brassica napus L.). Ammonium nitrate (33.5%N) was added as recommended at a rate of 60 kg N/fed. (full dose) and considered as a control. Experimental treatments were divided into three portions, i.e. 20% and 40% after 30 days from sowing, and the third was 40% added at the flowering stage, for the full N doses, whereas the others received half N dose in combination with PGPR. The experimental area was fertilized with super phosphate (15.5% P2O5) at a rate of 100 kg/fed. and potassium sulfate (48% K2O) at a rate of50 kg/fed., directly before sowing. Randomized complete blocks design, spilt-spilt plots with three replicates, was undertaken where the varieties lay out in the mean plots and the treatments in the sub plots (9 m2). Ordinary agricultural practices and drip irrigation were applied.
Initial analyses, for some physical and chemical properties of the experimental soil, were performed and data are presented in Table 1. Analytical procedures were those recommended by (Cottenie et al., 1982). The experimental soil was sandy loam with above neutral reaction.
The treatments applied were concisely as follows:
1. Inoculation with Azotobacter chrococcum + 30 kg N/fed.
2. Inoculation with Azospirillum brasilense + 30 kg N/fed. (T2).
Table 1 Physical and chemical properties of the experimental soil.
Particle size distribution Texture grade OM (%) pH* EC (dS m"1) CaCO3 CEC (mmol kg"1)
Sand Silt Clay
70.8 21.4 7.8 Sandy loam 0.63 7.75 0.63 6.50 146.22
* pH: Measured in soil suspension 1:2.5.
3. Inoculation with Paenibacillus polymyxa + 30 kg N/fed. (T3).
4. 30 kg N/fed without bacterial inoculation (T4).
5. 60 kg/fed without bacterial inoculation (T5).
Data obtained for canola plant growth and yield at harvest were statistically analyzed, according to Gomez and Gomez (1984), and the least significant difference (LSD), at a probability level of 5%, was used to compare the data of the measured yield.
3. Assay of microbial activities in the rhizosphere soil
Dehydrogenase activity was determined colourimetrically, for the 2,3,5- triphenyl formazan (TPF) produced from the reduction of 2,3,5-triphenyl tetrazolium chloride (TTC), using acetone for extraction (Thalmann, 1967). In this concern, the colorless TTC is changed to red colored TPF.
Microbial respiration in soil (CO2-evolution) was estimated according to (Jaggi, 1975).
4. Results and discussion
Analysis of variance shown in (Table 2) declared that there were high significant differences among the plant varieties in all of the studied traits in both cultivation seasons. This is certainly due to the genetic build up of the different varieties under study. Likewise, the experimental treatments contributed to such changes to some extent. Interaction of the crop
varieties and the applied treatments showed significant differences for most of the studied traits.
4.1. Effect of canola varieties
Data in (Table 3) showed that the varieties Duplo and Serw-4 were earliness, as their plants achieved 50% flowering after 83.27 and 83.80 days, in the first year and after 83.23 and 83.47 days, in the second year, respectively. However Pectol variety was relatively late to reach 50% flowering after 88.13 and 88.80 days, in the seasons of study, respectively. Concerning the plant height, Serw-4 variety was the highest (138.53 and 138.33 cm in both years, respectively), on the other hand Drakkar variety was the shortest (107.22 and 104.00 cm, in both seasons, respectively). For the number of primary branches per plant, Serw-4 and Duplo varieties attained the highest numbers of branches, i.e. 12.40, 11.95 and 12.84, 11.86 in both seasons, respectively. However, Drakkar variety possessed few branches (7.34 and 7.11 in both years, respectively). Regarding the number of siliquas per plant, Serw-4 variety showed the highest values, i.e. 663.87 and 660.67, in both seasons, respectively, where Drakkar variety had the lowest figure (311.53, in the first season) and Pactol (353.67, in the second year). In regard to the number of seeds per siliqua, Serw-4 variety was the best giving 24.13 and 23.54 in both seasons, respectively. On the other hand, Drakkar variety was the worst (21.47 and 21.96) in both seasons, respectively.
For 1000 seed weight, Serw-4 variety showed the highest value in the first year (3.31 g), however Drakkar variety was
Table 2 Mean squares of ordinary analysis for all treatments, canola varieties and their interaction with all studied traits in both
cultivated seasons.
SOVa Days to Plant height No of No. of No. of 1000 seed Seed Seed CO2-evolution DAb (ig
50% (cm) primary siliquas/plant seeds/siliqua weight (g) yield/plant yield/hectare (mgCO2/100 g TPF/100 g
flowering branches (g) (kg) soil/24 h) dry soil/24 h)
2008/2009 season
Varieties (V) 74.51** 2199.50** 61.95** 307779.75** 19.04** 0.74** 1771.21** 5767337.11** 76.52** 51.32**
Error (a) 0.29 82.61 4.23 2901.71 0.60 0.03 1.88 7449.93 0.79 0.60
Treatments (T) 9.51 687.33** 13.78** 161053.18** 5.81** 0.69** 1311.62** 4193003.17** 554.33** 261.54**
V • T 1.75** 125.67** 4.98** 13414.46** 2.44** 0.06** 107.13** 357910.89** 12.65** 1.63**
Error (b) 0.60 21.66 2.09 2297.13 0.26 0.03 12.70 77151.68 1.94 0.38
2009/2010 season
Varieties (V) 94.98** 2521.29** 71.23** 235932.00** 7.75** 0.72** 2295.20** 7592680.24** 114.48** 69.10**
Error (a) 0.28 19.54 0.92 1649.50 0.08 0.03 18.84 43048.53 1.83 0.38
Treatments (T) 8.75** 1324.79** 16.17** 139868.67** 13.92** 0.48** 1145.63** 3791771.27** 586.31** 251.87**
V • T 2.34** 83.54** 5.58** 9886.58** 0.39** 0.03** 92.67** 287149.77** 17.41** 0.75ns
Error (b) 0.21 13.94 1.26 1388.00 0.07 0.01 12.33 25821.49 1.58 1.02
* Significant at 0.05 levels of probability, respectively.
Significant at 0.01 levels of probability, respectively.
a SOV = Source of variance.
b DA = Dehydrogenase activity.
Table 3 Mean values of canola varieties (overall treatments).
Canola Days to Plant No. of No. of No. of 1000 Seed Seed yield/ Seed yield/ CO2-evolution Dehydro-genase
varieties 50% height primary siliquas/ seeds/ weight (g) plant (g) hectare (kg) (mgCÖ2/100 g activity (ig TPF/100 g
flowering (cm) branches plant siliqua soil/24 h) dry soil/24 h)
2008/2009 season
Sedo 87.73 127.96 11.71 511.07 23.41 3.14 34.18 973.72 33.32 15.58
Duplo 83.27 126.80 11.95 544.00 23.53 3.22 39.39 2249.22 34.73 15.39
Serw-4 83.80 138.53 12.40 663.87 24.13 3.31 53.11 3034.57 35.02 16.14
Pactol 88.13 115.47 9.13 358.13 22.13 2.73 25.11 1449.45 39.15 19.70
Drakkar 86.33 107.22 7.34 311.53 21.47 3.11 28.97 1655.16 36.93 18.02
LSD at 0.05 0.45 7.66 1.73 45.44 0.66 0.14 1.16 72.80 0.75 0.65
2009/2010 season
Sedo 87.80 126.47 11.82 460.00 22.77 2.96 35.21 2012.11 37.53 16.26
Duplo 83.23 128.67 11.86 530.00 23.32 3.22 39.57 2329.42 37.26 16.53
Serw-4 83.47 138.33 12.84 660.67 23.54 3.23 56.20 3211.28 36.82 16.58
Pactol 88.80 117.33 9.12 354.87 22.05 2.77 26.29 1502.41 43.31 20.97
Drakkar 86.60 104.00 7.11 371.27 21.96 3.28 26.07 1489.51 40.43 19.56
LSD at 0.05 0.45 3.71 0.81 34.26 0.24 0.15 3.66 155.01 1.14 0.52
LSD = Least significant difference.
the highest in the second year (3.28 g). Regarding to seed yield per plant and seed yield per hectare, Serw-4 variety obtained highest values (53.11 g, 3034.57 kg and 56.20 g, 3211.28 kg) in both years of the study, respectively. Pactol variety was the lowest in the first year (25.11 g, 1449.45 kg) in both treats, respectively. But in the second year, Drakkar variety was the lowest (26.07 g and 1489.51 kg), respectively. These results reflex not only the variety back ground characterists, but also the interaction of the variety and the applied treatments. These results are in harmony with those of Hassan and Hakeem (1996), Said and Keshta (1999), Sharief and Keshta(2000), Leilah et al. (2003), and Asfour (2006).
Data of soil respiration presented in Table 3 exhibit that Pactol variety produced the highest rates of CO2-evolution from the rhizosphere soil (39.15 and 43.31 mgC02/100 g soil/ 24 h) in both seasons, respectively, compared to the other varieties. Drakkar variety followed Pactol variety (36.93 and 40.43 mgC02/100 g soil/24 h). On the other hand, Sedo and Duplo varieties exhibited the lowest values (33.32, 37.35 and 34.73, 37.26) in both seasons, respectively.
Dehydrogenase activity (DA) in the rhizosphere soil was significantly influenced by the plant variety performance. Pac-tol showed the greatest values of DA (19.70 and 20.97 ig TPF/ 100 g dry soil/24 h) in both season, respectively, compared to the other varieties, whereas the lowest values of DA were scored by Duplo (15.39), in first season, and Sedo (16.26), in the second season.
Such results were opposite to the variety performance of the other studied treats especially yield and it's components, which could be referred to absence of certain relationship between varieties and rhizosphere biological activities.
4.2. Effects of the experimental treatments
Data of days elapsed prior to 50% flowering (Table 4), revealed no significant differences among the first four treatments, but significant differences occurred between the fifth treatment and each of the others, where the nitrogen fertilizer full dose, 60 kg N/fed., was applied, leading to extend the period required for 50% flowering to 87.27 and 87.33 days in both
seasons, respectively. The highest values of plant height were 134.53 and 136.53 cm with 60 kg N/fed. (T5) in both years, respectively. But inoculation with Azospirillum brasilense + 30 kg N/fed. (T2) and Azotobacter chrococ-cum + 30 kg N/fed. (T1) showed good results for this trait, i.e. 124.00, 122.43 cm and 124.33, 122.42 cm, in the 2 years for both traits, respectively. As for the number of primary branches per plant, the highest values were 11.99 and 12.44 with 60 kg N/fed. in both seasons, respectively. The treatment of Azospirillum brasilense + 30 kg N/fed. (T2) was the best, as it gave 11.30 and 11.15, in both years, respectively. Regarding the number of siliquas per plant, the highest values were 639.2 and 620.67 siliqua/plant, in both seasons, respectively, with adding 60 kg N/fed. (T5), but the best treatment was that of Azospirillum brasilense + 30 kg N/fed. (T2) which gave 518.80 and 519.00 siliqua/plant, in both seasons, respectively, from the economic and environmental sides. On the other hand, the lowest values were 379.27 and 377.33 siliqua/plant, in both seasons, respectively with adding 30 kg N/fed. only (T4). Concerning the number of seeds per siliqua, the highest values were 23.71 and 24.04 seed/siliqua with 60 kg N/fed. (T5), whereas the best treatment was that of Azospirillum brasilense + 30 kg N/fed. (T2), which showed 23.20 and 23.17 seed/siliqua in both years, respectively. The lowest values in such concern were 21.87 and 21.49 seed/siliqua in both years, respectively, with the dose of 30 kg N/fed. (T4) and without bacterial inoculation. The 1000-seed weight exhibited the values of 3.41 and 3.35 g with the treatment of 60 kg N/fed. (T5) in both seasons, respectively, followed descendingly by the treatment of Azospirillum brasilense + 30 kg N/fed. (T2) which showed 3.21 and 3.17 g in both seasons, respectively. On the other hand, the lowest values were 2.85 and 2.88 g with 30 kg N/fed. only (T4). Regarding the seed yield per plant and seed yield per hectare, the greatest values were 50.96 g, 2927.79 kg and 50.52 g, 2886.77 kg in both seasons, respectively, with 60 kg N/fed. alone (T5). The best treatment appeared to be with Azospirillum brasilense + 30 kg N/fed. (T2), revealing 37.58 g, 2147.05 kg and 37.92 g, 2235.33 kg in both seasons, respectively, whereas, the least values were 26.33 g, 1525.29 kg and 27.35 g, 1562.59 kg in both years,
Table 4 Mean values of treatment (over all canola varieties).
Treatments* Days to Plant No of No. of No. of 1000 seed Seed yield/ Seed yield/ CO2-evolution Dehydro-genises
50% height (cm) primary siliquas/ seeds/ weight (g) plant (g) hectare (kg) (mgCÜ2/100 g activity (ig TPF/100 g
flowering branches plant siliqua soil/24 h) dry soil/24 h)
2008/2009 season
T1 85.60 122.76 10.30 431.67 22.83 2.99 33.74 1927.91 34.94 17.00
T2 85.33 124.00 11.30 518.80 23.20 3.21 37.58 2147.05 42.47 20.70
T3 85.53 118.93 9.95 419.67 23.07 3.04 32.40 1851.36 41.66 20.14
T4 85.53 115.78 8.97 379.27 21.87 2.85 26.33 1525.29 29.02 10.20
T5 87.27 134.53 11.99 639.20 23.71 3.41 50.96 2934.73 31.07 16.78
LSD at 0.05 0.57 3.90 1.07 35.35 0.38 0.13 2.63 151.52 1.03 0.45
2009/2010 season
T1 85.80 124.33 10.43 414.53 22.71 3.03 35.84 2047.55 37.80 17.63
T2 85.47 122.42 11.15 519.00 23.17 3.17 37.92 2235.33 46.23 21.35
T3 85.73 121.00 10.01 445.27 22.23 3.03 31.72 1812.49 44.79 21.41
T4 85.60 110.33 8.81 377.33 21.49 2.88 27.35 1562.59 31.97 11.35
T5 87.33 136.33 12.44 620.67 24.04 3.35 50.52 2886.77 34.55 18.16
LSD at 0.05 0.34 2.75 0.41 27.48 0.20 0.09 2.59 118.52 0.93 0.74
* T1 = Inoculation with Azotobacter chrococcum + 30 kg N/fed., T2 = Inoculation with Azospirillum brasilense + 30 kg/fed., T3 = Inocu-
lation with Peanobacillus polymyxa + 30 kg N/fed., T4 = 30 kg N/fed. Without inoculation, and T5 = 60 kg N/fed. without inoculation.
respectively, with 30 kg N/fed. alone (without bacterial Inoculation) (T4). These results are in agreement with those obtained by Hassan and Hakeem (1996), Said and Keshta (1999), Sharief and Keshta (2000), Leilah et al. (2003), and
Asfour (2006), confirming that the PGPR have a high potential for application in agriculture because they can improve plant growth through phytohormones (IAA, GA) production, solubilization of mineral phosphate, antagonism of plant patho-
Table 5a Interaction mean values between canola varieties and treatments for all studied traits in the first season (2008/2009).
Canola Treatments Days to Plant No. of No. of No. of 1000 seed Seed Seed CO2-evolution Dehydro-genises
varieties 50% height primary siliquas/ seeds/ weight (g) yield/ yield/ (mgC02/100 g activity (ig TPF/100 g
flowering branches plant siliqua plant (g) hectare (kg) soil/24 h) dry soil/24 h)
Sedo T1 87.33 124.80 11.60 427.33 23.45 2.94 29.46 1683.73 30.28 15.22
T2 88.00 128.33 11.33 552.00 23.73 3.40 32.13 1834.67 41.50 18.97
T3 88.33 117.00 10.80 470.67 22.00 3.16 27.94 1596.13 40.63 19.67
T4 87.00 132.33 11.33 461.33 23.20 2.80 27.18 1657.07 26.63 8.07
T5 88.00 137.33 13.47 664.00 24.67 3.40 54.20 3097.00 27.57 15.97
Duplo T1 82.33 122.67 11.60 514.67 22.80 2.17 37.73 2156.10 30.83 15.50
T2 83.33 122.67 13.60 590.00 24.00 3.33 40.07 2289.43 42.40 18.15
T3 83.00 128.33 12.13 561.33 24.00 3.13 38.47 2198.03 43.50 18.33
T4 83.00 118.33 8.67 360.67 22.13 3.07 25.93 1481.83 27.27 9.13
T5 84.67 142.00 13.73 693.33 24.73 3.40 54.75 3120.75 29.67 15.83
Serw-4 T1 85.00 138.67 12.67 718.67 24.53 3.17 55.77 3186.53 34.83 17.20
T2 82.33 143.33 13.60 713.33 24.27 3.37 59.57 3403.67 38.73 20.63
T3 82.67 135.00 12.67 595.33 24.67 3.20 46.97 2683.74 40.10 18.83
T4 83.33 119.33 8.93 430.00 22.00 3.13 29.54 1687.67 29.53 9.02
T5 85.67 156.33 14.13 862.00 25.17 3.67 73.70 4211.24 31.90 15.00
Pactol T1 88.00 115.33 8.93 273.33 22.00 2.72 20.93 1196.13 40.30 19.87
T2 87.67 119.67 10.53 378.00 22.00 2.83 20.97 1540.87 46.60 23.87
T3 87.67 110.00 7.40 252.67 22.67 2.62 20.73 1184.70 41.80 22.20
T4 89.67 110.00 8.67 370.67 22.00 2.33 21.28 1217.10 33.00 13.50
T5 85.33 122.00 10.13 516.00 22.00 3.13 36.90 2108.47 34.07 19.07
Drakkar T1 85.33 112.23 6.72 224.33 21.33 2.97 24.80 1417.07 38.47 17.23
T2 85.33 106.00 7.43 360.67 22.00 3.13 29.17 1666.60 43.10 21.87
T3 86.00 104.33 6.75 218.33 22.00 3.10 27.90 1594.20 42.27 21.67
T4 86.67 98.89 7.27 273.67 20.00 2.93 27.70 1582.80 28.67 11.30
T5 88.33 114.67 8.50 480.67 22.00 3.40 35.27 2101.51 32.17 18.03
LSD at 0.05 1.28 7.68 2.38 79.05 0.84 0.29 1.09 62.94 2.30 1.02
Table 5b Interaction mean values between canola varieties and treatments for all studied traits in the second season (2009/2010).
Canola Treatments Days to Plant No of No. of No. of 1000 seed Seed Seed yield/ CO2-evolution DA
varieties 50% height (cm) primary siliquas/ seeds/ weight (g) yield/ hectare (kg) (mgCÜ2/100 g (lg TPF/100 g
flowering branches plant siliqua plant (g) soil/24 h) dry soil/24 h)
Sedo T1 87.00 125.00 11.67 466.67 22.57 2.93 34.31 1959.93 34.23 16.00
T2 88.00 127.33 11.77 473.33 23.00 3.00 35.37 2020.90 47.00 18.97
T3 88.67 121.67 11.00 400.00 22.07 2.83 27.47 1569.43 46.73 20.30
T4 86.67 120.00 11.50 363.33 22.03 2.73 32.70 1868.52 30.83 9.29
T5 88.67 138.33 13.67 596.67 24.20 3.30 46.23 2641.78 28.83 16.77
Duplo T1 82.00 126.67 12.00 453.33 23.60 3.10 36.03 2059.00 33.60 16.13
T2 83.00 125.00 12.33 600.00 23.87 3.30 42.80 2445.60 45.13 19.16
T3 83.33 130.00 12.33 513.33 22.47 3.23 39.17 2237.99 44.87 20.13
T4 83.00 116.67 8.70 363.33 22.13 3.00 24.50 1399.90 30.47 10.43
T5 85.00 145.00 13.93 720.00 24.53 3.47 61.33 3504.60 32.23 16.77
Serw-4 T1 85.33 140.00 12.90 510.00 23.37 3.20 57.73 3298.90 37.10 16.20
T2 82.33 143.33 14.03 723.33 23.73 3.30 60.10 3434.10 41.23 20.63
T3 82.00 135.00 12.83 683.33 22.87 3.20 49.80 2845.60 41.57 19.37
T4 83.00 118.33 9.17 510.00 22.40 3.13 37.03 2116.10 31.07 10.02
T5 84.67 155.00 15.27 876.67 25.33 3.30 76.33 4361.70 33.13 16.70
Pactol T1 88.67 120.00 8.57 296.00 22.03 2.70 27.73 1584.70 43.27 20.83
T2 87.67 123.33 10.97 415.00 22.60 2.93 29.63 1695.15 51.87 24.50
T3 87.00 111.67 6.70 340.00 21.73 2.63 22.37 1278.03 46.20 24.70
T4 88.33 106.67 8.53 290.00 20.87 2.37 20.27 1158.03 35.23 14.23
T5 90.33 125.00 10.83 433.33 23.00 3.20 31.43 1796.10 39.97 20.57
Drakkar T1 86.00 110.00 7.00 346.67 22.00 3.20 23.37 1335.20 40.80 18.97
T2 85.33 93.33 6.67 383.33 22.67 3.30 27.67 1580.90 45.90 23.50
T3 86.67 106.67 7.20 289.67 22.00 3.23 19.80 1131.40 44.60 22.53
T4 87.00 90.00 6.17 360.00 22.00 3.17 22.23 1270.40 32.27 12.80
T5 88.00 120.00 8.50 476.67 23.13 3.50 37.27 2129.66 38.60 20.00
LSD at 0.05 0.67 6.16 1.85 61.45 0.44 0.16 5.79 265.03 2.07 1.66
gens under limited or stressed conditions (Glick, 1995; Vessey, 2003; Dobbelaera et al., 2003). El- Howeity (2008) found that bacterial inoculation increased shoot and root fresh and dry weights of phaseolus plants.
Data of rhizosphere respiration (Table 4) showed that Azospirillum brasilense + 30 kg N/fed. (T2) gave the highest rates, i.e. 42.47 and 46.23 (mgC02/l00 g soil/24 h) in both seasons, respectively, followed by Bacillus polymyxa + 30 kg N/fed. (T3) which produced 41.66 and 44.79 (mgC02/100g soil/24 h), then Azotobacter chrococcum + 30 kg N/fed. (Tl) giving 34.94 and 37.80 (mgC02/100 g soil/24 h). The treatment of 30 kg N/fed. (T4) produced the lowest values 29.02 and 31.97(mgC02/100 g soil/24 h) in both seasons, respectively.
Results indicated that combination between PGPR and lower dose of nitrogen fertilizer gave significant increases in soil respiration, as compared with the higher dose of such fertilizer without PGPR inoculants. Also, addition of PGPR had a pronounced positive action on DA, Azospirillum brasilense + 30 kg N/fed. (T2) recorded the highest increases with all plant varieties (20.70 and 21.35 ig TPF/100 g dry soil/ 24 h) in both seasons, respectively, followed by Bacillus polymyxa + 30 kg N/fed. (T3) which showed (20.14 and 21.35 ig TPF/100 g dry soil/24 h), then Azotobacter chroococ-cum + 30 kg N/fed. (T1) (17.00 and 17.36 ig TPF/100 g dry soil/24 h). T4 gave the lowest values (10.20 and 11.35 ig TPF/100 g dry soil/24 h) in both seasons, respectively. All PGPR improved the microbial activity in the rhizosphere soil and recorded significant increases, compared to the uninocu-
lated treatments (T4) and (T5). These increases may be due to production of phytohormones such as indolacetic acid, gibberellic acid, cytokinins and ethylene (Arshed and Franken-berger, 1993 and Glick, 1995), a symbiotic N2 fixation (Dobbelaera et al., 2003), antagonism against phytopathogenic microorganisms by production of siderophores (Scher and Baker, 1982), solubilization of mineral phosphates and other nutrients (De Freitas et al., 1997). Stimulating the proliferation of soil biomass certainly improve C02-evolution and DA in the rhizosphere soil. In this concern, Shalaby et al. (2010) observed an improved DA and C02-evolution in the rhizosphere soil of wheat plants with foliar applications of Azospirillum brasilense alone and/or mixed with potassium humate.
4.3. Interaction of plant varieties and experimental treatments
Data of days to 50% flowering (Tables 5a and 5b) showed that the variety Duplo with the treatment Azospirillum brasilense + 30 kg N/fed. (T2) was earliest (83.00 and 83.00 days in the 2 years, respectively), followed by Serw-4 variety (82.33 days in first year, and 82.00 days in the second year). 0n the other hand, Pactol was latest variety (89.67 and 90.33 days) with T3 and T4 in both seasons, respectively. Concerning the plant height Serw-4 variety had the highest values 156.33 and 155.00 cm with adding 60 kg N/fed. (T5), followed by Serw-4 variety with the treatment Azospirillum brasilense + 30 kg N/fed. (T2) 143.33 and 143.33 cm in both seasons, respectively. 0n the other side, Drakkar variety
showed significant decreases in plant height with adding 30 kg N/fed. only (T4), which gave 98.89 and 90.00 cm in both seasons, respectively. For the number of primary branches, Serw-4 variety, with the treatment of 60 kg N/fed. gave the highest values 14.13 and 15.27, and followed descendingly the Serw-4 variety treated with Azospirillum brasilense + 30 kg N/fed. producing 13.60 and 14.03 in both seasons, respectively. Regarding the number of siliquas per plant, the highest values were gained with 60 kg N/fed. by Serw-4 variety (862 and 876.67) in both seasons, respectively. The best treatment for Serw-4 variety was that of Azospirillum brasilense + 30 kg N/fed. (T2), to give 713.33 and 723.33 in both seasons, respectively, on the other side, the lowest values were obtained by Drakkar varieties treated with Paenibacillus poly-myxa + 30 kg N/fed. (T3) (218.33 and 289.67), in both years, respectively. Concerning the number of seeds per siliquas, the Serw-4 variety with 60 kg N/fed. had 25.17 and 25.33 and followed by Duolo variety with 60 kg N/fed. had (24.73 and 24.53) in both seasons, respectively. On the other hand, Drakkar and Pectol varieties had the lowest values (20.00, 22.00 and 22.00, 20.87) with 30 kg N/fed. only in both seasons, respectively. The 1000 seed weight showed its best values at 60 kg N/fed. with the most studied varieties and followed by Azospirillum brasilense + 30 kg N/fed. (T2) in both seasons, respectively. The Seed yield per plant and seed yield per hectare for the Serw-4 variety treated with 60 kg N/fed. achieved the figures of 73.70, 76.33 g and 4211.24, 4361.70 kg in both seasons, respectively. However, the same variety with (T2) Azospirillum brasilense + 30 kg N/fed. gave 59.57, 60.10 g and 3403.76, 3434.10 kg in both seasons, respectively. In regard to soil respiration (CO2-evolution), data in Tables 5a and 5b illustrated also that Azospirillum brasilense + 30 kg N/fed. (T2) recorded the largest increases for all varieties, followed by Bacillus polymyxa + 30 kg N/fed. (T3) then Azotobacter chrococcum + 30 kg N/fed. (T1). Increases by using T2 reached 29.71%, 62.87%, 40.1%, 24.46% and 19.16% compared to 60 kg N/fed. for Serw, Drakkar, Pactol, Sedo and Duplo varieties, respectively. T4 produced the lowest values, compared to any other treatment for all varieties.
Results indicated that combination between PGPR and a low dose of nitrogen fertilizer gave significant increase in soil respiration, as compared with the high dose of nitrogen fertilizer without PGPR inoculant. Increases in CO2-evolution could be attributed to the well furnished habitat provided to the PGPR for the rhizosphere microorganisms.
5. Conclusion
The results obtained suggested that the introduction of plant growth promoting rhizobacteria as inocula can be recommended to increase canola yield and to improve the microbial activities in the rhizosphere soil. Our present investigation revealed that the best variety of canola was Serw 4, under the Egyptian field conditions.
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