Evaluation of drought resistance and yield in PGPR-primed seeds of Festuca arundinacea Schreb under different levels of osmotic potential and field capacity.
Priming offers a means to raise seed performance in many crop species (Chiu et al., 2002). Heydecker et al. (1973) defined seed priming as a pre-sowing treatment in osmotic solution that allows seeds to imbibe water to proceed to the first stage of germination. Taylor et al. (1998) used a broader term, seed enhancement, which includes presoaking hydration (priming), coating technologies, and seed conditioning. Therefore, seed priming can be accomplished through different methods such as hydro priming(soaking in water), osmopriming (soaking in osmotic solutions such as polyethylene glycol, potassium salts, e.g. KCl, K2SO4) solid matrix priming, and using plant growth regulators(PGRs) (Capron et al., 2000; Chiu et al., 2002; Dearman et al., 1987; Harris et al., 2002). Priming has been known as a viable technology to enhance rapid and uniform emergence, high vigor, and better yields mostly in vegetable and flower species (Bruggink et al., 1999; Dearman et al., 1987; Parera and Cantliffe, 1994) and some field crops (Basra et al., 1988; Chiu et al., 2002; Giri and Schillinger, 2003; Harris, 1999; Hartz and Caprile, 1995; Murungu et al., 2004). Seed priming has been a common seed treatment to reduce the time between seed sowing and seedling emergence and the synchronization of emergence (Parera and Cantliffe, 1994).
Forages are the backbone of sustainable agriculture and contribute extensively to the world economy (Barnes and Baylor, 1995). On a worldwide basis, grassland acreage is estimated to be twice that of cropland (Jauhar 1993). Tall fescue (F arundinacea) is a cool-season forage grass that is widely grown throughout the temperate regions of the world (Sleper, 1985). It is the most important perennial forage species of the genus Fistula (Malay et al., 2005). Tall fescue (F. arundinacea) is native to Europe and North Africa (Hannaway et al., 1999). The use of tall fescue in forage, soil conservation and turf increased dramatically during the early 1980s (Sleper and West 1996). Tall fescue grows naturally in pastures in the northern, central and western of Iran, it plays an important role in the production of forage and soil conservation. Although tall fescue cultivation is not common in Iran, but it has large potential for the production of crops and pasture forage (Sharifi Tehrani et al., 2009)
This study evaluated the effectiveness of (i) bio-priming method on the species F. arundinacea Schreb using inoculation of Azotobacter and Azospirillum at different levels of osmotic pressure which is under drought stress and (ii) the effectiveness of bio-priming of Azotobacter compared with the effectiveness Azospirillum on F. arundinacea Schreb.
MATERIALS AND METHODS
This study was carried out as a factorial experiment based on completely randomized design (CRD) with three factors and three replacing in greenhouse of Isfahan (Khorasgan) Branch, Azad University of Iran, during 2014. Tall fescue (F. arundinacea) seeds were purchased from Pakan Seed Company of Isfahan. Bio-priming method is considered as one of the most common methods for seed priming. Tall fescue seed biopriming carried out with -0.5, -1, -1.5 and -2 Mpa osmotic potential. This osmotic potentials had been used in previous studies on various grasses (Hardegree & Emmerich, 2000, Hardegree & Van Vactor, 2000). Time priming, according to studies Hardegree et al. (2002), was chosen 2 and 4 days in order to verify the short and long term effects of bio-
priming. The first factor was seed bio-priming with Azotobacter and the second factor was biopriming with Azospirillum at -0.5, -1, -1.5 and - 2 Mpa osmotic potentials levels and control (C1 and C2 without bio-priming). Poly ethylene glycol 6000 used to create osmotic potential.
Preparation of bio-osmotic solution priming
Michel and Kaufmann (1972) stated that the effects of concentration and temperature on osmotic potential of PEG-6000 solutions differ from those for most salts and sugars and apparently are related to structural changes in the PEG polymer and an empirical equation (Equation 1) permits calculation of Osmotic potential; from known concentrations of PEG-6000 over a temperature range of 15 to 35 C. Viscometery and gravimetric analysis are convenient methods by which the concentrations of PEG-6000 solutions may be measured. In this study, equation 1 was used to determine the exact amount of osmotic potential. [PSI] = -(1.18 x [10.sup.-2]) C - (1.18 x [10.sup.-4]) [C.sup.2] + (2.67 x [10.sup.-4]) CT + (8.39 x [10.sup.-7]) C2T ... (1)
[PSI] = osmotic potential of PEG-6000
C = Weight of PEG-6000 in grams in a kilogram of water
T = the temperature of the solution to C[degrees]
Preparation of seed samples
Mass of seeds were randomly selected and weighed and poured into mesh bag. The two bags seeds were considered as controls that kept at 20[degrees]C, and the remaining bags were used for priming. The seeds were rinsed with distilled water for two minutes and seed were air dried until the moisture level comes back to its original. Inoculation process was carried out using rhizobacteria powder that was prepared by the Institute of Soil and Water Research in Tehran. Plastic pots with 19 cm height and 15 cm diameter was prepared, drainage of the pots was normal. A height of 16.5 cm of soil was placed in each pot; this was in accordance with the winter wheat seed priming that was done by Giri and Schillinger (2003). Each pot was consisted of three parts: sand, soil and leaf soil with ratio of 2, 1 and 1 respectively. There were sprayed 25 seeds in each pot evenly. The seeds were covered with 1.5 cm of soil and pressed a little. The pots were placed in greenhouse at 20[degrees]C in several completely random rows. With regard to the water holding capacity in pots, drought stress was considered as third factor. Four levels of drought stress, in the amount of 100% of field capacity (without stress)--75%, 50% and 25% of field capacity, were applied.
The amount of drought stress according to water holding capacity of the soil in each pot was reviewed and applied every day. According to the last day of counting, emergence percentage was calculated for each treatment. Emergence rate was calculated using equation (2)
GR = [[summation].sup.n.sub.i=1][n/t] ...(2)
n is the number of grown seeds in time t and t is the number of days since the start of experiment(Reyes et al, 2002).
Mean germination time was calculated using equation (3)
MGT = [A.sub.1][D.sub.1][A.sub.2][D.sub.2][A.sub.n][D.sub.n]/[A.sub.1][A.sub.2] ... [A.sub.n] (3)
A is the number of seeds that germinated during the D and n is the number of days until the last day of counting (Cantliffe, 1991).
Three months after planting, 10 plants were randomly selected from each pot and stem length was measured. Wet and dry biomass of stems were measured with a digital scale.
To determine the root biomass, pots were shaken in the water for a long time, the soil and other materials were removed from the root. Fresh weight of separated roots was measured after the initial impounding.
The analysis of variance of the data was performed using SPSS and MSTATC software and if the variance was significant, mean comparison with Duncan's multiple range test was performed at p = 5%.
Analysis of variance main effects, biopriming and levels of drought stress and the interaction effects between the treatments' biopriming at stress levels showed significant differences in studied traits in F. arundinacea species (Table 1).Comparison of the mean length of roots and shoots of the main effects of treatments bio-priming on F.arundinacea species is presented in Figure 1. The maximum length of shoot (34.37 cm) obtained by 5.1 MPa Azospirillium brasilense treatment for 4 days. The difference was statistically significant (P < 0.05) with the control. The minimum shoot length (28.13 cm) related to the control treatment. The maximum length of the roots (29.23 cm) obtained by the treatment of Azotobacter 2 MPa for 4 days, which was significantly different from control treatment (22.96 cm). Minimum root length (22.95 cm) created by the treatment of Azospirillium brasilense 2 MPa for 4 days; it not showed significant different compared with control. Root length of the other treatments of Azospirillium 2 MPa for 4 days showed higher mean value than the control.
Comparison of the main effects of biopriming treatments on fresh weight root is presented in Fig 2A. The highest fresh root weight (44 g) was obtained in the treatment of Azotobacter 0.5 MPa for 4 days. The difference was statistically significant (P < 0.05) with the control. This treatment didn't show significant difference by fresh root weight compared with treatments of Azotobacter 5.0 MPa for 2 days (39.40 gr), Azotobacter 1 MPa for 4 days (42.91 gr), Azotobacter 2 MPa for 2 days (29.75 gr), and azosprilium 1 MPa for 2 and 4 days by values of 35.5gr and 29.45 gr. Treatment of control didn't show significant difference with treatments of Azospirillium 0.5 MPa for 2 days and Azotobacter 2 MPa for 4 days. Difference was significant with other treatments.
Figure 2B offers emergence percentage of the seeds in the treatments. The highest emergence percentage (53%) was obtained by the Azotobacter 0.5 MPa for 2 days. it showed significant difference than treatments of the control (39.5%) and Azotobacter 2 MPa for 2 days.
Difference was not significant between the Azotobacter 0.5 MPa for 2 days compared with Azospirillium 0.5 MPa for 2 and 4 days, the Azospirillium 1.5 MPa for 2 days and Azospirillium 2 MPa for 2 and 4 days, however the impact of these treatments was higher than control. Lowest emergence percentage (36%) was created by Azotobacter 1.5 Mpa for 2 days, there was not significant difference compared to control.
Figure 3 provided comparison of the effects of drought stress (based on field capacity) in shoot and root length, and fresh shoot and root weight. The figure shows a decreasing trend with increasing drought stress in all traits. With increase in stress level reduction trend in the fresh weight of root was more severe compared with other traits.
Fig3. Comparison of the mean ([+ or -] standard error) the effects of drought stress (based on field capacity) in root and shoot length (cm) and fresh root and stem weight (gr) F. arundinacea species.
Bio-priming treatments comparing means of interactions at the level of drought stress in stem length are presented in Table 1. Stem length (34.33 cm) was highest at 100% of field capacity (without stress) and treatment of Azotobacter 2 MPa for 4 days. This treatment had significant difference compared with control treatment and other treatments; also its effect was incremental at all levels of drought stress. Minimum stem length (18.16 cm) related to drought stress treatment 25% of field capacity of Azotobacter 0.5 MPa for 4 days. This treatment didn't show significant difference with control. The mean stem length of bio-priming treatments was higher than the control.
Comparing the means of interaction effects of bio- priming treatments in levels of drought stress in stem and root length and fresh shoot weight is presented in Table 1. The stem length was higher at 100% of field capacity (without stress). The highest amount of stem length (34.33 cm) at 100% of field capacity (without stress) related to the treatment of Azotobacter 2 MPa for 4 days. This treatment showed significant difference compared with control and many other treatments of different drought stress levels. The stem length was less of drought stress at 25% of field capacity. The lowest stem length (18.16 cm) related to Azotobacter treatment of 5.0 MPa for 4 days. This treatment showed no significant difference with control of drought stress at 25% of field capacity.
Comparing the means of fresh shoot weight (table 1) indicates that fresh shoot weight is higher in 100% of field capacity (without stress). Highest fresh shoot weight (45.33) obtained in 100% of field capacity by the treatment Azotobacter 2 MPa for 2 days, and had significant difference compared with the control. The minimum fresh shoot weight was related to drought stress at 25% of field capacity. Shoot fresh weight (11.66) was the lowest in Azotobacter treatment of 5.0 MPa for 4 days. For this treatment difference was not statistically significant compared with the control.
Comparing the means of root length (table 1) indicated that the impacts are higher in 100% of field capacity (without stress). The highest root length (41.72 cm) observed in 100% of field capacity by Azospirillium treatment 1.5 MPa for 4 days. This treatment caused statistically significant difference compared with the control and other treatments in different levels of drought stress. The minimum root length was obtained in the drought stress with 50% of field capacity. The treatment Azotobacter 0.5MPa for 2 days created lowest root length (25.35) at drought stress with 50 % of field capacity. There was no significant difference compared with the control.
Plants are constantly exposed to abiotic stresses, among which drought is a major limiting factor for growth and crop production because it can elicit various biochemical and physiological reactions (Glick, 2004). Abiotic stress tolerance in PGPR has been studied to provide a biological understanding of the adaptation and survival of rhizobacteria under stress conditions (Arkhipova et al., 2007; Creus et al., 1998). Priming is an important mechanism of various induced resistance phenomena in plants (JM Beckers and Conrath, 2007).
Seed priming has been shown to advance germination and emergence rate for many agricultural plant species (e.g. Brocklehurst et al., 1984; Helsel et al., 1986; Alvarado et al., 1987; Evans and Pill, 1989; Bradford et al., 1990; Khan et al., 1992; Suzuki and Obayashi, 1994; Yamamoto et al., 1997). Studies of rangeland species are more limited. There is little knowledge about the response of microorganisms when released at water absorption conditions by seeds(Okon & Labandera-Gonzalez, 1994). In this study, root length improved in culture conditions the pot of F. arundinacea. Most of the compounds of biopriming treatments effectively and significantly increased in root length. Root length can be considered as a factor affecting for improvement yield in drought stress conditions. In drought stress conditions, increasing the length and extent of the root will be able to guarantee plant survival. Azotobacter and Azospirillum bacteria caused the root length improved in the application drought stress conditions. Combination of priming with plant growth promoting bacteria (PGPR) showed that the root length of F. arundinacea increased drought stress conditions. In this species, treatment Azospirillum 1.5 Mpa for 4 days, compared with the other bio-prime treatments and decreasing trend that occured as a result of drought stress was appropriate treatment. Ahmad et al., (2005) pointed out that Azotobacter by secretion of indole acetic acid increased the root length. Many of the studies reported effect of inoculation with bacteria on the growth root growth is increasing root length such as increase the number root, dry root weight and increase cell division in the root meristem (Arsac et al., 1990[degrees] Levanony & Bashan, 1989). In this study, the most dry and fresh weight of the roots in the F. arundinacea was obtained by inoculation Azotobacter treatment. Fulchieri et al., (1993) reported that Azotobacter, by the production of gibberellin, caused the development root and its weight.
Bashan, (1986) and Kucey, (1988) in their study pointed out that root biomass of plants inoculated with Azosprillum is less compared with plants inoculated with Azotobacter. Although the researchers reported that increasing indices of stem growth with Azosprillum inoculation is more than Azotobacte.
Weight producted biomass from forage plants is an important index to improve the performance especially under stress conditions. In fact, the increase in weight per unit area of forage is considered as one of the symptoms management quality. Reduce application chemical fertilizers are an important indicator in the sustainable management, it obtained by biological fertilizers replacing. Interest in the use of biological methods instead of chemicals to fertilize the soil, and improve plant resistance against pathogens is currently growing.
The results showed that the bio-priming treatments significantly increased biomass production. Based on the results the Azotobacter in additive effects was better than Azosprillum in the F. arundinacea.
The use of plant growth promoting bacteria leads to several natural ways growth including non-symbiotic nitrogen fixation (Boddey & Do bereiner, 1988), increase the solubility of phosphorus (Reyes et al., 2002), Production of phytohormones (Bent et al., 2001), and production of various compounds (e.g., antibiotics and lytic enzymes) with antipathogenic properties (Romero et al., 2007). Despite the decrease in fresh and dry weight of shoot with increased drought stress, decreasing trend in seeds treated with Azosprillum and Azotobacter was significantly lower compared with the control. This could be considered as useful way to increase biomass production in F. arundinacea. These results are consistent with findings of Nanda et al., (1995) in the increasing fresh and dry weight of corn seed inoculation with bacteria, Azotobacter and Azospirillum, Youssef et al., (2004) in the increasing fresh and dry weight of Salvia officinalis seed inoculation with bacteria, Azotobacter and Azospirillum and the research results Chabot et al., (1993) and Zahir et al., (2000), which reported inoculated Azosprillum increased corn shoot dry weight. Increasing the germination and emergence is known as the most important capabilities of priming (Heydecker & Coolbaer, 1977). These two traits are the most important parameters in determining the seedling vigor (Alizadeh & Jafari, 2006).
In this study, the combination of osmotic priming with beneficial microorganisms caused increasing in the emergence vigor percentage of F. arundinacea. Osmotic seed priming as one of the most effective methods to increase the percentage emergence of grass is confirmed (Hardegree et al., 2002). Therefore, the convergence of these methods of plant growth promoting bacteria can enhance the beneficial effects. The significant increase of the percentage emergence (about 13.5 %) was observed for F. arundinacea by the treatment 5.0 MPa 2 days Azotobacter compared with control. The results showed that decreasing trend of the percentage emergence by treatment Azotobacter half MPa for 2 days the stress level zero (100% of field capacity) to the highest levels of stress, i.e. 25 % of field capacity was only 5%. So the significant difference was not found between the levels of stress. Emergence percentage in the control treatment showed 10% decrees of the stress level zero (100% of field capacity) to the highest level of stress (25 % of field capacity). This was about twice related the reduction made in the treatment of Azotobacter 0.5MPa for 2 days. So decreasing trend in the emergence percentage affected by stress in the seeds that were treated with bio-priming was much lower than the control.
The results showed that plant growth promoting bacteria with the technology of osmotic priming of seeds can be increased yield of forage F. arundinacea species under glasshouse conditions. Bio-priming of seeds with Azosprillum and Azotobacter were significantly increased the growth compared with control treatment. Azotobacter showed relatively higher performance than in Azospirillum. Accordingly, there can be of Azotobacter a greater ability to coexist with F. arundinacea species. Bio-priming treatments improved the yield. However, in the case of F. arundinacea the treatment of Azotobacter 0.5 and 2 MPa for 2 days could be considered as superior treatments as other treatments used in this study.
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Hadi Radnezhad  *, Forogh Mortazaeinezhad , Ali Asghar Naghipour , Behzad Behtari  and Maryam Foroughi Abari 
 Department of Environmental Sciences, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.
 Department of horticulture, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.
 Ph.D Student in Range Sciences and Member of Young Researchers Club Islamic Azad University, Isfahan(khorasgan)Branch, Iran.
 Ph.D Candidate of Rangeland Science and Management, Faculty of Natural Resources, Sari Agricultural sciences and Natural Resources University (SANRU), Iran.
(Received: 23 May 2015; accepted: 08 July 2015)
* To whom all correspondence should be addressed. E-mail: email@example.com
Table 1. Comparison of the mean of the interaction effects of bio-priming treatments at drought stress levels in the stem and root length (cm) and shoot fresh weight (gr) of Festuca arundinacea species Drought Osmotic Time Root length stress potential Azospirillum Azotobacter 25% FC 0.5 Mpa 2days 31.7 b-l 27.5 g-l 4days 28.3 e-l 26.9 h-l 1 Mpa 2days 28.5 d-l 25.6 kl 4days 28.6 d-l 29.8 d-l 1.5 Mpa 2days 32.7 b-j 26.5 ijkl 4days 30.9 b-l 29.1 d-l 2Mpa 2days 28.8 d-l 28.4 e-l 4days 28.5 d-l 29.8 d-l Control -- 25.7 jl 50%FC 0.5 Mpa 2days 30.4 b-l 25.3 l 4days 32 b-l 30 d-l 1 Mpa 2days 30.4 b-l 33.4 b-i 4days 30.2 c-l 26.5 ijkl 1.5 Mpa 2days 25.5 kl 33.2 b-i 4days 31.5 b-l 27.3 g-l 2Mpa 2days 29.7 d-l 33.2 b-i 4days 27.7 f-l 33.3 b-i Control -- 26.9 h-ll 75%FC 0.5 Mpa 2days 32.8 b-i 32.5 b-k 4days 34.4 b-g 35.5 b-d 1 Mpa 2days 34.1 b-g 32.3 b-l 4days 31.6 b-l 33.4 b-i 1.5 Mpa 2days 33.1 b-i 31.7 b-l 4days 33.2 b-i 30.6 b-l 2Mpa 2days 31.3 bl 32.4 b-k 4days 31.4 b-l 35.1 b-e Control -- 31.7 b-l 100% 0.5 Mpa 2days 30.9 b-l 33.7b-h 4days 34.4 b-g 35.1 e-b 1 Mpa 2days 33.6 b-i 34.8 b-f 4days 33.2 b-i 37.2 abc 1.5 Mpa 2days 29.5 d-l 37.4 ab 4days 41.7 a 33.4 b-i 2Mpa 2days 32.8 b-i 33.5 b-i 4days 29.9 d-l 32 b-l Control -- 28.1 e-l Drought Osmotic Time Fresh shoot weight stress potential Azospirillum Azotobacter 25% FC 0.5 Mpa 2days 20 b-f 16.6 def 4days 15 def 11.6f 1 Mpa 2days 16.6 def 18.3 c-f 4days 15 def 16.6 def 1.5 Mpa 2days 16.6 def 25 b-f 4days 21.6 b-f 23.3 b-f 2Mpa 2days 21.6 b-f 23 b-f 4days 13.3 ef 21.6 b-f Control -- 16 def 50%FC 0.5 Mpa 2days 23.3 b-f 15.3 def 4days 25 b-f 28.3 b-f 1 Mpa 2days 21.2 b-f 21.6 b-f 4days 20 b-f 23.3 b-f 1.5 Mpa 2days 20 b-f 30 abcde 4days 20.3 b-f 21.6 b-f 2Mpa 2days 23.3 b-f 23.3 b-f 4days 31.6 a-d 30.3 a-d Control -- 15.3 def 75%FC 0.5 Mpa 2days 26.6 b-f 35 abc 4days 28.3 b-f 30 abcde 1 Mpa 2days 31.6 a-d 28.3 b-f 4days 26.6 b-f 28.3 b-f 1.5 Mpa 2days 25 b-f 26.6 b-f 4days 26.6 b-f 23.3 b-f 2Mpa 2days 28.3 b-f 35.6 ab 4days 36.6 ab 35 abc Control -- 21 b-f 100% 0.5 Mpa 2days 28.3 b-f 30 abcde 4days 30 abcde 30 abcde 1 Mpa 2days 31.6 a-d 28.3 b-f 4days 31.6 a-d 23.3 b-f 1.5 Mpa 2days 26.6 b-f 26.6 b-f 4days 31.6 a-d 30 abcde 2Mpa 2days 26.6 b-f 45.3 a 4days 25 b-f 18.3 c-f Control -- 26.3 b-f Drought Osmotic Time Stem length stress potential Azospirillum Azotobacter 25% FC 0.5 Mpa 2days 25 c-j 21.36g-k 4days 24.9 c-j 18.1k 1 Mpa 2days 20.4ijk 23d-k 4days 24.2 c-k 22.1e-k 1.5 Mpa 2days 24.1c-k 24.6 c-k 4days 24.1c-k 23.5 d-k 2Mpa 2days 21.7 f-k 23.7d-k 4days 18.7jk 26.5c-i Control -- 23.1 d-k 50%FC 0.5 Mpa 2days 24.1 c-k 24 d-k 4days 20.4 ijk 23.6 d-k 1 Mpa 2days 28.4 a-f 26.9 b-i 4days 24.7 c- k 28.1 a-f 1.5 Mpa 2days 22.6 e-k 25.5 c-i 4days 28 b-g 24.7 c-k 2Mpa 2days 28.3 a-f 27.2 b-h 4days 24.2 c-k 26.6 b-i Control -- 23 d-k 75%FC 0.5 Mpa 2days 27.8 b-h 27.6 b-h 4days 26.2 c-i 23.7 d-k 1 Mpa 2days 26.4 c-i 29.5 abcd 4days 24.4 c-k 23.9 d-k 1.5 Mpa 2days 25.7 c-i 24.5 c-k 4days 22.9 d-k 22.9 d-k 2Mpa 2days 27.7 b-h 25.6 c-i 4days 25 c-j 29.5 abcd Control -- 21 b-k 100% 0.5 Mpa 2days 22.1 e-k 28.5 a-e 4days 26.6 b-i 27.3 b-h 1 Mpa 2days 26.9 b-i 33 ab 4days 24.4 c-k 25.1 c-j 1.5 Mpa 2days 24.7 c-k 25.7 c-i 4days 25 c-j 23.2 d-k 2Mpa 2days 24.3 c-k 23.5 d-k 4days 23.8 d-k 34.3 a Control -- 24.5 c-k Similar letters are indicative of no significant difference between the means (Duncan test p = 5%)
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|Author:||Radnezhad, Hadi; Mortazaeinezhad, Forogh; Naghipour, Ali Asghar; Behtari, Behzad; Abari, Maryam Foro|
|Publication:||Journal of Pure and Applied Microbiology|
|Date:||Sep 1, 2015|
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