The effect of rhizobacterial inoculation on growth and nutrient accumulation of tissue-cultured banana plantlets under low N-fertilizer regime

Banana, an important fruit crop, requires high amounts of N-fertilizers for commercial cultivation. This, however, is costly and can be hazardous to the soil environment when used excessively. Biofertilizer is globally accepted as an alternative source of N-fertilizer and can substantially supplement the N requirement while enhancing the uptake of water and mineral nutrients of crop plants. An experiment was conducted to observe the effect of plant growth promoting rhizobacterial inoculation on growth, nutrient uptake of bananas grown under hydroponics condition. The design of the experiment was randomized complete block with five replicates. The following six treatments were imposed: T 1 (control; N 0 -PGPR), T 2 : (N 0 +Sp7), T 3 : (N 0 + UPMB10), T 4 : (N 33% + Sp7), T 5 : (N 33% + UPMB10), and T 6 : (N 100% -PGPR). The results showed that inoculation by UPMB10 with minimal fertilizer-N supply increased (P < 0.05) the primary root elongation and secondary root initiation and subsequently increased (P < 0.05) the root biomass. The same treatment also increased (P < 0.05) N concentration in pseudostem and leaves and Ca concentration in roots. The total accumulation of N, P, K, Ca and Mg were increased due to inoculation; a consequence of increased plant growth. Plants with this treatment produced an equivalent total dry matter as those supplied with 100% N.


INTRODUCTION
The banana fruit crop is widely cultivated in tropical areas where high dosages of chemical fertilizers (NPK fertilizer) are commonly applied.Commercial cultivation of banana requires a substantial amount of inorganic fertilizers namely urea.Banana plants cannot store N and such deficiency symptoms quickly develop if supply is not sufficient.Therefore, N should be supplied at short intervals during growth, which is costly and difficult to maintain (Robinson, 1996).Furthermore, excessive N, that is, beyond the critical level is not only wasteful and uneconomical but also pollutes the soil environment and water bodies through leaching.Banana suffers from a mismatch of its nitrogen demand and its nitrogen supplied *Corresponding author.E-mail: zulsham@agri.upm.edu.my.
as chemical fertilizer, resulting in a 50-70% loss of the fertilizer applied.Two approaches may be used in resolving this problem; one is to regulate the timing of nitrogen application based on the banana plant nutrient requirement, thus increasing the efficiency of the plant's use of applied nitrogen.The other is to increase the efficiency of the use of available soil nitrogen and meet the additional N-demand by making banana capable of fixing its own nitrogen either directly, or via a close interaction with diazotrophic bacteria (Ladha et al., 1997).
Biofertilizer, inoculants of microorganisms, an alternative source of N-fertilizer, can be applied to increase crop growth through biological N 2 fixation, availability of soil nutrients and water uptake (Cocking, 2000) and to ensure a sustainable banana production.Over the last decades there has been a great interest in nitrogen fixing-bacteria associated to non-legumes, principally gramineous plants.The biological nitrogen fixation could be an alternative for this crop system, once the plants are able to establish association with Herbaspirillum-like and Burkholderia related bacteria, which are not well known yet.In N-free hydroponics condition, the plant growth promoting rhizobacteria (PGPR) inoculated plants were not able to perform normal growth due to lack of needed N which require additional N-fertilizer for a good synergy (Saad et al., 1999).Fertilizer-N has the most prominent influence on biological N 2 fixation (BNF) which efficiency increases in the presence of moderate levels of soil riched fertilizer-N but declines at high levels, reflecting an inhibitory effect of N-fertilizer on N 2 fixation (Marschner, 1995).PGPR inoculation together with 33% of the total N requirement has been shown to produce a similar biomass and yield in sweet potatoes as the plants with complete fertilizer-N (Saad et al., 1999).Significant increases in crop yields following application of PGPR have been documented under diverse field conditions (Bashan, 1998;Mia et al., 2005).They have been widely reported to fix atmospheric N 2 with grasses and cereals (Dobereiner, 1997) and enhance nutrient uptake (Kapulnik, 1991;Bashan and Holguin, 1997;Sheng, 2005;Mia et al., 2007).This demonstrates a potential saving on fertilizer cost.Based on these studies it necessitates investigating the benefits of PGPR interaction with minimal starter-N.Thus, the present study was carried out to observe the effect of PGPR inoculation with minimal fertilizer-N on nutrient uptake, root and shoot growth of banana plantlets.
The primary root elongation was measured with a meter scale and secondary root initiation was counted at alternate days for 15 days.The plant height, leaf number and leaf chlorophyll content were measured fortnightly and net photosynthesis was measured 30 DAI (days after inoculation).Leaf chlorophyll content of youngest fully expanded leaf (third leaf from the shoot) was indirectly measured using a chlorophyll meter (SPAD 502, Minolta Camera Ltd.Japan) (Takebe and Yoneyama, 1989).The chlorophyll meter value was calibrated against leaf chlorophyll content determined by chemical method with acetone extraction as described by Coombs et al. (1985).The rate of net photosynthesis was measured with a Portable Photosynthesis System (LI-6200, LI-Cor, Inc., USA).The plants were terminally harvested at 45 DAI and the following parameters were recorded: plant height, leaf number, leaf area and total dry matter (TDM).Root parameters, namely root number, root length, root volume (cm 3 plant -1 ) and root dry weight were also recorded.Plant parts were separated into roots, pseudostems and leaves, dried in oven at 71 0 C for 48 h and weighed for TDM.Harvested plants were separated into roots, corm, pseudostem and leaves and were prepared for chemical analyses.Banana leaves were sampled following the International Reference Method (Lahav and Turner, 1983).The oven-dried samples were ground in a Willey hammer mill, passed through a 2 mm sieve, mixed throughly and stored in plastic vials.The ground samples were digested by Micro-Kjeldahl method (Thomas et al., 1967).The digested samples were analysed for N, P, K, Ca and Mg.The N and P were determined by Autoanalyzer (Technicon II, Technicon Ltd.) while the remaining elements were analysed by Atomic Absorption Spectrophotometer (Perkin-Elmer, 5100 pc).The collected data were analyzed statistically using the Statistical Analysis System (SAS, version 6.12, 1989).Following the analysis of variance procedure (ANOVA), differences among treatment means were determined using the Least Significant Difference (LSD) and Duncan's New Multiple Range Test (DMRT) comparison method (whenever applicable) at 5% level of significance.Correlation analysis was performed for the estimation relationships between different traits.

Root growth
Primary (1 0 ) root elongation PGPR inoculation positively influenced the 1 0 root elongation (Figure 1).Plants inoculated without N-fertilization showed lower 1 0 root length compared to those inoculated with minimal N-fertilization.Inoculation with 33% N showed higher root elongation; UPMB10-inoculated plants with 33% N recorded the highest root elongation.Plants inoculated with Sp7 along with 33% Nfertilization increased their root elongation from 2 DAI to 10 DAI compared to control.On the other hand, roots of UPMB10-inoculated plants with 33% fertilizer-N increased from 3 DAI until 12 DAI when compared to control.There were no significant differences (P < 0.05) among the controls (N 0 and N 100% ) and both showed shorter 1 0 root length, when compared with the inoculated plants.

Secondary (2 0 ) root initiation
Secondary roots were initiated at 2 DAI.Plants inoculated with Sp7 and provided with 33% N showed positive influence on secondary root initiation (Figure 2).This treatment also showed the highest initiation of secondary roots.Plants inoculated with UPMB10 without fertilizer-N  showed higher 2 0 root initiation compared to control (N 0 -PGPR) until 8 DAI thereafter no differences were observed.Plants inoculated with UPMB10 and provided with 33% fertilizer-N could not increase 2 0 root initiation compared to control.Uninoculated plants fertilized with 100% N showed the lowest initiation of secondary roots.

Root number
PGPR inoculation positively influenced the number of primary roots especially the inoculated plants with 33% N fertilization (Table 1).Plants inoculated with Sp7 and UPMB10 and supplied with 33% fertilizer-N produced

Total 1 0 root length
Total 1 0 root lengths were significantly increased due to inoculation with PGPR (Table 1).Plants inoculated with UPMB10 without fertilizer-N application showed 44% longer primary roots compared to control (N 0 -PGPR) whereas Sp7 did not show any significant increment.PGPR inoculated plants together with 33% fertilizer-N produced similar root length as 100% N control plants but could not increase root length compared to inoculated plants with N 0. Uninoculated plants with 100% fertilizer-N showed longer 1 0 roots (372 cm plant -1 ) compared to uninoculated plants without fertilizer-N (236 cm plant -1 ).

Root base diameter
Root base diameter, indication of the thickness of a root and vigour of a plant, is positively influenced by PGPR inoculation.Plants inoculated with UPMB10 and without fertilizer-N showed larger (77% more) base diameter in feeder root compared to control (N 0 -PGPR).Plant inoculated with UPMB10 and provided with 33% N-fertilization showed an equal base diameter in pioneer roots (0.42 mm) as the 100% N applied control plant (0.42 mm) whereas Sp7 did not produce a similar effect.Plant with 100% fertilizer-N increased their pioneer root base diameter compared to N 0 while the similar trend was not found in feeder root.However, inoculated plant provided with 33% fertilizer-N could not show any increment in root base diameter neither in feeder nor in pioneer when compared to inoculated plant without fertilizer-N.

Root volume
Remarkable increment in root volume was observed in inoculated plants with and without N-fertilization (Table 1 and Plate 1).Inoculated plants with Sp7 and UPMB10 without N-fertilization produced more root volume compared to the control (N 0 -PGPR) by 59 and 142%, respectively.Similarly, these inoculated plants with 33% fertilizer-N also increased root volume by 10 and 18% respectively, an equivalent root volume as control plant with 100% fertilizer-N.Root volume increased with the application of fertilizer-N.The plant supplied with 100% fertilizer-N produced significantly more root volume (342%) compared to those without fertilizer-N.

Root dry weight
Root dry weight significantly increased due to inoculation with PGPR (Table 1).Plants inoculated with Sp7 and UPMB10 without fertilizer-N produced more root dry weight compared to the control (N 0 -PGPR) by 141 and 126%, respectively.Similarly plants inoculated with Sp7 and provided with 33% fertilizer-N produced significantly greater root-dry weight (1.02 g plant -1 ) compared to 100% fertilizer-N applied control plants.It is interesting to note that plants inoculated without N-fertilization produced similar amounts of root dry weight as the 100% Nfertilized plants.Application of fertilizer-N, especially uninoculated plants, increased their root dry weight compared to plants without fertilizer-N.

Plant height
In general, there were no differences among the treatments fertilizer-N.However, inoculation with PGPR showed positive effect on plant height.Inoculated plants with 33% fertilizer-N showed an equivalent plant height (48.8 to 49.8 cm) as the control plant with 100% fertilizer-N (49.0 cm).Similarly inoculated plants without fertilizer-N showed taller plant compared to control (N 0 -PGPR) at 45 DAI.

Leaf development
Leaf development, measured by leaf number and area, was positively influenced by PGPR inoculation (Figure 4  and 5).Initially at D 15 there was no difference of leaf number among the treatments with and without inoculation.Uninoculated plants without fertilizer-N showed the lowest number of leaves from 30 to 45 DAI unlike those supplied with 100% fertilizer-N.Inoculated plant with 33% fertilizer-N resulted in similar leaf number as the 100% Napplied plants at 30 DAI but higher at 45 DAI.Inoculated plant without fertilizer-N produced similar leaf number as the uninoculated plant with fertilizer-N (100% N).However, inoculated plant with 33% fertilizer-N produced significantly more leaf number compared to plants inoculated without fertilizer-N at 45 DAI.Inoculated plants without fertilizer-N produced more leaf area compared to the control (N 0 -PGPR) (Figure 5).Similarly inoculated plants provided with 33% fertilizer-N produced an equivalent leaf area as the 100% N applied control plant.Plants with fertilizer-N showed higher leaf area when compared with the plants without fertilizer-N under both inoculated and uminoculated conditions.

Leaf chlorophyll content
Leaf chlorophyll content significantly increased by PGPR inoculation especially plants without N-fertilization (30 -45 DAI) (Figure 6).There was a decreasing trend of chlorophyll content with the plant age among the treatments of N 0 with inoculated or uninoculated conditions.However, inoculated plants together with 33% N-fertilization showed an equivalent chlorophyll content as the 100% N-fertilized plants.Plants with 100% fertilizer-N showed higher chlorophyll content compared to plants without fertilizer-N (30 to 45 DAI).Similarly, inoculated plants with 33% fertilizer-N showed higher chlorophyll content compared to inoculated plants without fertilizer-N (30 -45 DAI).

Net leaf photosynthesis (Pn)
There were no significant differences of net leaf photosynthesis by the inoculation process without fertilizer-N (Figure 5).But inoculation with PGPR (Sp7 and UPMB10) using 33% fertilizer-N resulted in similar photosynthetic rate (11.9 to 14.1 µ mole CO 2 m -2 sec -1 ) as the 100% N applied control (13.1 µ mole CO 2 m -2 sec -1 ).Plants with 100% fertilizer-N showed higher Pn when compared with the plants without fertilizer-N.Similarly plants inoculated with 33% fertilizer-N showed significantly higher Pn compared to inoculated plants without fertilizer-N.(Figure 5).On the other hand, inoculated plants with UPMB10 and provided with 33% fertilizer-N produced an equivalent amount of shoot dry weight as the 100% Nfertilized control plants while Sp7 could not show the similar effect.There were significant differences of shoot dry weight between the treatment of N 100 and N 0 .Similarly inoculated plants with 33% fertilizer-N showed significantly higher shoot dry weight compared to inoculated plants without fertilizer-N.

Root to Shoot Ratio (R/S)
Application of fertilizer-N resulted in lower R/S value (0.13 to 0.22) indicating better shoot growth and without N-fertilization showed higher R/S value (0.33 -0.54) reflecting less shoot growth (Figure 7).Inoculated plants without fertilizer-N could not show any difference of R/S value compared to the control (N 0 -PGPR).However, inoculated plants with 33% fertilizer-N showed an equivalent R/S values as the 100% N-applied control plants.Plants using 100% fertilizer-N significantly showed lower R/S values compared to plants without fertilizer-N.Similarly plants inoculated with UPMB10 and given with 33% fertilizer-N showed lower R/S value when compared with inoculated without fertilizer-N.However, Sp7 could not show similar effect.

Nutrient uptake
The PGPR inoculation and fertilizer-N application significantly increased the N concentration and accumulation in banana plantlets grown under hydroponics condition for 45 days (Tables 2 and 3).Application of fertilizer-N resulted in higher N concentration in root, pseudostem and leaf.Plant using 100% fertilizer-N showed significantly higher N concentration compared to plant without fertilizer-N.Similarly, inoculated plants with 33% fertilizer-N resulted in higher N concentration in pseudostem and leaf while no significant difference was found in root.Inoculated plants without fertilizer-N could not increase the N concentration in root and leaf while Sp7 showed higher N in pseudostem.Inoculated plants with UPMB10 and provided with 33% fertilizer-N increased their N concentration in pseudostem and leaf which resulted in an equivalent concentration as the 100% fertilizer-N applied plant.However, inoculated plants with Sp7 and supplied with 33% fertilizer-N showed similar increment in leaf only.Plants inoculated with UPMB10 and provided with 33% fertilizer-N showed significantly higher P concentration in root compared to inoculated plants with UPMB  especially in plants inoculated and supplied with 33% fertilizer-N (14% more over 100%-N control).However, inoculation without fertilizer-N could not show any increment.Application of fertilizer-N decreased Ca concentration in pseudostem and leaf.Using 100% fertilizer-N showed significantly lower Ca concentration in pseudostem compared to the control (N 0 -PGPR).Similarly, inoculated plants provided with 33% fertilizer-N also showed lower concentration when compared to inoculated plants without fertilizer-N.However, in leaf, application of 100% fertilizer-N showed lower Ca concentration compared to the control (N 0 -PGPR) while other treatments were unaffected.
Plants inoculated with Sp7 and supplied with 33% fertilizer-N recorded higher (30% more over 100% N control) Mg concentration in root compared to uninoculated plants fertilized with 100% N. On the other hand inoculated plants with UPMB10 and given with 33% fertilizer-N showed higher Mg concentration in pseudostem when compared to plants fertilized with 100% N. Magnesium concentration in leaf was not influenced by PGPR inoculation.The total accumulation of N, P, K, Ca and Mg were significantly increased with PGPR inoculation.Inoculated plants without fertilizer-N showed significantly higher accumulation compared to the control (N 0 -PGPR).Inoculated plants provided with 33% fertilizer-N recorded an equivalent amount of P and K as the 100% N applied control plant.Application of 100% fertilizer-N showed significantly higher accumulation of those nutrients (N, P, K and Ca) compared to the control (N 0 -PGPR).Similarly inoculated plants with 33% fertilizer-N also showed significantly higher accumulation of nutrient compared to inoculated plants without fertilizer-N.Moreover, plants inoculated with UPMB10 and supplied with 33% fertilizer-N accumulated significantly higher amounts of Ca and Mg compared to 100% N-fertilizer applied plants while Sp7 showed higher Ca but similar Mg.

DISCUSSION
The results strongly indicated that PGPR strains Sp7 and UPMB10 inoculation influenced the plant growth of banana plantlets grown for 45 days.Highly positive responses were observed in root stimulation.Primary root elongation and 2 0 root initiation of inoculated plant increased due to PGPR inoculation.The strain UPMB10 with 33% fertilizer-N improved 1 0 root elongations while Sp7 with 33% fertilizer-N promoted 2 0 root initiations.Uninoculated plants with N 0 and N 100 showed lowest response in root elongation and initiation.This indicated that N supply is not critical in root stimulation.The results showed that PGPR inoculation with low fertilizer-N could produce a synergistic effect on root growth parameters.Higher initiation of 2 0 roots of Sp7 inoculated plants may be due to the presence of more bacterial cells and their beneficial interaction in this root zone.Root colonization study supported this results that more bacterial cells of Sp7 were colonized in the root hair proliferation zone.The findings are in agreement with the results of Bilal et al. (1993) who found that the area around the point of emergence of lateral roots usually shows more bacterial colonization in grasses.
The study indicated that PGPR inoculation increased the root function and when supplemented with fertilizer-N could accelerate root growth.Using 33% of the total fertilizer-N contributed a similar or even higher root growth (1.02 g plant -1 ) compared to the 100% N-applied plants (0.69 g plant -1 ).Inoculated plant with UPMB10 and provided with 33% fertilizer-N significantly increased root volume (18%), root mass (43%) and root diameter.Inoculation alone increased the thickness of the root while fertilizer-N could not produce any synergistic effect.PGPR inoculation showed positive effect on root volume and this increment is enhanced with the application of fertilizer-N indicating a synergistic effect with both strains.Similarly root dry weight increased due to inoculation and fertilizer-N application; strain Sp7 showed a highly synergistic effect (48% increased) with 33% fertilizer-N whereas UPMB10 could not produce the same effect.This might be due to production of more 2 0 roots rather than length in the Sp7 inoculated plants which increased the root mass.Application of fertilizer-N alone did not increase root number whereas inoculated plants together with 33% fertilizer-N had a highly synergistic effect on 1 0 root emergence.Plant inoculated with UPMB10 increased 1 0 root lengths but could not show the synergy with fertilizer-N.Thus, the effect may be due to bacterial interaction alone which is sufficient to increase 1 0 root length.However, a highly synergistic effect was observed in root mass and volume.
The findings concerning increased root growth are supported by Morgenstern and Okon (1987) who found that inoculation with Azospirillum spp affected the root function by stimulating the appearance of lateral roots and enhancement in the number of adventitious roots in wheat and sorghum.Tien et al. (1979) also found that inoculation of PGPR in Setaria increased the number of lateral roots and root hairs.Azospirillum inoculation also increased the diameter and length of the lateral roots in maize seedlings (Hartmann et al., 1983).
The study revealed that PGPR inoculation could increase N, P and Ca concentrations in root, stem and leaves.Plants inoculated with UPMB10 especially those supplemented with 33% fertilizer-N resulted in an equivalent N concentration in stem and leaves as the 100% fertilizer-N treated plants.On the other hand, Sp7 could not produce a similar trend but showed higher N concentration in leaves only.The latter strain also showed higher N concentration in pseudostem under N 0 condition.The higher N uptake in fertilizer-N treated plant diluted the P concentration in leaf, similarly Ca concentration in pseudostem and leaf.The dilution capacity of inoculated plants with 33% fertilizer-N is similar as 100% fertilizer-N applied plant.Moreover, plants inoculated with UPMB10 with 33% fertilizer-N showed higher dilution of P and Ca which are indication of more N accumulation.The increased N concentration of stem and leaves may be due to N 2 fixation and enhanced uptake of NO 3 -from the nutrient solution.Similarly, Kapulnik et al. (1985) concluded that beneficial effects of host plants by PGPR inoculation might be due to increase uptake of combined-N from the soil.Inoculation of Azospirillum spp.increases N content and consequently increases the plant growth in carrots (Govedarica et al., 1994).PGPR can contribute about 31% of the total N requirement in maize through BNF process (El Kommy et al., 1998).Similarly, Malik et al. (2000) found increased plant biomass by PGPR inoculation through N 2 fixation in wheat and rice.
The higher level of fertilizer-N decreased the ionic ratio of P/N (diluted the P concentration) in the tissue of leaf whereas increased in root.In leaf, N concentration of Nfertilized plant is higher which may have restricted the luxuriant accumulation of P. In N 0 condition, P was not diluted due to the absence of NO 3 -.The lower P concentration in leaf indicated an increased uptake of NO 3 from the nutrient solution.
A higher Ca concentration was observed in roots of inoculated plants with 33% fertilizer-N application which might be due to minimum mobility of this element from root to shoot.Application of fertilizer-N (33 and 100%) resulted in low Ca concentration in pseudostem and leaves.This may be due to higher dry matter production which diluted the Ca concentration.However, total accumulation of Ca in inoculated plant was greater, an effect accelerated by the application of fertilizer-N which led to a good synergistic effect between PGPR strain and fertilizer-N.Lahav and Turner (1983) concluded that the uptake of Ca during the course of plant growth follows dry matter accumulation until bunch emergence.The higher Ca uptake by the inoculated plants in this experiment might not only be due to higher plant growth but also higher uptake capacity which is induced by bacterial interaction through the acceleration of proton efflux, which results in the acidification of the rhizosphere.It is one of the important mechanism in cation uptake by the roots which is the consequence of stimulation of root membrane ATP-ase activity.PGPR inoculation could increase this enzyme activity through bacteria-root interaction as both the strain successfully colonized banana roots.Higher activity of this enzyme resulted in higher Ca concentration in roots (Marschner, 1995).Similarly, Bashan (1990) concluded that Azospirillum could increase the proton efflux by stimulating ATP-ase activity in the root of wheat seedlings.PGPR might improve the efficiency of absorbing applied mineral nutrients by helping the plant scavenge limiting nutrients.The enhanced root growth could absorb more nutrients and consequently more total nutrient accumulation.Inoculation process could increase root volume vis-a-vis more root surface area which assisted plants to absorb more nutrients.Similarly Bashan (1990) concluded that A. brasilense is capable of increasing the mineral nutrient content in maize plants.Enhancement in uptake of NO 3 -, NH 4 + , HPO 4 2-, K + , Rb + and Fe 2+ by Azospirillum was suggested as the cause for an increase in accumulation of minerals in stems and leaves (Kapulnik et al., 1985;Morgenstern and Okon, 1987;Sarig et al., 1988).
Baset Mia et al. 5865 PGPR inoculation stimulated shoot growth namely plant height, leaf number, leaf area and shoot dry weight.These growth attributes increased with plant age and fertilizer-N application.Positive responses of inoculation on those growth attributes were clearly marked within 30 -45 DAI.This increased shoot growth can be attributed to the observed improvement in root growth which consequently enhanced nutrient uptake.The better root development also helped to colonize more bacterial cells which increased N 2 fixation.The findings are supported by Saad et al. (1999) who found out that Azospirillum inoculation increased the grain yield and total N content in wheat and sweet potato.Photosynthetic activity was increased due to PGPR inoculation especially to plants supplied with 33% fertilizer-N resulted in an equivalent Pn as the 100% fertilizer-N applied control plants.This indicated that minimal fertilizer-N along with PGPR inoculation produced a synergistic effect on Pn activity.Several researchers have shown that photosynthetic capacity of N 2 -fixing plants were higher compared to nonfixing plants, since the former need more photosynthate to meet the demand of microorganisms for BNF process (Quilici and Medina, 1998).Similarly Amir et al. (2001) found higher photosynthetic capacity in oil palm seedlings inoculated with PGPR.

Conclusion
The results of this study concluded that PGPR inoculation increased the root growth, namely length, thickness, volume and root mass.Plant inoculated with UPMB10 and provided with 33% fertilizer-N could increase the primary root elongation while Sp7 increased 2 0 root initiations.Root volume and root mass were also increased due to synergy with PGPR and minimal fertilizer-N.Plants inoculated with UPMB10 with 33% fertilizer-N produced an equivalent shoot growth as those with the 100% fertilizer-N treatment.PGPR inoculation could increase the nutrient concentration in different plant parts.Plants inoculated with both PGPR strains with 33% fertilizer-N increased the Ca concentration in root.Those inoculated with Sp7 and supplied with 33% fertilizer-N recorded higher Mg concentration in root, while the same with UPMB10 treatment showed higher concentration only in the pseudostem.The total accumulation of plant nutrients (N, P, K, Ca and Mg) were increased due to PGPR inoculation.The study suggested that PGPR strains Sp7 and UPMB10 could be used together with minimal fertilizer-N as bioenhancer for improved root and shoot growth and more nutrient accumulation of banana plantlets at seedling stage.

Figure 2 .
Figure 2. Secondary root initiation of banana plantlets inoculated with PGPR strains Sp7 and UPMB10 (vertical bar represents LSD at 0.05 significant level)

Table 1 .
Root growth of banana plantlets inoculated with PGPR strains Sp7 and UPMB10 grown under low fertilizer-N regimes

Table 2 .
The N, P, K, Ca and Mg concentrations in root, pseudostem and leaves of banana plantlets inoculated with PGPR strains Sp7 and UPMB10 grown under hydroponics condition under low fertilizer-N regimes for 45 days Means having same letter (s) in a column of a parameter do not differ significantly at 0.05 level by DMRT

Table 3 .
Total accumulation of N, P, K, Ca and Mg in banana plantlets inoculated with PGPR strains Sp7 and UPMB10 at low fertilizer-N regimes for 45 days N also showed lower P concentration in leaf compared to inoculated plant without fertilizer-N.PGPR inoculation could not increase K concentration except in root in the treatment of UPMB10 without fertilizer-N.PGPR inoculation greatly increased Ca concentration in root