Evaluation of Ochrobactrum anthropi TRS-2 and its talc based formulation for enhancement of growth of tea plants and management of brown root rot disease


Usha Chakraborty, Department of Botany, University of North Bengal, Siliguri-734013, Dt. Darjeeling, West Bengal, India.
E-mail: chakrabortyusha@hotmail.com


Aim:  To evaluate Ochrobactrum anthropi TRS-2 isolated from tea rhizosphere and its talc based formulation for growth promotion and management of brown root rot disease of tea.

Methods and Results: Ochrobactrum anthropi TRS-2, isolated from tea rhizosphere could solubilize phosphate, produce siderophore and IAA in vitro and also exhibited antifungal activity against six test pathogens. Application of an aqueous suspension of O. anthropi to the rhizosphere of nursery grown tea seedlings of five varieties of tea (TV-18, T-17, HV-39, S-449, UP-3 and) led to enhanced growth of the treated plants, as evidenced by increase in height, in the number of shoots and number of leaves per shoot. Treatment with O. anthropi also decreased brown root rot of tea, caused by Phellinus noxius. Multifold increase in activities of chitinase, β-1,3-glucanase, peroxidase and phenylalanine ammonia lyase in tea plants was observed on application of O. anthropi to soil followed by inoculation with P. noxius. A concomitant increase in accumulation of phenolics was also obtained. Further, talc based formulation of O. anthropi was prepared and its survival determined every month up to a period of 12 months. Ochrobactrum anthropi could survive in the formulation up to a period of 9 months with a concentration of 7·0 log10 CFU g−1, after which there was a decline. Talc formulation was as effective as aqueous suspensions in both plant growth promotion and disease suppression.

Conclusion: Ochrobactrum anthropi, either in aqueous suspension or as talc formulation induced growth of tea plants and suppressed brown root rot disease. It induced defense responses in tea plants.

Significance and Impact of the Study: Ochrobactrum anthropi and its talc based formulation can be considered as an addition to available plant growth promoting rhizobacteria (PGPR) currently being used for field application. The present study offers a scope of utilizing this bacterium for growth promotion and disease management which would help in reduction of the use of chemicals in tea plantations.


The rhizosphere, a zone very rich in nutrients, supports large microbial populations, which exert beneficial, neutral or detrimental effects on plant growth. Plant growth promoting rhizobacteria, first defined by Kloepper and Schroth (1978), include those bacteria, which, on inoculation into the soil, colonize the roots of plants and enhance plant growth. With more and more emphasis on organic farming, efforts are on to isolate and identify beneficial microbes, and hence, plant growth promoting rhizobacteria (PGPRs) are finding increasing applications today as biofertilizers and bioprotectants (Vessey 2003). Undoubtedly, excess use of chemical fertilizers and fungicides has resulted in several problems including persistence of chemicals in plant products and adverse impact on soil environment which in turn leads to loss in productivity.

One of the major plantation crops of India is tea (Camellia sinensis), the leaves of which are used in the production of the world’s most common hot beverage. The use of chemicals as fertilizers, insecticides and fungicides in tea cultivation has posed serious problems in recent years. Pesticide residues have often been reported to be above the permissible limits and besides, incorporation of by-products of pesticides into soil humus has deteriorated soil condition (Bezbaruah et al. 1996). Hence, there is a pressing need in tea industry for utilizing either biological products completely or reducing the use of chemicals by supplementing with biological products in integrated management practices.

Mechanisms of action of PGPRs include phosphate solubilization, and production of siderophore, auxin, volatile or HCN (Kloepper 1993; Ryu et al. 1993; Kishore et al. 2005). PGPRs have also been reported to protect plants from various pathogens by activating defense genes, for example those encoding chitinase, β-1,3-glucanase (GLU), peroxidase (POX), phenylalanine ammonia lyase (PAL) etc. (M’Piga et al.1997).

One of the common means of application of bacterial inoculants to soil is in the form of bioformulations. Powder formulations of different bacteria have been developed and are effective against plant diseases (Schmidt et al. 2001; Meena et al. 2002; Hassan-El and Gowen 2006).

In the present study, we have evaluated the effects of Ochrobactrum anthropi from tea rhizosphere on tea growth and suppression of a root rot disease of tea, as well as determining the mechanisms involved. Ochrobactrum anthropi has been used both as actively growing cells and as formulation.

Materials and methods

Test organisms

Ochrobactrum anthropi TRS-2 was isolated from tea rhizosphere and preliminary biochemical and morphological tests were performed. The bacterium was sent to the Plant Diagnostic and Identification Services, UK, and the identification was obtained from them. Other test pathogens (Phellinus noxius, Poria hypolaterita, Sphaerostilbe repens, Sclerotium rolfsii, Sclerotinia sclerotiorum and Alternaria alternata) were obtained from the culture collection of Immuno-Phytopathology Laboratory, Department of Botany, University of North Bengal.

In vitro tests

Phosphate solubilization was noted as clear halo around the bacterial streak in Pikovskaya’s (1948) medium.

Siderophore production by the bacterium was indicated by the change in colour of medium using chrome azurol S, as described by Schwyn and Neiland (1987). Production of IAA in culture was detected in culture filtrate by Pilet-Chollet method as described by Dobbelaere et al. (1999). Bacterium was grown in tripticase soya medium supplemented with tryptophan.

Detection of HCN production was done by the method of Wei et al. (1991) where a colour change of filter paper soaked in picric acid gave positive indication.

Antagonism of the bacterium to test pathogens was determined by paired culture on Nutrient Agar Medium as described by Chakraborty et al. (2006).

Determination of plant growth promoting activity of O. anthropi

Aqueous suspension of O. anthropi (1 × 108 CFU ml−1) was applied as soil drench to the rhizosphere of five varieties (TV-18, T-17, HV-39, S-449, UP-3) of 2-year-old bushes (100 ml per plant) twice at an interval of 15 days. Plants were grown in natural conditions of light and temperature (30 ± 2°C). Soil was nonsterile. Plant growth assessment was done two and four months after application as increase in height of plants, number of branches and number of leaves.

Pathogen inoculation and disease assessment

Inoculation of tea rhizosphere with the pathogen and disease assessment was done following the method of Chakraborty et al. (2006). For coinoculations, the bacterium was first applied to the soil and after three days, plants were inoculated with pathogen. Disease assessment was done after 15, 30 and 45 days of inoculation.

Biochemical analyses

All biochemical analyses were performed from leaves of plants grown in treated or control soil. Samplings were done 72 h after inoculation with the pathogen.

Enzyme assays


Extraction of chitinase (EC.3·2·1·39) and assay of its activity was done following the method described by Boller and Mauch (1988) with modifications. N-acetyl glucosamine (GlcNAc) was used as standard (Reissig et al. 1959). The enzyme activity was expressed as μg GlcNAc released min−1 g−1 fresh tissue.


Extraction of β-1,3-glucanase (GLU) (EC.3·2·1·39) from leaf samples and its assay was done following the method described by Pan et al. (1991). Laminarin was used as substrate and the enzyme activity was expressed as μg glucose released min−1 g−1 fresh tissue.

Phenylalanine ammonia lyase

Extraction of phenylalanine ammonia lyase (EC.4·3·1·5) was done following the method described by Chakraborty et al. (1993) with modifications. Enzyme activity was determined by measuring the production of cinnamic acid from l-phenylalanine spectrophotometrically. The enzyme activity was expressed as μg cinnamic acid produced in 1 min g−1 fresh weight of tissue.


Peroxidase (EC.1·11·1·7) was extracted from plant tissues and assayed following the method described by Chakraborty et al. (1993) with slight modifications. Activity was expressed as ΔA 465 nm g−1 tissue min−1.


Total phenols were extracted and estimated from tea leaves following the method of Mahadevan and Sridhar (1982).

Determination of sustainability of O. anthropi in rhizosphere

The sustainability of O. anthropi in soil was determined immunologically using enzyme linked immunosorbent assay (ELISA), up to 180 days following application. For preparation of antigens from O. anthropi, the bacterium was first grown in nutrient broth and after 48 h the actively growing cells in log phase were harvested by centrifugation at 21 000 g, and the cells were suspended in 0·05 mol l−1 sodium phosphate buffer. This suspension was then sonicated for 5 min, with 1 min treatments being separated by 1 min cooling periods (Mazarei et al. 1992). The sonicated cells were used as immunogens and polyclonal antibody (PAb) was raised in NewZealand white male rabbits against the prepared immunogen as described by Mazarei and Kerr (1990). The serum obtained from the blood sample was purified and IgG fraction obtained following the method described by Clausen (1988). IgG was used for ELISA where the antigen source was the rhizosphere soil previously inoculated with the bacterium. Prior to detection of the bacterium in soil, specificity of the antibody was checked by agar gel double diffusion test, ELISA and Dot-immunobinding assay. Soil antigens were prepared both from untreated and O. anthropi treated soil following the method of Walsh et al. (1996). ELISA was performed following the method described by Chakraborty et al. (1995). Secondary antibody labelled with alkaline phosphatase was used as the enzyme source and pNPP as the substrate (Sigma Chemicals, USA). Absorbance in ELISA was determined in a Multiscan Ex (Thermo Electro, Mumbai, India) ELISA Reader at 405 nm.

Bioformulation with O.anthropi

Ten g of carboxy methyl cellulose sodium salt (Himedia) was mixed with one kg of talcum powder and pH was adjusted to 7·0 by adding calcium carbonate. It was then sterilized twice for 30 min each. The bacterium was first grown in nutrient broth and after 48 h the actively growing cells in log phase were harvested by centrifugation at 21 000 g, and aqueous suspension was made to achieve a concentration of 3 × 109 CFU ml−1 which was determined spectrophotometrically. To 1 kg of sterilized talcum powder 400 ml of bacterial inoculum was added and mixed well under sterile condition. The talc mix was dried under shade to bring moisture to less than 20%. The formulation was packed in milky white colour polythene bags to eliminate UV exposure, sealed and stored at room temperature for future use. The talcum based formulation was applied in the field at the rate of 100 g per pot (12 × 1010 bacterial cells).

Determination of survival of O. anthropi in formulation

Survival of O. anthropi in talc formulation was determined using direct plating method in nutrient agar medium. Population of bacterium in the formulation was recorded every month for a period of 12 months. The data was log transformed for analysis.


Ochrobactrum anthropi was initially subjected to in vitro tests associated with plant growth promotion (Table 1). It showed good phosphate solubilization activity which was evident as a halo zone around the bacterial inoculum on Pikovskaya agar medium. Siderophore production was also confirmed by the change in colour of the medium. IAA production was detected in tryptophan amended medium. However, it did not produce HCN. Ochrobactrum anthropi showed antagonistic activity to some of the tested fungi in both solid and liquid culture, but not to all tested organisms. Among the six tested fungi, O. anthropi was least inhibitory to Sclerotium rolfsii and maximum to Sphaerostilbe repens and Poria hypolaterita.

Table 1.   Growth of test fungi and Ochrobactrum anthropi in dual culture
Interacting micro-organismsIn solid medium*In liquid medium†
Diameter of fungal growth (cm)% inhibitionMycelial dry weight (mg)% inhibition
  1. *At the end of 7 days of growth on Nutrient agar.

  2. †At the end of 10 days growth in nutrient broth. Average of three replicates; ±=SE.

Sclerotinia sclerotiorum8·7 ± 0·5 432 ± 4·8 
S. sclerotiorum + O. anthropi6·8 ± 1·021·8 ± 1·2356 ± 4·317·6 ± 1·2
Sphaerostilbe repens8·4 ± 1·2 468 ± 3·7 
S. repens + O. anthropi2·8 ± 0·666·7 ± 2·7243 ± 3·548·1 ± 3·2
Phellinus noxius8·5 ± 1·1 288 ± 3·0 
P. noxius + O. anthropi1·8 ± 0·578·9 ± 3·9120 ± 2·0858·3 ± 2·7
Sclerotium rolfsii8·8 ± 1·0 468 ± 4·6 
S. rolfsii + O. anthropi6·9 ± 0·921·6 ± 1·9454 ± 4·022·9 ± 0·2
Poria hypolaterita8·3 ± 0·7 350 ± 3·0 
P. hypolaterita + O. anthropi2·6 ± 0·367·5 ± 3·2143 ± 2·148·9 ± 3·2
Alternaria alternata8·9 ± 1·0 450 ± 4·3 
A. alternata + O. anthropi4·8 ± 0·546·1 ± 2·5232 ± 3·348·4 ± 1·3

Plant Growth promotion

Application of O. anthropi to the rhizosphere of five varieties of tea plants was done as described in materials and methods. Bacterial cells applied directly to the soil were considered as live cells whereas those grown in the talc formulation constituted the ‘formulation’. Bacterial application led to an increase in growth of the plants. Growth rate was commuted in terms of percent increase in height, number of leaves and number of branches over similar increase in control. In all varieties, there was a significant increase in growth rate in treated plants over that observed in control plants. Maximum increase in growth was observed in the tea variety T-17, followed by the variety HV-39. However, differences among the different cultivars were not significant, indicating that all varieties responded to the PGPR. Observations were computed after two and four months of application. Application of formulation also resulted in comparable increase in growth rate (Fig. 1).

Figure 1.

 Effect of application of live cells and formulations of O. anthropi on growth promotion in tea plants, in terms of (a) increase in plant height, (b) increase in number of leaves and (c) increase in number of branches. Data presented is mean and SE of 10 plants/cultivar of each of three replicate sets. (inline image, Live cells and inline image Formulations).

Disease suppression

Effect of treatment of soil with aqueous suspension of O. anthropi, or its formulation on incidence of brown root rot of tea, caused by P. noxius was demonstrated in green house condition. Experiments were in triplicate, with 10 plants/cultivar in each replicate. Applications to the soil were done three days prior to pathogen inoculation and the disease incidence was compared with the pathogen inoculated plants. The disease assessment was done in all five selected varieties (TV-18, T-17, HV-39, UP-3 and S-449) of tea. It was observed that application of O. anthropi formulation was as effective as aqueous suspension in reducing brown rot incidence when applied three days prior to artificial inoculation of pathogen (Table 2).

Table 2.   Effect of O. anthropi on development of root rot in tea caused by Phellinus noxius
VarietiesTreatmentRoot rot index*
15 dai30 dai45 dai
  1. Results are average of 10 plants/cultivar of each of three replicate sets; DAI = days after inoculation. L = live cells; F = formulation.

  2. *Root rot index: 0 – no symptoms; 1 – small roots turn brownish and start rotting; 2 – leaves start withering and 20–30% of roots turn brown; 3 – leaves withered and 50% of the roots affected; 4 – shoot tips also starts withering; 60–70% roots affected; 5 – whole plants die, with upper withered leaves still remaining attached; roots fully rotted. Difference in root rot index between control (P. noxius inoculated alone) and treated (with bacterial cells or formulation) significant in all cases at = 0·05, when analysed by Student’s t-test; difference between L and F insignificant. ±=SE.

TV-18P. noxius2·70 ± 0·263·92 ± ·0·384·89 ± 0·26
P.noxius + O. anthropi (L)1·08 ± 0·322·01 ± 0·162·45 ± 0·21
P.noxius + O. anthropi(F)1·12 ± 0·242·34 ± 0·162·98 ± 0·34
UP-3P. noxius2·65 ± 0·173·54 ± 0·364·76 ± 0·48
P.noxius + O. anthropi (L)1·02 ± 0·301·25 ± 0·242·87 ± 0·21
P.noxius + O. anthropi(F)1·25 ± 0·381·76 ± 0·183·08 ± 0·34
T-17P. noxius2·82 ± 0·283·31 ± 0·264·85 ± 0·32
P. noxius + O. anthropi (L)0·77 ± 0·111·46 ± 0·403·12 ± 0·48
P. noxius + O. anthropi(F)1·08 ± 0·381·76 ± 0·103·46 ± 0·37
HV-39P. noxius2·65 ± 0·463·68 ± 0·154·54 ± 0·28
P. noxius + O. anthropi (L)1·03 ± 0·152·06 ± 0·263·09 ± 0·36
P. noxius + O. anthropi(F)1·26 ± 0·342·88 ± 0·273·28 ± 0·21
S-449P. noxius2·68 ± 0·253·96 ± 0·284·98 ± 0·34
P. noxius + O. anthropi (L)1·04 ± 0·142·08 ± 0·243·08 ± 0·48
P. noxius + O. anthropi(F)1·34 ± 0·252·56 ± 0·253·31 ± 0·47

Defense enzymes in tea leaves grown in O. anthropi amended soil

Activities of all four tested enzymes – POX, PAL, CHT and GLU were assayed in extracts from the tea leaves of plants grown in O. anthropi treated soil. Treatment with PGPR increased the defense enzyme activities especially when there was pathogen challenge. Changes in PAL were statistically significant (P = 0·01) whereas significant change was observed for POX and GLU only with combined treatments. Changes in CHT were not statistically significant (Fig. 2a–c).

Figure 2.

 Activities of four enzymes in extracts of tea leaves following different treatments. (a) peroxidase (b) phenyl alanine ammonia lyase (c) chitinase and (d) β-1,3 glucanase. Data of three replicate experiments and SE. C = Uninoculated control; Pn = inoculated with P. noxius; Oa = inoculated with O. anthropi and Pn + Oa = inoculated with both (inline image, C; inline image, Pn.; inline image, Oa; inline image, Pn+Oa).


Application of PGPRs to the soil increased accumulation of phenolics in tea leaves, which was maximum in plants which were subsequently inoculated with the pathogen (Fig. 3). Analysis of variance revealed significant differences between varieties and treatments at P = 0·01.

Figure 3.

 Total phenolic contents of tea leaves following different treatments. UI C = Uninoculated control; PN = inoculated with P. noxius; OA = inoculated with O. anthropi and PN + OA = inoculated with both (inline image, ULC; inline image, PN; inline image, OA; inline image, PN+OA).

Bacterial sustainability in soil

ELISA was conducted with antigens obtained from rhizosphere soil inoculated with O. anthropi, using PAb raised against O. anthropi. Sampling was done thrice – immediately after inoculation, 15 days after inoculation and 180 days after inoculation. For preparation of soil antigen, soils were collected from the immediate vicinity of the root. It was observed that in treated soils, significantly higher absorbance values were obtained in ELISA when compared to uninoculated soil. The values showed a decline with time, which however, was insignificant, as tested by Student’s t-test (Table 3). The polyclonal antibodies were specific and they did not cross react with other tested bacteria, i.e., Bacillus meagterium, Bacillus pumilus and Serratia marcescens, which were also isolated from tea rhizosphere. In the control uninoculated soils, the ELISA values were very low.

Table 3.   ELISA values of untreated and O. anthropi treated rhizosphere soil antigens reacted with PAb of O. anthropi
Antigens from rhizosphere ofTreatmentA405 values
0 days15 days180 days
  1. Average of three replicates; PAb dilution: 1 : 1000; Alakaline phosphatase dilution: 1 : 10 000. ±=SE; Difference between control and treated significant at = 0·01 in all cases as tested by Student’s t-test; rest insignificant.

TV-18Control0·35 ± 0·040·32 ± 0·030·35 ± 0·04
O. anthropi treated1·16 ± 0·131·15 ± 0·061·11 ± 0·15
UP-3Control0·22 ± 0·030·23 ± 0·050·24 ± 0·03
O. anthropi treated1·34 ± 0·041·32 ± 0·321·36 ± 0·21
T-17Control0·40 ± 0·070·44 ± 0·060·43 ± 0·04
O. anthropi treated1·47 ± 0·091·50 ± 0·121·49 ± 0·09
HV-39Control0·31 ± 0·020·32 ± 0·030·32 ± 0·03
O. anthropi treated1·35 ± 0·161·36 ± 0·221·40 ± 0·13
S-449Control0·29 ± 0·010·29 ± 0·010·29 ± 0·02
O. anthropi treated1·41 ± 0·211·46 ± 0·181·46 ± 0·15

Viability of PGPR in formulation during storage

The viability of PGPR in formulation was tested during the storage period of 12 months at one-month interval. Results revealed that the isolate was viable till 9 months of storage, after which the decline was rapid (Fig. 4).

Figure 4.

 Survival of O. anthropi in talc formulation. Viable cell count determined at 1 month intervals up to 12 months.


Ochrobactrum anthropi TRS-2, isolated from tea rhizosphere was tested on tea for its plant growth promoting activity when applied either as aqueous suspension or in a talc based formulation to nonsterile soil. The bacterium was thus introduced into a natural environment expected in the field, and not an artificial, sterile environment. The ability of the bacterium to induce growth promotion was noted in all five varieties of tea that were tested. The increase in growth in the bioformulation was not due to any effect of talc alone, since this is a neutral substance with no known plant growth promoting activity and has also been reported by earlier workers (Hassan-El and Gowen 2006). In a study conducted on groundnut, Kishore et al. (2005) reported that Bacillus firmis GRS123, B. megaterium GPS 55 and P. aeruginosa GPS 21 promoted seedling emergence, root length, shoot length, dry weight and pod yield. It is well known that micro-organisms in soil are critical in maintaining soil functions in both natural and managed agricultural soils and play key roles in suppressing soil borne diseases, in promoting plant growth and in changes in vegetation (Garbeva et al. 2004). PGPRs may increase plant growth through a number of mechanisms – both direct and indirect. Indirect mechanisms include suppression of plant pathogens in the soil or induction of resistance in the host. In the present study, in order to determine the mechanisms of plant growth promotion, initially, in vitro tests were conducted, which revealed that the bacterium could solubilize phosphate, produce siderophore, secrete IAA and could also inhibit certain pathogenic fungal strains. However, it was a non-HCN producing strain. The direct mechanisms of plant growth promotion did not involve HCN which is a volatile inhibitor of micro-organisms. For in vivo tests of antifungal activity, the influence of O. anthropi on root rot disease development was examined. Results revealed that O. anthropi could reduce disease intensity significantly. There are a large number of previous reports of PGPRs suppressing development of root diseases either in field experiments or in green house experiments. In green house experiments, Guo et al. (2004) reported that three strains of PGPRs –Serratia sp.J2, fluorescent pseudomonad J3 and BB11 – provided disease control in tomato against tomato wilt and increased yield. Hassan-El and Gowen (2006) reported that wilt incidence in lentil was less when the soil was drenched with vegetative cells of Bacillus subtilis. They assumed that the bacterium and/or its toxins proliferated in the rhizosphere and provided protection against Fusarium oxysporum f.sp. lentis. In the present study, since the bacterium showed antagonistic activities in vitro, and since it produced siderophore, it is quite probable that the pathogen was directly inhibited in the rhizosphere. On the other hand, biopriming with some PGPRs can also produce systemic resistance against a broad spectrum of plant pathogens. PGPR-induced systemic resistance was first observed on carnation where reduced susceptibility to Fusarium wilt was observed (Van Peer et al. 1991) and on cucumber against Colletotrichum orbiculare (Wei et al. 1991). In order to determine whether the PGPR could also induce systemic resistance (ISR) in the host, several biochemical analyses known to be associated with ISR were studied. In such cases, similar to SAR, several defense mechanisms are activated. While there are several reports of ISR in vegetative plants, information regarding woody plants are rather less. In our study, it was observed that soil treatment with O. anthropi could induce enhanced activities of enzymes – PAL, POX, GLU and, to a lesser degree, CHT and also phenolic contents in the leaves. This is a clear indication of induction of systemic response in tea by O. anthropi, as the observed response was in the leaves while the application was in the soil and there are no reports of O. anthropi colonizing the leaves. PAL is the first enzyme of phenylpropanoid metabolism in higher plants and it has been suggested to play a significant role of regulating the accumulation of phenolics, phytoalexins and lignins, which are mainly responsible for the defense of the plants against the diseases (Daayf et al. 1997). In the present work also highly significant increase among the different enzymes was observed in case of PAL activity. POX plays a key role in the biosynthesis of lignin which limits the extent of pathogen spread because of the antifungal activity (Bruce and West 1989). In bean, rhizosphere colonization with various bacteria induced peroxidase activity (Zdor and Anderson 1992). Maurhofer et al. (1994) reported the induction of systemic resistance by P. fluorescens was correlated with the accumulation of GLU. Similar findings of accumulation of PR proteins such as CHT, GLU, POX and PAL after application with biocontrol agents and their involvement in inducing systemic resistance against the pathogen have been reported by several workers in different crops (De Meyer et al. 1998; Yedidia et al. 1999; Meena et al. 2000; Oostendorp et al. 2001; Bargabus et al. 2004; Bharati et al. 2004).

Thus the present study indicates that higher accumulation of enzymes involved in phenylpropanoid metabolism and other PR-proteins are involved in plant growth promotion and disease suppression in tea.

Sustainability of the applied bacterium was tested immunologically by ELISA in which the observed absorbance gives an indication of the population of bacteria in the soil as in this case there is specific binding of the bacterial antigen to the antibody raised against it. The bacterium was found to survive well in the rhizosphere when tested even after six months of application. Since it was originally isolated from tea rhizosphere, there would be no problem of its acclimatization in the rhizosphere following artificial inoculation. In the tests, a nonsterile natural environment was maintained. In spite of the bacterium being able to sustain well in the rhizosphere, application of the bacteria as formulations are better suited for practical use. Hence, in the present study, a talc based formulation was prepared and applied to the soil. Both plant growth promotion and disease suppression were noted and was found to be at par with the live cells, showing no significant difference. Application of PGPRs as several kinds of formulations have been reported by several previous workers (Mathivanan et al. 2005;Trivedi et al. 2005; Hassan-El and Gowen 2006; Tilak and Reddy 2006).

Certain strains of O. anthropi are known to be pathogenic, but the present isolate, TRS-2, isolated from tea rhizosphere, did not show any apparent human pathogenic effect. In conclusion, it can be stated that the present study was undertaken with a new PGPR, O. anthropi and results of the experiments have shown that the bacterium was effective in plant growth promotion and disease suppression; could induce ISR in the host and the talc formulation was also effective in both growth promotion and disease suppression.


Financial help received from Department of Biotechnology, Ministry of Science & Technology, Government of India, for this work is gratefully acknowledged.