review of literature - inflibnetshodhganga.inflibnet.ac.in/bitstream/10603/33743/11/11_review...

Review of literature

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Tea [Camellia sinensis (L.) O. Kuntze] is one of the most popular beverages

throughout the world. Indigenous tea was discovered in India during 1823 by

Robert in Assam. After nine years (1832) tea was experimentally planted in Nilgiris

by Dr. Christie. In 1935, tea plants raised from the China seed were sent to Assam

and south India for planting. The tea bushes are pruned on every four or five years

to maintain their vegetative growth as well as to adopt crop-husbanding practices.

This will help to adopt the proper soil conservation practices and prevent further

degradation of soil resources for sustainable productivity of tea (Verma and Adbul

kareem, 1995). Tea being a foliage crop, the shoots is harvested at regular intervals.

In this process, nutrients are removed from the plant-soil system and they should be

replenished to maintain the nutrient status of the soil.

Soil fertility has been described as the capacity of soils to make nutrients

available to plants. The nutrient status of arable soils can be related to yields in

order to develop proposals for fertilization (Tisdale et al., 1985). Nutrient

management in tea plantations is an important aspect and nutrients are supplied

mainly through chemical fertilizers. However, it is widely accepted that a balanced

fertilizer application with efficient use of other inputs is the key to achieve higher

crop production (Karthikeyini, 2002). Repeated and heavy applications of chemical

/ mineral fertilizers lead to the deterioration of soil properties besides causing

environmental damage. The application of organic manures and bioinoculants

could minimize these problems as they are advantageous over chemical fertilizers

to improve soil fertility. Thus, it is felt necessary to integrate three different sources

of nutrients viz., organics, chemicals and bioinoculants, for more efficient and

economical productive system in the long run. Bioinoculants are environmentally

safer and a cost effective supplement to chemical fertilizers (Karthikeyini, 2002).

The literature pertaining to the use of organics and biofertilizers in tea crop is very

much limited. Hence, there is an urgent need to study the influence of straight /


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integrated application of organic manure and biofertilizers with possible reduction

of inorganic fertilizers on yield and quality of tea.

In recent years, the concept of PGPR mediated plant growth promotion is

gaining worldwide importance and acceptance. They are naturally occurring soil

microorganisms that colonize roots and stimulate plant growth. Such bacteria have

been applied to a wide range of plants for the purpose of plant growth enhancement

and disease control (Barka et al., 2000; Chakraborty et al., 2005). They promote

plant growth by several mechanisms including nitrogen fixation, phosphate

solubilization, hormone secretion and suppression of soil borne plant pathogens.

Disease suppression may be due to iron sequestration, production of antimicrobials

or induction of systemic resistance (Chakraborty et al., 2005). Thus, biofertilizers

containing beneficial organisms are cost effective, pollution free and a perennially

renewable source of plant nutrients, making them ideal partners and essential

supplements to chemical fertilizers. To maximize the beneficial plant growth

responses, it is important to identify the efficient strains of PGPRs for the planting

situation. Beneficial effects of PGPRs have been reported by various workers on a

wide range of crops including cereals, pulses, vegetables, oilseeds and plantation

crops (Alagawadi and Gaur, 1992; Bashan and Holquin, 1997; Riggs et al., 2001;

Muthuraju and Jaysheela, 2005; Jayaprakashvel et al 2006). Though scientific

information on the use of PGPRs in tea is meager, their usage should be having

many benefits as indicated by Tennakoon (2007).

Tea rhizosphere

In general, the rhizosphere effect is expressed by greater microbial activity

and bacteria are the group most stimulated by the rhizosphere (Katznelson, 1965).

In the rhizosphere, roots provide shelter to the microbial communities, resulting in

apparently higher rhizosphere: soil values, compared with the normally low


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rhizosphere: soil values recorded for the established tea rhizosphere. Cultivated tea

bushes grow in close proximity to each other and the root exudates may accumulate

in the rhizosphere from all sides, causing a marked inhibitory effect. Leaf litter may

also contain antimicrobial substances which could be slowly released upon

decomposition. (Pandey and Palni, 1996).

The rhizosphere is one of the largely unexplored frontiers in plant-microbes

interaction. The rhizosphere microbial population and communities influenced on

plant nutrition, plant diseases and root architecture (Patten and Glick, 2002). Both

direct and indirect promotion of mineral nutrition through increased root mining

from soil and functions of the root-colonized microorganisms are visible effects of

nursery inoculation. Increased scope of resistance to (escape from) deleterious

microorganisms and pathogens due to increased root density is an invisible effect.

There is also the possibility of carry forward of pathogen escape by niche exclusion

of the heavily colonized roots. Growth-inhibitory relationships or the antagonistic

behaviour of microbial groups growing around established tea roots may also result

in a reduced or smaller microbial population. This includes various categories of

antagonism, such as competition, antibiosis, parasitism, and predation. These

antagonistic activities in a suppressive rhizosphere may maintain a low microbial

(harmful) population in the rhizosphere. Also, the age of a plant should not be

neglected as a factor influencing the microbial population (Pandey and Palni 1996).

The bioinoculants, through natural selection and continued exposure to

antimicrobial metabolites, may have developed a kind of tolerance or resistance to

the inhibitory components of root exudates. Every plant species provides an

individual and specific site of microbial activity in the form of a rhizosphere.


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Biofertilizers

The concept of biofertilizers was developed with the discovery of nitrogen

fixing Azospirillum by Dobereiner and Day (1976) and phosphate solubilizers by

Pikovskaya (1948). Their population level naturally varies with soil and

agroclimatic zones. Further, the population level most often may not be enough to

bring out significant contribution to the plant nutrition as their efficiency varies

with strains. Biofertilizers are most useful and they are not yet explored much in tea

(Baby, 2002). Biofertilizer is a wide term which includes a diverse category of

bioinoculants such as nitrogen fixers, phosphate solubilizers, phosphate mobilizers

and plant growth promoting rhizobacteria (Jayaraj et al., 2004).

Since most of the plantation crops are long duration crops use of

biofertilizers may have some limitations. For example, in plantation crops

biofertilizers could be used more effectively during the plant establishment phase

either in the nursery or field to increase the health of the planting stock to enable

subsequent successful establishment in the field. In most of the plantation crops,

initial experimentation has been carried out to explore the possibilities to use

biofertilizers, including manures/composts, for enhancing growth and productivity.

Performance has been either equally good or better than inorganic fertilizers. The

mineral mobilizer, arbuscular mycorhizal fungus has been found to be quite

effective for growth improvement and 25% saving in phosphorus nutrition of

plantation crops and spices such as pepper, cardamom, cashew, coconut, ginger and

turmeric under field conditions (Nautiyal 2006). Similarly application of P –

solubilizing bacteria, Bacillus megaterium along with inorganic P improved P

nutrition of cashew plants and continual application of AMF, Azospirillum and

phosphate solubilizers has shown synergistic effect among themselves (Sharma,

2006).


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However, recent studies in tea microbial inoculants illustrated the efficient

strains of nitrogen fixing, phosphate solubilising or cellulolytic microorganisms

used for application in soil or composting organic matter (Verma et al., 2001).

Biofertilizers may supplement to the organic fertilizers too in recent years or it can

be integrated with chemical fertilizers to reduce the cost of production and

conserving the soil health in tea plantation. Following the initial research on

biofertilizers, there are several reports appeared on microbes in relation to fertilizer,

pest and disease management in tea (Baby et al., 2004 a, b; Ajay et al., 2005 and

2007; Ponmurugan and Baby, 2005).

Plant growth promoting activity by biofertilizers

Several soil microorganisms including nitrogen fixers and phosphate

solubilizers are known to produce plant growth promoting substances (PGPS). The

beneficial effect of bioinoculants is attributed to increase the nitrogen input from

biological nitrogen fixation, higher phosphate solubilization, production of plant

growth promoting hormones like auxins, gibberellins and cytokinins and reduction

of plant diseases and nematode infection. Beneficial effects reflect as direct plant

growth promotion and or including host resistance. Specific PGPR strain brings

about Induced Systemic Resistance (ISR) against multiple pathogens attacking the

same host. Broad spectrum of diseases control using PGPR strains would be an

effective and economical way to plant protection measures. Moreover, certain

PGPR strain mixture showed the synergistic action in growth promotion as well as

plant protection (Megha, 2005).

Phytohormones or plant growth hormones in the rhizosphere are originated

from plants through root exudates and also by microbial synthesis in situ, of which

microbial production is considered as the primary source. The phytohormones

induce plant growth as well as dry matter production. Inoculation with Azospirillum


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resulted in better growth and higher dry production in maize and was mainly

attributed to nitrogen fixation and the production of plant growth regulators

(Arshad and Frankenberger, 1991). The major hormone produced was indole – 3-

acetic acid (IAA) (Fallik et al., 1989). Other hormones detected at much lower, but

biologically significant level were indole -3 –lactic acid (Xie et al., 2005), indole -

3- methanol (Crozier et al., 1988), unidentified indole compounds (Hartmann et al.,

1983), abscissic acid (ABA) (Kolb and Martin, 1985), cytokinins and indole – 3-

butyric acid (IBA) (Fallik et al., 1994) and several gibberellins (Bottini et al.,

1989). Frietas and Germida (1990) showed that the inoculation of P. aeroginosa, P.

cepacia, P. Putida and P. fluorescens strains on winter wheat increased the plant

height, root and shoot mass and number of tillers in growth chamber. Govindarajan

and Kavitha (2004) observed higher IAA production by Azospirillum isolates in the

presence of tryptophan in the medium. Radwan et al. (2005) observed enhanced

growth and production of indole compounds by Azospirillum brasilense Cd and A.

lipoferum Br17 due to aeration of the medium.

In recent years, more attention is being given for searching early root

colonizers which directly or indirectly benefit plant growth. Beneficial root

associating soil bacteria are usually referred to as Plant Growth Promoting

Rhizobacteria (PGPR) (Piao et al., 1992; Ona et al., 2005; Somers et al., 2005).

Among the root associated bacteria Pseudomonads are the early root colonizers,

which contribute considerably to plant production and protection. Plant growth

promoting rhizobacteria belong to several genera viz., Azospirillum, Azotobacter,

Bacillus, Bradyrizobium, Erwinia, Pseudomonas, Rhizobium and Serratia.

Nitrogen fixers

Nitrogen is one of the major element and which is essentially involved in

most of the metabolic pathway in the tea crop. The applied nitrogen has the

possibilities to leach, converted to many other forms then the chance to avail to tea


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crop is less. When nitrogen fixers are incorporated, the fixation process could be

activated so as to improve the nitrogen content in the soil may be improved.

Nitrogen fixers are organisms which assimilate molecular nitrogen present in the

atmosphere to ammonical nitrogen. Biological nitrogen fixers offer economical,

attractive and ecologically sound means of reducing nitrogen fertilizers. The most

important nitrogen fixers are Azospirillum, Rhizobium, Azotobacter and Azolla.

Among these, the most promising organism capable of colonizing roots and

exerting this miracle process is the bacterium belonging to the genus of

Azospirillum. Azospirillum is microaerophillic, gram negative and spiral shaped

bacteria, which fixes atmospheric nitrogen asymbiotically. Azospirillum brasilense,

A. lipoferum, A. amazonense, A. halopraeferans, A. irakense and A. dodereinera

are the different species of the genus. Azospirillum used to be present

predominantly in acidic soil environment.

Azospirillum population was reported from 104 to 10

6 cells per gram of soil

(Magalhaes et al., 1981). Rao and Venkateswaralu (1985) reported that the most

portable number of Azospirillum varied in the root zone of pearl millet with the

maximum in the rhizosphere compared to rhizoplane and inside roots. Further, its

population was found to be maximum in laterite soil and the minimum in extremely

acid sulphate saline kari soil (Charyulu and Rao, 1980). Attachment of A.

brasilense to wheat (Michiels et al., 1990) and maize roots (Jofre et al., 1996)

taken place in two steps. First, bacteria adsorbed rapidly on the root surface. In this

step, a protein cell surface component was used for adsorption. In the second step,

the adsorption was mediated by surface polysaccharides (exopolysaccharides) or

lipopolysaccharides (Schloter et al., 1984). Some Azospirillum strains penetrate the

roots of their host and become endophytes. In such cases, they establish in the

intercellular spaces between the epidermis and the cortex (Dobereiner, 1983b;

Whallon et al., 1985) and even in the vascular system (Baldani et al., 1983).


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Bashan and Levanony (1988) reported the colonization of A. brasilense in the

endodermis of wheat roots.

Greenhouse and field trials have been conducted in many places with

different crops which revealed that biological nitrogen fixation by root associated

Azospirillum contribute significant amounts of nitrogen to the plants thereby saving

inorganic nitrogenous fertilizers. Azospirillum inoculation benefits plant growth

and increases yield of crops by improving root development, mineral uptake and

plant water relationship (Okon, 1985). The effect of Azospirillum inoculation on the

total yield increases of field grown plants generally ranged from 10 to 30 per cent.

The responses varied with crops, cultivars, locations, seasons, agronomic practices,

bacterial strains, levels of soil fertility and interaction with native microflora (Wani,

1990). Significant yield increase was observed in tomato plants with the

inoculation of Azospirillum spp. (Bashan and Holquin, 1997). Inoculation of

Azospirillum sp. to wetland rice under acidic condition improved shoot growth,

straw yield and N uptake (Govindan and Bagyaraj, 1995). Moreover, Salomone and

Dobereiner (1996) observed significant increase in grain yield of maize on

inoculation with Azospirillum spp. Hemawathi (1997) observed improved plant

growth and flower yield of Chrysanthemum on inoculation with Azospirillum spp.

over the uninoculated control. Alagawadi and Krishnaraj (1998) studied the effect

of two Azospirillum strains viz., ACD-15 and ACD-20 on growth and yield of

sorghum under field condition. They observed significant increase in grain yield of

sorghum over the control. Dobbelaere et al. (2001) observed a significant increase

in plant dry weight due to inoculation of wheat plants with A. brasilense SP-245

and A. irakense KBC1 in Belgium.

Baby et al. (2002) reported that inoculation of Azospirillum bioformulation

or liquid near the rhizosphere of tea seedlings significantly increased growth.

Polyanskaya et al. (2002) studied the growth promoting effect of two new strains of


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Beijerinickia mobilis and Clostridium sp. isolated from pea rhizosphere on some

agricultural crops and reported that application of B. mobilis and Clostridium sp.

cultures in combination with mineral fertilizers increased the crop yield by 1.5 to

2.5 times. Significant growth and yield increase was observed in rice plants due to

the inoculation of Azospirillum lipoferum by Govindan and Varma (2004).

Enhanced shoot growth and nitrogen content of the whole tomato plant was

observed by Meunchang et al. (2006a) in soil amended with sugar mill by product

compost inoculated with N2 fixing bacteria, Azotobacter vinelandii, Bejerinickia

derxii and Azospirillum sp. than uninoculated control. Inoculation of foxtail millet

with three strains of Azospirillum lipoferum either alone or in combination with N

fertilizer increased the plant height, dry weight and total N content of shoot and

root (Rao and Charyulu, 2006).

Mechanism of Nitrogen fixation

Biological nitrogen fixation by non-symbiotic nitrogen fixing bacteria like

Azotobacter and Azospirillum which requires a complex enzyme system since the

reaction is highly endergonic and it is widely being exploited all over the world for

non-leguminous crops. Azospirillum is a rhizospheric bacterium colonized the roots

of crop plants in large numbers, making use of root exudates and fixes substantial

amount of atmospheric nitrogen. The protons and electrons required for this

process are generated in metabolic reactions and catalyzed by an enzyme

nitrogenase. It is found only in prokaryotic microorganisms and so eukaryotes can

benefit from nitrogen fixation only if they interact with nitrogen fixing prokaryotes

to obtain the fixed nitrogen after their death and decomposition. Nitrogenase

enzyme is highly essential for reducing nitrogen to ammonia and is composed of Fe

(dinitrogenase) and Mo-Fe protein of nitrogenase have been sequenced and

characterized from a variety of nitrogen fixing bacteria (Burgess and Lowe, 1996).

Fixation of atmospheric nitrogen by Azospirillum was evaluated mainly by


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acetylene reduction assay and this method was useful for quantitative evaluation of

nitrogen fixation by Azospirillum and their screening (Van Berkum and Bohlool,

1980).

Okon and Vanderleyden, (1997) exerted beneficial effects of Azospirillum

on growth and yield of many economically important crops. They are extensively

used in rice and other cereal crops as a biofertilizers (Singh, 2010). These are free-

living bacteria and fix atmospheric nitrogen in cereal crops without any symbiosis.

Many Azospirillum strains produce plant hormones both in liquid culture and

natural situation. Colonization of Azospirillum in roots was known to be non-

homogenous. The bacterial cells were observed throughout the entire root system

of many plant species, however it preferred root tips and zone of elongation

(Levanony et al., 1989). The colonization of root tips was advantageous for

Azospirillum cells because when the roots penetrate deeper into the soil layer, the

oxygen supply was lower and competition with the aerobic bacterial population of

the rhizosphere was therefore reduced, however analysis of Azospirillum sites along

the roots revealed that they are found particularly on young roots and much less

frequently on the older parts of the roots (Cohen et al., 2004). They have the ability

to produce antifungal compounds against many plant pathogens. They also increase

germination and vigour in young plants leading to an improve stand in crops.

Phosphate Solubilizers

Phosphorus is another major element required for plant growth and higher

yields. Rock phosphate is one of the basic raw materials for phosphatic fertilizers.

Direct application of rock phosphate is limited to acidic soil, while in other types of

soil the applied phosphate becomes insoluble within a short time. Monocalcium

phosphate are converted to dicalcium phosphate which is slowly available to plants.

Under such conditions large amount of phosphorus is fixed in the soil which is

unavailable to the plants. The most efficient phosphate solubilizing bacteria


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includes of Bacillus and Pseudomonas and that of fungi include species of

Aspergillus and Penicillium (Baby, 2002) make available insoluble phosphorus to

the plants. The main mechanism in solubilizing insoluble phosphate by soil

microbes is on their ability to secrete organic acids. The organic acids bring down

soil pH resulting in the dissolution of immobile forms of phosphate (Hedge and

Dwivedi, 1994) and production of organic acid by Pseudomonas strains decreases

soil pH reported by Rashid et al., (2004). The effect of phosphate solubilizers on

plants are attributed to P solubilization plus other factors like release of

phytohormones, supporting nitrogen fixation, mineralization and mobilization of

other nutrients, antagonism to plant pathogens and promotion of plant growth

promoting rhizosphere microorganisms (Gaur, 1990). Further, the potential of

phosphate solubilizers in solubilizing P and mycorrhizae in mobilizing P made

agricultural scientists to think over the possibility of exploiting these organisms in

integrated nutrient management programme.

Pikovskaya (1948) made a pioneering attempt in isolating an organism

capable of actively solubilizing tricalcium phosphate and coined the name

"Bacterium P". Later he had formulated a medium having glucose as carbon source

and ammonium sulphate as nitrogen source with enrichment technique and special

media for the isolation of acid producing and phosphate dissolving microorganisms

from soils and rhizosphere were designed by Katznelson and Bose (1959).

Mahmoud et al. (1973) made a comparative study of the population of PSB in the

rhizosphere of board bean and wheat. Broad bean had more population of

phosphate solubilizers than the wheat plants. Phosphate solubilizing

microorganisms were found in all soils but their number varies with soil climate as

well as history (Gupta et al., 1986). Soil samples collected from sugarcane growing

belt of north Bihar indicated that the population level of phosphate solubilizers

range from 27-112 x 103 per gram of soil. This large variation in their distribution


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in different soils might be due to the differences in organic carbon content (Yadav

and Singh, 1991).

Bacteria, fungi, actinomycetes are active in solubilizing insoluble inorganic

phosphate with high efficiency (Kapoor et al., 1989; Narsian and Patel, 1995).

Parameters affecting the ability of PGPR to express different attributes include soil

and environmental conditions, microbes–plant host interactions, and microbes–

microbes interactions (Dey et al., 2004). De Freitas et al., (1997) assessed the

potential use of P solubilizing Bacilli and other rhizobacteria as biofertilizers for

canola and reported that Bacillus thuringiensis isolate was the most effective

inoculant which significantly increased the number and weight of pods and seed

yield without rock phosphate. Kundu et al., (2002) studied host specificity of

phosphate solubilizing bacteria isolated from different crop rhizospheres and

observed greater establishment of the isolates in the rhizosphere of their respective

crop plants than other plants.

Afzal et al., (2005) reported increased yield and P uptake of wheat plants

due to inoculation of mixture of Pseudomonas and Bacillus spp. Frietas and

Germida (1990) isolated the phosphate solubilizing microorganisms such as

Pseudomonas aeruginosa, P. cepacia, P. fluoresence and P. putida from the

rhizosphere of wheat and Bacillus licheniformis, B. mycoides, B. megaterium from

the rhizosphere of paddy (Watanabe and Hayano, 1993). Phosphate solubilizing

microorganisms are also known to produce plant growth promoting substances

(PGPS). P-solubilizing bacteria isolated from the rhizosphere of wheat and rye

plants produced auxin type of PGPS, when they were grown in liquid medium

supplemented with tryptophan (Leinhos and Vasek, 1994). Production of IAA and

GA to a considerable extent by P-solubilizing Bacillus polymyxa (Sattar and Gaur,

1987) and Erwinia, Pseudomonas and Serratia from bamboo rhizosphere was

observed by Maheshkumar (1997). Veena (1999) recorded IAA and GA3


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production by P-solubilizing Enterobacter, Xanthomonas and Pseudomonas

isolated from rhizosphere of sorghum plants. Megha (2005) examined 52

fluorescent pseudomonads for the production of IAA and GA and found them to

produce IAA in the range of 80 to 760 μg per L of broth and GA in the range of

24.8 to 262.8 μg per L of broth.

The use of P-solubilizers as bioinoculants has been found to increase

growth, yield and phosphorus uptake by many crop plants. The field and pot trials

with phosphate solubilizers with or without phosphatic fertilizers, tri calcium

phosphate, pyrite or hydroxy apatite showed increase in yield and P uptake from

marginal to significant levels (10 – 27%) (Altomare et al., 1999). Alagawadi and

Gaur (1988) reported the increase in nodulation, nitrogenase activity, dry matter

yield, P uptake and grain yield of chickpea plants as well as available P content in

soil due to inoculation of P. striata and B. polymyxa as compared to uninoculated

control. Increase in grain and straw yield of sorghum under field condition and

nutrient uptake as well as available P content in soil has also been reported by Jisha

and Alagawadi (1996) due to inoculation of the bioinoculants.

Mechanism of phosphate solubilization

Phosphate solubilizing microorganisms were found to produce mono

carboxylic acids (acetic acid, formic acid), monocarboxylic hydroxyl acids (lactic,

gluconic) dicarboxylic acids (oxalic, succinic), dicarboxylic hydroxyl acids (malic,

maleic) and tricarboxylic hydroxyl acids (citric) in liquid medium from simple

carbohydrates (Sperberg, 1958a). A fall in pH accompanied phosphate

solubilization due to the production of organic acids, but no correlation could be

established between acidic pH and quantity of P2O5 liberated (Dave and Patel,

1999). Kapoor et al., (1989) reported that organic acid produced and their quantity

differ with different microorganism. Tri and dicarboxylic acids are more effective


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compared to mono basic acids and aromatic acids. Aliphatic acids are also found to

be effective in P-solubilization than phenolic acids while citric acid and fumaric

acids had highest P-solubilization ability. The organic acid production by PSB is

capable of solubilizing the inorganic phosphorus in to available state so as to

nourish the crop. This is the main mechanism to bring acidic soil environment

which retains higher phosphorus content was reported by Rashid et al 2004.

Arbuscular Mycorrhizae Fungi (AMF)

The symbiotic association between plant roots and fungal mycelia is termed

as mycorrhiza (Fungal roots). AM fungi are known for their mutualistic association

with most of the vascular plants and for helping in the absorption and assimilation

of the elements, which are less soluble and non-available to the plants, i.e., P, Zn,

Cu, etc., from the rhizosphere thereby increasing growth and productivity of the

plant (Hayman and Mosseae, 1972; Neelima et al, 2002). These fungi are obligate

symbionts and have not been cultured on nutrient media. AMF fungi infect and

spread inside the root system. They possess special structures known as vesicles

and arbuscules. The arbuscules help in the transfer of nutrients from soil to the root

system and the vesicles, which are saclike structures, store P as phospholipids. AM

fungi colonize the root cortex of plants and develop an extrametrical hyphal

network that can absorb nutrients from the soil. Enhanced plant growth due to

arbuscular mycorhizae (AM) association was well documented by Bagyaraj (1984).

Also he reported that improved plant growth is attributed to increased nutrient

uptake, especially of phosphorus, tolerance to water stress, root pathogens and

adverse soil environments and production of growth-promoting substances.

Mycorrhizal fungi enhancing the numerous and activity of beneficial soil

organisms like nitrogen fixers and phosphate solubilizers with consequential

beneficial effect on plant growth have also been substantiated by Linderman


24

(1992). It has also been suggested that AMF stimulate plant growth by

physiological effects other than the enhancement of nutrient uptake or by reducing

the severity of diseases caused by the soil pathogens.

Conversely, soil microorganisms can affect AM formation and function

(Azco´n-Aguilar and Barea, 1992; Zapata and Axmann, 1995; Barea et al., 1997).

The mycorrhiza helper bacteria are known to stimulate mycelial growth of

mycorrhizal fungi or to enhance mycorrhizal formation (Garbaye, 1994; Frey-

Klett,1997). The microbiologically solubilized phosphate could, however, be taken

up by a mycorrhizal mycelium, thereby developing a synergistic microbial

interaction (Barea et al., 1997). Phosphorus (P) is added in the form of phosphatic

fertilizers, part of which is utilized by plants and the remainder converted into

insoluble fixed forms (Narsian, and Patel, 2000). The contribution of their process

to plant nutrition is unclear and because of the possible refixation of solubilized

phosphate ions on their way to the root zone. Mycorrhizal colonization may alter

the host root physiology which may in turn influence the microbial population.

The flow of carbon from shoot to root may be increased by AM

colonization (Muthukumar and Udaiyan, 2000) which may alter the carbon

availability for bacteria in the rhizosphere. Furthermore, it is well known that root

exudates strongly modify microbial composition and activity in the rhizosphere and

AM fungi can modify the quantity and quality of root exudates (Andrade et al.,

1997). Mycorrhizal dependency of plant species is often related to the

morphological properties of the root; the root system of neem, with short sparse

root hairs, tends to make it more mycorrhiza- dependent like several other tree

species. The enhanced uptake of P in AM-fungi-inoculated seedlings may be due to

an increase in the number of uptake sites per unit area of roots and a greater ability

of these roots to exploit the soil nutrients (Bolan, 1991). AM fungi allow the root

system to exploit a greater volume of soil P by (i) extending away from the roots


25

and translocating P away from the root zone, (ii) exploiting smaller soil pores not

reached by the root hairs and (iii) effective acquisition of organic phosphates by

production of extracellular acid phosphatases (Marschner and Dell 1994).

Enhancement of uptake of phosphorus and other nutrients by fungal hyphae

is the primary mechanism responsible for plant growth stimulation by arbuscualr

mycorrhizal fungus (AMF) (Bolan, 1991) and improved shoot and root length

(Hayman, 1980). However, AM fungi also helps in the production of plant

hormones such as cytokinins, IAA and IBA, all of them have a role in plant

metabolic process (Barea and Azcon-Aguilar, 1982). Inoculation with AM fungi

(Phavaphutanon et al., 1996) or Azospirillum (Okon and Labandera-Gonzalez

1994) can reduce fertilizer requirement in plant production. Studies of

Muthukumar et al., (2001) indicated that microbial inoculations can substantially

reduce fertilizer requirement in neem seedling production. Moreover, mycorrhizal

colonization may also alter the pH of the substrate through release of certain

substances, which are not well-documented (Filion et al., 1999). Results of several

workers indicated that a drop in soil pH with phosphobacteria inoculation and in

certain treatments involving Glomus intraradices (Kim et al., 1998). In addition, A.

brasilense and phosphobacteria might affect plant growth as a result of their ability

to synthesize plant hormones (Rodríguez and Fraga, 1999). The colony forming

units of B. coagulans and T. harzianum were also highest when all three organisms

were inoculated together and the least when these were inoculated alone (Jayanthi

et al., 2003).

Influence of bioinoculants consortium

Group of bioinoculants than a single perform better and proves high yield,

productivity, nutrient uptaken and soil health improvement in various crops.

Inoculation with asymbiotic nitrogen fixers like Azospirillum may improve plant


26

growth and yield due to supplementing the growing plants with fixed nitrogen and

growth-promoting substances (Sumner, 1990). Phosphate- solubilizing bacteria

(PSB) on the other hand solubilize insoluble phosphorus by producing organic

acids which are taken up by plants (Rodríguez and Fraga, 1999). VAM fungi

enhance the uptake and translocation of phosphorus (P) and other minerals from the

soil solution to the root cells (George et al., 1995). So the inoculation along with

AM fungi, PSB and Azospirillum could enhance the growth of tree seedlings in

nurseries, the synergistic effect of indigenous AM fungi, PSB and Azospirillum on

growth, nutrient status and seedling quality of neem has been reported by

Muthukumar et al (2001).

Dual inoculation increased yields in sorghum (Algawadi and Gaur, 1992),

barley (Belimov et al., 1995), black gram (Tanwar et al., 2002), soybean (Abdalla

and Omer, 2001) and wheat (Galal, 2003, Aftab and Asghari 2008). The most

efficient and dominant solubilizers were Bacillus and Pseudomonas and these

bacteria behaved as mycorrhiza helper bacteria (Garbaye, 1994; Frey-Klett et al

1997; Sabannavar and Lakshman, 2009). Because they promoted root colonization

when associated with mycorrhizal fungi and other phosphate solubilizing bacteria

combinations (Azco´n-Aguilar, and Barea, 1992). Gaur (1985) observed that

increased grain yield and phosphorus uptake by response of crops to Pseudomonas

striata. Microorganisms in the mycosphere of AM fungi may affect mycorrhizal

functions such as nutrient and water uptake carried out by the external hyphae of

AM fungi (Duponnois et al., 2005). Synergistic effects of PGPRs during combined

inoculation have also been reported in various crops, for examples potatoes (Kundu

and Gaur, 1980a), rice (Tiwari et al., 1989) and sugar beet and barley (Cakmakci et

al., 1999). In case of co-inoculation of P solubilizing and K solubilizing bacterial

strains synergistically solubilized rock P and K sources of fertilizers which were

added into the soil and make them much more available for uptake by plant roots.


27

Higher N, P and K uptake may subsequently promote the plant growth. So the

combined inoculation with N2

fixing and phosphate solubilizing bacteria was more

effective for providing a more balanced nutrition for plants (Belimov et al., 1995).

Sensitivity of bioinoculants to organic and inorganic fertilizers

Bioinoculants are able to compatible with possible reduced dose of either

organic and/or inorganic fertilizers. They act on external sources of fertilizers so as

to get energy for their establishment by producing certain organic acids, enzymes

and other secondary metabolites. When the concentration of such inorganic and/ or

organic manures may influence the growth of bioinoculants. In case of organic

based materials, they survive very well by utilizing it and later the minerals could

be released from the organic sources of fertilizers in the soil. Whereas the inorganic

fertilizers adversely affect them but at the minimized doses may have the

possibility to support the bioinoculants. Interactions of A. fumigatus with K –

bearing minerals release potassium through three different reaction pathways. The

first involves the smaller and soluble components of the secretion, the second

concerns the insoluble part of the macromolecules and membrane-bound

biopolymers, and the third may be related to the physical activities of the cells

including direct ingestion of mineral particles (Adeleke et al., 2010). While the

interactions of free aqueous biomolecules with minerals do not seem to require

active involvement of fungal activities, the routes that entail the participation of

immobile organic matrices and cell-mineral physical contact appear to have a

strong dependence upon the vitality of the microbes and therefore are correlated to

the optimal living conditions of the organisms.

Biomolecules can penetrate hard mineral materials for the purpose of

nutrient absorption (Van Breemen et al., 2000). Their primary role is to search for

and absorb nutrients under severe soil conditions on behalf of their host plants


28

(Smith and Read, 2008). Both ecological and weathering roles of ectomycorhiza

fungi have been investigated and linked to their ability to produce metabolites such

as organic acids. These acids are low molecular weight compounds and confirmed

to have great potential in the solubilisation of complex or hard mineral materials

(Paris et al., 1995; Gadd, 1999; Van Breemen et al. 2000). It suggests that

microbial mediated mineral weathering cannot be approximated by simple

dissolution reactions with the participation of organic or biochemical molecules.

While the pH decrease resulting from metabolic activities and the complelx

reactions involving organic ligands derived from metabolites and biomass

decomposition are active participants in microbe-mineral interactions, the immobile

biopolymers (either attached to the cell surfaces or insoluble secretion), combined

with cell-mineral mechanical interactions, may be a more forceful agent, leading to

an effective destruction and transformation of minerals in biogeochemical

processes (Adeleke et al., 2010).

Integrated Nutrient Management

The supplementary and complementary use of organic manures and

inorganic chemical fertilizers integrated with beneficial proven bioinoculants

augment the efficiency of both the substances to maintain a high yield and soil

productivity (Thakuria et al., 1991). The beneficial effects of combined application

of chemical fertilizers with organic manures viz., farmyard manure, vermicompost,

biofertilizers, panchagavya and many more of such materials are universally

known. Application of organic manures in general improves the availability of

micronutrients like zinc, iron, manganese and copper. A balanced application of

both organic, inorganic and bio-fertilizers appear to be an ideal proposition to meet

nutrient requirements of dry land crops rather than single application. In view of

this, henceforth research on integrated nutrient management involve intensively to

assess the effect of organic and inorganic sources of nutrients integrated with


29

biofertilizers on the nutrient uptake and residual soil fertility (Kondapa naidu. et al.,

2009). Possibilities of INM were tried in tea with inclusion of biofertilizers like

Azospirillum and phosphobacteria in manuring programme of tea and results

revealed that bacterial fertilizers in tea can be good supplement. It was found that

integrated approach of inorganic and organic sources like 100Kg nitrogen + 5Kg

farmyard manure / hectatre provided yield significantly higher than when 150 Kg

nitrogen from purely inorganic source was given and which has eco-friendly effect

with the environment (Saikia, 2006). Application of AM fungi, phosphobacteria,

Azotobacter, Azospirillum are beneficial in nutrient management to the plants and

reducing the consumption of inorganic fertilizers (Jamaludin, 2006). It has now

become possible to meet a large part of our total nitrogen demand through proper

husbandry of biological nitrogen fixation by microorganisms in crop production

system.

Biofertilizers are capable of providing an economically viable level for

achieving the ultimate goal of enhanced productivity. The crop microbial soil

ecosystem can, therefore, be energized in sustainable agriculture (Nautiyal, 2006).

The use of chemical fertilizer, organic fertilizer or biofertilizer has its advantages

and disadvantages in the context of nutrient supply, crop growth and environmental

quality. The advantages need to be integrated in order to make optimum use of each

type of fertilizer and achieve balanced nutrient management for crop growth (Chen,

2006). The integrated nutrient management favourably affects the physical,

chemical and biological environment of soils (Singh et al., 2011). Increasing

importance of INM in maintenance of soil fertility and of plant nutrient supply for

sustaining desired crop productivity can be achieved through optimization of

benefits from all possible sources of plant nutrients in an integrated manner

(Nautiyal, 2006). The development of biofertilizers formulation would be

immensely exploited in crop production to reduce the chemical fertilizers inputs


30

and to develop sustainable production systems. Plantation crops did not receive the

same attention as that of field crops. Balasubramani et al. (1997) reported that the

soil and seed treatment of Azospirillum alone recorded the higher number of fruits

per plant followed by the Azospirillum treated seeds and soil application of nitrogen

at 30 kg per ha. Kundu and Gaur (1980 b) observed a synergetic interaction

between Azotobacter and phosphate solubilizing bacteria when the two organisms

were inoculated together in cotton. In the combined inoculation treatments, the

population of both the organism was enhanced in addition to increase in yield of

cotton.

Kalyani et al., (1996) studied the interaction of Azospirillum and fertilizer

nitrogen on cauliflower Cv. Jawahar moti and reported that soil inoculation of

Azospirillum coupled with less nitrogen (80 Kg/ha) had beneficial effect in

improving the growth and yield, besides saving of recommended nitrogen upto

50%. Balasubramani (1988) reported that the seed and soil treatment of

Azospirillum with 75% recommended dose of nitrogen per ha recorded the higher

yield (17.5 t/ha) compared to control (9.6 t/ha) in bhendi. Thamizh and Nanjan

(1998) stated that the combined application of Azospirillum, phosphobacteria and

VAM with 75% of recommended NPK (90:90:90 Kg/ha) recorded higher yield

(14.96 t/ha) which was 21 per cent higher than uninoculated control (11.93 t/ha) in

potato. Nanthakumar and Veeraghavathatham (1999) noticed that combined

nutrition of organic manure through FYM (2.5 t / ha.) Azospirillum (2 Kg / ha) and

phosphobacteria (2 Kg / ha) along with 75% of recommended dose of inorganic

nitrogen and phosphorus increased the yield and yield components in brinjal. So

there is a wide scope to develop biofertilizers to supplement/substitute the use of

inorganics to enhance productivity of plantation crops (Thomas 2006). Ragland et

al. (1989) observed that 75 per cent of the recommended N and P levels (112.5:

112.5 Kg N and P/ha) along with Azospirillum and AM produced significantly


31

higher bulb yield of Bellary onion as compared to the uninoculated control, which

was on par with 100 per cent recommended dose of NPK and biofertilizers (Mog,

2007). Prabhu et al. (2002) reported that, application of biofertilizer and FYM with

reduced dose of inorganic fertilizers increased yield and yield attributes in okra.

The treatment combination of FYM (10 t/ha) + 2/3 RDF + Azospirillum + VAM

resulted in higher yield, Kropisz (1992) observed that application of FYM (25 t/ha)

+ NPK recorded significantly higher yield compared to FYM alone and NPK in

cabbage, onion and carrot.

Mandal and Mazumdar (1986) indicated application of RDF in combination

with FYM (15 t/ha) resulted in higher potato tuber yield compared to control.

Luzzati et al. (1975) found that organic manures alone did not generally increase

the yield of carrot. Kropisz and Wojciechowski (1978) reported that compost in

combination with NPK had beneficial effect in carrot. Patil (1995) reported that

application of vermicompost (4 t/ha) with 50% RDF increased potato yield (34

t/ha) as compared to control (14.2 t/ha). Tomar et al. (1998) indicated that brinjal

and carrot plants were grown in pots and addition of FYM or urea, vermicompost

and vermicompost + FYM (1:1) recorded maximum yield with soil amended with

FYM and vermicompost compared to unamended soil. Integrated use of inorganic

nitrogenous and phosphatic fertilizers and biofertilizers is the most efficient way of

economizing the fertilizer use and improving agronomic efficiency besides

improving physical, chemical and biological properties of the soil (Ramanjaneyulu

et al., 2010).

Influence of INM on biochemical and quality parameters

Mineral nutrients are essential to plant growth and development which also

influence the quality attributes of plant products. The beneficial effect of adding

mineral elements to soils to improve plant growth and it has been known well in


32

agriculture for more than 2000 years. The growth, development and quality of tea

plants, also require the continuous supply of mineral nutrition, especially N, K, Mg

and S that are essential to tea plants. This is because such minerals tend to

influence the level of polyphenols and N-containing compounds and thus affect the

quality of made tea. Nutrient deficiency in soils and poor fertilization are possibly

two important issues and reasons for low yield and quality of tea (Malenga and

Wilkie 1994). With the fast development of tea production in China, great attention

has been paid to the balanced fertilization in tea cultivation for good quality and

high yield of tea in recent years. It is necessary to study the background of nutrients

and the soil properties in tea-grown soils, and their effects on tea quality and yield

in order to develop efficient fertilization (Jie, 2005). Panwar and Singh (2002)

studied the role of biofertilizers in wheat and revealed that N2 fixing bacteria

(A.brasilense) and phosphate solubilizing bacteria (B.subtilis) significantly

increased chlorophyll content, nitrate reductase activity and achieved better quality

over other treatments. The application of increasing levels of chemical fertilizers

will lead to increasing crop yields but quality of its products may get deteriorated.

Continual and excessive use of chemical fertilizers may adversely affect the

soil health and fertility resulting in environmental and ground water pollution. The

application of chemical, organic and biofertilizers in a balanced manner can meet

the nutrient requirement of the tea plant for sustainable productivity. In this

context, possible reduction of chemical fertilizers and regaining of soil health can

be achieved by incorporating the organic and/or biological fertilizers. The organic

and biofertilizers provide not only nutrient supply to the plants but also impart

resistance to plants against pests and diseases. Utilization of biofertilizers and

organic manures becomes essential at this juncture to maintain soil productivity and

to supply nutrients to the plants due to its plant growth promoting and disease

control abilities by keeping ideal quality too. The use of biofertilizers in


33

combination with chemical fertilizers and/or organic manure offers a great

opportunity to increase the crop productivity with greater quality at different

growth stages of tea crop (Baby 2006). Integrated schedule of biofertilizers with

possible reduction of inorganic fertilizers in plantation crop like tea has not yet

been explored. Inoculation with AM fungi, PSB and Azospirillum enhanced the

growth of tea seedlings and improved the biochemicals related to quality of tea

which were comparable to 100% inorganic fertilizers treated and much higher over

un inoculated seedlings under nurseries (Balamurugan et al., 2011). The present

study was undertaken to evaluate the synergistic effect of indigenous AM fungi,

PSB and Azospirillum on growth, nutrient status and seedling quality of tea.

The present study was focused on the standardization of the ideal

combinations of inorganic, organic fertilizers and biofertilizers to meet the nutrient

requirements of tea plant. The possible reduction of nitrogenous and phosphatic

fertilizers as well as exploiting the indigenous biofertilizers strains were attempted

for getting better yield and quality of tea. The advantages and beneficial effects of

bioinoculants on tea seedlings were also studied under nursery conditions. The

physico-chemical parameters and microbial studies, influence of root extracts and

synergistic effects of manuring chemicals on the survival of bioinoculants, were too

studied in detail. Apart from this, studies on beneficial bioinoculants for their

growth promoting abilities and their role in controlling diseases were also

undertaken. This study on integrated nutrient management in tea by exploiting of

bioinoculants would be useful to the southern Indian tea industries and which may

immensely get benefited from the outcome of these present findings.

review of literature - inflibnetshodhganga.inflibnet.ac.in/bitstream/10603/33743/11/11_review...

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