13

2. REVIEW OF LITERATURE

Ulrich et al., (2008) stated that different kinds of

microorganisms, including fungi, actinomycetes and other bacteria

present inside the plants and designated as endophytes.

Endophytes inhabit plant tissues in their life cycle without causing

any apparent harm to their host. These bacteria, that generally

colonize the intercellular spaces, have been isolated from all plant

tissues and from many plant species constituting a great reservoir

of bacterial diversity with a remarkable biotechnological potential.

He also described that the endophytes are found in virtually

every plant studied, where they colonize in the internal tissues of

their host plant and can form a range of different relationships

including symbiosis, mutualism, neutralism and commensalism.

Endophytic bacteria can promote plant growth and yield and can

act as biocontrol agents.

Jacobson et al., (1994) reported that the endophytic bacteria

differ from biocontrol strains in that they do not necessary inhibit

pathogens but enhance plant growth through increasing nutrient

uptake and secreting phytohormones. A diverse array of bacterial

endophytes including Acetobacter, Arthrobacter, Bacillus,

Burkholderia, Enterobacter, Herbaspirillum and Pseudomonas have

been reported by Lodewyckz et al., (2002).

14

The studies of James et al., (1997) revealed that Sorghum

bicolor inoculated with endophytic bacteria - Herbaspirillum

seropedicae did not express the disease or showed very mild

symptoms. Denise et al., (2002), isolated 853 endophytic strains

from aerial tissues of four agronomic crop species and 27 prairie

plant species and the highest endophytic population levels were

obtained in monocot hosts - onion and wheat.

Kobayashi and Palumbo, (2000) have also looked at the

recovery of endophytes from monocot plants like corn and banana.

Quadt-Hallmann et al., (1997) studied the bacterial endophytes in

cotton and their interaction with other plants associated bacteria.

Pharm Quang Hung and Annapurna, (2004) isolated 65 bacterial

endophytes from soya bean tissues of stem, root and nodule.

In recent years various novel endophytic nitrogen-fixing

bacteria have been discovered, such as Acetobacter seropedicae

(Cavalcante and Dobereiner, 1998), Herbaspirillum serepedicae

(Baldiani et al., 1986) and “Pseudomonas”, now established as a

second species of Herbaspirillum, Azoarcus spp. (Reinhold-Hurek et

al., 1993) and Alcaligenes faecalis (Zhou and you, 1988). Also, some

strains of Azospirillum brasilense have been found to the plant

interior (Schloter et al., 1994).

Xu et al., (2007) have studied the plant growth promotion and

biocontrol potential of bacterial strains in members of Bacillus sp.

Serratia sp. and Arthrobacter sp. Ting et al., (2008) suggested that

15

Serratia marcescens can be used as a plant growth promoter and to

control plant diseases in blue berry and also in banana.

Lifshitz et al., (1987) stated that bacterial plant growth

promotion is a well-established and complex phenomenon that is

often accomplished via the activities of more than one plant

growth promoting trait exhibited by the associated bacterium.

Ahmad et al., (2008) suggested that many studies have been

undertaken to understand the nature and properties of these

unique microbes, which harbor unique habitat inside the plants

and potential plant growth promoting traits with increasing

awareness of the problems of chemical fertilizer based agricultural

practices.

2.1 Plant growth-promoting endophytes

Robert Ryan et al., (2007) reported that several research has

been conducted on the plant growth-promoting abilities of various

rhizobacteria. They differ from biocontrol strains in that they do not

necessarily inhibit pathogens but increase plant growth through the

improved cycling of nutrients and minerals such as nitrogen,

phosphate and other nutrients. Endophytes also promote plant

growth by a number of similar mechanisms. These include

phosphate solubilization activity reported by Verma et al., (2001)

and Wakelin et al., (2004) and the production of a siderophores

16

reported by Costa and Loper (1994). Pirttila et al., (2004) reported

that the endophytic organisms can also supply essential vitamins to

plants. Moreover, a number of other beneficial effects on plant

growth have been reported by Compant et al., (2005a,b) attributed

to endophytes includes osmotic adjustment, stomatal regulation,

modification of root morphology, enhanced uptake of minerals and

alteration of nitrogen accumulation and metabolism. The recent

areas where these plant growth-promoting bacterial endophytes are

being used in the developing areas of forest regeneration and

phytoremediation of contaminated soils.

2.2.1 Plant Growth Effects — General Modes of Action

Frommel et al., (1991) and Kloepper et al., (1980); (1991)

stated that plant growth effects attributed to rhizobacteria that have

encompassed endophytes include growth and developmental

promotion, growth inhibition growth stimulation through the direct

production of phytohormones (Barbieri et al., 1986; Brown, 1974;

Jacobson et al., 1994 and Holland, 1997) indirect growth

stimulation through the induction of phytohormone synthesis by

the plant and growth promotion through the enhanced availability

of minerals (Murty and Ladha, 1988). Elmerich (1984) reported that

some inoculants (Azospirrillum spp.) are also able to code for plant

growth hormones, such as auxins and cytokinins. Early seedling

vigour and nitrogen fixation may be the primary factor in some

17

reports of enhanced yields. New research efforts have focused on

the development of endophytic diazotrophs that are able to supply

biologically fixed nitrogen directly to their host.

2.2.2 Brief History of the Discovery of Nitrogen-fixing

Organisms

Ann Hirsch, (2009) stated that, probably since from the time

of the Egyptians, that legume such as pea, lentil, and clover are

important for soil fertility. Such practices as green manuring, crop

rotation, and intercropping have been known for millennia and were

extensively described by the Romans, but it was not until the 19th

century that an explanation for the success of the legumes in

restoring soil fecundity, especially after a crop such as wheat had

been grown, was uncovered. In the 19th century, agriculture in

Europe had progressed to the point that both green manuring and

intercropping using legume crops was standard practice. The

leguminous plants were known in German as “Stickstoffsammler”

or nitrogen accumulators, whereas non-leguminous crops such as

wheat were called “Stickstofffreser” or nitrogen consumers.

However, that microbes were responsible for nitrogen accumulation

was not recognized until the last quarter of the 19th century when

rhizobia were discovered.

If the bacteria do not induce a specialized structure such as a

nodule, it is possible that they are still providing nitrogen to roots

by associative nitrogen fixation. Up to the 1970’s, little attention

18

was given to the possibility that nitrogen-fixing bacteria were

associated with non-legume crops, particularly the cereal grasses,

and furthermore, that these bacteria promoted plant growth by

providing fixed nitrogen to their hosts. This changed when Johanna

Dobereiner came to Brazil to work in the Research Department of

the Brazilian Ministry of Agriculture.

In his early work, Dobereiner found a number of bacteria in

Brazilian soils, including Azotobacter (later named Azorhizophilus)

paspali and Beijerinckia fluminenesis, surrounding cereal grasses,

the latter in the rhizoplane of sugarcane. He also studied a number

of Brazilian species of Azospirillum, the only other genus other than

the rhizobia used as inoculants for crops (Ann Hirsch, 2009). In the

1980’s, Dobereiner and her colleagues found a number of nitrogen-

fixing bacteria that colonized the inner tissues of plants

(diazotrophic endophytes). He isolated Herbaspirillum seropedicae

from maize, sorghum and rice and Gluconoacetobacteria

diazotrophicus from sugarcane. Indeed, various sugarcane varieties

were found to obtain 30 to 50% of their nitrogen from biological

nitrogen fixers (BNF) and the discovery of Gluconoacetobacteria led

to a tripling of the production of bioethanol in Brazil. Nitrogen-fixing

ability of these bacteria was later confirmed by her co-workers

using 15N2 incorporation and Nif- mutants. Thus, associative

nitrogen fixation was firmly established as a means of providing

19

fixed nitrogen to plants and shows the potential for partnerships

between biofuel crops and nitrogen-fixing bacteria.

Ann Hirsch, (2009) stated that the research efforts are now

focusing heavily on the associative nitrogen-fixers as well as the

symbiotic species because these bacteria have considerable

potential for generating alternative energy sources. For example, in

addition to the enzyme nitrogenase, which reduces nitrogen gas to

ammonia, many bacteria possess hydrogenase, a reaction coupled

to nitrogen fixation where by hydrogen gas is oxidized. However, if

no nitrogen is present, nitrogenase produces hydrogen as long as

sufficient chemical energy is supplied as ATP. Hydrogen is

considered to be a powerful alternative fuel source, but much more

research is needed to get nitrogen-fixing microbes to produce

hydrogen efficiently and rapidly.

2.2.3 Nitrogen fixation

Nitrogen is generally considered one of the major limiting

nutrients in plant growth. The biological process responsible for

reduction of molecular nitrogen into ammonia is referred to as

nitrogen fixation. A wide diversity of nitrogen-fixing bacterial species

belonging to most phyla of the bacteria domain has the capacity to

colonize the rhizosphere and to interact with plants. Fixed nitrogen

is a limiting nutrient in most environments, the main reserve of

20

nitrogen in the biosphere being molecular nitrogen from the

atmosphere.

Claudine et al., (2009) stated that molecular nitrogen cannot

be directly assimilated by plants, but it becomes available through

the biological nitrogen fixation process that only prokaryotic cells

have developed. Proliferation of bacteria in soil adhering to the root

surface was discovered at the end of the nineteenth century, at the

same time the discovery of nitrogen fixation happened.

Rennie (1980), Elmerich et al. (1992) formulated classical

microbiological techniques involving cultivation and identification of

soil bacteria belonging to genera such as Azospirillum, Azotobacter,

Alcaligenes, Bacillus, Beijerinckia, Campylobacter, Derxia, and for

several members of Enterobacteriaceae (Klebsiella Pantoae) and

Pseudomonas sp.

Okon (1985), Dobbelaere and Okon, (2007) observed that the

colonization of bacteria – Azospirillum on the plant root affects both

the morphology and physiology of the host plant and after

inoculation enhanced proliferation of lateral roots and root hairs. In

general, this is accompanied by changes in root physiology by

Azospirillum sp., such as increased mineral and water uptake,

increased root respiration, delay in leaf senescence and increased

dry weight.

21

Sajjad Mirza et al., (2006) have isolated a nitrogen-fixing

phytohormone-producing bacterial isolate from kallar grass (strain

K1) and further confirmed (in addition to acetylene reduction

activity) the presence of a nitrogen fixation ability in this strain and

identified the isolate as Pseudomonas sp. by 16S ribosomal RNA

gene sequence analysis. They have also reported that the effect of

Pseudomonas strain K1 on grain yield of rice was comparable to

those of A. brasilense. These results show that nitrogen-fixing

pseudomonads deserve attention as potential bacterial inoculants

for crop production.

The isolation of nitrogen-fixing Pseudomonas strains from

rhizospheres has been reported by Barraquio et al., (1983) and

Watanabe et al., (1987) though some controversy existed over the

nitrogen-fixing ability in some members of this genus. The ability to

fix nitrogen claimed earlier for Pseudomonas glathei was later

shown to be due to nitrogen scavenging (Zolg and Ottow 1975), but

this species has been reclassified as belonging to the Burkholderia

genus.

2.3 Bacterial endophytes harboring seeds

Natarajan et al., (2012) reported the efficacy of eight isolates

of putative endophytes from surface-sterilized seeds of the crop

plants tomato and chilli. Lopez-Lopez et al., (2010) isolated

endophytic bacteria from the seeds and roots of the common bean.

22

Gholami et al., (2009) observed that the transition from seed

to root was marked by a shift in bacterial community composition

and in an increase in dominance values. Size and richness of the

seed-associated bacterial community were clearly determinate by

the bacterial community in the germination medium. In contrast,

for fully developed and active roots, the medium effect on these

parameters was negligible. Inoculation of maize seeds with

Azospirillum strains compared with Pseudomonas strains under

experiment conditions resulted in a more visible increase in shoot

development, especially during the establishment of the plant.

Phyllis Ann Carde, (2010) found that the isolates from

spinach seeds belonging to the genera Pantoea inhibited the growth

of E. coli in vitro. Hernandez et al., (2006) reported that vegetable

seeds harbor large numbers of microorganisms. Some of the

microorganisms on seeds are harmless while others are plant

pathogens.

2.4 Bacterial endophytes harboring root

Rupa Giri and Surjit Singh Dudeja, (2013) stated that the

root colonization is the first and the critical step in establishment of

plant-microbe association which is greatly influenced by the

chemotactic response of endophytes towards root exudates. This is

probably among the strongest determinants for successful

23

endophytic colonization. Andrews et al., (2002) reported that the

microbial communities are known to populate plants at all stages of

plant development; from seed to maturity.

Mbai et al., (2013) isolated seventy three bacterial isolates

from rice farms and research fields. Barraquio et al., (1997) also

reported that rice include diverse types of nitrogen-fixing and non-

nitrogen-fixing bacteria, which were found mainly in the roots,

culms and seeds of various wild, traditional and cultivated varieties.

Surette et al., (2003) observed higher endophyte

concentration in carrot (Daucus carota) crowns compared with

metaxylem tissues was due to higher concentrations of

photosynthate in crown regions, supplying more resources for a

larger bacterial community to proliferate.

Similarly, Andreote et al., (2009) observed differences in the

diversity of the root-associated bacterial communities in plants

colonized by a bacterial endophyte, Pseudomonas putida.

Berendsen et al., (2012) stated that the root exudates

influence microbial communities in the rhizosphere, determining

the abundance and diversity of bacterial species that may colonize

the host plant. Engelhard et al., (2000) found that the roots of

modern strains of rice had a higher diversity of endophytic nitrogen-

fixing bacteria compared with wild strains.

24

Morris and Monier (2003), Rosenblueth and Martínez-Romero

(2006) and Rudrappa et al., (2008) observed that the coordinated

invasion by microbes on the root surface involves multiple signaling

pathways and reciprocal signaling between plants and endophytes

and between endophytes.

Balachandar et al., (2006) observed the presence of flavonoids

and certain growth hormones were also found to significantly

improve the endophytic colonization ability of Serratia spp. in rice

seedlings

Zinniel et al., (2002) reported that the microorganisms can

live in the vascular vessels or in the intercellular spaces. Similar

reports were founded by Simarmata et al., (2007); Bacon (2006) in

roots, stems, leaves and fruit. Jacobs et al., (1985) and Larran et

al., (2004) reported the presence of endophytic

bacteria within healthy sugarbeet roots. Yingwu et al., (2009)

isolated 84 bacterial endophytes from the root of sugar beet.

Aravind et al., (2009) reported that, P. aeruginosa was the only

endophytes colonized, endogenous population in the root of Black

pepper and B. megaterium, P. putida and C. luteum was

predominantly found in root cuttings.

Fernado et al., (2009) observed and stated that, Pseudomonas

fluorescens is an extensive colonizer of potato plants, competing

25

with microbial populations indigenous to the potato phytosphere.

RupaGiri and Surjit Singh Dudeja (2013) identified 11 most efficient

strains out of 200 endophytic bacteria isolated from roots of

chickpea (Cicer arietinum), field pea (Pisum sativum), Lucerne

(Medicago sativa), wheat (Triticum aestivum) and oat (Avena sativa).

Marquez et al., (2010) studied the diversity of bacterial

endophytes in roots of Mexican husk tomato plants (Physalis

ixocarpa). Prasad et al., (2001) isolated six closely related N2-fixing

bacterial strains from surface-sterilized roots and stems of four

different rice varieties. The strains were identified as Serratia

marcescens and the detailed studies was carried out using light and

transmission electron microscopy combined with immunogold

labeling, and they confirmed that the strains were endophytically

established within roots, stems, and leaves. Large numbers of

bacteria were also observed within intercellular spaces, senescing

root cortical cells, aerenchyma and xylem vessels.

Kloepper et al., (1980) isolated two strains of fluorescent

pseudomonas from potato peridermis and celery roots which

significantly increased growth of potato plants than controls.

Czaban et al., (2007) isolated more than 800 rhizobacterial

strains from winter wheat “rhizosphere” (the soil tightly adhering to

the roots), “rhizoplane” (the root surface) and “endorhiza” (the

interior of the roots) at different plant growth stages. The data

26

obtained clearly show that the proportion of motile strains gradually

increased from “rhizosphere”, through “rhizoplane”, to “endorhiza”.

These results strongly suggest that flagellar motility is an important

factor in the colonization of plant roots, especially the root interiors

by bacteria.

Abdul munif et al., (2012) studied total population density of

endophytic bacteria from tomato roots. Fabio et al., (1996) recorded

the occurrence of the endophytic diazotrophs Herbaspirillum spp. in

roots, stems and leaves in Gramineaeous members.

Elvira-Recuenco and Van Vuurde (2000) isolated nine fast-

growing bacteria from mung bean nodules and characterized for

plant growth promoting properties and also stated that the

colonization varied between 3 × 10-3 to 3 × 10-7 cfu/g fresh weight.

Rajendran et al., (2008) isolated putative endophytes from the

surface sterilized root nodules of pigeon pea (Cajanus cajan)

designated as non-rhizobial (NR) isolates and they found that plant

growth promotion with respect to increase in plant fresh weight,

chlorophyll content, nodule number and nodule fresh weight when

co-inoculated with the rhizobial bioinoculant strain.

Tian Xue-liang et al., (2006) observed that the population of

the endophytic bacteria was highest in roots, which were 2.63×10-5

CFU/g in fresh weight; secondly in stem, thirdly in cotyledon and

lowest in seed.

27

Baset et al., (2010) observed that the inoculation plant growth

promoting rhizobacterial strains increased the yield and fixed N2 in

association with banana roots subsequently increased the yield,

improved the physical attributes of fruit quality and initiated early

flowering. Reports from various experimental findings suggested

that plant growth promoting bacteria (PGPB) strains could

successfully formed colonies on the root surface of bananas, where

more bacterial cells were found in the root hair proliferation zone.

Application of PGPB alone could not produce significant benefits

that require minimal or reduced levels of fertilizer-N consequently

could produce a synergistic effect on root growth and development.

Samrah Tariq et al., (2009) isolated seven strains of Pseudomonas

aeruginosa from inner roots of healthy chili plants growing under

field condition. Pseudomonas aeruginosa strains also showed

positive impact on plant growth by increasing the plant height and

fresh shoot weight.

Mark Jacobs et al., (1985) observed an increased bacterial

population in the secondary root emergence zone tissue of sugar

beet roots as compared with core and peripheral tissue of the same

beet.

2.5 Bacterial endophytes harboring in stem

Arundhati et al., (2012) isolated 20 phenotypically

distinguishable bacterial endophytes from surface sterilized stem

28

and leaf tissues and reported more diverse types of endophytes in

leaves of Passiflora foetida than in stem and the bacterial isolates

belonged to Bacillus, Paenibacillus, Pseudomonas, Ralstonia,

Micrococcus and Alcaligenes.

Hudson et al., (2010) isolated six unique isolates from the

stem of sugarcane and seventeen isolates from grape xylem sap.

Garbeva et al., (2001) found that the Pseudomonas spp. were more

common in the stems than in the roots of potatoes (Solanum

tuberosum) after one month of growth. Aravind et al., (2009) isolated

bacterial endophytes from the stem of Black pepper. They reported

that the bacterial isolates, B. megaterium, P. putida and C. luteum

was predominantly found in stem cuttings.

Maria et al., (2014) isolated endophytic bacteria (BS1 isolate)

from the stem of plant Piper betle [L.] and demonstrated the

antibacterial ability against pathogenic bacteria, such as:

Escherichia coli, Bacillus cereus and Staphylococcus aureus, with the

greatest inhibition against Staphylococcus aureus. The result of 16S

rRNA analysis using BLAST showed that BS1 isolate was related to

Pseudomonas sp. with 98% identity.

Yong Wan, et al., (2012) screened eleven pea cultivars at the

flowering stage for the presence of endophytic bacteria and they

observed that the endophytic bacterial populations decreased from

29

the lower to the upper part of the stem. The amount of endophytic

bacteria in adult plants of resistant tomato cultivars was 2.43×10-5

CFU/g Fresh weight (FW) in the root and 22.9×10-4 CFU/g FW in

the stem, while the amount of endophytic bacteria in adult plants of

tomato cultivars was 9.8×10-4 CFU/g FW in the root and 13.4×10-4

CFU/g FW in the stem.

2.6 Bacterial endophytes harboring leaves

Pradeepa and Jennifer, (2013) isolated and studied five

endophytic bacteria from the leaves of Tabernaemontana divaricata

and the bacterial endophyte was identified as Alcaligenes faecalis by

16S rRNA sequencing. The results tend to suggest that the bacterial

endophyte of T. divaricate that produce cytokinin like compounds

might have a role in the growth and development of T. divaricata.

Stephen et al., (2005) observed that the endophytic bacteria

were found in xylem vessels of the fifth internode and the fifth leaf

of plantlets in in Vitis vinifera. Moreover, he observed that the

bacteria were more abundant in the fifth leaf than in the fifth

internode and were found in substomatal chambers.

Umesh Kumar et al., (2011) isolated 5 types of the

actinomycetes from different parts of Emblica officinalis, three were

from Emblica twig and two from the leaves. Elvira-Recuenco and

van Vuurde, (2000) observed two actinomycetes which showed the

30

production of antibacterial compound, resulting in more biomass

production and higher photosynthetic pigments content of leaves

compared with non-symbiotic ones.

Brandl et al., (2008) reported that the leaves also support a

diverse microbial population that is dependent on factors such as

leaf age, the presence of various organic compounds that may be

used as nutrients (Ruppel et al., 2008) and adverse factors such as

UV radiation.

2.7 Bacterial endophytes in vegetables

Julia and Vorholt, (2008) reported that a few bacterial phyla

predominate in the phyllosphere of different plants and few factors

are involved in shaping these phyllosphere communities, which

feature specific adaptations and exhibit multipartite relationships

both with host plants and among community members. He also

suggested that insights into the underlying structural principles of

indigenous microbial phyllosphere populations will help us to

develop a deeper understanding of the phyllosphere microbiota and

will have applications in the promotion of plant growth and plant

protection.

Pham Quang Hung and Annapurna, (2004) isolated 65

bacterial endophytes from three tissues of stem, root and nodule

from two species of soyabean i.e, cultivated (Glycine max) and wild

(Glycine soja) of soybean.

31

Monique et al., (2003) observed more bacterial endophytes

colony-forming units (CFU) from the carrot crown tissues (96%)

compared to the periderm and metaxylem tissues of carrot storage

tissues irrespective of the cultivars and field locations. In carrots,

83% of the bacterial strains tested were found to be plant growth

promoting, 10% remained plant growth neutral and 7% inhibited

plant growth. Fisher et al., (1992) found high population density of

endophytes in carrot crowns, indicates the preferential colonization

of these tissues by bacterial endophytes.

Andrews, (1992) stated that the phylloplane provides a

diversity of beneficial bacteria because of the frequent drift in the

microbial communities.

Mishra et al., (2009) studied co-inoculation of Pseudomonas

with rhizobia enhance nodulation, nitrogen fixation, plant biomass

and grain yield in various leguminous crops such as alfalfa, pea,

soybean, green gram and chickpea. Similar reports were observed

by Halverson and Handelsman (1991) in co-inoculation of rhizobia

with Bacillus, specifically Bacillus thuringiensis, Bacillus megatrium

and Bacillus cereus.

Pandey and Maheshwari, (2007) observed that bacteria

belonging to Burkholderia, Azotobacter, Azospirillum, Enterobacter

and Kurthia have improved plant growth when co-inoculated with

rhizobia. Yasmeen et al., (2012a and b) also reported that the co-

32

inoculation of arbuscular mycorrhizae with Bradyrhizobium sp.

proved to be very helpful in improving mung bean growth.

Weber et al., (1999) demonstrated the association of nitrogen-

fixing bacteria with banana and pineapple. Samples from roots,

stems, leaves and fruits of different genotypes showed the

occurrence of diazotrophic bacteria. Bacteria related to the groups

of Azospirillum amazonense, Azospirillum lipoferum, Burkholderia

sp. and a group similar to the genus Herbaspirillum could be

detected in samples of both crops. However, Azospirillum brasilense

and another two groups of Herbaspirillum-like bacteria were

detected only in banana plants.

Ying wu et al., (2010) investigated the impact of three

endophytic bacteria, Bacillus pumilus, Chryseobacterium

mindologene and Acinetobacter johnsonii on the photosynthetic

capacity and growth of sugar beet. Measurements of total

chlorophyll content revealed very significant differences between

endophyte-free beet plants and some infected by endophytic

bacteria. The light response curves of beet showed that

photosynthetic capacity was significantly increased in endophyte-

infected plants.

Yingwu et al., (2009) reported that the promotion of

photosynthetic capacity in sugar beet was due to increased

33

chlorophyll content, leading to a consequent increased

carbohydrate synthesis. It is possible that the increased maximum

yield of photosynthesis in sugar beet was promoted by

phytohormones and produced by the bacteria. The diversity of

endophytic microbial communities from seeds (spermosphere), roots

(endorhiza), flowers (anthosphere) and fruits (carposphere) of three

different pumpkin cultivars was studied to develop a biocontrol

strategy.

Furnkranz et al., (2012) stated that among the 2,320

microbial isolates from pumkin analyzed in dual culture assays,

165 (7%) were tested positively for in vitro antagonism against

Didymella bryoniae. Out of these, 43 isolates inhibited the growth of

bacterial pumpkin pathogens (Pectobacterium carotovorum,

Pseudomonas viridiflava and Xanthomonas cucurbitae). Disease

severity on pumpkins of D. bryoniae was significantly reduced by

Pseudomonas chlororaphis treatment and by a combined treatment

of strains (Lysobacter gummosus, P.chlororaphis, Paenibacillus

polymyxa, and Serratia plymuthica).

Fikrettin et al., (2004) investigated the effects of two N2-fixing

bacteria and a strain of P-solubilizing bacteria by single, dual and

combined inoculation on sugar beet and barley yields under field

conditions. All inoculations and fertilizer applications significantly

increased leaf, root and sugar yield of sugar beet and grain and

34

biomass yields of barley over the control. Single inoculations with

N2-fixing bacteria increased sugar beet root and barley yields by

5.6–11.0% depending on the species while P-solubilizing bacteria

alone gave yield increases by 5.5–7.5% compared to control. Dual

inoculation and mixture of three bacteria gave an increase by

7.7–12.7% over control as compared with 20.7–25.9% yield increase

by nitrogen and phosphorous application.

Tripathi et al., (2013) recorded highest yield (808.3 q ha-1) of

tomato under field conditions inoculated with Azospirillum sp.

under partial mist conditions, all Azospirillum strains were capable

of colonizing leaf surfaces (10-3-10-7 cfu/g dry weight) regardless of

the plant species. These results provide experimental evidence that

Azospirillum sp. might be considered safe for the inoculation of

several plant species.

Zehra Ekin et al., (2009) reported that the highest yield of

potato possible with N fertilizer was achieved with about 120 kg N

ha-1 in addition to N2-fixing Bacillus sp. inoculation and they

suggested that Bacillus sp. alone or nitrogen fertilizer combinations

have a great potential to increase yield and yield components of

potato and to reduce the need for chemical fertilizers as in many

other crops previously tested.

Jeevajothi et al., (1993) and Chatoo et al., (1997) suggested

that Bacillus sp. as plant growth-promoting bacteria can be suitable

bio-fertilizer for potato in organic and low-nitrogen input

35

agriculture. Application of microbial inoculants like Azospirillum

and Azotobacter particularly in vegetable crops has been of great

significance in terms of yield and quality attributes.

Ardanov Pavlo (2011) suggested that some endophytes have the

potential to activate both basal and inducible plant defence

systems, whereas the growth promotion by biocontrol strains may

not correlate with induction of disease resistance.

Ramesh et., al, (2009) reported that Pseudomonads, an

antagonistic endophytic bacteria suppressed bacterial wilt pathogen

- Ralstonia solanacearum in the eggplant (Solanum melongena L.).

Sandeep (2011) reported the effect of inoculation of Bacillus

megaterium isolates on growth, biomass and nutrient content of

Peppermint.

Ravi kumar Patil et al., (2013) found an increase in plant

initial height, number of branches, fresh and dry weight of the roots

and shoots, when inoculated with Bacillus megaterium compared

with the control (Uninnoculated plants).

Nowadays increasing population leads to food demand.

Among the major food crops, vegetables are the most important one

by cultivation and consumption in India, particularly in Tamilnadu.

Vegetables are eaten in a variety of ways, as part of main meals and

as snacks. The nutritional content of vegetables varies considerably;

36

they contain protein and little fat and varying proportions of

vitamins such as Vitamin A, Vitamin K, and Vitamin B6,

provitamins, dietary minerals and carbohydrates. Vegetables

contain a great variety of other phytochemicals, some of which have

been claimed to have antioxidant, antibacterial, antifungal, antiviral

and anticarcinogenic properties. As nitrogen is the major element

required for its production, focusing on isolation and identification

of effective nitrogen fixing bacteria for increasing growth and yield

with reduction of the hazardous fertilizer use is essential. Most of

the studies have explored the properties of these isolates in relation

to their as agronomical inoculants. Fixation of nitrogen by bacterial

community that inhabits particularly with vegetables has been

poorly studied. Hence, with the collected review of literature on role

of endophytic bacteria on crop growth, it has planned to study the

effect of endophytic bacterial isolates of Azospirillum sp. and

Pseudomonas sp. isolated from brinjal and bhendi in enhancing the

growth, yield and quality of the same crops under pot and field

experiments.