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2. REVIEW OF LITERATURE

Bell pepper is affected by fungal pathogens (Colletotrichum capsici

(Synd.) Butler and Bisby, Phytophthora nicotianae Breda de Haan, Fusarium

oxysporum (Schlect.) emend. Synd. and Hans. f.sp. capsici Riv., F. solani (Mart.)

Appel and Wollenw, Sclerotium rolfsii Sacc., Rhizoctonia solani Kuhn and

Sclerotinia sclerotiorum (Lib.) de Bary); and bacterial pathogen causing bacterial

wilt (Ralstonia solanacearum (Smith) Yabuuchi et al) under polyhouse conditions.

These diseases have been reported to be managed by spraying of fungicides or

by adopting cultural methods. But due to many problems associated with

chemicals, these management practices are no longer economical and

ecofriendly. Therefore, it becomes necessary to devise non-chemical methods

for the control of diseases. However, not much information is available on the

management aspects of capsicum diseases of capsicum under protected

cultivation. The pertinent literature is reviewed under the following sub-headings:

2.1 Use of organic inputs

2.2 Microbes in organic inputs and their antifungal potential

2.3 Use of bioagents

2.4 Use of botanicals

2.5 Organic inputs in disease management

2.5.1 Bacterial wilt

2.5.2 Fungal diseases

2.6 Plant growth promoting traits

2.6.1 Phosphate solubilization

2.6.2 Indole acetic acid production

2.6.3 Siderophore production

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2.6.4 Ammonia production

2.6.5 Hydrogen cyanide production

2.6.6 Lytic enzymes

2.6.7 Nitrogenase activity

2.1 Use of organic inputs

Various organic composts showed antifungal activity against soil borne

and foliar pathogens. Aqueous extracts of vermicompost and organic compost

inhibited the mycelial growth of Botrytis cinerea, Sclerotinia sclerotiorum,

Sclerotium rolfsii, Rhizoctonia solani and Fusarium oxysporum f.sp. lycopersici in

vitro (Nakasone et al. 1999).

Sugha (2005) evaluated the antifungal potential of panchgavya against R.

solani, S. rolfsii, F. solani, S. sclerotiorum and Phytophthora colocasiae and

advocated that the mycelial bits dipped for 6 h in panchgavya caused complete

suppression of mycelial growth of R. solani and in other pathogens, the growth

inhibition ranged between 88.1-92.3 per cent. Dogra (2006) observed the

antifungal activity of panchgavya against major soil borne pathogens viz. F.

solani f.sp. pisi, F. oxysporum f.sp. pisi, R. solani, S. solfsii and S. sclerotiorum.

Mycelial bits dipped for 12 h in panchgavya caused more than 90 per cent

inhibition of F. oxysporum f.sp. pisi and F. solani f.sp. pisi and 100 per cent

inhibition of S. rolfsii, S. sclerotiorum and R. solani.

Basak and Lee (2005) conducted the experiment to study the efficacy and

in vitro activities of cow urine and dung for controlling wilt caused by F.

oxysporum f.sp. cucumerinum of cucumber and F. solani f.sp. cucurbitae. Cow

dung solution showed 80-84 per cent inhibition of wilt pathogens and cow urine

showed 100 per cent inhibition of wilt pathogens.

Fresh cow dung, urine, milk and cow dung based preparations namely

cow dung slurry, dried powder and ash were evaluated against R. solani causing

damping-off of okra and root rot of pea pathogens. Complete inhibition in

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mycelial growth was obtained by amending potato dextrose agar with cow dung

and cow dung ash @ 5 g/100 ml medium followed by cow dung powder (0.5 mm

radial mycelial growth) (Ashlesha et al. 2009). Out of twelve organic inputs

tested, eight inputs viz. biosol, matka khad, agnihotra ash + cow urine,

panchgavya, vermicompost, cow pat pit compost, NADEP compost and

biodynamic compost showed 60.2-100 per cent inhibition in mycelial growth of S.

sclerotiorum without autoclaving (Shalika 2009).

Sinha et al. (2010) studied the antifungal properties of vermicompost and

vermiwash against soil borne pathogens (Pythium ultimum, R. solani and

Fusarium sp.) and recorded 51-72 per cent inhibition in mycelial growth of

pathogens. Sang et al. (2010) reported the reduction in mycelial growth of

Phytophthora capsici and Colletotrichum coccodes in pepper and C. orbiculare in

cucumber by water extracts of compost.

Joseph and Sankarganesh (2011) studied the antifungal activity of

panchgavya and cow urine against soil borne pathogens. Sreenivasa and Naik

(2011) observed 92.1 and 57.3 per cent inhibition in mycelial growth of Fusarium

sp. at 15 and 20 per cent concentrations of cow urine in vitro.

2.2 Microbes in organic inputs and their antifungal potential

Plotnikova (1977) observed the presence of mycolytic bacteria in cow

manure. The extract of cow dung compost showed the presence of bacterial

isolates which inhibited the mycelial growth of Fusarium oxysporum f.sp.

cucumerinum and Helminthosporium sigmoideum (Kai et al. 1990).

Czaczyk et al. (2000) isolated four strains of Bacillus from cow dung

compost. All the strains possessed strong inhibition properties against the

mycelial growth of R. solani, Bipolaris sorokiniaria, S. sclerotiorum,

Trichothecium roseum, F. solani and F. oxysporum and recorded 56.2-71.0 per

cent inhibition of these pathogens.

Chung et al. (2000) isolated Paenibacillus koreensis from compost and

observed the antifungal activity against Fusarium oxysporum, Colletotrichum

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lagenarium, Sclerotinia sclerotiorum, Botrytis cinerea and Rhizoctonia solani.

Quarles (2001) revealed that compost tea was rich source of nutrients and

microorganisms. These organisms were inhibitory to soil borne pathogens.

Aspergillus niger, Trichoderma harzianum, Bacillus cereus and Bacillus

subtilis were the major microbes in cow dung compost. When these microbes

were cocultured with the seedling blight inducing pathogens such as Sclerotium

rolfsii, F. oxysporum, Pythium aphanidermatum, Helminthosporium maydis and

R. solani, the mycelial growth of all tested pathogenic fungi was inhibited to the

tune of 40.0-57.8 and 35.5-53.3 per cent, respectively by Bacillus subtilis and B.

cereus (Muhammad and Amusa 2003).

Streptosporangium pseudovulgare – an actinomycete caused the

complete inhibition of mycelium of Lasiodiplodia theobromae, a causal agent of

rot of guava (Garg et al. 2003). Garg et al. (2004) isolated an actinomycete from

compost and found this isolate inhibitory to Colletotrichum gloeosporioides.

Raja et al. (2004) reported the presence of large number of bacteria in

animal excreta viz. Pseudomonas, Bacillus, Serratia, Flavobacterium and

Streptomyces; majority of which had the capacity to degrade cellulose,

hemicelluloses and pectin, quickly colonized the seed and induced systemic

resistance.

Velazquez et al. (2004) recovered the xylan-degrading sporulated

bacterium from fresh and old cow dung. The isolate was identified as

Paenibacillus favisporus. Edward and Arancon (2004) studied the antifungal

activity of Actinomycetous isolate obtained from vermicompost against Pythium

and Fusarium. Burkholderia cepacia (F-66) isolated from compost showed

mycelial inhibition of Rhizoctonia solani (Quan et al. 2005).

Charest et al. (2005) observed the presence of two bacteria

Pseudomonas aeruginosa and Rhizobium radiobacter in cow dung manure. Both

bacterial isolates were evaluated against Pythium ultimum. The fungal inhibition

was increased 2-3 per cent by R. radiobacter. Microbes present in compost

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protected the cucumber seedlings against damping off caused by Pythium

aphanidermatum (Larbi 2006). Prabhu (2006) reported the presence of large

number of plant growth promoting micro organisms in coconut leaf vermiwash.

Dogra (2006) evaluated the antifungal potential of bacterial isolates

present in panchgavya against Sclerotium rolfsii, R. solani and S. sclerotiorum.

These bacterial isolates showed 97-100 per cent inhibition in the mycelial growth

of pathogens. Swaminathan et al. (2007) showed the presence of naturally

occurring beneficial micro-organisms predominantly lactic acid bacteria, yeast,

actinomycetes, photosynthetic bacteria and certain fungi in panchgavya.

Khaing et al. (2008) reported the presence of ten species of beneficial

microbes such as Serratia marcescens, Bacillus megatarium, Azotobacter

chroococcum, Pseudomonas medocina and Flavobacterium spp. in vermiwash.

Species of Bacillus, Serratia, Pseudomonas and Actinomycetes were obtained

from panchgavya and evaluated for their antifungal potential against soil borne

pathogens viz. S. rolfsii, F. oxysporum, F. solani and R. solani (Ashlesha and

Sugha 2008). Maximum inhibition (99.0%) was possessed by Serratia followed

by species of Bacillus (72.7-99.0%) and Actinomycetes (48.6-99.0%) against all

the test pathogens.

Several phosphate solubilizing bacteria with lytic enzyme activity

(Proteases, amylases, phosphatases) were obtained from vermiwash and these

bacteria also exhibited antifungal properties against soil borne pathogens

(Zambare et al. 2008). Kerkeni et al. (2008) isolated the bacterial cultures from

animal manure compost extract and evaluated these against Fusarium

oxysporum f.sp. radicilycopersici causal agent of crown and root rot of tomato.

Out of 14 isolates screened, 8 isolates inhibited the mycelial growth of pathogen

by 8-47 per cent. Most effective isolates were Chryseomonas luteola, Serratia

liquifaciens and Aeromonas hydrophila.

Bacillus thermocloacae found in compost showed antifungal activity

against Fusarium (Niisawa et al. 2008). Meenatchi et al.(2009) observed the

appearance of beneficial bacteria, fungi and actinomycetous population in

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vermicompost. Naik and Sreenivasa (2009) studied the presence of bacterial

isolates in panchgavya which resulted in increased seed germination (99%),

seedling length and vigour in wheat. Beejamrutha exhibited the presence of

several beneficial microorganisms (Sreenivasa et al. 2009).

Raoudha et al. (2009) investigated the effect of bacterial isolates from

compost amended with solid olive mill wastes against Pythium aphanidermatum.

Maximum inhibition was obtained by Bacillus subtilis (38%) followed by B.

thuringiensis (37%), Pseudomonas fluorescens (35%) and P. pseudoalcaligenes

(34%).

Six bacterial strains isolated from compost showed antifungal properties

against soil borne pathogens (Abdel et al. 2010). Gopal et al. (2010) reported

that Pseudomonas fluorescens was predominantly present in coconut leaf

vermiwash.

Actinomycetes present in cow dung compost possessed antimicrobial

activity against fifty three pathogens (Pinto et al. 2010). Sinha et al. (2010)

documented the presence of nitrogen fixing and phosphate solubilizing bacteria,

Actinomycetes and mycorrhizal fungi in vermicompost and vermiwash which

showed antifungal activity against soil borne pathogens. Thakur (2010) isolated

fifty three bacteria from vermiwash and screened in vitro for various plant growth

promoting traits. Only four out of fifty three tested bacterial isolates showed

antifungal activity against S. rolfsii, F. oxysporum and F. solani. Bacterial isolates

were found to be the species of Pseudomonas, Bacillus, Alcaligens and

Micrococcus.

Sreenivasa and Naik (2011) exhibited the presence of beneficial

microorganisms in panchgavya and beejamrutha which resulted in improved

seed germination, seedling length and vigour in wheat and soybean.

2.3 Use of bioagents

Although research on exploitation of biocontrol agents in the management

of major plant diseases has advanced considerably but the limited work has been

done on Phytophthora blight, anthracnose and soil borne diseases of capsicum.

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Dennis and Webester (1971) found that many isolates of Trichoderma spp.

produced volatile and non volatile antibiotics active against wide range of fungi.

T. harzianum has been recognized as a strong mycoparasite against soil borne

pathogens such as R. solani, S. rolfsii and F. oxysporum (Papavizas 1985; Chet

1987). Singh and Sekhon (1990) noticed antagonistic activity of T. viride against

R. solani in dual culture and checked the development of black scurf on potato

tubers in greenhouse. Strong antagonism by Trichoderma spp. against F.

oxysporum f.sp. lycopersici and F. oxysporum f.sp. radicis lycopersici has been

reported (Monaco et al. 1991). Trichoderma and Gliocladium gave best control of

pathogens of pea mainly R. solani, F. solani and S. sclerotiorum (Lacicowa and

Pieta 1994).

Singh (1998) confirmed that T. harzianum showed strong mycoparasitism

and covered 100 per cent, colony growth of S. sclerotiorum. Kapil (2002)

reported maximum inhibition (73.3%) of S. sclerotiorum with T. viride in dual

culture. T. harzianum and T. viride were found to decrease the root rot caused by

R. solani in bell pepper plants upto 70.9 per cent (Gaikward and Nimbalkar

2003). T. harzianum alongwith farm yard manure was most effective in reducing

the disease incidence of S. rolfsii upto 20 per cent (Parakhia and Akbarj 2004).

Vijnan et al. (2004) evaluated T. viride and T. harzianum against nine

isolates of Colletotrichum capsici collected from red pepper fruits. Both

antagonists were found inhibitory to pathogen with 69-77 per cent inhibition in

mycelial growth. Isolates of T. viride and Pseudomonas fluorescens were tested

for their antagonistic activity against S. rolfsii, causing stem rot of groundnut. The

disease was suppressed upto 58.0 and 70.0 per cent, respectively by both the

isolates under controlled conditions (Manjula et al. 2004). Out of four antagonists

(T. viride, T. harzianum, Gliocladium virens and Aspergillus nidulans), T. viride

resulted in 86.0 per cent disease control followed by T. harzianum (81.0%) in

case of F. oxysporum f.sp. lycopersici under glass house conditions (Singh et al.

2004).

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Meena and Paul (2005) reported the effectiveness of Himbio (combination

of different bioagents) against pea wilt/root rot complex. Out of six bioagents

tested, T. harzianum (SMA-5) and T. koningii (DMA-8) showed 82.4 to 87.1 per

cent mycelial inhibition in mycelial growth of S. rolfsii and Drechslera maydis.

Nine isolates of Trichoderma spp. were screened for their ability to inhibit soil

borne fungal pathogens of chickpea viz., R. solani, S. rolfsii and F. oxysporum

f.sp. ciceri in vitro. Among these, T. harzianum showed 72.1 and 59.9 per cent

mycelial inhibition of R. solani and S. rolfsii whereas T. virens exhibited 86.6 per

cent inhibition of F.oxysporum f.sp. ciceri (Rudresh et al. 2005). Sharma et al.

(2005) studied the efficacy of T. harzianum against Colletotrichum capsici with

69.4 per cent inhibition in mycelial growth. Wang et al. (2005) demonstrated the

effect of Trichoderma spp. against Fusarium root rot of coneflower which caused

65 per cent inhibition of pathogen in dual culture technique. Sood (2005)

evaluated six bioagents against Rhizoctonia solani and Trichoderma HB15

caused 86.7 per cent mycelial inhibition.

Srivastava et al. (2006) conducted studies on the effect of seed treatment

with T. viride @ 4 g/ha + soil application of farm yard manure against soil borne

pathogens (Rhizoctonia, Pythium and Fusarium) of cauliflower. They observed

31 per cent increase in germination and 65 per cent decrease in disease. A

combination of two antagonists Streptomyces rochei and T. harzianum achieved

75 per cent reduction in disease severity of Phytophthora capsici (Ezziyyani et al.

2007). Abeysinghe (2008) revealed maximum antagonistic activity of T.

harzianum and Bacillus subtilis CA32 against R. solani and Pythium in brinjal and

pepper.

The antagonistic activity of T. virens, T. viride, T. harzianum, T. koningii,

Pseudomonas fluorescens and Bacillus subtilis was evaluated against Fusarium

solani and Rhizoctonia solani causing root rot of sage (Mallesh et al. 2008). Out

of these bioagents, T. viride provided maximum inhibition (94.4%) of F. solani

and R. solani. Shashidhara et al. (2008) reported the effectiveness of

antagonistic microbes viz., Bacillus sp., Pseudomonas sp., Trichoderma viride

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and T. harzianum against Phytophthora capsici. T. viride provided maximum

inhibition of the pathogen (72.5%). T. harzianum showed 82.8 per cent inhibition

of F. oxysporum f.sp. cumini followed by T. viride with 74.0 per cent inhibition in

mycelial growth under in vitro conditions (Deepak et al. 2009).

Bhat et al. (2009) obtained 65.8 and 65.1 per cent reduction in mycelial

growth of Rhizoctonia solani when tested in dual culture with T. harzianum and T.

viride, respectively. Four bioagents, T. harzianum, T. viride, T. virens and

Pseudomonas fluorescens were evaluated against R. solani causing banded leaf

and sheath blight of maize (Akhtar et al. 2010). 86.9 per cent mycelial inhibition

was shown by T. harzianum followed by T. viride (77.9%) in dual culture.

Pandey et al. (2011) demonstrated the antagonistic activity of T. virens

and T. harzianum against S. sclerotiorum, F. solani, R. solani and S. rolfsii

causing 62.7-69.1 per cent inhibition in mycelial growth of pathogens. Isolates of

T. viride, T. harzianum and T. pseudokoningii caused 64.4-65.6 per cent

inhibition in mycelial growth of Phytophthora capsici of black pepper (Mathew et

al. 2011).

2.4 Use of botanicals

The presence of antifungal components in higher plants has long been

recognized as an important factor for disease resistance (Mahadevan 1982).

Such components being biodegradable and selective in their toxicity are

considered valuable in controlling some plant diseases (Singh and Dwivedi

1987). Michael et al. (1985) noticed the inhibition of R. solani with aqueous

extract of Vitex negundo. Kaushal and Paul (1989) studied inhibitory effects of

some plant extracts (Cannabis sativa, Pinus longifolia, Eupatorium sp. and

Lantana indica) on some legume pathogens and found that all the plant extracts

inhibited Colletotrichum truncatum and L. indica was most effective. Tiwari and

Nayak (1991) observed that extract of Ocimum sanctum was effective in

reducing the growth of R. solani both in vitro and in vivo. Qasem (1996) studied

the antifungal effect of aqueous extract of Ranunculus sp. against F. oxysporum

f.sp. lycopersici in vitro and observed strong inhibition in mycelial growth of

pathogen.

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The antifungal activity of O. sanctum, V. negundo, Lantana indica and

Azadirachta indica against Macrophomina phaseolina and F. oxysporum f.sp.

tracheiphilum causing charcoal rot of cow pea was determined by Ushamalini et

al. (1997). Shivpuri et al. (1997) reported the toxicity of ethanol leaf extracts of

neem and Datura against F. oxysporum and R. solani in vitro.

Sharma and Kapoor (1999) evaluated plant extracts of Saussurea lappa,

Lantana camara, wheat and garlic for control of S. sclerotiorum and reported that

S. lappa and L. camara were most inhibitory to pathogen. Leaf extracts of Datura

stramonium, O. sanctum and A. indica caused more than 94.0 per cent inhibition

as well as reduced production of sclerotia of S. sclerotiorum causing stem rot of

mustard (Shivpuri and Gupta 2001). Sharma et al. (2003) studied that seed

treatment with Datura and Neem extracts showed good seed germination,

seedling vigour and least mortality due to F. oxysporum f.sp. pisi, R. solani,

Macrophomina phaseolina and Alternaria alternata.

Owalade et al. (2003) observed significant control of Colletotrichum

capsici on cowpea and Fusarium moniliforme on maize using the crude extracts

from the leaves of Ocimum gratissium. Leaf extract of Maesa lanceolata was

found effective against R. solani, F. oxysporum, Sclerotium rolfsii, Aspergillus

niger and Pythium ultimum in vitro (Okemo et al. 2003). The aqueous and

ethanolic extracts of Melia azedarach were studied as potential antifungal agents

for F. oxysporum, F. solani and S. sclerotiorum. Ethanolic extract was highly

effective on all test fungi with inhibitory concentrations ranging from 0.5 to 25

mg/ml (Carpinella et al. 2003). The fungicidal properties of extracts from

Azadirachta indica, Datura stramonium, Ocimum sanctum, Melia azedarach and

Cuscuta reflexa against Colletotrichum capsici were studied in vitro (Sinha et al.

2004). The radial growth of C. capsici was lowest (30.9 mm) with O. sanctum

compared to control (71.4 mm).

Tiwari et al. (2004) evaluated 213 plant extracts against S. rolfsii. Out of

these, extracts of Ranunculus sclerotus, Aloe vera, Murraya paniculata,

Colocasia sp. and Datura metel were found effective against the pathogen. Liu et

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al. (2004) screened ethanolic extracts of 16 plant species for their antifungal

activity against Colletotrichum musarum, F. oxysporum, Alternaria alternata and

Botrytis cinerea. Among 16 plant extracts, Euphorbia hirta, Myrica rubra and

Rhodomyrtus tomentosa exhibited 60 per cent inhibition in mycelial growth of all

the pathogens. Methanol extracts of fresh materials of 183 plants were tested for

in vivo antifungal activity against Magnaporthe grisea, Corticium sasakii, Botrytis

cinerea, Phytophthora sp., Puccinia recondita and Erysiphe graminis f.sp. hordei

by Kim et al. (2004) and 33 plant extracts showed more than 90 per cent disease

control in all the cases.

Devi (2005) studied aqueous extracts of 10 plants (Melia azedarach,

Eupatorium odoratum, E. adenophorum, Cannabis sativa, Ranunculus muricatus,

Ocimum sanctum, Lantana camara, Vitex negundo, Camellia sinensis and

Datura stramonium) against F. solani f.sp. pisi, F. oxysporum f.sp. pisi, R. solani,

S. sclerotiorum and Phoma medicaginis var. pinodella, R. muricatus completely

inhibited the growth of R. solani, S. sclerotiorum and P. medicaginis while E.

adenophorum caused 72.2 per cent inhibition of F. solani and F. oxysporum.

Rodriguez et al. (2005) investigated the antifungal efficacy of leaf pulp of

Aloe vera against R. solani, F. oxysporum and Colletotrichum coccodes isolated

from pepper and observed 8.1, 2.7 and 4.3 cm of inhibition zones, respectively.

Yadav et al. (2005) found that 20 per cent extract of Datura stramonium gave

44.8 per cent growth inhibition of R. solani.

Zhang et al. (2006) evaluated the extracts of tea leaves against

Colletotrichum camelliae and recorded 75 per cent inhibition in mycelial growth of

pathogen when PDA medium was amended with 25 mg/ml concentration. The

aqueous extracts of Terminalia arjuna (Roxb.), Mangifera indica L. and

Azadirachta indica were tested for their antifungal activity against Fusarium

solani by Irum et al. (2006). All the extracts exhibited significant reduction in

radial growth of pathogen with 74.0, 67.0 and 54.0 per cent inhibition caused by

T. arjuna, M. indica and A. indica, respectively.

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Farzaneh et al. (2006) studied the effect of extracts of aerial parts of

Artemisia sieberi. The extracts were obtained through hydrodistillation and

evaluated against soil borne pathogens (Rhizoctonia solani, Fusarium solani and

Fusarium moniliforme). Distillates showed strong antifungal activity against R.

solani (75%) and intermediate (65.7%) against other pathogens.

Huang et al. (2006) screened extracts of 10 medicinal plants against

Phytophthora capsici, Botrytis cinerea, Verticillium dahliae, Fusarium oxysporum

and Sclerotinia sclerotiorum. The aqueous extracts of Eugenia caryophyllata,

Coptis chinensis and Glycyrrhiza uralensis were found most effective against all

the pathogens.

Dar et al. (2007) investigated the inhibitory effect of the extracts of Allium

sativum, Datura stramonium, Mentha arvensis and Thuja orientalis at 25-50 per

cent concentration on S. sclerotiorum by poisoned food technique. The A.

sativum extract resulted in the greatest reduction in dry mycelial weight (81.2%)

and sclerotial production (65.3%) over the control reported by Kekuda et al.

(2007). They studied the antifungal activity of distillate of cow urine by poisoned

food technique against soil borne pathogens.

Jarald et al. (2008) reported the anti-microbial property of cow urine and

its distillate against soil borne pathogens and found fresh cow urine to be more

effective than its distillate. Aqueous and ethanol extracts of Azadirachta indica

and Melia azedarach were evaluated against two pathogenic fungi of tomato;

Alternaria solani and F. oxysporum (Hassanein et al. 2008). At 10 per cent

concentration, aqueous extracts of A. indica and M. azedarach provided 70.5 and

15.7 per cent inhibition of A. solani and 100 and 16.5 per cent inhibition of F.

oxysporum, respectively.

Shashidhara et al. (2008) tested the effectiveness of Clerodendron

inerme, Duranta plumeri, Eupatorium sp., Allium sativum, Vitex negundo,

Lantana camara and Azadirachta indica against Phytophthora capsici in black

pepper. Among these, Duranta and Garlic (10%) provided 35.5 and 26.6 per cent

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mycelial inhibition of P. capsici, respectively. Aqueous, petroleum ether and

methanol extracts of fenugreek (3%) expressed the strongest inhibition (71.4%)

against F. graminearum, Botrytis cinerea, Alternaria sp. and R. solani (Haouala

et al. 2008). Bhattarai and Shrestha (2009) revealed that the aqueous and

ethanolic extracts of Eupatorium adenophorum (50 and 10% concentration) were

found highly effective against F. oxysporum, F. moniliforme and Aspergillus

niger.

The aqueous extracts of 46 plants were screened for antifungal activity

against species of Fusarium (Satish et al. 2009). The extracts of Emblica

officinalis, Eucalyptus globules and Punica granatum were found inhibitory to

fungi. Solvent extracts (petroleum ether, methanol and ethanol) of Polyalthia

longifolia and Murraya koenigii exhibited strong antifungal potential.

Roat et al. (2009) studied the inhibitory effects of some plant extracts

(Diospyros cordifolia, Datura stramonium, Cassia fistula, Solanum indicum,

Santalum album, Annosa sqamosa and Justicia adhatoda) in vitro and in vivo

against fruit rot of chilli incited by Colletotrichum capsici. D. cordifolia (bitter

temru) fruit and D. stramonium (datura) leaves inhibited the maximum mycelial

growth and spore germination of C. capsici. Isopropanol alcohol-1 extract of

Melia azedarach and aqueous extract of Ocimum basilicum and Vitex negundo

completely inhibited the growth of S. sclerotiorum (Shalika 2009).

In vitro studies conducted by Anand and Bhaskaran (2009) indicated that

leaf extracts of Abrus precatorius, Aegle mamelos and Eupatorium sp. showed

highest inhibition of spore germination and mycelial growth of C. capsici and

Alternaria alternata. Among 44 plant extracts tested, Allium sativum gave strong

inhibition i.e. 5.75 mm at 10 ppm concentration followed by A. cepa and Emblica

officinalis i.e. 3.25 mm each against R. solani isolated from rice (Sehajpal et al.

2009).

Zang et al. (2009) studied the antifungal efficacy of Ocimum basilicum var.

pilosum against Botrytis cinerea, F. oxysporum, S. sclerotiorum, F. solani and

Phytophthora capsici and found it most inhibitory to all the pathogens.

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Plant extracts of Houttuynia cordata and Eupatorium odoratum obtained

by water distillation gave highest inhibition (0.86 and 0.68 cm clear zone of F.

solani and 0.92 and 0.79 cm clear zone of C. capsici, respectively) whereas

ethanolic extracts showed 0.67 to 0.73 cm inhibition zone of both the pathogens

(Puttawong and Wongroung 2009). Shahnazdawar et al. (2010) studied the

effect of Datura alba and Cynodon dactylon against Macrophomina phaseolina

and R. solani in okra and cow pea. Both pathogens were completely suppressed

by D. alba extract.

Sathasivam et al. (2010) analyzed the antibacterial and antifungal activity

of cow urine distillate against Pseudomonas aeruginosa, Klebsiella pneumoniae,

Aspergillus flavus and A. niger. Maximum growth suppression was observed in

A. flavus (7.06 mm in diameter). Subudhi et al. (2010) demonstrated the effect of

petroleum ether, methanol, water extracts and water distillates of Stevia

rebeudiana, Ocimum sanctum and Murraya koenigii against Alternaria solani,

Helminthosporium solani, F. solani and R. solani. Methanol extract of S.

rebeudiana showed highest activity against plant pathogens A. solani and H.

solani. Water extract and distillate of O. sanctum and M. koenigii showed

optimum antifungal activity against all the pathogens. Methanol extracts of

Lawsonia inermis, Withania somnifera, Datura metel, D. stramonium and

Bauhinia racemosa were evaluated by Khan and Nasreen (2010) against C.

capsici, C. lindemuthianum, F. moniliforme, R. solani, F. oxysporum and

Alternaria alternata. Among these, L. inermis exhibited maximum inhibition in

mycelial growth of F. moniliforme (87.7%) followed by C. capsici (84.4%), F.

oxysporum (83.5%) and R. solani (81.1%).

Goel et al. (2011) studied the antifungal activity of hexane, ethyl acetate

and methanol extracts of Parmelia reticulata against S. rolfsii, R. solani, F. udum

and Pythium aphanidermatum. Maximum inhibition was exhibited by hexane and

ethyl acetate extracts against all pathogens.

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2.5 Organic inputs in disease management

2.5.1 Bacterial wilt (Ralstonia solanacearum)

Schonfeld et al. (2003) studied the effect of compost addition on the

survival of Ralstonia solanacearum strain 1609. Addition of household compost

resulted in decline in population of bacterium from log 6.67 to log 3.0 CFU per g

dry soil after 30-62 days. Incorporation of cow dung manure and pig slurry have

been found to reduce the bacterial wilt incidence and severity (Garisson et al.

2004).

Islam and Toyota (2004) reported the suppression of bacterial wilt of

tomato in soils amended with poultry manure and farm yard manure. Bora and

Deka (2007) found that vermicompost along with Pseudomonas fluorescens

reduced the disease incidence of Ralstonia solanacearum upto 50 per cent when

applied in soil.

Application of organic composts in soil reduced the incidence of brown rot

of potato caused by R. solanacearum upto 92.5 per cent (Messiha et al. 2007).

Nguyen and Ranamukhaarachchi (2010) screened 8 antagonists out of 73

isolated from soil amended with organic compost and evaluated against R.

solanacearum causing bacterial wilt in tomato and capsicum in pot experiments.

Three antagonists Bacillus megaterium, Enterobacter cloacae and Pichia

guillermondii suppressed the pathogen upto 56 per cent.

Yadessa et al. (2010) conducted the experiment on the effect of organic

amendments in soil against R. solanacearum, a causal agent of bacterial wilt of

tomato. Complete suppression of bacterium was observed in soil amended with 5

and 10 per cent farm yard manure, 1 per cent green compost and 10 per cent

cocopeat.

Vermicompost and farm yard manure were found to be good carrier of

Pseudomonas fluorescens and Bacillus sp. Seed, root and soil application of

compost performed significantly better providing 83.3 per cent control of bacterial

wilt of brinjal in field (Chakravarty and Kalita 2011). Organic compost mixed with

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Bacillus amylolique faciens strain QL-5 effectively decreased R. solanacearum

incidence in green house and field conditions upto 75 per cent (Zhong et al.

2011).

2.5.2 Fungal diseases

The oldest document on the use of organic materials to control crop

disorders is probably the Kautilya‟s Arthasastra (C-300 B.C.). The potential

disease suppressive characteristics of compost have been well documented

(Hunt et al. 1973). Compost seed dips, plant and soil sprays based on compost

and other plant materials were reported in organic farming as early as 1924

(Koepf 1992). Use of cow dung for dressing seeds, plastering cut ends of

vegetatively propagating units such as sugarcane setts, dressing wounds,

sprinkling diluted suspension on plants and applying to soil, have been indicated

by Kautilya (Nene 1999). Varahamihira suggested the use of milk, ghee and cow

dung for dressing seeds before sowing. In the 17th century, in document of Dara

Shikoh, use of cow dung for smearing the cutting of fig before planting is

mentioned (Razia Akbar 2000). There are numerous reports on the effectiveness

of cow milk, cow urine and cow dung in the management of viral diseases of

ornamental and other plants (Kumar et al. 2002).

Sharma and Gupta (1977) advocated the use of cow dung paint in the

control of smoky blight canker of apple and obtained 86.7 per cent healing of

wounds. Application of clay with cow dung to stems and branches of apple trees

gave good control of canker disease and increased yield (Kamchatyi and Prikhod

1989).

Cattle, equine and poultry waste was found highly effective against

Sclerotinia sclerotiorum in lettuce, which showed decreased number of sclerotia

in soil and dead plants (Asirifi et al.1994). Brinton et al. (1996) examined

compost tea in relation to its development and use for controlling plant diseases

such as late blight in potato and found that older composts were more effective

than the freshly prepared compost tea.

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Reddy and Padmodaya (1996) for the first time reported that panchgavya

was most effective against soil borne pathogen Fusarium oxysporum f.sp.

lycopersici, a causal agent of tomato wilt. Panchgavya-3 (MPG-3) was superior

to carbendazim in reducing the plant disease and in increasing the vigour of plant

and yield. Kim et al. (1997) observed 30 per cent reduction in disease severity of

Phytophthora capsici in bell pepper with the application of compost made from

sewage sludge + cow manure + peanut waste @ 8 t/ha in soil. Nakasaki et al.

(1998) reported 65 per cent reduction in Rhizoctonia solani in Turfgrass with the

application of compost of cow manure and chicken manure. Das et al. (1998)

conducted the field experiments with fresh cow dung, asafoetida and plantomycin

(antibiotic) for the management of bacterial leaf blight of rice (Xanthomonas

oryzae pv. oryzae) and noticed that foliar spray of cow dung significantly reduced

the incidence of BLB (18.5%). Leaf extracts of papaya were also found effective

in the control of powdery mildew of bell pepper (Amdioha 1998).

Raja and Kurucheve (1999) studied the fungitoxicity of animal dung and

urine against Fusarium oxysporum f.sp. lycopersici, the causal agent of tomato

wilt. The highest (96.6%) germination percentage was found when seeds of

jamun were treated with cow dung and urine for 24 h with increased shoot length

in the cow urine treatment (Swamy et al. 1999).

Kannangara et al. (2000) observed 40-80 per cent reduction in stem and

root rot of cucumber caused by Fusarium with the application of vermicompost.

Aryantha et al. (2000) studied the effect of fresh and composted animal manure

on root rot and dieback caused by Phytophthora cinnamomi and found 90 per

cent reduction in disease severity.

Jahagirdar et al. (2001) found that the biocontrol agents Trichoderma

viride-6, Pseudomonas fluorescens-17 and Bacillus subtilis-16 and MPG-3 were

effective against Fusarium oxysporum f.sp. cubense causing panama wilt of

banana. The treatments not only influenced growth and development but also

decreased the population of Fusarium in wilt sick soil. They revealed the use of

MPG-3 as soil application for suppression of soil borne pathogens.

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The treatment comprising organic manures (farm yard manure, neem

cake and vermicompost) in combination with NPK superimposed with alternate

sprays of garlic and chilli extracts (1/2 kg garlic + 50 g green chilli in 200 litre of

water) + tobacco leaves (1/2 kg in 30 litre of water) + cow urine (1/2 litre diluted

in15 litre of water) resulted in lowest incidence of leaf curl and dieback of

capsicum caused by Colletotrichum capsici (Fugro 2000).

Ribeiro et al. (2001) in Brazil investigated the efficacy of raw cow milk (20

and 30%) and bougainvillea leaf extract (5 and 10%) against powdery mildew

and Zucchini yellow mosaic virus (ZYMV) on zucchini and found that there was

no incidence of powdery mildew and lowest incidence of ZYMV with mixture of

30 per cent raw milk and 10 per cent bougainvillea. Handoro et al. (2001)

observed that farm yard manure, neemax, sheep manure and horse stable

manure were effective in the management of white rot of pea.

Extracts obtained by mixing vermicompost and organic compost with

water 1:1 ratio were evaluated for the control of zucchini squash powdery mildew

(Sphaerotheca fuliginea). Sprays of aqueous extracts at concentrations higher

than 50 per cent and application twice a week reduced the severity of the

disease (Ishida et al. 2001). Cotxarrera et al. (2002) studied the effect of compost

made from vegetable waste and animal manure against Fusarium oxysporum

f.sp. lycopersici in tomato and observed 90 per cent reduction in wilt disease.

Abbasi et al. (2002) conducted the field trial to evaluate compost of animal

manure + cannery waste against anthracnose of tomato. Soil amended with

compost @ 24-30 t/ha caused 50 per cent reduction in disease severity. Basak et

al. (2002) found that spray of cow urine was effective in controlling Sclerotinia rot

of cucumber caused by Sclerotinia sclerotiorum.

Perumal et al. (2003) conducted an experiment on carrot in which field soil

was amended with 7 kg biodynamic compost (BD-502, BD-507), 7 kg

vermicompost, 250 mg cow horn manure (BD-500) and 1 kg cow pat pit (CPP)

manure. There was no occurrence of any disease in crop until the harvest stage

and yield was also increased. The foliar application of panchgavya increased the

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yield attributes of sunflower, maize and green gram (Somasundaram 2003). The

water extract from cattle manure compost, kaligrin (potassium bicarbonate),

neemgard and Rifol (fish oil) gave efficient control of powdery mildew of pepper

caused by Leveillula taurica (Tsror et al. 2003).

Application of compost containing saw dust and cow manure in soil

resulted in 30-50 per cent reduction in disease severity of crown rot and leaf

blight of cucumber caused by Phytophthora capsici (Khan et al. 2004). Sible et

al. (2004) obtained 50 per cent reduction in bacterial leaf spot infection on leaves

with spray of 20 per cent cow dung water extract on 45 days old rice plants.

Rivera et al. (2004) evaluated the vermicompost suppressiveness in nurseries of

white pumpkin infested with Rhizoctonia solani and 60-65 per cent reduction in

disease was observed. Edward and Arancon (2004) reported the disease

suppressing effect of application of vermicompost on attack of fungus Pythium on

cucumber and Rhizoctonia solani on radish in green house.

Soils amended with composts provided 20-60 per cent reduction in

Pythium ultimum, Rhizoctonia solani, Phytophthora, Fusarium oxysporum,

Verticillium dahliae and Sclerotinia (Noble and Coventry 2005). Yadav and

Lourduraj (2006) reported the effect of panchgavya spray on the yield attributes,

grain yield and economics. It significantly increased the productive tillers per hill,

panicle length and filled grains per panicle. Foliar sprays with aqueous

vermicompost extracts on tomato provided reduction in late blight disease

(Phytophthora infestans) and yield was increased (Zaller 2006).

Sharma and Deshpande (2006) soaked pigeon pea seeds in 10 per cent

cow urine, vermiwash, neem leaf extract, biogas slurry, cow dung slurry, homa

farming ash and cow dung slurry (10%) + homa farming ash (10%) for 6 h. All the

treatments significantly enhanced seed germination, shoot length, root length

and vigour index. Fruit yield in guava was maximum (38.8 kg/tree) which were

exposed to homa atmosphere followed by 29.2 kg with homa + Rishi Krishi and

homa + panchgavya (Ram and Pathak 2007).

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Amendment of soil with cow dung compost caused more than 50 per cent

reduction in Fusarium, Sclerotinia and Phytophthora and 26 per cent reduction in

Rhizoctonia solani (Bonanomi et al. 2007). Extracts of ten composts (compost

tea) were tested against F. oxysporum, F. solani, F. graminearum, Alternaria sp.

Colletotrichum coccodes, Botrytis cinerea, S. sclerotiorum, R. solani, Aspergillus

niger, Pythium sp. and Verticillium dahliae. Two composts viz., 60 per cent cattle

manure + 30 per cent sheep manure + 10 per cent ground straw and 40 per cent

cattle manure + 40 per cent sheep manure + 20 per cent vegetable waste found

most effective and gave 38.1 and 31.8 per cent disease control (Kerkeni et al.

2007).

Mallesh et al. (2008) reported that soil amended with farm yard manure

showed 62.5 per cent reduction in disease incidence of root rot of sage caused

by F. solani and R. solani. Mughrabi et al. (2008) conducted the field trial to study

the effect of compost, compost tea and compost + compost tea on common scab

of potato caused by Streptomyces scabies. All the treatments significantly

reduced the severity by 81.0, 42.0 and 81.0 per cent respectively compared to

untreated.

Sahni et al. (2008) showed 25 per cent reduction in disease incidence

while studying the effect of vermicompost amendment in soil alongwith seed

bacterization with Pseudomonas syringae against Sclerotium rolfsii. Manandhar

and Yami (2008) observed 25.6 per cent control of foot rot disease of rice caused

by F. moniliforme with the application of vermicompost tea.

Hurali and Patil (2009) investigated the effect of panchgavya (3%), cow

urine (10%), butter milk (2%), cow milk (10%) and vermiwash (50%) against

soybean rust. Cow urine resulted in reduced disease index (36.0%) followed by

butter milk (39.5%), cow milk (40.8%), panchgavya (41.5%) and vermiwash

(43.1%). Soil application of compost tea resulted in decreased incidence of

Fusarium wilt (Gunaseeli and Maheswari 2009).

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Yadav et al. (2010) evaluated the effect of Trichoderma harzianum, farm

yard manure and vermicompost individually and in combination under field

conditions against Alternaria leaf spot of cabbage. Seedling treatment with T.

harzianum and its application alongwith vermicompost recorded maximum

disease control (62.5%). Maha panchgavya, a concoction made from five cow

products was tested against Pythium aphanidermatum causing damping-off in

tomato and results showed 48.2 per cent control of disease in nursery beds

(Kumar et al. 2010).

Saadi et al. (2010) studied the suppressive action of compost (tomato

plant and cow manure) against Fusarium oxysporum in melon. The results

showed that compost suppressed the Fusarium wilt upto 83 per cent. Madhavi

and Bhattiprolu (2011) reported that application of vermicompost @ 100 g/kg soil

and Trichoderma viride @ 10 g/pot in pot experiments exhibited 77.4 and 56.2

per cent inhibition of dry root of chillies caused by Sclerotium rolfsii in comparison

to check.

2.6 Plant growth promoting traits

For millennia, diverse microorganisms have yielded important biological

materials useful to plants such as enzymes, herbicides and growth promoters.

The equilibrium among microorganisms and between microorganisms and crop

plant resists plant disease and promotes plant growth. Shen (1997) reported that

the use of Yield-Increasing Bacteria (YIB), which consisted of several wild-type

bacteria (mainly Bacillus spp.), promoted the growth of crops and suppressed the

diseases.

Plant growth promoting bacteria (PGPB) support plant growth indirectly,

by improving growth restricting conditions either via production of antagonistic

substances or by inducing resistance against plant pathogens (Kloepper et al.

1999). PGPB are those bacterial strains that have a beneficial effect on plant

growth and development (Andrews and Harris 2003). Plant growth promoting

strains applied as seed treatment resulted in significant reduction in anthracnose

disease caused by Colletotrichum orbiculare in cucumber (Wei et al. 1996).

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Cartiaux et al. (2003) found that plant growth promoting bacteria were

responsible for inducing resistance in plants by augmenting the

levels/biosynthesis of defense proteins. These organisms possess various traits

like nitrogen fixing ability, production of siderophores, facilitating the uptake of

certain plant nutrients from the environment. Indirect promotion of plant growth

occurs when PGPB lessen or prevent the deleterious effect of phytopathogenic

synthesis of phytohormones and solubilization of minerals which are otherwise

unavailable to the plants (Altn and Bora 2005).

Joseph et al. (2007) isolated a total number of 50 bacterial isolates

belonging to Bacillus, Pseudomonas, Azotobacter and Rhizobium from different

rhizosphere soil of chick pea and characterized these isolates biochemically and

screened in vitro for their plant growth promoting traits like production of indole

acetic acid (IAA), ammonia (NH3), hydrogen cyanide (HCN), siderophore and

catalase.

PGPB are more advantageous than chemical fertilizers for the

development of sustainable agriculture as chemical fertilizers have several

negative environmental impacts. PGPB promote plant growth directly or

indirectly. They directly promote plant growth either by providing the plant growth

promoting substances or by microorganisms (Mehta et al. 2010). Saharam and

Nehra (2011) described the effects of plant growth promoting strains viz, Bacillus,

Streptomyces, Pseudomonas and Burkholderia against Colletotrichum capsici,

Phytophthora, Macrophomina, Rhizoctonia and Fusarium oxysporum.

2.6.1 Phosphate solubilization

Phosphorus (P) is an essential nutrient required by the plant for vital

cellular functions. Phosphorus is frequently limiting macronutrient next only to

nitrogen for plant growth and make up about 0.2 per cent of plant dry weight

(Schachtman et al. 1998). It is an integral part of the cellular activities of living

organisms. It has a defined role in plant metabolism such as cell division,

development, photosynthesis, breakdown of sugar, nutrient transport within the

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plant, transfer of genetic characteristics from one generation to another and

regulation of metabolic pathways (Tandon 1987; Armstrong 1998; Theodorou

and Plaxton 1993).

Phosphorus deficiency is a major constraint to crop production due to its

low solubility and fixation in the soil. To convert insoluble phosphates to a form

accessible to the plants, like orthophosphate, is an important trait for a PGPB for

increasing plant yields (Rodriguez et al. 2006). Phosphate solubilizing

microorganisms enhance plant growth under conditions of poor phosphorus

availability by solubilizing insoluble phosphates in the soil. The primary

mechanism of mineral phosphate solubilization is the action of organic acids

synthesized by soil microorganisms. Production of organic acids results in

acidification of the microbial cell and its surroundings (Rodriguez and Fraga

1999).

Application of phosphate solubilizing strains in carnation protected the

plants systemically against Fusarium wilt caused by F. oxysporum f.sp. dianthi

(Van Peer et al. 1991). Inoculation of pepper with phosphate solubilizing bacteria

significantly reduces the Phytophthora blight of peppers caused by Phytophthora

capsici and increased the yields (Akgiil and Mirik 2008).

Increased solubilization of fixed soil phosphates and applied phosphates

ensuring higher crop yields has been reported on inoculation of phosphate-

solubilizing bacteria including Pseudomonas, Bacillus, Rhizobium, Micrococcus,

Flavobacterium, Burkholderia, Achromobacter, Erwinia and Agrobacterium.

Several Pseudomonas species have been reported among the most efficient

phosphate-solublizing bacteria and as important bio-inoculants due to their

multiple biofertilizing activities of improving soil nutrient status, secretion of plant

growth regulators and suppression of soil-borne pathogens (Botelho and

Mendonça-Hagler 2006 ; Vyas et al. 2009).

Yazdani et al. (2009) reported that application of phosphate solubilizing

microorganisms and plant growth promoting bacteria together can reduce

phosphorus application by 50 per cent without any significant reduction in grain

yield. PSB can be used as biofertilizers, which is friendly for environment and is a

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possible way to increase the efficiency of phosphorus fertilizers. Phosphorus

biofertilizers may help increase the availability of accumulated phosphate by

solubilization process for crop production (Panhwar et al. 2009).

2.6.2 Indole acetic acid production

In 1880, Charles Darwin proposed that some plant growth responses are

regulated by „a matter which transmits its effects from one part of the plant to

another‟. Several decades later, this „matter,‟ termed auxin (from the Greek

„auxein‟ which means „to grow‟), was identified as indole-3-acetic acid (IAA) (Kogl

and Kostermans 1934). Indole-3-acetic acid (IAA) is the most abundant member

of the auxin family of phytohormones and has a role in development of lateral

and adventitious roots and a number of other processes related to the

differentiation and proliferation of plant tissue (Arshad and Frankenberger 1998;

Patten and Glick 2002; Vessey 2003). IAA has since been implicated in virtually

all aspects of plant growth and development (Woodward and Bartel 2005; Teale

et al. 2006).

Tryptophan is the main precursor for IAA synthesis and thus plays a role

in modulating the level of IAA biosynthesis (Spaepen et al. 2007). Application of

exogenous tryptophan increases IAA production in various bacteria e.g.

Azospirillum, Pseudomonas agglomerans, P. putida and Rhizobium (Prinsen et

al. 1993; Brandl and Lindow 1996; Theunis et al. 2004). While tryptophan

stimulates IAA production in Azospirillum, anthranilate, a precursor for

tryptophan, reduces IAA synthesis. By this mechanism, IAA biosynthesis is fine-

tuned because tryptophan inhibits anthranilate formation by a negative feedback

regulation on the anthranilate synthase, resulting in an indirect induction of IAA

production (Hartmann and Zimmer 1994).

PGPB producing IAA hormone have dual role in influencing plant growth,

by involving in the biocontrol together with glutathione-s-transferases in defence-

related plant reactions and inhibit the germination of spore and growth of

mycelium of different pathogenic fungi (Brown and Hamilton 1993). A balanced

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interplay of different factors including bacterial IAA biosynthesis rather than IAA

production per se is needed to stimulate plant growth (Xie et al. 1996). IAA exerts

a stimulatory effect on plant growth within a narrow concentration range only,

beyond which the plant is either unresponsive or its growth is inhibited (Biswas et

al. 2000).

IAA hormone when supplied to excised potato leaves eventually reduced

the severity of the disease provoked by Phytophthora infestans (Martinez Noel et

al. 2001). Ahmad et al. (2005) isolated a total of 21 bacterial isolates

(Azotobacter sp., 10 and fluorescent Pseudomonas sp., 11) from different

rhizosphere soils in the vicinity of Aligarh city and tested these isolates for the

production of indole acetic acid (IAA) in a medium with 0, 1, 2, and 5 mg/ml

tryptophan.

Mali and Bodhankar (2009) isolated a total number of 25 isolates of

Azotobacter chroococcum from the rhizospheric soils of groundnut of different

varieties from various localities of Sangli District (Maharashtra) and tested these

for their ability to produce antifungal metabolites and phytohormones such as

indole acetic acid and gibberellins. Khare and Arora (2010) reported direct role of

bacterial IAA in suppression of charcoal rot disease of chickpea by the

development of root system, providing nutrients and support the plants infected

by Macrophomina phaseolina.

2.6.3 Siderophore production

The term „siderophore‟ is Greek word for “iron carrier” and is named so

because these molecules have an extremely high affinity for ferric iron (Lankford

1973). Siderophores are low molecular weight (500-1000 daltons) ferric-specific

ligands produced by many microorganisms (Neilands 1981). Iron is required for

the growth of nearly all microorganisms. The availability of ferric iron in well

aerated soils is very low and highly dependent on soil pH. To acquire iron from a

host, certain microorganisms have been found to produce specific high affinity

iron binding compounds, termed siderophores (Yang et al. 1991). Siderophores

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help a particular microorganism to compete against pathogens for available iron

and the role of siderophores in controlling diseases has been well documented

(Baker et al. 1986).

Arora et al. (2001) isolated two root-nodulating bacteria from medicinal

plants which were able to produce siderophores. Siderophore production in iron

stress conditions have an added advantage, resulting in exclusion of pathogens

due to iron starvation. Sayyed et al (2005) reported the production of iron

chelators by Pseudomonas fluorescens which were effective in the suppression

of Fusarium wilt. Rahi et al. (2009) reported that siderophore production

influences plant growth through the suppression of fungal pathogens. They

studied siderophore production by Discosia sp. on CAS agar plates and iron-free

Czapek-Dox liquid medium. Vargas et al. (2009) observed decreased mycelial

growth (about 65%) by two siderophore producing isolates.

Two hundred and sixteen bacterial isolates were tested by Chaiharn et al.

(2009) for sidedrophore production and their effectiveness in inhibiting mycelial

growth in vitro of rice pathogenic fungi viz., Alternaria sp., Fusarium oxysporum,

Pyricularia oryzae and Sclerotium sp., the causal agent of leaf spot, root rot, blast

and stem rot in rice respectively. Siderophore producing bacteria showed strong

antagonistic effect against the Alternaria (35.4%), F. oxysporum (37.5%), P.

oryzae (31.2%) and Sclerotium sp. (10.4%).

Khare and Arora (2010) stated that microbial siderophores are well known

for their ecological significance. They directly promote plant growth by supplying

iron. Siderophores contribute to disease suppression by conferring a competitive

advantage to biocontrol agents for the limited supply of essential trace minerals

in natural habitats. The various compounds of siderophores produced by

fluorescent pseudomonads are ferribactin, ferrichrome, ferrioxamine,

phytosiderophores, pseudobactin B10, pyochelin, pyoverdine etc (Latha and

Natarajan 2010). Siderophore rich supernatant of Alcaligenes sp exerted

antifungal activity against F. oxysporum, Aspergillus niger, A. flavus, Cercospora

arachichola, Pseudomonas solanacearum and Alternaria alternata with minimum

fungicidal concentration required was 25 μl (Sayyed and Patel 2011).

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2.6.4 Ammonia production

The increasing cost of petroleum products required in nitrogen fertilizer

production has focused attention on the development of biological system for

nitrogen fixation. Narula and Gupta (1987) found that inoculation of wheat and

barley with ammonia excreting strains caused increased dry weight and enzyme

activity. Whitehead and Cotta (2004) isolated 40 bacterial cultures, which were

capable of producing at least 40 Mm ammonia in peptone-amino acid medium,

concentrations similar to those produced by hyper-ammonia producing (HAP)

bacteria isolated from the rumen of cattle.

Production of volatile compound ammonia was involved in suppression of

Pythium ultimum – a damping-off pathogen (Harman et al. 2004). Joseph et al.

(2007) isolated a total of 150 bacterial isolates belonging to Bacillus,

Pseudomonas, Azotobacter and Rhizobium from different rhizospheric soil of

chick pea in the vicinity of Allahabad. Ammonia production was detected in 95

per cent of isolates of Bacillus followed by Pseudomonas (94.2%), Rhizobium

(74.2%) and Azotobacter (45.0%).

Selvakumar et al. (2008) reported that two isolates viz., KR-3 and KR-4

were able to excrete ammonia into the growth medium, which was further

confirmed by their ability to grow on Jensen‟s N free medium. Both of these

isolates, were able to grow in N-free medium and excrete extracellular ammonia,

which is indicative of their ability to fix atmospheric nitrogen.

2.6.5 Hydrogen cyanide production

Bacterial HCN modifies the metabolism of host plant in such a way that

induces some plant defence mechanisms against the pathogen. Voisard et al.

(1989) suggested that some Pseudomonads were able to synthesize HCN to

which these Pseudomonads were resistant. Defago et al. (1990) reported that

cyanide play an important role in suppression of pathogenic microorganisms viz.,

Gaeumannomyces graminis var. tritici and Rhizoctonia solani. They stated that

the ability of bacteria to produce HCN, to suppress root rot and to stimulate root

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hair formation is positively correlated. Strain CHAo which was HCN-positive

increased the weight of wheat plant infected with G. graminis var. tritici and

reduced the number of running hyphae of the pathogen in natural, partially

sterilized soil, but the HCN-negative mutant CHA5 had no such effect (Ramette

et al. 2003). It is a broad-spectrum antimicrobial compound. Microbial production

of HCN has been reported as an important antifungal trait to control root infecting

fungi.

The production of HCN by certain fluorescent pseudomonads involved in

suppression of root pathogens (Harman et al. 2004). Cyanogenic bacteria

produce hydrogen cyanide (HCN) and have been shown to play direct as well as

indirect role in biological control of plant diseases and increasing the yields

(Latha and Natarajan 2010). Khare and Arora (2010) reported that plant growth

stimulation and suppression of charcoal rot disease by the isolate TO3 in their

study is most likely the synergic effect of numerous modes (siderophore and

HCN production).

2.6.6 Lytic enzymes

A variety of microorganisms also exhibit hyperparasitic activity, attacking

pathogens by excreting cell wall hydrolases (Chernin and Chet 2002). It has

been also demonstrated that extracellular chitinase and laminarinase synthesized

by Pseudomonas stutzeri digest and lyses mycelium of F. solani (Lim et al.

1991). Bacillus cepacia synthesizes ß-1,3-glucanase that destroys the integrity

of R. solani, S. rolfsii and Pythium ultimum cell walls ( Fridlender et al. 1993).

The ß-1,3-glucanase synthesized by Paenibacillus sp. strain 300

and Streptomyces sp. strain 385 lyses fungal cell walls of F. oxysporum f.

sp. cucumerinum (Singh et al. 1999).

Chitinase produced by Serratia plymuthica C48 inhibited spore

germination and germ-tube elongation in Botrytis cinerea (Frankowski et al.

2001). Although, chitinolytic activity appears less essential for PGPB such as S.

plymutica IC14 when used to suppress Sclerotinia sclerotiorum and B. cinerea,

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synthesis of proteases and other biocontrol traits are involved (Kamensky et al.

2003). The ability to produce extracellular chitinases is considered crucial

for Serratia marcescens to act as antagonist against Sclerotium rolfsii (Compant

et al. 2005) and for Paenibacillus sp. strain 300 and Streptomyces sp. strain 385

to suppress Fusarium oxysporum f.sp. cucumerinum a,b-1,3-glucanase

contributes significantly to biocontrol activities of Lysobacter enzymogens strain

C3 (Palumbo et al. 2005).

Pseudomonas strain and Bacillus luciferensis KJ2C12 reduced

Phytophthora capsici of pepper by protecting infection courts through enhanced

effective root colonization with protease production and an increase of soil

microbial activity (Paul and Sharma 2006; Kim et al. 2009).

2.6.7 Nitrogenase activity

Nitrogenase enzyme responsible for nitrogen fixation also reduces

acetylene (C2H2) to ethylene (C2H4). Activity of nitrogenase enzyme determined

by acetylene reduction assay developed by Dilworth (1966). Bazylinski et al.

(2000) reported the nitrogenase activity in species of Magnetospirillum and

Geobacter as it reduced the acetylene to ethylene (11.5+/-5.9 n moles C2H4

produced minute-1 mg-1 cell protein) and thus bacteria were able to fix

atmospheric dinitrogen. Staal et al. (2001) measured the nitrogenase enzyme

activity of cyanobacteria by acetylene reduction technique. Heloiza et al. (2002)

studied the ability of bacterium Beijerinckia derxii ICB-10 to reduce acetylene to

ethylene.

Husen (2003) reported the ability of Azotobacter vinelandii Mac259 and

Bacillus cereus VW 85 to fix dinitrogen by assessing nitorgenase enzyme activity

to reduce acetylene to ethylene. Nitrogenase activity of cyanobacteria isolated

from paddy fields was determined through acetylene reduction technique. Nostoc

showed highest level (0.09 ethylene µl/mg) followed by Anabaena (0.006

ethylene µl/mg) (Gulten et al. 2007). Acetobacter, Bacillus, Burkholderia,

Pseudomonas and Enterobacter possessed nitrogenase enzyme activity and

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able to fix atmospheric nitrogen (Dutta and Gachhcii 2006; Sachdev et al. 2009).

Chengqun and Huang (2010) observed the nitrogenase enzyme activity in strains

of Enterobacter, Burkholderia, Rhizobium, Erwinia, Agrobacterium, Bacillus,

Serratia and Pseudomonas isolated from rhizosphere of Pinus massoniana

Lamb.

Magnani et al. (2010) screened 32 bacterial isolates for nitrogenase

enzyme activity by acetylene reduction technique. Among these, only 4 isolates

Klebsiella, Enterobacter, Pantoea and Pseudomonas exhibited nitrogenase

activity. Glucanacetobacter diazotrophicus R3, obtained from roots of rice

seedlings, showed appreciable nitrogenase activity (416.93 n moles (C2H4 hr-1

mg-1 cell protein) (Anitha and Tharigaraju 2010).