2. REVIEW OF LITERATURE -...
Transcript of 2. REVIEW OF LITERATURE -...
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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).