. root-knot nematode, M. incognita. Plants treated with Cow

. Plant Growth Parameters

The
root-knot Nematode M. incognita
caused significant decrease in all the plant growth parameters of Ammi majus. Plant length, Plant fresh
weight, and plant dry weight were found to decrease by 65.20%, 69.12% and 71.88%
respectively, when the plant was inoculated with M. incognita. Application of all the five organic matter (Cow Dung,
Vermicompost, Ricinus communis, Amaranthus viridis and Euphorbia
hirta) caused considerable enhancement in all the  plant growth parameters as compared to
control in the presence as well as in the absence  of the root-knot nematode, M. incognita. Plants treated with Cow
Dung showed maximum improvement in plant length (57.22%), plant fresh weight
(60.65%) and plant dry weight (63.09%) as compared to other treatments as well
as the untreated control. The least improvement in Plant growth  parameters was observed in case of plants
treated with  Amaranthus viridis where plant length,
plant fresh weight and plant dry weight 
increased only by 30.11%, 31.91% and 
33.17% respectively ( Table 1).

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2.
Physiological Parameters

2.1. Chlorophyll Content: M. incognita caused significant decrease
in chlorophyll content by 69.46%. Application of all the five organic matter
(Cow Dung, Vermicompost, Ricinus communis, Amaranthus viridis and Euphorbia
hirta) caused considerable enhancement in chlorophyll content as compared
to control in the presence as well as in the absence of the root-knot nematode,
M. incognita. Cow Dung showed maximum
improvement in total chlorophyll content (61.06%) as compared to other
treatments as well as the untreated control. The least improvement was observed
in the case of Amaranthus viridis where
chlorophyll content increased only by 32.06% (Table 1).

2.2. Phenol Content: The phenol content was
significantly greater in the pathogen inoculated plants than uninoculated
plants, highest increase being (71.16%) in plants inoculated with M. incognita alone. Although all the
organic matters resulted in increasing the phenolic content of plant, but this
increase was found non-significant when compared to control, in case where
organic matter was applied alone. When organic matters were applied in the
presence of M. incognita, the
increase in phenol content was found significant as compared to control (Table
1).

3
Gas Exchange Parameters                                                                                                         

3.1. Stomatal Conductance: Stomatal
Conductance of plant was decreased significantly (44.32%) when inoculated with M. incognita alone. All the organic
matters caused enhancement in stomatal conductance both in presence and absence
of the pathogen. The highest increase was observed in case of plants treated
with Cow Dung (56.66%), where as the lowest increase was found in plants treated
with Amaranthus viridis alone
(30.22%) (Table 2).

3.2. Transpiration Rate: The rate of transpiration of Ammi majus plants decreased
significantly (49.64%) when inoculated with M.
incognita. All the organic matters significantly enhanced rate of
transpiration in plants both in the presence as well as in the absence of M. incognita. The highest increase was
found in plants treated with Cow Dung (63.64%), while the lowest increase was
recorded in plants treated with Amaranthus
viridis (32.23%) in the presence of nematode (Table 2).

3.3. Photosynthetic Rate:
Photosynthetic rate was found significantly decreased (57.64%) in plant treated
with M. incognita alone when compared
to control. All the organic matters caused significant increase in
Photosynthetic rate when compared to control in the presence as well as in the
absence of pathogen. The highest increase was observed in plants treated with
Cow Dung alone (70.22%), while the lowest was found in case of plants treated
with  Amaranthus
viridis in presence of M. incognita
(30.15%) (Table 2).

4. Nematode related Parameters

The number of galls per root system
and the multiplication of nematode were high when M. incognita was applied alone (Table 3). All the five organic
matters significantly decreased number of galls, the highest reduction being in
case of Cow Dung (92.22%) and the lowest in Amaranthus
viridis (38.22%). Number of eggs per eggmasses (fecundity) was found
significantly decreased in plants treated with organic matters, the highest
(81.50%) in case of Cow Dung and lowest in case of Amaranthus viridis (40.13%). A significant decrease in nematode population
(both soil and root) was observed in all the plants treated with organic
matter. The highest decrease was observed in case of Cow Dung (91.3%, 91.55%)
and lowest in case of Amaranthus viridis
(42.04%, 43.33%) respectively ( Table 3).

DISCUSSION

Due
to the wide host range and adaptability to varying environments, M.
incognita is able to infect plants like Ammi
majus inspite of its medicinal properties. Pandey (1992) also reported the
infection of this plant by root-knot nematode at 2000 inoculum level causing
quantitative as well as qualitative loss. Organic matter plays a vital role
that affects the growth and yield of crop by providing nutrients or by enchancing
soil physical properties which can improve the root environment and promote the
growth of plant (Mahmood and Saxena, 1992; Bridge, 1996; Watson et al., 2002;
Westerman and Bicudo, 2005; Agyarco et al., 2006; Ramesh et al., 2006).

The
result shows that all the five organic matter when amended in soil before 20
days of sowing seeds caused considerable enhancement in all the plant growth
parameters even in the presence of the pathogen. The highest improvement in
plants was observed in soil amended with Cow Dung in the absence of nematode M. incognita,
while least improvement was observed in the case where soil was amended with Amaranthus viridis in the presence of M. incognita.
This might be due to nematode-toxic substance released by organic amendment as
well as improvement in soil fertility on decomposition (Riegel and Noe, 2000;
Oka, 2010). Our results are supported by number of studies in which organic
matter was used  as soil amendments and
showed beneficial effects on yield of crops and reductions in
plant-parasitic-nematode  (Nwaguma et
al., 2005; Orisajo et al., 2008; 
Pakeerathan et al., 2009; Iqbal et al., 2011; Renco and Ková?ik, 2012;
Chaudhary and Kaul, 2013). These toxins may have killed the juveniles of M. incognita in the soil. Organic
matters are rich in nitrogen and phenolic compounds (Agyarko et al., 2006;
Renco and Ková?ik, 2012). Nitrogen is converted to ammonia on decomposition (Lazarovits
et al., 2001; Adetiloye et al., 2006; Oka, 2010; Thoden et al., 2011) and this
has been reported to kill several nematode spp. (Lazarovits et al., 2001). It
could also be due to enhancement in the activities of other soil micro
organisms which is being facilitated by the organic amendments. Some of which
are antagonistic to M. incognita such
as antagonistic fungi which  have been
isolated from juveniles and egg masses of nematodes in organic soils in New
York (Viaene and Abawi, 1995). Many earlier workers Sikora, 1992; Jaffee et
al., 1994; Riegel and Noe, 2000 reported an increase in microbial organisms due
to the incorporation of organic matter. Thus the addition of organic matter in
the soil provides better environment for the root growth, improves the
utilization of soil nutrients and resulted a reduction by nematode damage
(Vander-Borgett et al., 1994). The observed decrease in number of nematodes may
be responsible for the increase in growth of the seedlings, by decreasing less
disturbances to the seedlings (Vander-Borgett et al., 1994). Cattle manure used
in this experiment had relevant nutrient content (Table 1). Also, the
incorporation of organic manure to the soil may increase the solubility of some
nutrients such as zinc and phosphorus (Swietlik, 1999; Khan and Joergensen,
2009).

The
plant response to nematode parasitism causes measurable morphological and
physiological changes that affects the process of photosynthesis (Melakeberhan
et al., 1986; Hussey & Williamson, 1998). Root-knot nematodes  alters the morphology and physiology of the
host (Williamson & Gleason, 2003). 
Root-knot nematodes causes severe changes on the root system of host
plant and are measured by a root gall index that assess the frequency of root
galls (Taylor and Sasser ,1978). However, the root gall index does not give the
impact of nematode infestation on the fine roots, which are important for
absorption of water and necessary for normal physiological and biochemical
processes in plants (Melakeberhan et al., 1986; Hussey & Williamson, 1998).
The morphological analyses of the root system shows the effect of the nematode
inoculum density on plant physiological processes (Williamson & Gleason,
2003; Jaleel et al., 2008; Strajnar et al., 2012). In the present case all the
three gas exchange parameters (stomatal conductance, transpiration rate and
photosynthetic rate) decreased significantly due to nematode infection. As a
result of nematode infection, the roots got severely damaged; which in turn
hindered the water absorption ability of the plant. RKN invade the root in the
zone of elongation and migrate intercellularly to the vascular bundle, where
they develop the feeding site and disrupts the vascular tissue (Fuller et al.,
2008). As a result, water supply to the root is disturbed. Infestation of roots
due to M. incognita  has shown to increase axial resistance to
water flow and decrease the total water uptake in tomato plants .This might be due
to nematode-induced water stress, generated by the effect of root galls on root
hydraulic conductivity leading to reduced leaf water potential, stomatal
conductance and transpiration rate. There are several reports of decreased
water potential, stomatal conductance and decreased photosynthesis in the
plants infested by RKN. Our results are in conformity with Strajnar et al.,
2012. The photosynthetic rates were also decreased in French beans infested by M. incognita. In this the author
suugested that the reduction in the rate of photosynthesis was related to lower
level of potassium in leaves (Melakeberhan et al., 1986). Organic matter
application enhanced the gas exchange parameters in Ammi majus plant, this may be due to improvement in overall health
of the plants. Our results are in accordance with that of (Mahmood and
Saxena,1986; Ghazalbash and Abdollahi, 2013).

Phenols
contribute in the self defence of plants against pathogen attack. In the
present case also the phenol content was highest in the plants inoculated with M. incognita
alone. The finding is also supported by the previous works done by several
scientists (Nicholson and Hammerschmidt, 1992; Meena et al., 2000). This may
also be due to the hinderance in direct uptake of nutrients due to infection by
pathogen and changed plant physiology (Pandey, 1992). All the organic matters
notably increased the phenol contents, this may be due to enhanced vigour of
plants as a result of easy availability of nutrients on organic matter
decomposition.

CONCLUSION

The
root-knot nematode M. incognita caused
significant effect on various plant growth, physiological as well as
biochemical parameters of Ammi majus. Application
of all the five organic matters considerably enhanced plant growth and resulted
in reduced nematode multiplication, root galls and eggs/eggmasses. Among all
the organic matter most effective was found to be Cow Dung followed by
vermicompost, Amaranthus viridis, Ricinus
communis and Euphorbia hirta. The conclusion drawn from the present study clearly
states that organic amendments are effective alternatives as a source of macro-
and micronutrients and have a potential to improve and enhance plant growth and
yield, and avoid use of costly hazardous chemical fertilisers. In addition,
these organic substances supply nutrients for nematode antagonistic
micro-organisms for the abatement of plant-parasitic nematodes population. Such
type of study will definitely increase the interest amongst the people to
formulate ideas to develop organic agriculture, which increase the crop
production without harming our environment.

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