Journal of Phytopathology and Pest Management 7(1): 79-90, 2020
pISSN:2356-8577 eISSN: 2356-6507
Journal homepage: http://ppmj.net/
∗
Corresponding author:
Waleed M. A. Abd-Elmagid,
E-mail: waleedabdel-magid.5419@azhar.edu.eg
79
Copyright © 2020
Control of peanut root and pod rots diseases
using certain bioagents
Waleed M. A. Abd-Elmagid
*
, Mohamed M. El-Sheikh Aly, Rafeek M. I. El-Sharkawy
Agricultural Botany Department, Faculty of Agriculture, Al-Azhar University, 71524 Assiut, Egypt
Abstract
Keywords: peanut, root rot, pod rot, Trichoderma spp., Pseudomonas fluorescens, Bacillus subtilis.
80
1. Introduction
Peanut or groundnut (
Arachis
hypogaea
L.) is a leguminous plant belonging to
family Fabaceae. It is considered one of
the most important crops in Egypt, as
well as in many countries of the world,
which is due to its seeds high nutritive
value for humans, as well as the produced
green leafy hay for feeding livestock, in
addition to the importance of the seed oil
for industrial purposes (Abdalla et al.,
2009). Root and pod rots are serious
worldwide diseases attacking roots and
pods underground (Hilal et al., 1990).
Damping–off, root and pod rot diseases
caused by
Macrophomina
phasolina
,
Rhizoctonia
solani
and
Fusarium
oxysporum
are the most destructive
fungal diseases, which attack peanuts
causing quantitative and qualitative losses
of yield (Abdel-Elkhair et al
.
2016).
Fusarium
spp is known as a pathogen
causing different symptoms of infected
roots and pods (Hussin Zeinab, 2011;
Marei, 2000)
.
Various strategies were
developed for controlling such diseases
by using plant growth promoting
rhizobacteria (PGPR). Different strains of
PGPR genera such as
Azoarcus,
Pseudomonas, Azospirillum, Azotobacter,
Arthrobacter, Bacillus, Clostridium,
Burkholdaria, Enterobacter, Gluco-
nacetobacter, Rhizobium, Erwinia,
Mycobacterium, Mesorhizobium, Flavo-
bacterium
, are soil inhabitants that are
able to colonize plant roots, stimulate
plant growth, and increase crop yield, and
employ a direct and indirect mechanisms
to enhance plant growth and diseases
prevention (Mroz et. al. 1994; Kloepper
et al
.
, 1989). Fungi of the genus
Trichoderma
are economically important
due to their plant growth- and
performance-promoting effects, such as
improved nutrient supply, myco-
parasitism of plant-pathogens and
priming of plant defense (Guo et al.,
2019). El-Sharkawy (2006) mentioned
that
T. harzianum, T. hamatum
and
G.
virens
reduced mycelial growth of
R.
solani
,
M. phaseolina, F. oxysporum
and
Verticilium albo-atrum
. The main
objective of the present study was to
evaluate the efficacy of certain bacterial
and fungal bioagents against
Macrophomina
phasolina
,
Rhizoctonia
solani
and
Fusarium
oxysporum
which
causing peanut root and pod rots
diseases.
2. Materials and methods
2.1 Isolation and identification of the
causal pathogens of peanut root and
pod rots diseases
Peanut samples were collected from
different localities in Minia, Assiut and
Sohag governorates, Egypt. The infected
roots and pods (Shell and kernel), were
cut into small pieces, washed thoroughly
with tap water, surface sterilized by
immersing for 2 minutes in 70% ethayl
alcohol. After rinsing several times in
sterilized distilled water, samples were
dried between two sterilized filter papers,
The surface sterilized plant pieces were
plated on sterilized Potato Dextrose Agar
(PDA) medium in Petri dishes and
incubated at 27°C. After 4-5 days of
incubation, the developed fungal growth
was purified using hyphal tip and single
spore techniques. The pure fungal
isolates were kept on PDA medium at
27°C and have been used in this study.
The isolated fungi were identified based
on the morphological characters of
mycelium and spores as described by
Barnet and Hunter (1977) and Domsch et
al
.
(1980).
81
2.2 Pathogenicity tests
The pathogenic capabilities of the
obtained fungal isolates were carried out
on peanut cultivar NC under greenhouse
conditions in the Farm of Faculty of
Agriculture, Al-Azhar University (Assiut
Branch), Egypt during 2017 growing
season. Inocula of the tested isolates were
prepared by inoculating sterilized conical
flasks (250 ml) containing sorghum
medium, which contains 75 g sorghum
cereal, 25 g clean sand, 2 g sucrose and
50 ml water according to Abdel-Moneem
(1996), with equal discs (0.5 cm) taken
from 7 days old cultures of the tested
fungal isolates. The inoculated flasks
were incubated at 27°C for two weeks,
then each isolate was mixed with sand
clay soil sterilized with formalin 5% at
the rate of 2% w/w. Sterilized pots (30
cm in diameter) were filled with infested
sand clay soil 7 days before sowing.
Uninfested soil pots were used as control.
Seeds of peanut cultivar NC were seeded
in infested and non-infested sand clay
soil (7 seeds /pot). Disease severity of
root rot was recorded after 100 days from
sowing. The arbitrary (0-5) disease index
scale as described by Grunwald et al
.
(2003) was adopted, where: 0= No
visible symptoms, 1= slight hypocotyls
lesions, 2= lesions coalescing around
epicotyls and hypocotyls, 3= lesions
starting to spread into the root system
with root tips starting to be infected, 4=
epicotyls, hypocotyls and root system
almost completely infected and 5=
completely infected root. Pod rot severity
was recorded by adopting the scale based
on area of spots covered on pods and
percent disease index (PDI), calculated
mean disease index, pods were grouped
into six categories described by Wheeler
(1969), Where 0=non disease symptoms
(disease free), 1=spots cover 1-10%, 2=
spots cover 10-30%, 3= spots cover 30-
50%, 4= spots cover 50-70% and 5=
spots cover >70%. The percentages of
disease severity of root rot and pod rots
diseases were estimated using the
following formula:
Disease severity (%) = ∑ [(n x V) /5xN)] x 100
Where; n= number of root or pod within
each infection category, V= numerical
values of infection categories, N= total
number of root or pods examined, 5=
constant, the highest numerical value.
2.3 Evaluation of certain antagonistic
bacteria against the pathogenic fungi
in vitro
The antagonistic bacteria were obtained
from MIRCEN, Faculty
of AgricUlture,
Ain Shams University, Cairo, Egypt. The
used bacteria in this study were five
isolates of
Azotobacter
spp. (AZ1, AZ2,
AZ3, AZ4 and AZ5), two isolates of
Bacillus
subtilis
(BS1 and BS2), two
isolates of
Bacillus
megaterium
(BM1
and BM2), one isolate of
Penibacillus
polymyxa
as well as two isolates of
Pseudomonas fluorescens
(PF1 and
PF2). These isolates were tested against
the most aggressive pathogenic
fungi
F.
solani
No. 7
,
R. solani
No. 6
and
M.
phaseolina
No.4
in
vitro.
The
antagonistic
bacteria were grown on
nutrient agar medium. Plates were
streaked with the bacterial growth which
obtained from 2 days old cultures at the
periphery using sterilized loop. At the
same time, one disc of the pathogen was
placed at the center of each plate, then
plates incubated at 27°C. Inoculated
plates with fungal disc without bacteria
82
served as control. When growth of the
pathogen covered the plate surface (9.0
cm in diameter) of control treatment,
antagonistic effect was determined by
measuring the free inhibition zone, then
percentage of mycelial growth inhibition
was calculated according to the formula:
Mycelial growth inhibition % = [A – B /A] × 100
Where: A = length of hyphal growth of
the control. B = length of hyphal growth
of the treatment.
2.4 Evaluation of some
Trichoderma
isolates against the pathogenic fungi
in
vitro
Petri dish was divided into equal halves.
The first half was separately inoculated
with standard disc (0.5 cm) of
Trichoderma
spp.
isolated from peanut
rhizosphere. The second half was
inoculated with an equal disc of
pathogenic fungi, each treatment was
replicated three times, and inoculated
plates with the pathogen
only were used
as control. All Petri dishes were
incubated at 27°C for 4 days and data
were recorded. The percentage of
mycelial growth inhibition was calculated
according to the following formula:
Mycelial growth inhibition % = [A – B /A] × 100
Where: A= the length of mycelial growth
in control. B= the length of mycelial
growth in treated Petri plates.
2.5 Evaluation of certain bioagents on
controlling peanut root and pod rots
diseases under greenhouse conditions
Pot experiments were carried out during
2019 and 2020 growing seasons. The
inoculum of
Trichoderma harzianum
isolates (T7 and T10) and isolate of
T.
asperellum
T34 as antagonistic fungi as
well as
F. solani
,
R. solani
and
M.
phaseolina
were grown on sorghum
medium as mentioned before in
pathogenicity tests and mixed with
sterilized soil at the rate of 2% (w/w) of
soil for each of antagonistic and
pathogenic fungi, 15 days before
planting. Also, seven antagonistic
bacteria
Azotobacter
spp. (AZ2 and
AZ5),
Bacillus
(BS1, BM2 and BP) and
Pseudomonas
fluorescens
(PF1 and PF2)
were applied as soil treatment 15 days
before planting by adding 100 ml of
bacterial suspensions (10
8
cfu /ml) for
each pot, which previously infested with
the pathogenic fungi. Seeds of peanut cv.
NC were sown (7 seeds /pot) in infested
soil with the pathogenic isolates as
mentioned before in the pathogenicity
tests experiments. After 100 days from
sowing, disease severity of peanut root
and pod rots diseases were recorded
(Hussin Zeinab, 2011).
2.6 Statistical analysis
Comparison of means was performed
using Fisher’s protected least significant
difference (LSD) at p≤0.05 (Gomez and
Gomez 1984) and the standard error was
calculated using the statistical analysis
software “CoStat 6.4” (CoStat, 2005).
83
3. Results and Discussion
3.1 Isolation and identification of the
causal pathogens of peanut root and
pod rots diseases
Thirty three fungal isolates were obtained
from the infected roots and pods of
peanut plants collected from different
localities in Minia, Assiut and Sohag
governorates, Egypt were identified as;
ten isolates as
Rhizoctonia solani
, seven
isolates as
M. phaseolina
, seven isolates
as
Fusarium solani
, three isolates as
Aspergillus
niger
, three isolates as
Aspergillus
flavus
and one isolate as
F.
moniliforme
,
F. equesti
and
F.
semitectum
.
3.2 Pathogenicity tests
Thirty three fungal isolates were tested to
study their pathogenic capability on
peanut cv. NC plants under greenhouse
conditions during 2017 growing season.
According to data presented in Table (1),
all tested fungal isolates proved
significantly to be pathogenic and
produced typical symptoms of pod and
root rots diseases on peanut plants.
Macrophomina phaseolina
No.4,
R.
solani
No. 6 and
F. solani
No.7 were the
most pathogenic as incited disease
severity of root rot 94%, 87%,
respectively and 82%, and disease
severity of pod rot 74%, 65% and 63%,
respectively on the tested peanut cv. NC.
On other hand, isolates
R. solani
No. 4
and
M. phaseolina
No. 2 followed by
A.
flavus
No. 2 showed the lowest disease
severity in peanut root rot disease, which
were 14%, 18% and 22% respectively.
While,
M. phaseolina
(No. 2 and No. 7),
A. flavus
No. 2 followed by
R. solani
and
F. solani
(No. 4 and 2) gave the lowest
disease severity of pod rot, as reached
14% and 19.5%, 20.25 and 21%,
respectively.
3.3 Efficacy of certain bacterial
bioagents against the causal pathogens
of peanut root and pod rots diseases
in
vitro
Data in Table (2) indicated that all test
bacterial bioagents were able to inhibit
the mycelial growth of all tested
pathogenic fungi compared with the
control.
Bacillus megaterium
BM2
recorded the highest reduction
percentage of mycelial growth of
M
.phaseolina
, followed by
Bacillus
subtilis
BS1 and
Bacillus
megaterium
BM1.
While, isolates
Azotobacter
spp. AZ5,
Pseudomonas fluorescens
PF1,
Azotobacter
spp. AZ2 and
Azotobacter
spp. AZ3 recorded the moderate degree
of inhibition against the same tested
pathogenic fungus.
Bacillus
megaterium
BM2,
Pseudomonas fluorescens
PF1,
Bacillus
subtilis
BS1 and
Azotobacter
spp. AZ5 showed the highest growth
inhibition against
Rhizoctonia
solani
,
while
Bacillus
subtilis
BS2,
Pseudomonas fluorescens
PF2,
Azotobacter
spp. AZ2 and
Penibacillus
polymyxa
BP showed moderate effects
on the mycelial growth of
R. solani
. On
other hand,
Azotobacter
spp. AZ5,
Bacillus
megaterium
BM2,
Azotobacter
spp. AZ2,
Bacillus
subtilis
BS1 and
Pseudomonas fluorescens
PF1 exhibited
the highest growth inhibition of
Fusarium
solani
, while
Bacillus
megaterium
BM1, (
Bacillus
subtilis
BS2,
Azotobacter
spp. AZ1,
Pseudomonas
fluorescens
PF2 and
Penibacillus
polymyxa
BP showed moderate effects
84
on the same pathogen. Generally, the
seven bacterial isolates (
Bacillus
subtilis
BS1,
Bacillus
megaterium
BM2,
P.
polymyxa
BP,
Pseudomonas fluorescens
PF1,
Azotobacter
spp. AZ2,
Azotobacter
spp. AZ5 and
Pseudomonas fluorescens
PF2)
achieved the highest records in
reducing mycelial growth of the three
tested pathogenic fungi. These results are
similar to those obtained by El-Mougy et
al
.
(2011)
who examined the influence of
the antagonistic isolates
B. subtilis
and
P.
fluorescens
and their culture filtrates
against soil-borne root rot pathogens
R.
solani
and
F. solani in vitro
. The tested
antagonists reduced the linear growth of
the fungal pathogens. Mahmoud et al.
(2006) tested seventeen bacterial isolates
in vitro
for their antagonistic effect
against
F. solani
and
M. phaseolina
and
they recorded that the most effective
isolates in reducing the mycelium growth
of pathogenic fungi were
P. fluorescens
followed by
B. subtills
and
Bacillus
sp.
Table 1: Pathogenicity tests of 33 fungal isolates on peanut cv. NC under greenhouse
conditions during 2017 growing season.
Fungal isolate
Isolate No.
Disease severity (%)
Root rot
Pod rot
Fusarium solani
1
58
42.5
2
23
21
3
64
25.75
4
75.5
55
5
50
34
6
52
32
7
82
63
Fusarium moniliforme
1
27
25
Fusarium semitectum
2
29
24
Fusarium equesti
3
43
25
Aspergillus niger
1
33
27.5
2
45
26.5
3
33.5
25.75
Aspergillus flavus
1
32
31
2
22
20.25
3
41
25.75
Rhizoctonia solani
1
36
22.25
2
35
27.25
3
57
32.5
4
14
21
5
59
40.5
6
87
65
7
44
25
8
44.5
30
9
25
34
10
42
41
Macrophomina phaseolina
1
29
26
2
18
14
3
27
24
4
94
74
5
24
28
6
39
24.25
7
37
19.5
Control
0
0
L.S.D. at 5%
4.5
4.94
85
Table 2: Antagonistic effects of various bacterial bioagents isolates against different pathogens of peanut pod
and root rots diseases.
Mycelial growth inhibition (%)
Bacterial isolate
Fusarium solani
Rhizoctonia solani
Macrophomina phaseolina
74
81.5
75.2
Bacillus subtilis BS1
59.2
74.8
9.2
Bacillus subtilis BS2
52.6
66.6
8.5
Penibacillus polymyxa BP
61.8
63
64
Bacillus megaterium BM1
79.3
89.6
78
Bacillus megaterium BM2
64
86.6
56
Pseudomonas fluorescens PF1
57.4
69
14
Pseudomonas fluorescens PF2
58
53
10.5
Azotobacter spp. AZ1
78
68
40
Azotobacter spp. AZ2
41
66.5
30
Azotobacter spp. AZ3
52.5
62.5
19.5
Azotobacter spp. AZ4
83
80
59.5
Azotobacter spp. AZ5
0
0
0
Control
4.34
4.19
4.34
L.S.D at 5%
3.4 Efficacy of dual culture of various
Trichoderma
isolates against the causal
pathogens of peanut root and pod rots
diseases
in vitro
Six isolates of
Trichoderma
spp.
were
tested to study their effect against
M.
phaseolina, R. solani
and
F. solani
, under
laboratory conditions. Data in Table (3)
indicated that all the tested isolates of
Trichoderma
spp.
exhibited different
degrees of reaction against
M.
phaseolina, R. solani
and
F. solani
. The
mycelial growth of
Trichoderma
spp.
T34 gave the high significant
antagonistic effect against the three tested
pathogenic fungi, followed by
Trichoderma
spp. T7 and
Trichoderma
spp. T10. While,
Trichoderma
spp. T9
exhibited the lowest antagonistic effect
on the fungal growth of tested pathogens.
The other isolates,
Trichoderma
spp. T5
and
Trichoderma
spp. T8 showed
moderate antagonistic effects on the
fungal growth of pathogens.
Trichoderma
spp. T7 and
Trichoderma
spp. T10 were
identified as
Trichoderma harzianum
.
While,
Trichoderma
spp. T34 identified
as
Trichoderma asperillum
. Generally,
T.
asperillum
T34
achieved the highest
records in reducing the mycelial growth
of the tested pathogenic fungi followed
by
T. harzianum
T7
,
respectively. These
results are similar to those obtained by
Ha (2010) who found that antagonistic
effect might be due to direct influence of
the tested fungi against pathogens
through coiling their hyphae around the
hyphae of the pathogens to prevent their
continued growth (Adekunle et al., 2006;
Chu & Wu, 1981). The antagonistic
properties of
Trichoderma
are based on
the activation of multiple mechanisms.
Trichoderma
strains act as biocontrol
agents against fungal phytopathogens
either indirectly or directly. Indirect
mechanism comprises competition for
nutrients and space, modification of the
environmental conditions, antibiosis and
induction of plant defensive mechanisms,
however direct mechanism encompasses
mycoparasitism (Harsukh et al., 2013).
3.5 Efficacy of certain bioagents on
controlling of peanut root rot disease
under greenhouse conditions
Data presented in Table (4) showed
that
86
tested bioagents significantly reduced the
disease severity of peanut root rot disease
compared with control.
Trichoderma
asperillum
T34,
Penibacillus polymyxa
BP,
Bacillus megaterium
BM2,
Azotobacter
spp.
AZ2 and
B. subtilis
BS1
exhibited the highest reduction of disease
severity of peanut root rot disease caused
by
M. phaeolina
recording 21.4, 24.38,
24.7, 24.8 and 28.5% respectively,
followed by
T. harzianum
T10 and
Pseudomonas fluorescens
PF2 with 37.2
and 38%, respectively. While
P.
fluorescens
PF1 recorded the lowest
reduction of disease severity, followed by
Azotobacter
spp. AZ5 and
T. harzianum
T7 (49, 45.22 and 43%, respectively).
Azotobacter
spp. AZ2,
T. asperillum
T34
and
T. harzianum
T10 exhibited the
highest reduction of disease severity of
peanut root rot disease caused by
R.
solani
(21.48, 21.57 and 25.7%,
respectively). In this respect,
B. subtilis
BS1,
P. polymyxa
BP,
B. megaterium
BM2 and
P. fluorescens
PF2 showed
moderate effects of the disease severity
reduction. While,
P. fluorescens
PF1
exhibited the lowest reduction of disease
severity of peanut root rot disease caused
by
R. solani
followed by
T. harzianum
T7 and
Azotobacter
spp. AZ5 with 43.8,
42.79 and 40%, respectively.
Bacillus
subtilis
BS1,
Azotobacter
spp. AZ2 and
T. asperillum
T34 isolates showed the
greatest decrease in disease severity
caused with the pathogen
F. solani
, as
reached
19, 19, and 23.3% respectively.
While, isolate
P. fluorescens
PF2
recorded the lowest reduction of the
disease severity followed by
Azotobacter
spp. AZ5 (40.94 and 35.7%
respectively). Such results are in line
with those reported by Gowily Ahlam et
al. (1993),
who found that inoculation
with
A. chroococcum
,
A. brasilense
and
B. japonicum
reduced soybean root-rot
disease caused by
R. solani
and
F. solani
.
El-Habbaa et al
.
(2002)
suggested that
addition of
Rhizobium
and
B. subtilis
to
soil before sowing peanut seeds
significantly reduced root-rot disease of
peanut caused by
S. rolfsii
,
R. solani, M.
phaseolina
and
F. solani
.
Mahmoud et
al. (2006) and Ibrahim
et al
.
(2008)
studied the effects of certain bacterial
isolates against
R. solani
,
S. rolfsii, F.
solani
and
M. phaseolina
causing root rot
disease of peanut in greenhouse
experiments and they were found that the
most effective isolates in reducing the
diseases of peanut were
P. fluorescens
followed by
B. subtills
and
Bacillus
sp.
Vargas et al
.
(2008) mentioned that
inoculation with
Trichoderma
spp.
recorded the lowest incidence of peanut
root rot disease caused by
F. solani
.
Table 3: Antagonistic effects of dual culture of various Trichoderma spp. isolates against different
pathogens of peanut pod and root rots diseases.
Mycelial growth inhibition (%)
Fungal isolate
Fusarium solani
Rhizoctonia solani
Macrophomina phaseolina
77
77.8
69
Trichoderma spp. T5
83.3
89
77
Trichoderma spp. T7
73.5
80
72.2
Trichoderma spp. T8
72
77
66.7
Trichoderma spp. T9
77
83.3
83.3
Trichoderma spp. T10
83.3
92
80
Trichoderma spp. T34
0
0
0
Control
5.63
5.12
5.9
L.S.D at 5%
87
Table 4: Effect of certain bioagents on disease severity percentages of peanut root rot disease under greenhouse
conditions during 2019 and 2020 growing seasons.
Bioagents isolate
Disease severity (%)
Macrophomina phaseolina
Rhizoctonia solani
Fusarium solani
2019
2020
Mean
2019
2020
Mean
2019
2020
Mean
Bacillus subtilis BS1
24.7
31.4
28.05
23.2
31.42
27.31
20
18
19
Bacillus megaterium BM2
28.55
20.9
24.7
21.87
36.18
29
23.76
31.41
27.6
Pseudomonas fluorescens PF1
45.7
52.36
49
37.14
50.45
43.8
27.6
24.73
26.2
Pseudomonas flurescens PF2
35.23
40.95
38
36.2
40.9
38.55
34.27
47.61
40.94
Azotobacter spp. AZ2
20.18
29.5
24.84
18.26
24.7
21.48
15.23
22.83
19
Azotobacter spp.AZ5
41.9
48.55
45.22
33.32
46.65
40
28.55
42.85
35.7
Penibacillus polymyxa BP
25
23.67
24.38
32.36
22.8
27.58
30.45
39
34.7
Trichoderma harzianum T7
40.9
45.2
43
41.9
43.68
42.79
33.32
35.23
34.3
Trichoderma harzianum T10
39
35.2
37.2
23.8
27.6
25.7
29.5
40.95
35.22
Trichoderma asperillum T34
25.69
17.14
21.4
26
17.14
21.57
24.73
21.86
23.3
Control
87.61
90.33
88.97
80
85.6
82.8
72.36
76
74.2
L.S.D at 5%
4.72
4.48
3.28
5.92
4.04
3.62
3.3 Efficacy of certain bioagents on
controlling of peanut pod rot disease
under greenhouse conditions
Data presented in Table (5) showed
that
treated soil with all bacterial and fungal
bioagents significantly reduced the
disease severity of peanut pod rot
disease compared with the control.
Trichoderma asperillum
T34,
Azotobacter
spp. AZ2,
Penibacillus
polymyxa
BP and
Bacillus subtilis
BS1
recorded the highest reduction of
disease severity of peanut pod rot
disease caused by
M. phaeolina
(32.48,
34.48, 36.83 and 37.5% respectively),
while BM2,
T. harzianum
T7 and
T.
harzianum
T10 gave moderate effects
of the reduction of the disease severity
(39.15, 40 and 40.5%, respectively).
Trichoderma asperillum
T34,
Azotobacter
spp. AZ2 and
B. subtilis
BS1 achieved the highest reduction of
disease severity of peanut pod rot
disease caused by
R. solani
(30.33,
30.65 and 30.98%, respectively).
Table 5: Effect of certain bioagents on disease severity percentages of peanut pod rot disease under greenhouse
conditions during 2019 and 2020 growing seasons.
Bioagents isolate
Disease severity (%)
Macrophomina phaseolina
Rhizoctonia solani
Fusarium solani
2019
2020
Mean
2019
2020
Mean
2019
2020
Mean
Bacillus subtilis BS1
35
40
37.5
31.67
30.3
30.98
30.3
21.67
25.98
Bacillus megaterium BM2
42
36.3
39.15
38.3
29
33.65
31.67
18.67
25.17
Pseudomonas fluorescens PF1
50.67
45.67
48.17
45.67
47.67
46.67
40.3
38.67
39.33
Pseudomonas flurescens PF2
47.67
41.67
44.67
43.67
37.67
40.67
41.67
37
39.48
Azotobacter spp. AZ2
36.67
32.3
34.48
35
26.3
30.65
35
17.3
26.15
Azotobacter spp.AZ5
49
50.3
49.65
42.67
46.3
44.48
45.3
40.67
42.98
Penibacillus polymyxa BP
43.67
30
36.83
36.67
33.67
35.17
43.67
44.3
43.98
Trichoderma harzianum T7
44
36
40
40
40.3
40.15
36.67
30
33.33
Trichoderma harzianum T10
48
33
40.5
41.67
32.3
36.98
37.3
35
36.15
Trichoderma asperillum T34
38.67
26.3
32.48
39
21.67
30.33
28
25.67
26.83
Control
87.3
77
82.15
80.67
72
76.33
77
71
74
L.S.D at 5%
3.3
2.55
2.88
3.06
3.17
2.9
Bacillus megaterium
BM2,
P. polymyxa
BP,
T. harzianum
T10 and
T. harzianum
T7 showed moderate reduction of the
disease severity (33.65, 35.17, 36.98 and
88
40.15%, respectively).
Bacillus
megaterium
BM2,
B. subtilis
BS1 and
Azotobacter
spp. AZ2 achieved the
highest reduction of disease severity of
peanut pod rot disease caused by
F.
solani
(25.17, 25.98 and 26.15%,
respectively). Generally,
P. fluorescens
PF1,
Azotobacter
spp. AZ5 and PF2 gave
the lowest reduction of disease severity
of pod peanut rot disease caused by the
three fungal pathogens
M. phaseolina,
R. solani
and
F. solani
. The results
obtained are in agreement with both
Mahmoud (2004)
and Ziedan (2000) who
found that
B. subtilis
and
P. fluorescens
significantly reduced incidence of all
types of pod rots caused by
Fusarium
spp
.
Ahmed (2006)
revealed the
superiority of
T. harzianum
followed by
commercial products
Rhizo-N and Plant-
guard which showed high reduction of
pod rot disease of peanut caused by the
R. solani, M. phaseolina, S. rolfsii
and
F.
moniliforme
. Plant growth promoting
rhizobacteria are applied as active
ingredients in several commercial bio-
inoculants. Each product has special set
of mechanisms for plant growth
promotion and biocontrol of plant
pathogens. In the same way,
Trichoderma
spp. parasitize other fungi
and induce systemic resistance in host
plants (Harman, 2011).
As for, bacteria
produce siderophore and provide N, P
and Fe for plant growth, release several
antibiotics and volatiles for suppression
of plant pathogens (Sharifi and Ryu,
2016; Sharifi et al., 2010), as well as
improve plant health and compete with
plant pathogens by colonizing root
tissues (Ghanbarzadeh et al., 2016). The
efficiency of
T
.
harzianium
to inhibit
fungal growth may be through
competition for space and nutrients,
mycoparasitism and production of
antibiotic compounds. It was found that
the hyphae of
T
.
harzianium
coil around
the hyphae of the pathogen and penetrate
the host mycelium through degrading
cell wall by secretion hydrolytic
enzymes followed by assimilation of cell
contents (Siameto et al., 2011; Howell,
2006).
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