Journal of Phytopathology and Pest Management 7(1): 91-108, 2020
pISSN: 2356-8577 eISSN: 2356-6507
Journal homepage: http://ppmj.net/
∗
Corresponding author:
Mohamed A. Eliwa,
E-mail: mohamedeliwa.5419@azhar.edu.eg
91
Copyright © 2020
Evaluation of different chemicals to control
Erysiphe
betae
the causal pathogen of sugar beet powdery mildew
Mohamed M. El-Sheikh Aly
1
, Ali H. ElShaer
2
, Anwar A. Galal
3
, Harbi M. Abd-Alla
3
, Mohamed A. Eliwa
1*
1
Agricultural Botany Department, Faculty of Agriculture, Al-Azhar University, 71524 Assiut, Egypt
2
Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
3
Plant Pathology Department, Faculty of Agriculture, Minia University, Minia, Egypt
Abstract
Keywords: sugar beet, powdery mildew, Erysiphe betae, macronutrients, fungicides.
92
1. Introduction
Sugar beet (
Beta vulgaris
L.), is an
herbaceous dicotyledonous plant belongs
to family Amaranthaceae (formerly
Chenopodiaceae). It is considered as one
of the two major sugar crops around the
world and an important crop of temperate
climates which provides nearly 40% of
the world’s annual sugar production and
is a source for bioethanol and animal feed
(Bastas and Kaya, 2019). Under field
conditions, several pathogenic fungi
attack sugar beet plants causing serious
diseases
i.e
., Cercospora leaf spot
(
Cercospora beticola
Sacc.) and rust
(
Uromyces betae
Press). Sugar beet
powdery mildew which is caused by
Erysiphe betae
(Vanha) Weltzien is
among the most important foliar diseases
of sugar beet worldwide (Gobarah &
Mekki, 2005). The disease is
economically significant for growers
worldwide and can cause sugar yield
losses up to 30 % (Francis, 2002). Gado
(2013) reported that powdery mildew is
considered as a major foliar disease of
sugar beet in areas with dry and relatively
warm weather conditions throughout the
world, devastating foliar disease affecting
plant growth and consequently sugar
production. Egyptian environmental
conditions help the fungus to spread
rapidly specially in the late sowings after
September. Losses in sucrose could reach
82.9 % for some cultivars due to powdery
mildew infection. Total soluble solids
percent and root weight were
dramatically affected by disease severity
under infected conditions (El-Fahhar,
2008).
Grimmer et al
.
(2007) reported
that if the disease is not controlled it can
cause a 20 to 35 percent loss in sugar
yield. Crop loss is due to a reduced root
yield and often to a lower concentration
of sugar in roots. Both effects apparently
are due to a reduced efficiency of
diseased leaves and to their premature
death, when roots are rapidly enlarging.
As part of the environment, nutrients
influence plant, pathogen and microbial
growth to remain an important factor in
disease control. The interaction of
nutrition in these components is dynamic
and all essential nutrients are reported to
influence the incidence or severity of
some diseases, mineral nutrients are the
components of plants and regulate
metabolic activity associated with
resistance of a plant and virulence of a
pathogen. Adequate nutrition is generally
required to maintain a high level of
disease resistance. Nutrient sufficiency
also may shorten a susceptible growth
stage for some plant-pathogen
interactions
(Huber & Haneklaus, 2007).
Macronutrients are well recommended as
fungicide alternatives for enhancing plant
health, subsequently inducing plant
resistance and controlling the disease in
parallel with their safe influence on
human health (Huber & Haneklaus,
2007). Control of sugar beet powdery
mildew is mainly achieved by
applications of broad spectrum systemic
fungicides
(Byford, 1996).
Although, the
wide spread use of the chemical
fungicides has become a subject of
research concern due to their harmful
effect on non-target organisms as well as
their possible carcinogenicity (Ziedan &
Farrag, 2011). However, further studies
should concern safe, applicable, reliable
and efficient replacement of chemical
fungicides by other safer chemical or
natural compounds harmless to plants or
human health. The objectives of this
study were to (1) investigate the spread
of sugar beet powdery mildew disease in
some governorates in Upper Egypt and
(2) to assess the role of some different
chemical compounds on reducing
powdery mildew disease incidence on
sugar beet.
93
2. Materials and methods
2.1 Survey of sugar beet powdery
mildew
Survey of sugar beet powdery mildew
was conducted in different districts of
two Governorates (3 districts) namely
Abnob, Dayrot and Manfalot (Assiut
Governorate) and Maghagha, Samallot
and AbuQurkas (El-Minia Governorate),
Egypt. At least 3 fields of each district
were concerned. Each field under survey
was determined with a field map, 5
sampling sites were designated per field
tested and one of each of the four corners
plus one in the center of the field.
Sampling sites were located at least 5
meter from the edge of the field (Ray &
McLaughlin, 1942). Severity of powdery
mildew was monitored 4 times at 20
days’ intervals. Area under disease
progress curve was conducted.
2.2 Powdery mildew disease
assessment
Evaluation of disease severity was
accomplished by examining both sides of
leaves and rating disease intensity as the
extent of leaf area covered by the fungus
mycelium on a scale of 0 to 4. Disease
severity was determined according to the
scale by Whitney et al. (1983). Scale
ranged from 0- 4 categories whereas 0=
no mildew colonies observed, 1=1-25%,
2=26-50%, 3=51-75% and 4=76-100% of
matured leaf area covered by mildew.
Area Under Powdery Mildew Progress
Curve (AUPMPC) was calculated for the
assessment period using the following
equation adopted by Chiha et al. (1997):
AUPMPC = D (1/2 (Y
1
+Y
k
) + (Y
2
+Y
3
k-1
)
Where: D= Time interval; Y
1
= First
disease score; Y
k
= Last disease score;
Y
2
and Y
3
= Intermediate disease score.
2.3 Estimating conidia survival
Greenhouse experiment was conducted
in 3 m × 3 m area well-isolated protected
one to study how long the time of
powdery mildew conidia still able to
attack sugar beet plants and initiate the
disease. Only powdery mildewed sugar
beet leaves were collected from the most
susceptible cv. FD.0807 grown under
open field and dried carefully on
sterilized benches with 70 % ethyl
alcohol to avoid rottenness, then packed
in plastic bag and stored at room
temperature until used. Two sugar beet
cultivars Sirona and F.D.0807 were sown
(4 seeds /pot) in 30 cm diameter plastic
pots, filled with sterilized sandy clay soil,
nine pots for each cultivar in three
replicates, each replicate consisted of
three pots and nine pots of each cultivar
which were isolated apart by thin white
plastic sheets served as control. Artificial
inoculation was done 60 days from
planting by shaking dried diseased sugar
beet leaves (after five months of storage)
over the growing plants at a height of
about 30cm. Disease severity was
estimated after seven days of inoculation.
2.4
In vitro
conidia germination tests
Conidia germination test was carried out
using light microscope, slides were
washed in 50 percent alcohol and wiped
with a cloth to remove inert particles in
order to prevent condensation of free
moisture on the glass surface at very high
relative humidity levels. The conidia
were detached and collected by
94
vigorously shaking infected leaves over
the glass slides placed at the bottom of a
plastic container 20×20×10 cm
3
. In order
to reduce variation in germination and to
obtain reproducible results, only 24 h old
conidia were utilized. For this purpose,
the plants were shaken every day to
prevent accumulation of old and
shriveled spores. Each slide was placed
on a U-shaped glass rod in a moist
chamber made up of sterile Petri dish
lined with filter paper saturated with
sterile distilled water. Petri dishes were
incubated at 25±2°C (Awad et al., 1990)
for 24 h before examination. One set of
chambers was kept in the light and
another in darkness. Three slides were
used as replicates for each particular
treatment. The percentage of germination
was based on the following formula:
2.5 Scanning electron microscopic
examination
Sample preparation: In order to study the
three dimensional structure through
scanning electron microscope (SEM) of
the haustoria and the infection mode on
the susceptible cultivar FD.0807, fresh
infected leaves (120 days old, 48 h after
symptom appearance) were collected, put
in paper bag and carried to Electron
Microscope Unit at Assiut University,
Egypt. The leaves were cut into
appropriate samples and were subjected
to fixation in 5 % cold buffered
gluteraldehyde for 2 days. The samples
were then washed by cacodylate buffer
for three times thirteen minutes for each
and post fixed in 1% osmium tetroxide
for 2 h. Samples were then washed in
cacodylate buffer for three times thirteen
minutes each and then dehydrated by
using ascending series of ethanol 30, 50,
70, 90 for 2 h, 100 % for two days, and
then to amyl acetate for two days.
Critical point drying was applied to the
samples by using liquid carbon dioxide.
Each sample was sticked on metallic
blocks by using silver paint. By using
gold sputter coating apparatus, samples
were evenly gold coated in a thickness of
15 nm (Bozzola et al.
,
1991).
2.6 Control of powdery mildew disease
Experiments were carried out at the
experimental field of the Faculty of
Agriculture, Al-Azhar University, Assiut,
Egypt during 2014/2015 and 2015/2016
growing seasons. Resistant and
susceptible sugar beet cultivars Sirona
and FD.0807, respectively were selected
for the experiments of powdery mildew
disease control. Field plots consisted of
two rows (9 m long and interspace
between plant and another 20 cm) and
arranged in a split plot design with three
replicates per treatment. One plot was
specified for one tested compound and
one plot was left for control. Field was
fertilized and irrigated as usual. Plants
were thinned to one plant /hole and left
for natural infection. Large area around
the plots was left without treatment to
avoid any contamination by any treated
chemicals from neighboring fields
(Gado, 2013).
2.6.1 Time of application
Treatment applications were started 105
days after sowing (the first sign of the
disease has appeared). Plants were
sprayed five times during each season
with 20 days’ intervals. Disease severity
95
was determined (5 times) in order to
evaluate treatments after ten days from
each time of spraying of tested
compounds. Solutions of each tested
compounds were applied using a hand
sprayer, at a volume of 2 liters of tap
water per plot (until run off). Thirty
plants were used for each treatment.
Plants without spraying were served as
control. AUPMPC values were calculated
as described before.
2.6.2 Estimation of total soluble solids
(TSS) percentage and root weight of
the treated sugar beet plants
At harvest, three replicate samples, each
sample of thirty roots for five sprays
treatments were randomly collected for
determination of root weight and sugar
analysis. Juice analysis were done by
using a digital refractometer to determine
TSS % of root juice and a precise hand
scale was used to measure root weight.
2.6.3 Effect of applying macronutrients
on the disease severity
Three chemical compounds containing
macronutrients
i.e.
calcium chloride,
potassium silicate and sodium
bicarbonate were tested to study their
effect against powdery mildew disease of
sugar beet plants Sirona cv. and
F.D.0807 line. Each compound was used
as foliar spraying at the concentrations of
0.1, 0.2 and 0.3 g /l. Sugar beet plants
were sprayed after 105, 125, 145, 165
and 185 days from sowing date. Bellis®
38 % WG Fungicide was used as a
comparative treatment which applied in
the dosage (0.5 g/l) as cited in its user
manual sheet as recommended by the
manufacturer (BASF™).
2.6.4 Effect of fungicides
In the study, the used fungicides were
Bellis 38 %
(25.2 % w/w boscalid and
12.8 % w/w pyraclostrobin), Collis 30 %
(20 % w/v boscalid and 10 % w/v
kresoxim–methyl), Camzin 50 %
(50 %
w/w carbendazim), Tilt 25 %
(25 % w/v
Propiconazole) and Permatrol 99 %
(99
% v/v Jojoba oil). Fungicides were
applied at the recommended dosage as
summarized in Table (1).
Table 1: Trade name, group name, chemical group, common name, recommended doses and
production Company of tested fungicides.
Trade name
Group name
Chemical group
Common name
Recommended
dose
Production
company
Bellis® 38% WG
Succinate dehydrogenase
inhibitors
Pyridine-
carboxamides
Boscalid
50 g/l
BASF™
Quinone outside Inhibitors
Methoxy-
carbamates
Pyraclostrobin
Collis® 30% SC
Succinate dehydrogenase
inhibitors
Pyridine-
carboxamides
Boscalid
50 ml/l
BASF™
Quinone outside Inhibitors
Oximino-acetates
Kresoxim-methyl
Camzin® 50% WP
Methyl Benzimidazole
Carbamates
Benzimidazoles
Carbendazim
75 g/l
CAM™
Tilt® 25% EC
DeMethylation Inhibitors
Triazoles
Propiconazole
15 ml/l
Syngenta
™
Permatrol™ 99% Oil
---------
-------
Jojoba oil
1000 ml/l
Soiltech™
96
2.6.5 Disease reduction
Disease reduction percent was calculated
according to
Ismail et al. (2012) as
follows:
2.7 Statistical analysis
Analysis of variance of the data was
carried out on the mean values of the
tested treatments according to the
procedures described by Gomez and
Gomez (1984). The least significant
difference (LSD) at 5% probability was
used for testing the significance of the
differences among the mean values of the
tested treatments for each character.
3. Results
3.1 Survey of sugar beet powdery
mildew
Data in Table (2) represent the survey of
powdery mildew disease which took
place in Assiut and Minia governorates
during 2012/2013 growing season. Data
showed that the highest AUPMPC value
was detected in Abnob locality followed
by Manfalot then Dayrot while, the
lowest AUPMPC value was found in
Maghagha locality followed by
AbuQurkas and Samallot localities
respectively.
3.2 Survival of conidia
Greenhouse experiment was conducted
on 2014/2015 growing season to
determine the overwintering capability of
vegetative mycelia and conidia of
Erysiphe betae
and their role in the
dissemination of the fungus. Obtained
results from consecutive observations
confirmed that the conidia collected from
the previous season (2013/2014) could
not initiate any type of infection or
disease symptoms which means that the
conidia could not survive as long as it
were stored in this experiment and the
conidia that remains on the crop debris at
the end of the season are not one of the
means which used by the fungus for its
overwintering.
Table 2: Area under powdery mildew progress curve (AUPMPC) values on sugar beet
plants (Glorius, Sirona and Samba cultivars) grown in different districts of Assiut and El-
Minia governorates, Egypt.
Governorate
District
Cultivar
AUPMPC
Assiut
Abnob
Glorius
660 ±1
Dayrot
Sirona
322 ±1
Manfalot
Samba
442 ±1
Minia
Maghagha
Sirona
118 ±1
Samallot
Glorius
190 ±1
AbuQurkas
Samba
228 ±1
Mean
------------
327 ±1
LSD at 0.05
53.9
3.3
In vitro
conidia germination tests
The purpose of this experiment was to
make a preliminary study on the
germination percentages of
E. betae
conidia on glass slides at 100 % relative
97
humidity at room temperature (25±2°C),
in light and in darkness. As shown in
Table (3) the percent germination in
darkness was lower than in light. A high
percentage of germinating conidia
formed appressorium on dry glass slides.
One appressorium was formed by the
germ tube of each conidium. The
appressorium formation was not affected
by light or darkness. The conidia of
Erysiphe betae
germinated at a fast rate
within 8 to 10 h of incubation. In the
same time 100 % relative humidity (RH)
was sufficient enough to prevent conidia
from shriveling.
Table 3: In vitro conidia germination percent at
light and darkness conditions.
Incubation conditions
Germination (%)
Light
74
Darkness
58
LSD at 0.05
18.27
3.4 Scanning electron microscope
examination
First observation on the scanning electron
microscopy (SEM) images of the
infection method of sugar beet with
powdery mildew pathogenic fungus
E.
betae
is that it penetrated the epidermis
of the leaves by the haustoria as shown in
Figure (1). On upper leaf surface, a great
amount of conidia was visible and
haustoria as well. Outer surface of the
haustoria is rough and wavy. The
haustoria are folded in many patches
forming a complex web which almost
completely covers the leaf. Haustoria
penetrated the leaf as a drilling machine
resulting at the side parts pieces of
mesophyll which are folded at the bottom
of the haustoria. It was clearly observed
that haustoria penetrated the stomata of
the leaf easily and successfully. The
convoluted haustoria penetrated the leaf
epidermis in many points infecting the
entire leaf surface. The haustoria were
convoluted and folded in multiple ways.
They entered perpendicularly the leaf
from the top. There were visible several
conidiphores formed, preparing new
source of secondary infection. The
entering zone of the haustoria, the hyphal
part is thickened, being like a connection
tube between the fungus and the leaf.
3.5 Effect of applying macronutrients
on disease severity of sugar beet
powdery mildew
Three compounds containing
macronutrients were tested for their
ability to control powdery mildew
disease on sugar beet. Data in Table (4)
showed that all the tested macronutrients
significantly reduced AUPMPC values
when sugar beet plants were sprayed
with them. It was noticed that increasing
macronutrients concentration sub-
sequently increased resistance of sugar
beet plants against powdery mildew
disease. The lowest (AUPMPC) on both
cultivars Sirona and FD.0807
respectively was achieved by 0.3 g/l of
sodium bicarbonate followed by 0.3 g/l
of calcium chloride and 0.2 g/l of sodium
bicarbonate respectively. The highest
(AUPMPC) was obtained by 0.1 g/l of
potassium silicate. The best treatment
(0.3 g/l sodium bicarbonate) was higher
in (AUPMPC) value than the tested
fungicide Bellis® 38 % WG.
98
Figure 1: Scanning microscope of haustoria and conidia where a: mature conidiospore freshly separated,
initiating germination tube turned towards a stoma on the adaxial leaf surface, note the root-like
appendages at the bottom trying to attach itself to the leaf, b: detached mycelial fragment with single
haustorium in the middle and about to enter a stoma, c: a network of hyphae on the abaxial surface of leaf
48 h after inoculation, successful penetration into the mesophyll (1), single haustorium seeking for stoma
(2) and fresh separated conidiospore ready for germination (3), d: magnifying successful penetration into
the mesophyll, e: one single haustorium about to enter an opened stoma on the abaxial leaf surface (1) and
two short conidiophores, each has single aged shriveled conidiospore at the top (2) and f: Enlarged view of
haustorium actually penetrated the mesophyll; using physical pressure is clear from the bending backward
resulted in visible folding in the upper side of the haustorium.
Table 4: AUPMPC values of sugar beet cultivars Sirona and FD.0807 as affected by macro nutrients
foliar spray under field conditions during 2014/2015 and 2015/2016 growing seasons.
Treatment
Conc. (g/l)
AUPMPC
cv. Sirona
cv. FD.0807
2014/2015
2015/2016
Mean
Disease
reduction (%)
2014/2015
2015/2016
Mean
Disease
reduction (%)
Calcium chloride
0.1
574
552
563 ±1
19.3
842
851
846 ±1
48.8
0.2
472
464
468 ±1
32.9
687
702
694 ±1
58
0.3
360
354
357 ±1
48.8
618
606
612 ±1
62.9
Mean
468
456
462 ±1
33.71
715
719
717 ±1
56.58
Potassium silicate
0.1
651
630
641 ±1
8.1
1070
1068
1069 ±1
35.3
0.2
582
597
589 ±1
15.6
922
910
916 ±1
44.5
0.3
514
495
504 ±1
27.7
801
772
786 ±1
52.4
Mean
582
574
578 ±1
17.16
931
916
923 ±1
44.11
Sodium bicarbonate
0.1
541
530
536 ±1
23.2
855
819
837 ±1
49.3
0.2
430
410
420 ±1
39.8
665
686
675 ±1
59.1
0.3
339
298
318 ±1
54.4
608
582
595 ±1
64
Mean
436
412
424 ±1
39.15
709
695
702 ±1
57.5
Bellis® 38% WG
78
68
73 ±1
89.5
191
138
165 ±1
90
Control
721
675
698 ±1
0.0
1652
1653
1653 ±1
0.0
LSD at 0.05
Treatment (T)
29.3
20.2
-----
-----
24.3
16.9
-----
-----
Concentration (C)
7.1
24.5
-----
-----
16.4
15.5
-----
-----
(T × C)
15.8
54.7
-----
-----
36.8
34.7
-----
-----
3.6 Estimation of total soluble solids
(TSS) contents of sugar beet plants
treated with macronutrients
Data in Figure (2) showed that the TSS
percentage in the roots of infected sugar
beet plants (Sirona and FD.0807
cultivars) and treated with the
compounds containing microelements
was increased significantly by all used
compounds as compared to control.
Sodium bicarbonate achieved the highest
99
TSS percentage at all rates of application
followed by calcium chloride, while
potassium silicate achieved the least TSS
percentage.
Figure 2: TSS percent in roots of sugar beet cultivars (Sirona and FD.0807) as affected by
macronutrients foliar spray under field conditions during 2014/2015 and 2015/2016 growing seasons.
3.7 Evaluation of root weight of sugar
beet plants treated with macro-
nutrients
Data in Figure (3) showed that the root
weight of infected sugar beet plants
(Sirona and FD.0807 cultivars) and
treated with the compounds containing
microelements was increased
significantly by all used compounds as
compared with the control. Sodium
bicarbonate achieved the highest root
weight at all rates of application followed
by calcium chloride, while potassium
silicate achieved the least root weight. In
general, the root yield representing in
their weight and TSS content inversely
related to the severity of the disease.
Significant differences among the tested
compounds and each other were noticed.
It was also noticed that there was
significant differences between the
treatments with the three different
concentrations.
3.8 Evaluation of the effect of
fungicides on controlling sugar beet
powdery mildew
Commercial fungicides were tested for
controlling sugar beet powdery mildew
on Sirona and FD.0807 cultivars under
field conditions in both 2014/2015 and
2015/2016 growing seasons. Data
represented in Table (5) revealed that in
case of Sirona cultivar Bellis 38 % was
significantly the most effective fungicide
in controlling the disease followed by
Collis 30 % then Tilt 25 %, Camzin +
Tilt and Camzin 50 % respectively while,
Permatrol 99 % came in the last rank.
Concerning FD.0807 cultivar in both
2014/2015 and 2015/2016 growing
seasons, Bellis 38 % WG was
significantly the most effective fungicide
followed by Collis 30 % SC then Tilt 25
% EC, Camzin + Tilt and Camzin 50 %
WP respectively while, Permatrol 99 %
came in the last order. In general, all
fungicides reduced the disease
significantly as compared with the
control, but each to a different extent.
0
5
10
15
20
25
Calcium
chloride
100ppm
Calcium
chloride
200ppm
Calcium
chloride
300ppm
Potassium
silicate
100ppm
Potassium
silicate
200ppm
Potassium
silicate
300ppm
Sodium
bicarbonate
100ppm
Sodium
bicarbonate
200ppm
Sodium
bicarbonate
300ppm
Bellis®
38% WG
Control
T.S.S. % Sirona 2014/2015 T.S.S. % Sirona 2015/2016
T.S.S. % FD.0807 2014/2015 T.S.S. % FD.0807 2015/2016
100
Figure 3: Root weight (Kg /plant) of sugar beet cultivars (Sirona and FD.0807) as affected by
macronutrients foliar spray under field conditions during 2014/2015 and 2015/2016 growing seasons.
Table 5: AUPMPC values for sugar beet cultivars Sirona and FD.0807 affected by fungicides foliar spray under
field conditions during 2014/2015 and 2015/2016 growing seasons.
Fungicides (Trade name)
Concentration
AUPMPC values for cultivars
Sirona
FD.0807
2014/2015
2015/2016
Mean
Disease
reduction (%)
2014/2015
2015/2016
Mean
Disease
reduction (%)
Bellis 38% WG
50 g
78
68
73±1
89.5
191
138
165±1
90
Collis 30% SC
50 ml
116
125
121±1
82.6
245
210
228±1
86.2
Camzin 50% WP
75 g
256
269
263±1
62.3
548
561
555±1
66.4
Tilt 25% EC
15 ml
123
139
136±1
80.5
310
275
293±1
82.2
Camzin 50% + Tilt 25%
75 g + 15 ml
186
189
188±1
73
372
391
381±1
76.9
Permatrol (Jojoba oil) 99%
1000 ml
663
592
628±1
10
944
885
915±1
44.6
Control
--------
721
675
698±1
0.0
1652
1653
1653±1
0.0
LSD at 0.05
17.5
22.6
--------
--------
52.6
36.5
--------
--------
3.9 Total soluble solids (TSS) contents
of sugar beet plants treated with
fungicides
Data in Figure (4) showed that the
highest TSS percentage was detected in
the roots of sugar beet plants (cv. Sirona)
naturally infected with powdery mildew
and treated with Bellis 38 % WG
fungicide followed by Tilt 25 % EC then
Collis 30 % SC, Camzin + Tilt and
Camzin 50 % WP respectively while, the
lowest significant TSS percentage was
detected after treatment by permatrol
99%. Concerning sugar beet cultivar
(FD.0807), the highest TSS percentage
was detected in the roots of sugar beet
plants treated with Bellis 38% WG
followed by Collis 30 % SC then Tilt 25
% EC, Camzin + Tilt and Camzin 50 %
WP respectively. On the other hand,
Permatrol 99 % treatment significantly
recorded the lowest TSS percentage.
3.10 Estimation of root weight of sugar
beet plants treated with fungicides
Data in Figure (5) showed that the
highest root weight of sugar beet plants
(cv. Sirona) infected with powdery
mildew was achieved by treating plants
with Bellis 38 % WG followed by Collis
30 % SC then Tilt 25 % EC, Camzin +
Tilt and Camzin 50 % WP respectively
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Calcium
chloride
100ppm
Calcium
chloride
200ppm
Calcium
chloride
300ppm
Potassium
silicate
100ppm
Potassium
silicate
200ppm
Potassium
silicate
300ppm
Sodium
bicarbonate
100ppm
Sodium
bicarbonate
200ppm
Sodium
bicarbonate
300ppm
Bellis®
38% WG
Control
Root weight (Kg/plant) Sirona cv. 2014/2015
Root weight (Kg/plant) Sirona cv. 2015/2016
Root weight (Kg/plant) FD.0807 L. 2014/2015
Root weight (Kg/plant) FD.0807 L. 2015/2016
101
while, Permatrol 99 % significantly
recorded the lowest root weight of sugar
beet plants naturally infected with
powdery mildew.
Figure 4: TSS % in roots of sugar beet cultivars Sirona and FD.0807 as affected by fungicides foliar spray
under field conditions during 2014/2015 and 2015/2016 growing seasons.
Figure 5: Root weight (Kg/plant) of sugar beet cultivars (Sirona and FD.0807) as affected by fungicides
foliar spray under field conditions during 2014/2015 and 2015/2016 growing seasons.
Whereas, the highest root weight of
sugar beet plants (cv. FD.0807) infected
with powdery mildew was achieved by
treating plants with Bellis 38 % WG
followed by Collis 30 % SC then Tilt 25
% EC, Camzin + Tilt and Camzin 50 %
WP respectively while, Permatrol 99 %
significantly recorded the lowest root
weight of sugar beet plants naturally
infected with powdery mildew. In
general, all treatments significantly
increased root yield as compared to
control, except Permatrol 99 % in the
case of Sirona cultivar.
0
5
10
15
20
25
Bellis 38% WG Collis 30% SC Camzin 50% WP Tilt 25% EC Camzin 50% + Tilt
25%
Permatrol (Jojoba oil)
99%
Control
T.S.S. % Sirona 2014/2015 T.S.S. % Sirona 2015/2016
T.S.S. % FD.0807 2014/2015 T.S.S. % FD.0807 2015/2016
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Bellis 38% WG Collis 30% SC Camzin 50% WP Tilt 25% EC Camzin 50% +
Tilt 25%
Permatrol (Jojoba
oil) 99%
Control
Root weight Sirona 2014/2015
Root weight Sirona 2015/2016
Root weight FD.0807 2014/2015
Root weight FD.0807 2015/2016
102
4. Discussion
The present study was carried out to
investigate the spread of
Erysiphe betae
the causal fungus of sugar beet powdery
mildew disease grown in Upper Egypt
and to find a best proper method to
control the disease. Survey at sugar beet
plantations around Minia and Assiut
governorates was resulted to confirm that
powdery mildew disease is the most
destructive among the foliar diseases
which attack sugar beet plantations. The
percentage of the disease was higher in
Assiut governorate plantations than in
Minia, which diversity could be
attributed to the arid hot climate
prevailing in Assiut region, providing
high temperature and low relative
humidity those are preferred by powdery
mildew on the whole. These results were
in accordance with those reported by
several researchers (Matsuda &
Takamatsu, 2003; Abd-ElKareem et al.,
2001). Laboratory experiment was
carried out to study on the germination
percentages of
Erysiphe betae
conidia on
glass slides. The percent germination in
darkness was lower than in light and all
germinating conidia formed
appressorium on dry glass slides. The
obtained high germination percentage
and the rapid germination of the conidia
indicate that the sugar beet powdery
mildew does not require that high
moisture of germination applied in the
experiment. Minassian (1967) reported
that only 50 percent relative humidity is
sufficient to prevent conidia from
shriveling in the atmosphere. Upon
reaching the host leaf the microclimate
probably provides efficient moisture
which prevents shriveling of conidia
during germination. It is therefore clear
that the atmospheric humidity in Assiut
region is favorable for the spread of the
fungus and suitable for its development
on sugar beets. To learn more about the
epidemiology of sugar beet powdery
mildew in Upper Egypt, greenhouse
experiment was conducted to determine
the overwintering capability of
vegetative mycelia and conidia of
Erysiphe betae
and their role in the
dissemination of the fungus. Obtained
results confirmed that the conidia
collected from the previous season could
not initiate any type of infection or
disease symptoms which means that the
conidia could not survive as long as it
were stored in this experiment and the
conidia that remain on the crop debris at
the end of the season are not one of the
means which used by the fungus for its
overwintering. So, the initiation of
infection could be caused by long
distance dissemination of the conidia
during the suitable growing date of sugar
beets. Long distance dissemination of
Erysiphe
spp. has also been recorded in
Europe (Hermansen & Stix, 1974). The
conidia of
E. betae
are not viable after
short periods at low temperature
(Dzhanuzakov, 1965). If the sexual stage
of the fungus is rare, overwintering by
this means may be of little importance
(Kontaxis et al., 1974). Observation on
the scanning electron microscopy (SEM)
images of the infection method of sugar
beet powdery mildew (
E. betae
) show
that the fungus penetrates the epidermis
of the leaves by the haustoria. It was
clearly observed that haustoria penetrate
the stomata of the leaf easily and
successfully. The convoluted haustoria
penetrated the leaf epidermis in many
points infecting the entire leaf surface.
The haustoria were convoluted and
103
folded in multiple ways. They entered
perpendicularly the leaf from the top.
There were visible several conidiphores
formed, preparing new source of
secondary infection. The entering zone of
the haustoria, the hyphal part was
thickened, being like a connection tube
between the fungus and the leaf. These
results are in accordance with those of
Hickey and Yoder (1990), Biggs et al.
(2009), Pintye et al. (2011) and
Jakabilyefalvi (2016) who studied
powdery mildew infection steps. The
effects of three macronutrients (
i.e.
calcium chloride, potassium silicate and
sodium bicarbonate) at the concentrations
of 0.1, 0.2 and 0.3 g/l were studied. The
results indicated that 0.3 g/l of sodium
bicarbonate achieved the best percentage
of disease reduction whereas; the least
disease reduction was obtained by 0.1 g/l
of potassium silicate on both Sirona and
FD.0807cultivars. It is well known that
mineral nutrients are essential for the
growth and development of plants and
microorganisms, and are important
factors in plant-disease interactions. Any
nutritional deficiency hinders plant
metabolism and results in a weakened
plant, which lowers disease resistance.
Plant nutrients may affect disease
susceptibility through plant metabolic
changes, thereby creating a more
favorable environment for disease
development. When a pathogen attacks a
plant, it alters the plant’s physiology,
particularly with regard to mineral
nutrient uptake, assimilation,
translocation, and utilization. There are
two primary resistance mechanisms that
mineral nutrition can affect; First by
formation of mechanical barriers,
primarily through the development of
thicker cell walls, Second by synthesis of
natural defense compounds, such as
phytoalexins, antioxidants, and
flavanoids that provide protection against
pathogens (Spann & Schumann, 2010).
Calcium compounds play an essential
role in the formation of healthy, stable
cell walls. Adequate Ca also inhibits the
formation of enzymes produced by fungi
and bacteria, which dissolve the middle
lamella, allowing penetration and
infection. Ca deficiencies trigger the
accumulation of sugars and amino acids
in the apoplast, which lowers disease
resistance (Kelman et al., 1989). Silicon
is combined with other components to
give cell walls greater strength as
physical barriers aginst penetration by
Pyricularia grisea
(rice blast) and
Erysiphe
spp. (mildews), and is involved
in physiological responses to infection by
increasing the availability of K and
mobility of Mn (Savant et al., 1997;
Datnoff et al., 1991). Mineral nutrition
also affects the formation of mechanical
barriers in plant tissue. As leaves age the
accumulation of silicon (Si) in the cell
walls helps in forming a protective
physical barrier to fungal penetration.
Potassium (K) is essential for the
synthesis of proteins, starch, and
cellulose in plants. Cellulose is a primary
component of cell walls, and K
deficiency causes cell walls to become
leaky, resulting in high sugar (starch
precursor) and amino acid (protein
building blocks) concentrations in the
leaf apoplast. Unlike for other nutrients,
the generalization can be made for K that
an adequate supply usually results in an
increased resistance to attack by all
parasites and pests. Potassium
deficiencies created by over application
of dolomite or magnesium lowers this
resistance (Spann & Schumann, 2010).
104
Fungicides have been used for a long
time as the main strategy for controlling
powdery mildew disease on sugar beet
and subsequently increase yield
production (Hassan & Berger, 1980;
Docea & Fratila, 1979). Five commercial
fungicides were tested for their
effectiveness against powdery mildew
disease on sugar beets. The results
indicate that, all tested fungicides
significantly reduced the disease severity
as compared to the control treatment. The
high noticeable significant disease
reduction was achieved by Bellis® and
Collis® fungicides followed by Tilt®,
Camzin® and Permatrol™ respectively.
The highest similar effect of Bellis and
Collis fungicides could be attributed to
their similar mode of action due to their
active ingredients which are related to the
same groups of fungicides (Succinate
dehydrogenase inhibitors and Quinone
outside Inhibitors) those affect the
respiration process in the fungal cell.
Those groups were found to be very
effective against powdery mildew fungi
in previous studies of Bartlett et al.
(2002), Hollomon and Wheeler (2002)
and Karaoglanidis and Karadimos
(2006). Propiconazole, the active
ingredient of Tilt fungicide is related to
(Demethylation Inhibitors) fungicide
group that affect sterol biosynthesis in
membranes of the fungal cells, which
explain its role in decreasing disease
severity, this result is in accordance with
those of Kontaxis (1978), Kolbe (1981),
Paulus
et al
. (1986), El-Desouky (1988),
El-Shami
et al
. (1995), Warkentin
et al.
(1996) and Gado (2013). Acceptable
disease reduction was achieved by
Camzin fungicide which contains
carbendazim that affect cytoskeleton and
motor proteins of the fungal cell this is in
agreement with Iqbal et al. (1994),
Ahmed (1995), He et al. (1998) and
Ziedan and Farrag (2011). The
combination of Camzin and Tilt
fungicides is more effective than Camzin
only due to the potential of
propiconazole the active ingredient of
Tilt fungicide which is clearly better than
Camzin as individual treatments. The
inhibitory effect of jojoba oil, the active
ingredient of Permatrol is also recorded
in previous findings (Moharam &
Obiadalla Ali, 2012; Alahakoon et al.,
2010; Nuñez-Palenius et al., 2009;
Singh, 2008; Konstantinidou-Doltsinis et
al., 2006; Rettinassababady et al., 2000).
The importance of plant derived agents
such as jojoba oil is not only for the
inhibitory effect on the pathogen, but in
way due to their ability to induce host
resistance through increasing the activity
of many enzymes which playing a
defense role against invading pathogens
(Nawar & Kuti, 2003; Caruso et al.,
2001). The compounds responsible for
the preventative and curative effects
could be fraction from these agents in
relation to host resistance. On the other
hand, the fungicides resistant races of
some pathogens have been reported by
Fernández Aparicio et al. (2009) and
O’Brien (1994). As well as the side and
undesirable effects of fungicides on
human
health and the
environment
(Durmusoglu et al., 1997; Garcia, 1993).
Despite that, fungicides are still the most
dependable method in controlling such
diseases. In this research, all studied
treatments, macronutrients or fungicides,
recorded the highest values concerning
sucrose and root weight. This may be
referred to the effect of the treatments on
the general health of the beets.
Meanwhile, the different treatments may
105
have effect on the storage parenchyma
tissues where the sucrose is stored, but
this point need further study in the future.
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