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The suppressive effect of sodium and calcium salts applied individually or combined with the yeast Saccharomyces cerevisiae against Alternaria solani the causal agent of early blight disease of potato was evaluated under laboratory, greenhouse and field conditions. In vitro test a complete inhibition in fungal growth was observed at concentration of 30 mg/ml of both sodium bicarbonate and calcium chloride. The commercial backing yeast S. cerevisiae (CBY) enhanced the inhibitory effect of tested salts reflected in increasing mycelial fungal growth reduction when combined at the rate of 1:1 at each concentration tested. In pot experiment, under artificial infestation with pathogenic fungus, application of sodium bicarbonate or calcium chloride significantly reduced the early blight incidence and severity by increasing their concentrations. Their most effective concentration were 30 mg/ml that reduced the disease incidence by 50 and 62.4%, respectively. Superior effect of sodium bicarbonate or calcium chloride in disease reduction was observed when they combined with CBY. Field trails for evaluating the most promising greenhouse treatments were preformed under natural infestations during two successive summer seasons. Calcium chloride proved higher efficacy for reducing both disease incidence and severity than that of sodium bicarbonate when applied either alone or combined with CBY. Also, it is observed that increasing concentrations of both sodium bicarbonate or calcium chloride showed parallel decrease in disease incidence and severity. Application of (CBY) enhanced the efficacy of salts spraying against early blight disease. Similar trend was also observed with the increase of potato tubers yield. On the light of the present study it could be suggested that the usage of combined application of the yeast S. cerevisiae with sodium bicarbonate or calcium chloride might be used as easily applied, safely and cost effective control methods against such plant diseases.
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JOURNAL OF PLANT PROTECTION RESEARCH Vol. 49, No. 4 (2009)
ȱ
*Corresponding address:
nehal_nrc@yahoo.com
SALTS APPLICATION FOR SUPPRESSING
POTATO EARLY BLIGHT DISEASE
Nehal S. El-Mougy*, Mokhtar M. Abdel-Kader
Plant Pathology Department, National Research Centre
El-Behhos St., 12622 Giza, Egypt
Received: February 24, 2009
Accepted: October 10, 2009
Abstract: The suppressive effect of sodium and calcium salts applied individually or combined with the yeast Saccharomyces cerevisiae
against Alternaria solani the causal agent of early blight disease of potato was evaluated under laboratory, greenhouse and field condi-
tions. In vitro test a complete inhibition in fungal growth was observed at concentration of 30 mg/ml of both sodium bicarbonate and
calcium chloride. The commercial backing yeast S. cerevisiae (CBY) enhanced the inhibitory effect of tested salts reflected in increasing
mycelial fungal growth reduction when combined at the rate of 1:1 at each concentration tested. In pot experiment, under artificial
infestation with pathogenic fungus, application of sodium bicarbonate or calcium chloride significantly reduced the early blight
incidence and severity by increasing their concentrations. Their most effective concentration were 30 mg/ml that reduced the disease
incidence by 50 and 62.4%, respectively. Superior effect of sodium bicarbonate or calcium chloride in disease reduction was observed
when they combined with CBY. Field trails for evaluating the most promising greenhouse treatments were preformed under natural
infestations during two successive summer seasons. Calcium chloride proved higher efficacy for reducing both disease incidence and
severity than that of sodium bicarbonate when applied either alone or combined with CBY. Also, it is observed that increasing con-
centrations of both sodium bicarbonate or calcium chloride showed parallel decrease in disease incidence and severity. Application of
(CBY) enhanced the efficacy of salts spraying against early blight disease. Similar trend was also observed with the increase of potato
tubers yield. On the light of the present study it could be suggested that the usage of combined application of the yeast S. cerevisiae
with sodium bicarbonate or calcium chloride might be used as easily applied, safely and cost effective control methods against such
plant diseases.
Key words: Alternaria solani, early blight, calcium chloride, control, potato, sodium chloride
INTRODUCTION
Early blight is a very common disease of both potato
and tomato. It causes leaf spots and tuber blight on potato,
and leaf spots, fruit rot and stem lesions on tomato. The
disease can occur over a wide range of climatic conditions
and can be very destructive if left uncontrolled, often re-
sulting in a complete defoliation of plants. In contrast to
the name, it rarely develops early, but usually appears
on mature foliage. Early blight is caused by the fungus,
Alternaria solani (Ellis & G. Martin) L.R. Jones & Grout,
which survives in infected leaf or stem tissues on or in
the soil. Wharton and Kirk (2007) reported that the patho-
gen survives between growing seasons in infested plant
debris and soil, in infected potato tubers and in overwin-
tering debris of susceptible solanaceous crops and weeds
including hairy nightshade (Solanum sarrachoides). This
fungus is universally present in fields where these crops
were grown. It can also be carried on tomato seed and in
potato tubers. Spores form on infested plant debris at the
soil surface or on active lesions over a fairly wide tem-
perature range, especially under alternating wet and dry
conditions. They are easily carried by air currents, wind-
blown soil, splashing rain, and irrigation water. Infection
of susceptible leaf or stem tissues occurs in warm, humid
weather with heavy dew or rain. Early blight can develop
quite rapidly in mid to late season and is more severe
when plants are stressed by poor nutrition, drought, or
pests. Infection of potato tubers occurs through natural
openings on the skin or through injuries. Tubers may
come in contact with spores during harvest and lesions
may continue to develop in storage.
In Egypt potato (S. tuberosum) is of the largest horti-
cultural export. In most recent years the EU has account-
ed for about 70%–90% of Egyptian potato. Potato early
blight disease occurs in most production areas to almost
every year although it has a significant effect on yield
only when frequent wetting of the foliage favours early
and rapid symptom development. Estimating total an-
nual crop losses due to any particular disease is difficult
to do accurately. Values in the literature for crop losses
due to early blight vary enormously from 5 to 78% (Waals
et al. 2004; Pasche et al. 2004, 2005).
Apart from the use of crop rotation, certified disease-
free seeds and resistant varieties, and control measures
354 Journal of Plant Protection Research 49 (4), 2009
are important to minimize infection. It is usually neces-
sary to apply fungicide sprays to fully protect plants from
early blight. Fungicide alternatives that have fungicidal
effect on disease incidence and development are safety of
application and environmental pollution concern.
There was a considerable interest in the use of so-
dium bicarbonate (NaHCO3) and potassium bicarbonate
(KHCO3) for controlling various fungal diseases in plants
(Karabulut et al. 2003; Smilanick et al. 2006). Bicarbonates
are widely used in the food industry (Lindsay 1985) and
were found to suppress several fungal diseases of cucum-
ber plants (Ziv and Zitter 1992). Spraying plants with
NaHCO3 solution provided good control of several plant
diseases (Horst et al. 1992; Arimoto et al. 1997; Palmer et al.
1997; Janisiewicz and Peterson 2005). Also, spraying with
KHCO3 solution provided the most effective protection
against plant diseases (Fallilk et al. 1996; Smilanick et al.
1999, 2006). Sodium or potassium bicarbonate combined
with oil were effective in controlling plant diseases (Horst
et al. 1992; Ziv and Zitter 1992).
Calcium chloride as CaCl2 was reported to suppress
growth of the citrus mould pathogen Penicillium digitatum
(Droby et al. 1997). Calcium chloride effectively reduced
silver scurf lesions on potato tubers, but not sporulation
of Helminthosporium solani. It is known that addition of
calcium chloride can also improve the activity of biocon-
trol agents (Droby et al. 1997; McLaughlin et al. 1990).
Certain strategies, such as pre- or postharvest appli-
cation of calcium salts, hydrogen peroxide and chitosan
against fruit decay are proposed (Conway et al. 1992,
1994). Pre- and postharvest calcium applications have
been used to delay ageing or ripening to reduce posthar-
vest decay and control of many diseases in fruits and veg-
etable (Poovaiah 1986). Saftner et al. (1997) reported that
postharvest calcium treatment of apples provided broad-
spectrum protection against the postharvest pathogens of
Penicillium expansum and Botrytis cinerea.
Biological control using either natural products or
antagonistic microorganisms proved to be successful for
controlling various plant pathogens in many countries
(Papavizas and Lumsden 1980). It is still not expensive
and is easy in application, however it can serve as the
best control measure under restricted conditions. In addi-
tion, its application is safe, un-hazardous for human and
avoids environmental pollution (Sivan and Chet 1989).
Saccharomyces cerevisiae was used as biocontrol agent and
systemic resistance mechanisms (El-Sayed 2000). Attyia
and Youssry (2001) reported that a local isolate of S. cere-
visiae had a reduction potential against radial growth of
pathogenic fungi Macrophomina phaseolina and Fusarium
solani, the cause of root rot diseases in tomatoes and egg-
plants.
The objective of this research was to evaluate the ef-
fects of some salts in addition to the commercial backing
yeast as natural products and bio-pesticides on in vitro
inhibition of A. solani in laboratory assays and determine
their effect on development and suppression of early
blight disease under field conditions.
MATERIALS AND METHODS
Fungal and yeast cultures
A virulent pathogenic isolate of A. solani was obtained
from the Plant Pathology Department, National Research
Centre, Egypt. The fungal cultures were maintained on
PDA medium at 5±1°C as stock cultures until use. In ad-
dition, one of local mixture isolates of the backing yeast
S. cerevisiae was also used in the present work. This yeast
mixture is produced commercially for the purpose of
backing and food industries.
Potato
Potato tubers cv. Diamond were used in the present
study. Potato tubers were stored in the dark at 4°C until
use.
Chemicals
Sodium bicarbonate (NaHCO3) and calcium chloride
(CaCl2) were purchased from Sigma-Aldrich.
In vitro tests
The inhibitory effect of sodium bicarbonate and calci-
um chloride, individually or combined, with commercial
backing yeast (CBY) was evaluated while measuring the
linear growth of A. solani in vitro. For each of the tested
salts four concentrations were prepared by dissolving in
sterilized distilled water. They were added individually
to conical flasks containing sterilized PDA medium be-
fore solidification to obtain the proposed concentrations
of 5, 10, 20 and 30 mg/ml. The supplemented media were
poured into Petridishes (9 cm Ø), nearly 20 ml per each.
A separate PDA plates free of salts were used as control
treatment. Mycelial discs (5 mm Ø) were taken from the
periphery of an actively growing PDA culture of A. solani
and placed at the centre of the prepared Petri dishes.
The efficacy of combined inhibitory effect of tested
salts and CBY against the growth of A. solani was also
evaluated. This test was carried out using Petri dishes
containing PDA supplemented with the above men-
tioned salts concentrations. Growth inhibition of patho-
genic fungus affected by CBY in the presence of sodium
bicarbonate or calcium chloride in the growth medium
was evaluated following a dual culture technique after
Ferreira et al. (1991). Different amounts of CBY as 5, 10, 20
of 30 mg/ml were suspended in sterilized distilled water,
shacked using a vortex for 5 min, then the cell concentra-
tions were determined with a haemocytometer slide. The
CBY cell concentrations were 6, 8, 10 and 12x108 cell/ml
in respective order to the weight used. A loopful of dif-
ferent CBY concentrations were streaked individually on
one side of 9 cm Petri dishes containing PDA supplement-
ed with different salt concentrations, and 5 mm disks of
fungal pathogen were placed on the opposite side of the
yeast inoculated plates. Both tested microorganisms were
placed 2 cm from the plate edges. A set of inoculated with
the fungus plates was used for control treatment.
All plates were incubated at 25±2°C until full fungal
growth in control plates. Five replicates were used for
each treatment. The diameter of the fungal colonies was
Salts application for suppressing potato early blight… 355
measured and percentage reduction in fungal growth was
calculated in relative to its growth in control treatment.
In vivo tests
The efficacy of different concentrations of sodium bi-
carbonate and calcium chloride, individually or combined
with CBY against early blight incidence on potato plants
was tested under greenhouse and field conditions.
Preparation of spraying solutions and fungal suspen-
sion
Four concentrations of each sodium bicarbonate and
calcium chloride were prepared by dissolving in steril-
ized distilled water to obtain the proposed concentrations
of 5, 10, 20 and 30 mg/ml. Also, different weights of CBY
5, 10, 20 and 30 mg/ml were suspended in sterilized dis-
tilled water, shacked using a vortex for 5 min, and then
they were ready to use.
The fungus A. solani was grown on PDA medium at
25±2°C until an abundant heavy growth of conidia was
evident. Conidia were harvested by scraping the surface
of the colonies with a spatula and transferred to sterilized
distilled water and filtered through nylon mesh, then
spore suspension was adjusted with sterile water to give
a spore concentration of 106–107 per millilitre.
Greenhouse experiment
The same treatments preformed in laboratory test
were evaluated in the greenhouse. The present experi-
ment was carried out in the greenhouse of Plant Pathol-
ogy department, National Research Centre, Egypt. Potato
tubers cv. Diamond were grown in plastic pots (30 cm
diameter) containing sandy loam soil at 22–25OC and RH
75–80%. The usual agricultural practices of irrigation and
fertilization were followed. When plants had 4–5 com-
pound leaves, three plants/pot and ten pots for each treat-
ment were used. Solutions of sodium bicarbonate and
calcium chloride were applied individually or combined
with CBY with respective concentrations as foliar spray to
potato plants. S. cerevisiae (CBY) was applied three days
after salts spray. Plants sprayed with sterilized distilled
water served as a control treatment. Plant inoculation was
carried out 5 days after of (CBY) treatments by spraying
with spore suspensions (106–107 spore/ml) of A. solani.
Field experiment
The most promising treatments were applied under
field conditions. Field experiment was carried out at at
the Experimental Farm of National Research Centre at
Al-Kanater country, Kaliobia Governorate, Egypt during
2007 and 2008 summer (January–April) growing seasons
to evaluate the efficacy of sodium bicarbonate and calcium
chloride individually or combined with CBY on the inci-
dence and severity of early blight disease of potato plants.
A field experiment consisted of plots 21 m2 (3 x 7 m) each
and comprised of 7 rows and 15 holes/row and was con-
ducted in completely randomized block design with five
plots as replicates for each particular treatment as well as
untreated control. Potato tubers cv. Diamond were plant-
ed in all treatments. All plots received traditional agricul-
tural practices as irrigation, fertilization and soil plung-
ing. The used mineral fertilization of NPK was 180, 75
and 95 unit/4 200 m2. In addition to 20 m3 organic manure
and 150 kg/4 200 m2 agricultural sulphur were added to
the soil before planting. Solutions of sodium bicarbon-
ate and calcium chloride individually or combined with
CBY with respective concentrations of 10 and 20 mg/ml
for all tested factors were applied as foliar spray of po-
tato plants. S. cerevisiae (CBY) was applied three days
after salts spray. Plants sprayed with sterilized distilled
water served as a control treatment. All treatments were
applied when plants had 4–5 compound leaves and re-
peated again after 15 days. For comparison fungicide
Ridomil MZ 72 WP was applied as foliar spray at the rec-
ommended dose (2.5 g/l). Early blight disease incidence
and severity were recorded after 30 days of the second
plant spray application. The average harvested yield was
calculated for all applied treatments as kg/m2 at the end
of each growing season.
Disease assessment
Early blight incidence was estimated as the number
of infected plants showing disease symptoms in rela-
tion to the whole number of potato plants. The average
of records of the surveyed replicates for each particular
treatment was calculated. Disease severity was estimated
following the scale from 0 to 4 suggested by Cohen et al.
(1991) as follows:
0 = no leaf lesion; 1 = lesions occupied < 25% of leaf
area; 2 = lesions occupy between 26–50% of leaf area;
3 = lesions occupy between 51–75% of leaf area and
4 = lesions occupy 76 up to 100% of leaf area. Then the
following formula was applied:
where:
D.S. = disease severity, n = number of infected plants per
category, c = category number and N = total number of
examined plants.
Statistical analysis
One way analysis of variance (ANOVA) was used to
analyze differences between toxic concentrations of fun-
gicide and the linear growth of A. solani as well as differ-
ences between toxicity of fungicide and early blight inci-
dence at different applied concentrations under labora-
tory and field conditions. MSTAT-C program (V2.1) was
used to perform the analysis of variance between toxicity
of fungicide and early blight incidence at different applied
concentrations under field conditions. Duncan’s Multiple
Range Test was used for means separation (Winer 1971).
RESULTS
In vitro tests
Inhibitory activity against the mycelial growth of
A. solani was observed at all concentrations of sodium bi-
carbonate and calcium chloride used either individually
or combined with CBY (Table 1). Fungal mycelial growth
decreased significantly with the increase in concentrations
356 Journal of Plant Protection Research 49 (4), 2009
of used salts to reach minimum mycelial growth with the
highest concentration used. Complete inhibition in fun-
gal growth was observed at concentration of 30 mg/ml
of both sodium bicarbonate and calcium chloride. The
yeast S. cerevisiae (CBY) enhanced the inhibitory effect of
tested salts reflected in increasing mycelial fungal growth
reduction when combined at the rate of 1 : 1 at each con-
centration tested. Superior complete inhibitory effect was
observed at both salts concentration combined with CBY
at 20+20 mg/ml and 30+30 mg/ml.
Table 1. In vitro linear growth of A. solani in response to different concentrations of sodium bicarbonate and calcium chloride used
individually or combined with S. cerevisiae
Treatment Concentration
[mg/ml]
Linear growth
[mm]
Reduction B
[%]
Sodium bicarbonate
5 48.8 b 45.77 A
10 24.4 f 72.88
20 12.8 j 85.77
30 0 k 100
Sodium bicarbonate + CBY
5+5 44.4 d 50.66
10+10 17.7 h 80.33
20+20 0 k 81.78
30+30 0 k 100
Calcium chloride
5 46.8 c 48.0
10 22.2 g 75.33
20 16.4 hi 81.78
30 0 k 100
Calcium chloride + CBY
5+5 42.2 e 53.11
10+10 18.7 h 79.22
20+20 0 k 100
30+30 0 k 100
Control 90 a 0
A mean values within columns followed by the same letter are not significantly different at p < 0.05
B reduction in fungal growth at different treatments, calculated relatively to its growth in control
In vivo tests
Greenhouse experiment
The different concentrations of sodium bicarbonate
or calcium chloride significantly reduced the early blight
incidence. This observed reduction was increased by in-
creasing salts concentrations (Table 2). Their most effec-
tive concentration were 30 mg/ml that reduced the dis-
ease incidence by 50 and 62.4%, respectively.
Superior effect of sodium bicarbonate or calcium chlo-
ride in disease reduction was observed when they were
combined with S. cerevisiae. The highest record of disease
reduction in respective order of 75.0 and 68.8% was ob-
tained for the applied concentration of 30+30 mg/ml.
Similar trend was recorded concerning the severity of
early blight disease. Data in Table 2 indicate that all pota-
to plants receiving both salts treatments have significant
reduction in disease severity which increased when com-
bined with CBY application. High reduction as 42.3 and
61.4% was obtained at 30 mg/ml of sodium bicarbonate
and calcium chloride and reached up to 65% when both
treatments combined with CBY. Individual application of
sodium bicarbonate and calcium chloride or combination
with CBY either at concentration of 20 mg/ml or 30 mg/ml
showed no significant reduction in disease incidence as
well as severity.
Field experiment
The promising treatments for reducing both disease
incidence and severity in pot experiment was applied un-
der natural field conditions during two successive grow-
ing seasons (Table 3). Although the fungicide treatment
reduced significantly early blight incidence and severity
(14.3 and 34.7%) compared with control (17.6 and 39.3%),
all applied treatments had a superior effect in this respect.
Presented data revealed that calcium chloride had higher
efficacy for reducing both disease incidence and sever-
ity than that of sodium bicarbonate when applied either
alone or combined with S. cerevisiae. Also, it was observed
that increasing concentrations of both sodium bicarbon-
ate or calcium chloride showed parallel decrease in dis-
ease incidence and severity. This reduction was also ob-
served when the applied salts were combined with CBY.
Obtained data also showed that the application of (CBY)
enhanced the efficacy of salts spraying against early blight
disease. Application of sodium bicarbonate at 10 and
20 mg/ml could reduce the disease incidence and severity
by 30.6, 17.3% and 47.7, 31.8%, while these records raised
to reach 41.4, 20.1 and 52.2, 45.8%, respectively when com-
bined with CBY treatment. As for calcium chloride treat-
ments, at the same concentration, the reduction in disease
incidence and severity was recorded in respective order:
Salts application for suppressing potato early blight… 357
42, 35.3% and 64.2, 66.6% that increased up to 55.6, 47.5%
and 70.4, 58.7% by combination with CBY treatment.
The average of harvested potato tubers, data in table 4
showed a considerable increase in potato yield at all
applied treatments during the two cultivation seasons.
A significant increase in harvested yield was observed
for calcium chloride treatments of 10, 20 mg/ml either as
individual application or combined with CBY which was
recorded as 38.4, 50.0% and 47.6, 50%, respectively. These
results were higher than those obtained by sodium bicar-
bonate at similar treatments recorded as 7.6, 26.9% and
19.2, 30.7%, respectively. The lowest increase in potato
yield of 3.8% was observed for fungicide treatment.
Table 2. The influence of sodium bicarbonate and calcium chloride individually or combined with CBY on early blight disease inci-
dence and severity of potato plants under greenhouse conditions
Treatment Concentration
[mg/ml]
Disease
incidence
Reduction
[%] Disease severity Reduction
[%]
Sodium bicarbonate
5 43.3 b A18.7 51.4 b A12.2
10 36.6 c 31.3 45.7 c 22.0
20 30.0 d 43.7 40.6 cd 30.7
30 26.6 d 50.0 33.8 de 42.3
Sodium bicarbonate + CBY
5+5 20.0 de 62.4 36.4 d 37.8
10+10 16.6 e 68.8 31.5 de 46.2
20+20 13.3 ef 75.0 23.2 ef 60.4
30+30 13.3 ef 75.0 20.5 f 65.0
Calcium chloride
5 40.0 b 24.9 42.8 cd 26.9
10 33.3 cd 37.5 38.8 d 33.7
20 23.3 d 56.2 28.4 e 51.5
30 20.0 de 62.4 22.6 ef 61.4
Calcium chloride + CBY
5+5 36.6 c 31.3 37.4 d 36.1
10+10 26.6 d 50.0 31.4 de 46.4
20+20 20.0 de 62.4 24.3 ef 58.5
30+30 16.6 e 68.8 20.5 f 65.0
Control 53.3 a 0 58.6 a 0
A mean values within columns followed by the same letter are not significantly different at p < 0.05
Table 3. The influence of sodium bicarbonate and calcium chloride applied individually or combined with CBY on early blight dise-
ase incidence and severity of potato plants under field conditions during two successive summer seasons 2007/2008 A
Treatment Disease
incidence
Reduction
[%] Disease severity Reduction [%]
Sodium bicarbonate (10 mg/ml) 12.2 c B30.6 32.5 c 17.3
Sodium bicarbonate (10 mg/ml) + CBY (10 mg/ml) 10.3 d 41.4 31.4 c 20.1
Sodium bicarbonate (20 mg/ml) 9.2 de 47.7 26.8 d 31.8
Sodium bicarbonate (20 mg/ml) + CBY (20 mg/ml) 8.4 e 52.2 21.3 e 45.8
Calcium chloride (10 mg/ml) 10.2 d 42.0 25.4 d 35.3
Calcium chloride (10 mg/ml) + CBY (10 mg/ml) 7.8 e 55.6 20.6 e 47.5
Calcium chloride (20 mg/ml) 6.3 f 64.2 19.1 e 66.6
Calcium chloride (20 mg/ml) + CBY (20 mg/ml) 5.2 g 70.4 16.2 f 58.7
Ridomil MZ 72 WP (2.5 g/l) 14.3 b 24.4 34.7 b 11.7
Control 17.6 a 0 39.3 a 0
A the recorded data of the two successive seasons were presented as average per cent
B mean values within columns followed by the same letter are not significantly different at p < 0.05
358 Journal of Plant Protection Research 49 (4), 2009
DISCUSSION
Although cultural practices such as crop rotation and
appropriate application of chemical management of po-
tato can help reduce diseases incidence, alternative con-
trol strategies are needed. An interesting alternative to
fungicide application for plant disease control involves
the use of some organic and inorganic salts with antimi-
crobial properties generally used in food processing and
preservation.
Selected organic and inorganic salts are active anti-
microbial agents and have been widely used in the food
industry. Many of these salts are effective against a range
of microorganisms; most of them have low mammalian
toxicity and therefore have potential for postharvest dis-
ease control. Salt treatments can inhibit plant pathogens
or suppress mycotoxin production (Roinestad et al. 1993;
Singh and Chand 1993). Sodium and ammonium bicar-
bonate were shown to inhibit fungal pathogens of fruits,
field crops, vegetables, and ornamentals (Ziv and Zitter
1992; Palmer et al. 1997).
Several studies dealt with the use of different salts to
control various postharvest diseases of potato and other
crops. Treatment of citrus fruit with sodium carbonate or
sodium bicarbonate was shown to reduce the incidence
of postharvest disease caused by Penicillium digitatum
(Smilanick et al. 1999, 2006). Postharvest application of
ammonium bicarbonate, sodium bicarbonate, potassium
carbonate, calcium propionate, and potassium sorbate re-
duced black root rot on carrots caused by Chalara elegans
(Punja and Gaye 1993). Recent studies suggest that salt
application reduces postharvest potato diseases. Olivier
et al. (1998) and Hervieux et al. (2002) showed that ap-
plication of potassium sorbate, calcium propionate, so-
dium carbonate, sodium bicarbonate, potassium carbon-
ate, potassium bicarbonate, and ammonium bicarbonate
at 0.2 M reduced silver scurf lesion development and
Helminthosporium solani sporulation on inoculated and
naturally infected potato tubers. These reports confirm
the obtained results in the present study showing that so-
dium bicarbonate was found to be strongly inhibiting to
mycelial growth of A. solani at concentrations of 20 and
30 mg/ml either under in vitro or in vivo trails. Moreover,
the efficacy of the inhibitory effect showed parallel corre-
lation with increasing the applied concentrations. Similar
trend was also observed for the increase of potato tubers
yield throughout the two successive seasons by increas-
ing the applied salts concentrations. A significant increase
in harvested yield was observed for calcium chloride
treatments either as individual application or combined
with CBY. These results were higher than that obtained
for sodium bicarbonate at similar treatments, while the
lowest increase in potato yield was observed for fungi-
cide treatment.
Previous studies demonstrated that increasing con-
centrations of sodium bicarbonate resulted in a corre-
sponding increase in efficacy (Mlikota and Smilanick
1998, 2001). The inhibitory effect of sodium bicarbonate
on microorganisms may be due to reduction of cell tur-
gor that causes a collapse and shrinkage of hyphae and
spores, resulting in fungistasis (Fallik et al. 1997).
The use of sodium bicarbonate alone to control
postharvest decays of fruit has its limitations (Palou et
al. 2001), but it can be combined with other alternative
treatments to synthetic fungicides, resulting in the con-
trol that is superior to individual treatments alone. For
example, sodium bicarbonate was successfully used in
combination with bacterial and yeasts biocontrol agents
to enhance control of postharvest decays on citrus, pome,
and stone fruits (Smilanick et al. 1999; Wisniewski et al.
2001; Janisiewicz and Peterson 2005). These reports are
clearly demonstrated in the present study and show
that the application of S. cerevisiae (CY) enhanced the
control of early blight incidence and severity of potato
plants when combined with either sodium bicarbon-
ate or calcium chloride spray. Petersson and Schnurer
(1995) reported that S. cerevisiae required an inoculum of
105 cfu/g to inhibit the growth of Penicillium roqueforti in
non-sterile high-moisture wheat grains. In this concern
Table 4. The influence of sodium bicarbonate and calcium chloride individually or combined with CBY on potato yield during two
successive summer seasons 2007/2008 A
Treatment Yield ([kg/m2] AIncrease [%]
Sodium bicarbonate (10 mg/ml) 2.8 a B7.6
Sodium bicarbonate (10 mg/ml) + CBY (10 mg/ml) 3.1 b 19.2
Sodium bicarbonate (20 mg/ml) 3.3 bc 26.9
Sodium bicarbonate (20 mg/ml) + CBY (20 mg/ml) 3.4 cd 30.7
Calcium chloride (10 mg/ml) 3.6 cd 38.4
Calcium chloride (10 mg/ml) + CBY (10 mg/ml) 3.8 d 47.6
Calcium chloride (20 mg/ml) 3.9 d 50.0
Calcium chloride (20 mg/ml) + CBY (20 mg/ml) 3.9 d 50.0
Ridomil MZ 72 WP (2.5 g/l) 2.7 a 3.8
Control 2.6 a 0
A the recorded data of potato yield for the two successive seasons were presented as average kg/m2
B mean values within columns followed by the same letter are not significantly different at p < 0.05
Salts application for suppressing potato early blight… 359
inoculum used in the present work was much more effec-
tive if reached 6, 8 and 10x108 cell/ml in respective order
to the weights of 10, 20 and 30 mg/ml. Moreover, the pres-
ent study clearly indicated the antagonistic activity of
yeast S. cerevisiae on early blight pathogen under in vitro
and in vivo conditions. The biocontrol activity of S. cere-
visiae against A. solani might have possibly resulted from
mycoparasitism (Hajlaoui and Belanger 1993), secretion
of lytic enzymes such as β –1, 3 glucanase (Punja 1997)
and production of antibiotics (Beyagoub et al. 1996). The
present study clearly indicated the antagonistic activity
of yeast S. cerevisiae on early blight pathogen under in vi-
tro and in vivo conditions. Also, Attyia and Youssry (2001)
reported that a local isolate of S. cerevisiae had a reduction
potential against radial growth of pathogenic fungi Mac-
rophomina phaseolina and Fusarium solani, the cause of root
rot diseases in tomatoes and eggplants. They added that
scanning electron microscopy revealed interaction be-
tween S. cerevisiae and both fungi. Also, calcium has been
considered to increase biocontrol efficacy of antagonists.
It may also replace the current requirement for addition
of low concentrations of fungicides to ensure consistent
performance of yeast control agents under large-scale
and commercial conditions (Droby et al. 1993).
Application of calcium chloride in the present study
either individually or combined with S. cerevisiae (CY)
proved to have a suppressive effect against the linear
growth of the pathogen A. solani in vitro and its disease
incidence and development under greenhouse and field
trails. Similarly, calcium chloride at 2% (20 mg/ml) obvi-
ously inhibited spore germination and germ tube growth
of R. stolonifer PDA medium (Tian et al. 2002). This result
further supports the results of Wisniewski et al. (1995),
who found that calcium chloride might reduce fungal
infection through direct inhibition of spore germination
and growth. Maouni et al. (2007) reported that in vitro,
calcium chloride significantly reduced pear fruit decay
caused by A. alternata and Penicillium expansum when
used at 4 and 6%.
Under field conditions multiple spray applications of
calcium chloride in the orchard was reported to reduce
postharvest Alternaria infection as well as postharvest
development of bitter rot following orchard infection by
Colletotrichum spp. in apple (Biggs et al. 1993; Biggs 1999).
In pear orchard, calcium chloride sprays were shown
previously to enhance pear fruit resistance to blue mould
decay and side rot (Sugar et al. 1991, 2003). The precise
mechanism by which calcium reduces fungal infection is
not yet understood, but the role of calcium in resistance
may be one of interference with the activity of pectolytic
enzymes (Conway et al. 1992) and may be partially attrib-
utable to a decrease in maceration of cell walls by poly-
galacturonase (PG) due to the improved structural integ-
rity caused by the increase in calcium content (Conway
et al. 1998). Furthermore, previous studies indicated that
the increase in cell walls of apple reduces the activity of
polygalacturonase extracted from the pathogenic invader
fungus P. expansum (Conway et al. 1988; Wisniewski et al.
1995; Saftner et al. 1997).
The present findings demonstrate that sodium and
calcium salts may have important implications for the
future use of antagonistic microorganisms on a commer-
cial scale for controlling such diseases especially under
organic cultivation regime.
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POLISH SUMMARY
ZASTOSOWANIE SOLI W CELU
OGRANICZENIA ALTERNARIOZY ZIEMNIAKA
W warunkach laboratoryjnych, szklarniowych i po-
lowych, badano ograniczające działanie soli sodu i wap-
nia, użytych indywidualnie lub łącznie z grzybem droż-
dżoidalnym Sacharomyces cerevisiae, przeciwko Alternaria
Salts application for suppressing potato early blight… 361
solani, który wywołuje wczesną alternariozę ziemniaka.
W teście in vitro obserwowano całkowitą inhibicję wzrostu
grzyba przy użyciu stężenia węglanu sodu lub chlorku
wapnia wynoszącego 30 mg/ml. Handlowe drożdże pie-
karnicze (S. cerevisiae) stymulowały działanie inhibicyjne
badanych soli, co wyrażało się redukcją ilości wytwarza-
nej przez patogena grzybni, wykorzystywanej w bada-
niach w stosunku: 1 : 1 dla każdego testowanego stężenia.
W doświadczeniu wazonowym, w warunkach sztucznej
inokulacji patogenem, zastosowanie jednej z badanych
soli powodowało istotne ograniczenie występowania
alternariozy, a jej nasilenie wzrastało wraz ze wzrostem
wykorzystanych stężeń soli. Najbardziej efektywne było
stężenie 30 mg/ml, ograniczające występowanie choro-
by, odpowiednio o 50 i 62,4%. Lepszy efekt zastosowania
węglanu sodu lub chlorku wapnia w ograniczaniu cho-
roby obserwowano wtedy, gdy zabiegi były wykonywa-
ne w warunkach naturalnego zakażenia, podczas dwóch
kolejnych sezonów letnich. Chlorek wapnia był skutecz-
niejszy zarówno w ograniczaniu występowania choroby
i jej nasilenia, niż węglanu sodu, zarówno gdy stosowano
go oddzielnie lub w połączeniu z S. cerevisiae. Zwiększając
stężenia obydwóch soli uzyskano równoległe ogranicze-
nie choroby i jej nasilenia. Zastosowanie drożdży stymu-
lowało skuteczność opryskiwania roślin ziemniaka solami
przeciwko alternariozie. Podobną tendencję obserwowano
również dla wzrostu plonu bulw. W świetle wykonanych
badań można sugerować, że wykorzystanie łącznej apli-
kacji S. cerevisiae i węglanu sodu lub chlorku wapnia mo-
głoby być wykorzystane jako łatwa w użyciu, bezpieczna
i tania metoda zwalczania tej choroby.
... Several documents are available proving this fact. (Hervieux et al. 2002, Jamar et al. 2007, Nahal and Mokhtar 2009, Turkkan 2013.). ...
... Four inorganic salts namely calcium chloride, sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate, have been used for their antifungal activity against mycelial growth and control of apple fruit decay caused by A.porri and A. mali. In all salt treatments, linear growth of fungi decreased with increasing salt concentrations (Table 2) and these results agree with Nahal et al (2009) who stated that the application of calcium chloride or sodium bicarbonate considerably reduced early blight and its severity by increasing their concentrations. Previous research showed that raising sodium bicarbonate concentrations caused in a constant improvement in efficacy Smilanick 1998, 2001). ...
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... In contemporary study, sodium (Na) contents were observed higher in un-inoculated resistant/ susceptible cultivars and lower in inoculated plants. El-Mougy& Abdel-Kader (2009) reported that the application of sodium against Alternaria solani resulted in the fungal growth inhibition in the in-vitro experiments. Zinc plays a key role among plant's minerals as it is an important component of many enzymes and proteins which triggers the growth and production hormones along with internode elongation. ...
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... Extracellular lytic enzymes such as chitinases, glucanase, protease, etc, producing bacterium holds a great promise as biological disease control due to their increased activities of mycoparasitism. For example, chitinolytic bacteria, Bacillius subtilis, and P. fluorescens and their chitinase enzymes exhibited antagonisim toward crop root rot pathogens (Rhizoctonia solani and Fusarium solani) in vitro assay (El-Mougy et al., 2009). Several authors have reported antifungal chitinase of B. subtilis demonstrating powerful growth inhibitory actions against several pathogenic fungi (Kobayashi et al., 2002;Yang et al., 2009). ...
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... Extracellular lytic enzymes such as chitinases, glucanase, protease, etc, producing bacterium holds a great promise as biological disease control due to their increased activities of mycoparasitism. For example, chitinolytic bacteria, Bacillius subtilis, and P. fluorescens and their chitinase enzymes exhibited antagonisim toward crop root rot pathogens (Rhizoctonia solani and Fusarium solani) in vitro assay (El-Mougy et al., 2009). Several authors have reported antifungal chitinase of B. subtilis demonstrating powerful growth inhibitory actions against several pathogenic fungi (Kobayashi et al., 2002;Yang et al., 2009). ...
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