Journal of Phytopathology and Pest Management 8(1): 1-14, 2021

pISSN: 2356-8577 eISSN: 2356-6507

Journal homepage: http://ppmj.net/

∗

Corresponding author:

Mohamed A. Eliwa,

E-mail: mohamedeliwa.5419@azhar.edu.eg

1

Control of root rot disease of sugar beet using

certain antioxidants and fungicides

Mohamed A. Eliwa

*

, Mohamed M. El-Sheikh Aly, Shaaban M. Saber

Agricultural Botany Department, Faculty of Agriculture, Al-Azhar University, 71524 Assiut, Egypt

Abstract

Keywords: sugar beet, Rhizoctonia solani, Macrophomina phaseolina, antioxidants, fungicides.

2

1. Introduction

Sugar beet (

Beta vulgaris

L.), a

specialized type of beet belonging to

family Chenopodiaceae, it is an important

part of the human diet, providing energy

to maintain body temperature activity.

Additionally, it is also widely used as a

sweetener and preservative for foods.

Beside sugar, it also provides valuable by

products,

i.e.

beet tops and molasses

being used as cattle feed. Root rot

diseases are one of the major constraints

in the profitable yield of sugar beet in the

form of tonnage and sugar content. There

are a number of soil borne fungal

pathogens that are responsible for poor

establishment and yield loss in sugar beet

crop (Harveson & Rush, 2002; Kiewnick

et al., 2001; Weiland & Sundsbak, 2000;

Windels & Lamey, 1998). In Egypt,

Rhizoctonia solani

primarily causes root

and crown rot disease on sugar beet.

Also,

Macrophomina phaseolina

causes

extensive damages in sugar beet.

Chemical inducers act as alternative and

safe trial for management of many

diseases, especially those of vegetable

crops (Abada et al., 2008). Plant

resistance can be achieved by the use of

antioxidants

(Dov & llana, 1992

)

. Plant

inducers may act on plants to induce high

levels of systemic resistance to

subsequent pathogen attack

(Ward et al.,

1991). Certain chemicals, such as

salicylic acid and potassium salts induced

systemic acquired resistance in plants

against some plant pathogens (Lin et al.,

2009). Growers typically use an

integrated system including early

planting, crop rotation, resistant varieties

as well as fungicide applications to

manage sugar beet root rot diseases. But,

fungicides are still the most effective and

dependable mean, achieving appreciable

results in diseases reduction. The aim of

the current study is to evaluate the

severity of root rot disease of sugar beet

crop and the efficacy of various chemical

compounds

i.e.

antioxidants and

fungicides and their proper doses in

controlling root rot disease.

2. Materials and methods

This work was carried out in the

Research Laboratory and Farm of

Faculty of Agriculture, Al-Azhar

University (Assiut Branch), Assiut,

Egypt.

2.1 Isolation and identification of

sugar beet root rot disease

Sugar beet root samples were collected

from naturally infected sugar beet plants

growing in different locations

representing four governorates

i.e.

Assiut, Minia, Fayoum and Kafr-

Elsheikh during 2017/2018 growing

season. Plant roots were taken to the

laboratory for the isolation and

identification of the causal pathogens.

Samples of roots were washed carefully

with tap water to remove adhering soil

particles, cut into small pieces of about

0.3 cm long, surface sterilized with

dipping in 70% ethyl alcohol for 2

minutes and left to dry on sterilized filter

paper, then transferred individually to

Petri dishes, each containing about 20 ml

potato dextrose agar (PDA) medium.

Petri dishes were incubated at 25±2°C

for 7 days and inspected for fungal

growth. The developed fungal colonies

were purified using hyphal tip or single

spore techniques. The purified fungi

were identified according to fungal

morphological and microscopical

characteristics as described by Barnett

and Hunter (1986), Booth (1977) and

Sneh et al. (1991)

and confirmed by

3

Agricultural Botany Department, Faculty

of Agriculture, Al-Azhar University

(Assiut Branch), Assiut, Egypt. The

obtained isolates were maintained on

PDA slants and kept in refrigerator at

5°C for further studies. The frequency of

the isolated fungi was calculated

separately for each of the collected

samples. Stock cultures were routinely

sub-cultured on fresh slants every month.

The frequency of the isolated fungi from

the infected roots was calculated

according to the following formula:

Fungal frequency % =





× 100

2.2 Pathogenicity tests

The pathogenic capability of the isolated

fungi was conducted under greenhouse

conditions in the Farm of Faculty of

Agriculture, Al-Azhar University (Assiut

Branch), Egypt during 2017/2018

growing season. Sugar beet seeds of

Farida, Lily and Pleno cultivars which

selected as three of the most common

cultivars grown in Egypt were sown in

sterilized sand clay soil in plastic pots (50

cm in diameter).

2.3 Inoculum preparation

The fungal inocula of 22 fungal isolates

representing 3 genera

i.e. Rhizoctonia

solani, Fusarium

spp

and

Macrophomina

phaseolina

were grown in 250 ml glass

jars containing the following substrate

per jar (75 g grain barley, 25 g coarse

sand and 25 ml tap water to cover the

mixture in jar). The jars were autoclaved

at 121°C for 30 minutes, left to cool, then

inoculated and incubated at 25±2°C for

15 days to obtain sufficient growth of the

fungi. Then, sterilized plastic pots in 5%

formalin solution (50 cm in diameter)

were filled with 5% formalin sterilized

soil (10 Kg /pot). After that, the

inoculum was mixed with the soil at the

rate of 2% (w/w) of soil, then, pots were

irrigated three times a week before

sowing to ensure even distribution and

growth of each particular fungus. Other

sterilized pots were filled with sterilized

soil and un-infested with the tested fungi,

which kept as control. The sugar beet

seeds were washed with sterile distilled

water to remove residual effect of seed

dressing fungicides before sowing in

plastic pots. Three seeds were planted in

each pot, replicated three times for each

tested fungus. The pots were irrigated

and fertilized regularly under greenhouse

conditions. Disease severity was

recorded after 120 days from sowing.

Disease severity index (DSI) was

calculated according to Liu et al. (1995)

as follows:

DSI =



  

× 100

Whereas: d is the disease rating of each

plant, d max is the maximum disease

rating and n is the total number of plants

examined in each replicate. The

inspected plants were classified into

seven categories according to Ruppel et

al

.

(1979). The root rot rating scale was

as follows: 0: Root surface clean with no

visible lesions, 1= Superficial, scattered

non-active lesion, 2= Shallow, dry rot

canker on < 5% of root surface, 3= Deep

dry rot cankers at crown or extensive

lateral lesions affecting 6-25% root

surface, 4= Extensive rot affecting 26-

50% of root, which cracks and canker up

to 5 mm deep, 5= > 50% of root

blackened with rot extending into

interior, 6= Entire root blackened except

4

extreme tip, 7= Root 100% rotted and

foliage is dead.

2.4 Evaluation of antioxidant against

sugar beet root rot disease

2.4.1

In vitro

test

The inhibitory effect of five antioxidants

on the mycelial growth of three fungal

isolates

i.e. Rhizoctonia solani

(No. 16

and 22) and

Macrophomina phaseolina

(No. 11) which causing sugar beet root

rot disease was estimated on PDA

medium. Different rates of the tested

antioxidants

i.e.

salicylic acid, ascorbic

acid, citric acid, catechol and potassium

silicate were individually added to

conical flasks containing sterilized PDA

medium before its solidification to obtain

the concentrations of 20, 40, 60, 80 and

100 mM (Millimole), on the basis of

molecular weight of each tested

compound, then rotated gently to ensure

equal distribution of antioxidant, poured

in sterilized Petri plates (9 cm in

diameter). Each Petri dish was contained

with 20 ml of PDA medium, then

individually inoculated in the center with

5 mm agar disc having active mycelial

growth of the pathogenic fungi. Three

replicate plates were used for each

concentration. A set of antioxidant free

PDA plates were inoculated by the tested

pathogens to serve as control. All

inoculated plates were incubated at

25±2°C for 7 days, when the fungal

growth completely filled the antioxidant

free plates, the inhibitory effects of the

tested antioxidants were estimated by

measuring the fungal growth in each

treatment. The fungal growth inhibition

percentage was calculated using the

formula of Chapagain et al. (2007) as

follows:

Inhibition percentage =

-



× 100

2.4.2

In vivo

test

The most effective antioxidants in the

laboratory tests were tested to study their

effectiveness under greenhouse

conditions during 2018/2019 and

2019/2020 growing seasons. Farida

cultivar sugar beet seeds, the highly

tolerant to root rot disease were used in

this study. Experiment was conducted

using sterilized sand clay soil in pots (50

cm in diameter). Inocula of three fungal

isolates

i.e. Rhizoctonia solani

(No. 16

and 22) and

Macrophomina phaseolina

(No. 11) were prepared by growing each

fungus on autoclaved barley sand

medium in 250 ml jars. Inoculated jars

were incubated at 25±2°C for 15 days.

The inoculum was thoroughly mixed

with the sterilized soil at the rate 2%

(w/w). The infested soil was watered

every three days for one week before

sowing the seeds. Three seeds were

planted in each pot, artificially infested

by any of the pathogenic fungi. In this

respect, salicylic acid, citric acid, and

catechol, the best antioxidants in

suppressing the pathogenic fungi

in vitro

were used at the concentrations of 60, 80

and 100 mM. After one month from

sowing, each tested compound was

added as soil drench. Then, Farida

cultivar plants in pots were sprayed every

15 days, four times, 45, 60, 75 and 90

days from sowing date. Infested soil

without addition of chemical inducers

served as control. Three replicates were

used for each treatment, each replicate

contained three plants. Disease

assessment was recorded after 120 days

from sowing date as previously

described.

5

2.5 Evaluation of fungicides against

sugar beet root rot disease

This study was carried out in both

laboratory and under greenhouse

conditions of Faculty of Agriculture, Al-

Azhar University (Assiut Branch),

Assiut, Egypt to evaluate the efficiency

of six fungicides for controlling root rot

disease of sugar beet caused by

M.

phaseolina

and

R. solani

(No. 16 and 22

isolates). Used fungicides were as

commercial products

i.e.

Actamyl 70%

WP, Chlorothalonil 50% SC, Evito 48%

SC, Pyrus 40% SC, Shenzy 34% SC and

Fentobein 32.5% SC. The trade name,

group name, chemical group, common

name, formulation and mode of action of

the fungicides were given in Table (1).

2.6.1

In vitro

test

Both systemic and contact fungicides

were used

In vitro

screening according to

Dhingra & Sinclair (1985). The tested

fungicides were suspended in sterile

distilled water and added to PDA

medium under aseptic conditions in

conical flasks to obtain final

concentrations of 5, 10, 25, 50, and 100

ppm. Medium without fungicides served

as control. After solidification of the

medium in Petri plates, 5 mm agar discs

taken from the edge of 7 days old culture

of each of the tested fungi were placed in

the center of Petri plates. Three Petri

plates were used for each concentration.

The inoculated plates were incubated at

25±2°C and daily radial colony growth

was checked till the upper surface in

control treatment was fully covered with

the mycelial growth of the fungus. The

fungal growth inhibition percentage was

calculated using the formula of

Chapagain et al. (2007) as follows:

Inhibition percentage =

-



× 100

Table 1: List of fungicides used against M. phaseolina and R. solani.

Trade name

Group name

Chemical group

Common name

Formula

Mode of action

Actamyl

Methyl

Benzimidazole

Carbamates

Thiophanates

Thiophanate methyl

70% WP

Systemic

Chlorothalonil

Chloronitriles

(Phthalonitriles)

chlorothalonil

50% SC

Contact

Evito

Quinone Outside

Inhibitors

Dihydro-dioxazines

Fluoxastrobin

48% SC

Systemic

Pyrus

Anilino-

Pyrimidines

Anilino-pyrimidines

Pyrimethanil

40% SC

Contact

Shenzy

2,6-dinitro-anilines

Fluazinam

34% SC

Contact

Quinone Outside

Inhibitors

Methoxy-acrylates

Azoxystrobin

Systemic

Fentobein

Azoxystrobin

32.5% SC

DeMethylation

Inhibitors

Triazoles

Difenoconazole

Systemic

2.6.2

In vivo

test

The most effective fungicides in the

laboratory were chosen and tested under

greenhouse conditions during 2018/2019

and 2019/2020 growing seasons. The

experiment was conducted using

sterilized soil with formalin solution

(5%). The inocula of the tested fungi

were prepared by growing each fungus

on autoclaved barley sand medium in

250 ml jars as previously mentioned. The

inoculum was thoroughly mixed with

sterilized soil at the rate 2% (w/w) and

6

the infested soil was watered every three

days for one week before adding the

fungicides and sowing the seeds. The

three different fungicides applied were

Evito 48%, Shenzy 34% and Fentobein

32.5% at 1, 2 and 3 g/Kg soil before

sowing Farida cultivar seeds. The tested

fungicides were mixed with infested soil

and watered again to ensure complete

distribution of the fungicides in the

infested soil. Each pot was planted with 3

seeds. Three pot replicates were used for

each treatment. The pots without any

fungicides were served as control. The

pots were irrigated and fertilized

regularly. After 120 days of application,

Plants were uprooted and disease severity

was recorded as mentioned before.

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 (L.S.D) 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

and Discussion

3.1 Isolation and identification of the

associated fungi with sugar beet root

rot disease

Different fungal isolates

i.e. Fusarium

spp.,

Rhizoctonia solani

(Kuhn) and

Macrophomina phaseolina

(Tassi) Goid

were isolated from rotted sugar beet roots

collected from different locations of

Assiut, Minia, Fayoum and Kafr-

Elsheikh governorates, Egypt. Data in

Table (2) indicated that different fungi

varied from one location to another were

able to infect sugar beet roots.

Fusarium

spp. was the most dominant fungal genus

in all locations as its frequency was 68%.

Also,

Rhizoctonia solani

reached about

18%, followed by

Macrophomina

phaseolina

as reached it 14%.

Table 2: Source and frequency of fungi associated with diseased sugar beet roots during 2017/2018 growing

season.

The isolated fungi

Source of isolates (governorate)

Occurrence

Frequency (%)

Fusarium spp.

Assiut, Fayoun, Minia and Kafr-

Elsheikh

15

68

Rhizoctonia solani

Fayoum and Assiut

4

18

Macrophomina phaseolina

Assiut,Minia and Kafr-Elsheikh

3

14

Total

22

100

These results are in agreement with El-

kazzaz et al. (1999) who reported that

Sclerotium rolfsii

and

Rhizoctonia solani

cause serious root rot diseases affecting

sugar beet crop in Egypt. Perfect stage of

R. solani

, (

Thanatephorus cucumeris

)

causes one of the most damaging sugar

beet diseases, wherever sugar beet was

grown. These fungi are considered

common soil inhabitants (Windels et al.,

1997).

Macrophomina phaseolina

survives in soil or host tissue for at least

two years, microsclerotia are formed in

sugar beet and other hosts such as

common bean, cotton, maize, potato,

sorghum, soybean, strawberry, sunflower

and sweet potato (Su et al., 2001; Collins

et al., 1991).

7

3.2 Pathogenicity tests

Twenty two fungal isolates were tested

for their pathogenic capabilities on sugar

beet plants (Farida cv.) under greenhouse

conditions during 2017/2018 growing

season. Data in Table (3) showed that all

tested fungal isolates were able to infect

sugar beet plants causing root rot disease.

All the infected sugar beet plants showed

typical symptoms of root rot disease.

Also, all the tested isolates significantly

increased root rot disease as compared

with the control.

Rhizoctonia solani

(No.

22) gave the highest percentage of

disease severity after 120 days from

inoculation. Also,

R. solani

(No. 16) gave

the same trend of disease severity after

the same period, followed by

M.

phaseolina

(No. 11) While,

Fusarium

sp.

(No. 14) recorded the lowest disease

severity after 120 days. In all cases,

R.

solani

isolates caused the highest disease

incidence of sugar beet roots.

Pathogenicity tests proved that the

obtained fungi were pathogenic to sugar

beet (Farida cv.). At the same time, the

most aggressive isolates were

R. solani

(No. 22)

, R. solani

(No. 16) and

M.

phaseolina

(No. 11), respectively. These

results are in harmony with EL-Kazzaz et

al. (2000), El-Kholi (2000) and Husseien,

Manal (2005) who reported that the most

important diseases affecting sugar beet

production in Egypt are damping-off and

root-rot caused by several pathogens,

i.e.

R. solani,

M. phaseolina, Sclerotium

rolfsii and Fusarium spp.

Table 3: Disease severity of sugar beet root rot disease caused by the most frequent fungi

under greenhouse conditions during 2017/2018 growing season.

The tested fungi

Source (governorate)

Severity of infection after 120 days (%)

Fusarium sp. No. 1

Minia

54.05

Fusarium sp. No. 2

Minia

42.85

M. phaseolina No. 3

Minia

65.07

Fusarium sp. No. 4

Minia

34.91

R. solani No. 5

Kafr-Elsheikh

47.61

Fusarium sp. No. 6

Kafr-Elsheikh

30.15

Fusarium sp. No. 7

Kafr-Elsheikh

46.02

Fusarium sp. No. 8

Kafr-Elsheikh

23.8

Fusarium sp. No. 9

Kafr-Elsheikh

39.67

Fusarium sp. No. 10

Kafr-Elsheikh

38.09

M. phaseolina No. 11

Kafr-Elsheikh

71.42

Fusarium sp. No. 12

Assiut

22.21

Fusarium sp. No. 13

Assiut

47.61

Fusarium sp. No. 14

Assiut

17.45

Fusarium sp. No. 15

Assiut

23.8

R. solani No. 16

Assiut

73.01

M. phaseolina No. 17

Assiut

42.85

Fusarium sp. No. 18

Assiut

31.74

Fusarium sp. No. 19

Fayoum

33.33

Fusarium sp. No. 20

Fayoum

23.8

R. solani No. 21

Fayoum

39.67

R. solani No. 22

Fayoum

77.77

Control

0

LSD at 5 %

6.32

Several soil-borne fungi attack sugar beet

causing a significant reduction of the

production

viz., Rhizoctonia solni, R.

crocorum, Aphanomyces cochlioides, M.

phaseolina, Phoma betae, Pythium

aphanidermatum

and

S. rolfsii

(Elwakil

8

et al., 2018).

3.3 Evaluation of different antioxidants

against sugar beet root rot disease

3.3.1

In vitro

test

Different concentrations of antioxidants

i.e.

catechol, salicylic acid, ascorbic acid,

potassium silicate and citric acid were

used to study their effectiveness on the

linear growth of

R. solani

(No.16 and 22)

and

M. phaseolina

(No. 11). Data

presented in Table (4) clarified that

catechol and salicylic acid completely

suppressed the mycelial growth of the

pathogenic fungi with all tested

concentrations. At the same time, citric

acid at 60, 80 and 100 mM completely

inhibited the fungal growth of the tested

fungi except,

M. phaseolina

and

R.

solani

(No. 16), wherever inhibition

percentage reached it 89.8 and 82.4 %,

respectively. Also, potassium silicate

completely suppressed the fungal growth

at 80 and 100 mM. The same data

exhibited that the increase in

concentrations of ascorbic acid,

potassium silicate and citric acid from 20

mM to 100 mM resulted in an obvious

decrease in the mycelial growth of

R.

solani

(No. 16 and 22) and

M.

phaseolina

(No. 11). Such findings agree

with those reported by Abdelaziz (2017)

who mentioned that salicylic acid and

catechol with tested concentrations were

the most effective antioxidants in

inhibiting the linear growth of

F. solani,

R. solani

and

M. phaseolina

.

Table 4: Evaluation of different antioxidants on the linear growth of the pathogenic fungi.

Antioxidants (A)

Conc.

(mM) (B)

Mycelial growth inhibition (%)

M. phaseolina

R. solani No. 16

R. solani No. 22

Salicylic acid

20

100

40

100

60

100

80

100

Citric acid

20

54.55

76.84

36.1

40

88.88

77.77

72.22

60

89.8

82.4

100

80

100

Ascorbic acid

20

28.69

0

40

54.62

0

60

87.03

33.33

34.25

80

100

35.18

65.73

100

64.8

100

Catechol

20

100

40

100

60

100

80

100

Potassium silicate

20

43.51

0

40

49.99

12.03

0

60

81.47

47.4

24.99

80

85.18

100

89.8

100

Control

0

LSD at 5%

A

0.82

2.7

0.78

C

0.79

2.11

0.66

A x C

1.94

5.18

1.62

9

While, thiourea followed by ascorbic acid

and sodium benzoate reduced the

mycelial growth only at high

concentrations. Catechol and salicylic

acid with all concentrations tested

entirely suppressed the mycelial growth

of

F. solani

,

F. oxysporum

and

R. solani

,

potassium silicate with all concentrations

tested strongly retarded the mycelial

growth of

F. solani

and

F. oxysporum

, as

well as entirely inhibited the linear

growth of

R.solani

. In this respect,

considerable reduction of the linear

growth took place with citric acid and

ascorbic acid at different concentrations

(Kasem Aya, 2018).

3.3.2

In vivo

test

The most effective antioxidants

in vitro

were chosen to study their effectiveness

against the pathogenic fungi on Farida

cv. plants in infested pots at the

concentrations of 60, 80 and 100 mM

under greenhouse conditions during

2018/2019 and 2019/2020 growing

seasons. It was shown from Table (5) that

all tested chemical inducers significantly

reduced sugar beet root rot incidence

caused by

R. solani

(No. 16 and 22) and

M. phaseolina

(No. 11) during

2018/2019 and 2019/2020 growing

seasons. Root rot disease of sugar beet

plants was decreased by using all tested

concentrations and reached its minimum

records at the highest concentration, 100

mM. The most effective treatment which

minimized

R. solani

(No. 16) during

2019/2020 season was salicylic acid

followed by catechol and citric acid,

respectively. It is obvious from the same

Table that all chemical inducers had

significantly protected sugar beet plants

against root rot pathogens as compared

with control. Under greenhouse

conditions, root rot diseases were

controlled with the most selected

antioxidants. Variability in the effect of

antioxidants could be referred to

differences in their activity or variation

in the responses of the tested fungi.

Control of root rot disease mainly

depends on fungicides. However,

intensive application of fungicides causes

hazards to human health and

environment.

Table 5: Effect of different antioxidants on controlling sugar beet root rot disease of Farida cv. under greenhouse

conditions during 2018/2019 and 2019/2020 growing seasons.

Antioxidants (A)

Conc.

(mM) (B)

Disease severity (%)

2018/2019

2019/2020

M. phaseolina

R. solani No. 16

R. solani No. 22

M. phaseolina

R. solani No. 16

R. solani No. 22

Salicylic acid

60

44.43

52.37

49.2

47.61

53.96

55.55

80

23.8

28.56

26.98

22.21

31.74

23.8

100

19.04

22.21

23.8

20.62

25.39

17.45

Citric acid

60

61.9

66.66

63.48

58.72

61.9

69.83

80

49.2

52.37

53.96

47.61

46.02

50.79

100

26.98

23.8

25.39

30.15

20.62

31.74

Catechol

60

34.91

41.26

39.67

42.85

36.5

44.43

80

20.62

28.56

31.58

15.86

22.21

26.82

100

11.1

9.52

14.28

12.69

7.93

Control

80.95

74.59

79.36

74.59

76.18

80.95

LSD at 5%

A

7.97

10.04

9.09

6.41

10.51

5.3

C

2.47

3.5

4.38

3.82

3.63

2.82

A x C

4.95

7

8.77

7.64

7.26

5.64

Therefore, alternative approaches for the

control of plant diseases should be

considered. Induction of resistance in

plants to overcome pathogens infection is

10

a promising approach for controlling

plant diseases. Exogenous or endogenous

factor could substantially affect host

physiology, lead to rapid and coordinated

activation of defense-gene in plants,

normally expressing susceptibility to

pathogen infection (El-Mougy et al.,

2004). This induced resistance to

pathogens can be achieved by the

application of various abiotic agents

(chemical inducers) such as salicylic

acid, potassium salts and sorbic acid

(Mandal et al., 2009; Abdel-Monaim,

2010 and Akram & Anjum, 2011). It

could be concluded that some chemical

inducers may also have a direct

antimicrobial effect and are involved of,

gene expression, phytoalexin production

and induction of systemic resistance.

Data are in agreement with those reported

by several researches when they used

such compounds against several plant

diseases caused by various pathogens

(Abdelaziz, 2017; El-Samawaty & Galal,

2009; Galal & Abdou, 1996).

3.4 Comparative effectiveness of

different fungicides against sugar beet

root rot disease

3.4.1

In vitro

test

The efficiency of certain fungicides

against the tested fungi was screened

in

vitro

in order to find out an effective

chemical control method. It was clear

from data presented in Table (6) that the

increase in fungicides concentration had

resulted an obvious increase in mycelial

inhibition percentage of fungi. In this

respect, all the tested fungicides

significantly reduced the mycelial growth

of the tested fungi. Shenzy fungicide was

the most effective in reducing the

mycelial growth of

M. phaseolina

with

concentrations 5, 10, 25 and 50 ppm and

completely suppressed the mycelial

growth at 100 ppm. The same effect was

obtained by using Evito and

Chlorothalonil at 50 and 100 ppm,

followed by Fentobein at the same

concentrations. While, Actamyl was the

least effective fungicide on the mycelial

growth of

M. phaseolina.

Mycelial

growth of

R. solani

(No. 16) was entirely

inhibited with Actamyl and Shenzy each

at 50 and 100 ppm. Whatever, Fentobein

gave the same effect at 100 ppm, while

Chlorothalonil and Pyrus fungicides were

less effective in reducing and inhibiting

mycelial growth. On the other hand,

Shenzy, Evito and Fentobein fungicides

each at 50 and 100 ppm significantly

reduced mycelial growth of

R. solani

(No. 22) at 50 ppm as well as completely

suppressed at 100 ppm. Pyrus and

Chlorothalonil were the least effective

fungicides on the mycelial inhibition of

R. solani

(isolate 22). It became clear

that the linear growth of all pathogens

was greatly retarded by increasing

fungicide concentrations, which reached

almost complete inhibition at 100 ppm.

Shenzy, Fentobein and Evito with the

highest concentration completely

suppressed the three pathogenic fungi.

The selective action of each fungicide

and their concentrations on fungal

growth might be due to the sensitivity of

the different pathogens. Results are in

agreement with the findings of

Bhanumathi and Ravishankar (2007)

who evaluated seven fungicides at 50,

100 and 150 ppm concentrations and

found carbendazim (Bavistin, Sendo or

Kema Z) most effective in inhibiting

radial growth of

F. solani.

11

Table 6: Effect of different concentrations of six fungicides on the mycelial growth of the

tested pathogenic fungi in vitro.

Fungicide (A)

Conc.

(ppm) (B)

Mycelial growth inhibition (%)

M. phaseolina

R. solani No. 16

R. solani No. 22

Actamyl 70% WP

5

9.25

0

10

26.84

0

10.18

25

34.25

67.58

74.99

50

65.73

100

81.47

100

78.69

100

89.8

Chlorothalonil

50% SC

5

45.36

0

8.33

10

53.69

0

23.14

25

67.58

7.4

40.73

50

84.25

37.03

51.84

100

54.62

57.4

Evito 48% SC

5

65.73

12.03

29.62

10

77.77

38.88

66.66

25

84.25

42.58

82.4

50

86.1

47.22

87.95

100

74.07

100

Shenzy 34% SC

5

81.47

60.18

57.4

10

83.33

77.77

60.18

25

87.95

87.03

71.29

50

88.88

100

87.95

100

Pyrus 40% SC

5

12.03

0

10

22.22

0

10.18

25

72.22

0

55.55

50

84.25

51.84

73.14

100

89.8

69.44

85.18

Fentobein 32.5%

SC

5

71.29

72.22

74.07

10

76.84

78.69

74.99

25

81.47

80.55

79.62

50

85.18

84.25

82.4

100

90.73

100

Control

0

LSD at 5%

F

1.35

1.14

1.46

C

1.09

1.03

1.06

F x C

2.9

2.75

2.82

3.4.2

In vivo

test

Application of the most effective

fungicides was carried out to study the

effect of fungicides on the development

of sugar beet root rot caused by

M.

phaseolina

and

R. solani

(isolates No. 16

and 22) under greenhouse conditions in

pot experiments during 2018/2019 and

2019/2020 growing seasons. Data

presented in Table (7) demonstrated that

all fungicides significantly reduced the

disease severity as compared with the

control. In this respect, Shenzy fungicide

exhibited distinct effect in reducing

disease severity of both

R. solani

No. 16

and No. 22 at 3 gm/Kg soil compared

with other treatment and with control

during both 2018/2019 and 2019/2020

growing seasons, Evito fungicide came at

the second order in the term of disease

reduction. Meanwhile, Evito fungicide

with the highest concentration 3 g /Kg

soil achieved the best effect in reducing

disease severity caused by

M. phaseolina

followed by Shenzy fungicide. Fentobein

fungicide gave less effect in reducing

disease severity although; it strongly

reduced the three causal pathogens to a

large degree as compared with the

control. Data also revealed that the

disease severity caused by all pathogens

12

was greatly reduced by increasing

fungicide concentrations, which reached

the highest reduction at 3 g /Kg soil for

all tested fungicides.

Table 5: Comparative effectiveness of fungicidal treatments on sugar beet root rot disease under

greenhouse conditions during 2018/2019 and 2019/2020 growing seasons.

Fungicide (A)

Conc.

(g/Kg soil) (B)

Disease severity

2018/2019

2019/2020

M. phaseolina

R. solani 16

R. solani 22

M. phaseolina

R. solani 16

R. solani 22

Evito 48% SC

1

25.39

30.15

28.56

31.74

30.15

2

15.86

20.63

17.45

14.28

22.21

3

6.34

17.45

14.28

7.933

15.86

12.69

Shenzy 34% SC

1

20.62

28.56

26.98

31.74

28.32

2

12.69

19.04

17.45

20.62

15.86

3

7.93

9.52

12.69

9.52

11.1

7.93

Fentobein 32.5%

SC

1

33.33

36.5

34.91

39.67

34.91

2

19.04

23.8

25.39

17.45

26.97

25.39

3

11.1

17.45

19.04

7.93

14.28

15.86

Control

80.95

74.59

79.36

74.59

76.18

80.95

LSD at 5%

A

5.3

9.67

8.39

5.69

9.67

8.31

B

2.42

4.06

4.34

3.03

4.78

5.37

A x B

4.85

ns

6.06

9.56

Ns

Results are in agreement with Elwakil et

al. (2018)

who mentioned that several

fungicides have been shown to be useful

in reducing disease incidence including

chlorothalonil, pencycuron, tebucona-

zole, azoxystrobin, trifloxystrobin and

pyraclastrobin. As regard, azoxystrobin

has provided the most consistent level of

control in both inoculated and natural

infection trials (Jacobsen et al., 2005;

Kiewnick et al., 2001).

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