Journal of Phytopathology and Pest Management 8(1): 92-105, 2021
pISSN: 2356-8577 eISSN: 2356-6507
Journal homepage: http://ppmj.net/
∗
Corresponding author:
Hoda A. M. Ahmed,
E-mail: hudafatah@yahoo.com
92
Copyright © 2021
Efficacy of biological therapies against onion basal rot
caused by Fusarium oxysporum f. sp. cepae under field
and storage conditions
Hoda A. M. Ahmed1*, Zeinab Soliman2, Mohamed A. Khalil1, Sayed B. M. Fawaz1
1Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
2Assuit University Moubasher Center (AUMMC), University Assiut, Egypt
Abstract
Keywords: Allium cepa, basal rot, antagonism, Fusarium oxysporum f. sp. cepae, yeasts.
Basal rot disease of onion is caused by Fusarium oxysporum f. sp. cepae (Hans.)
(FOC) economically significant losses wherever onion is grown. Fusarium
oxysporum were isolated from diseased onion cultivated in different places of
Assiut, Egypt. Efficacy of certain yeasts was evaluated for controlling the basal
rot of onion in vitro. Among of the tested isolates, Saccharomyces cerevisiae gave
the greatest inhibition (57.74%) and Candida tropicalis (1) significantly exerted
the greatest reduction of mycelial growth of F. oxysporum f. sp. cepae (51.18%).
Based on the in vitro screening, effective yeasts were evaluated under greenhouse,
field and storage conditions. Yeasts were applied by two methods (add the
pathogen and antagonistic yeasts to soil before sowing seedling onion, and seedling
onion soaking in yeasts for 20 minute). Both methods of inoculation showed
substantial impact on disease development and plant growth. Add method caused
maximum reduction in plant germination, followed by soaking method as
compared to control. Application of fungicide (Captain) as compared brought a
remarkable increase in seedling emergence of treated plants inoculated with F.
oxysporum as compared to the untreated plants. In conclusion, tested yeasts were
useful as an alternative to chemical control of the onion basal rot and to enhanced
growth and yield of onion.
Ahmed Hoda et al., 2021
93
1. Introduction
Onion (Allium cepa L.), is one of the oldest
vegetables, has been used as spice and
medicine for thousands of years (Keusgen,
2002). Fusarium basal rot of onion is an
economically important disease to which onion
bulbs and shallots are sensitive during all their
growth stages (Cramer, 2000). To manage the
disease, chemical control is very effective, but
it is not economical and pollutes the
environment. Use of resistant cultivars is
another acceptable strategy of control however
onion cultivars with acceptable level of
resistance are limited. Researchers have
recently considered biological control as a
complementary approach for controlling this
disease. Yeasts treatments were suggested to
play a beneficial role in cell division and cell
enlargement (Freimoser et al., 2019). yeasts
were demonstrated to be effective biocontrol
agents of seedlings onion post-emergence
damping off. Various yeast species have been
reported as active biological control agents.
Some effectively saccharomyces cerevisiae
was used as bioagents root rot pathogens under
greenhouse conditions (Abd El-kader et al.,
2012). Candida glabrata and C. maltosa
significantly reduced the incidence of late
maize wilt disease when applied by seed
inoculation (El-Mehalawy et al., 2004). Pichia
guilliermondii gave hence possess potential to
control wilt disease in tomato crop (Nguyen et
al., 2011). Shalaby and El-Nady (2008) found
that seed soaking, or soil inoculation with S.
cerevisiae increased germination rate, survival
of plants and reduction of pre and post
emergence damping off and inhibited
Fusarium oxysporum liner growth in vitro.
Also, they found that pre- and post- emergence
damping off was reduced significantly when
seeds of faba bean were coated with a water
suspension of the yeast (109 CFU ml-1). The
beneficial effects of these microorganisms last
longer than that of chemicals and can therefore
protect the plant throughout all growth stages.
Under greenhouse and field conditions, control
of plant diseases using antagonistic yeasts can
be effective. Also, biological control can limit
the instances of basal rot of onion caused by F.
oxysporum and reduced probability of disease
development. If pathogen attacks the host plant
late in the season, the symptoms may not
appear until onion bulbs are in storage (Ozer et
al., 2003) Present study found that biological
agents inhibit the growth of F. oxysporum.
Fusarium oxysporum f. sp. cepae (Hanz) Snyd
attack onion bulbs in storage and cause rotting
of onion bulbs during storage. In storage, onion
bulbs appear spongy or sunken, infected bulbs
are softened, brown and watery when cut open
during storage bulbs are affected by many
microorganisms leading to rot being
commercially important crop of the state; it
was felt necessary to carry out investigations
on storage rot of onion. Despite the
achievement in production technology and
availability of good varieties of onion, the post
harvest losses during storage is still an ailing
cause which leads to significant qualitative and
quantitative losses during storage up to 25-
30%. The onion postharvest losses were
estimated worth Rs 600 crores is found to be
due to desiccation, decay and sprouting,
(Kumar et al., 2015). The rationale behind such
post-harvest losses till today is the
unavailability of good storage facilities during
post-harvest storage phase. There seems a big
gap between the storage facility and the storage
capacity which is ultimately leading to the
unforeseeable postharvest decay and
deterioration of onion bulbs. Therefore, the
main objectives of this study were attempted to
apply a of some antagonistic yeasts, enhanced
the biocontrol of onion basal rot and studied
the suppressive effect of some free yeast
strains against Fusarium oxysporum, under
greenhouse, field and storage conditions.
2. Materials and methods
2.1 Isolation of the causal pathogen of onion
basal rot disease
Bulb samples of onion showing typical basal
Ahmed Hoda et al., 2021
94
rot symptoms were collected from different
locations in the Assiut governorate of Upper
Egypt. Isolation of the pathogen from the
infected bulbs was performed by the tissue
segment method described by Rangaswami
(1958). Infected portions of bulb samples were
cut into small pieces and washed thoroughly in
tap water. The pieces were then disinfected by
immersing in 1% sodium hypochlorite (SH)
solution for one minute, rinsed three times in
sterilized distilled water (SDW), and dried
between folds of sterilized filter papers.
Disinfected pieces were transferred aseptically
into Petri plates containing Potato Dextrose
Agar (PDA) medium supplemented with 400
mg streptomycin sulfate per liter of medium.
The plates were then incubated at 25±0.5 °C
for 5 days and examined daily for fungal
growth. The growing fungal colonies were
purified by single spore and hyphal tip
techniques, followed by sub-culturing onto a
freshly prepared PDA medium at the same
conditions. According to cultural and
microscopical characteristics of colony
mycelia and spores, isolated fungi were
morphologically identified (Leslie &
Summerell, 2006; Gerlach & Nirenberg,
1982). Pure cultures of isolated fungi were
maintained at 5 °C on PDA slants for further
studies.
2.2 Pathogenicity test
The pathogenic capability of all fungal isolates
obtained to cause basal rot disease was
investigated on the onion Giza 6 cultivar under
greenhouse conditions. The inoculum of each
isolate tested was prepared by placing two
disks (0.7 cm in diameter) taken from the 7-
day-old culture onto an autoclaved sand-maize
medium (80 g sieved fine river sand, 20 g
maize meal, and 50 ml water) in conical flasks
tightly closed with cotton plugs. Then flasks
were incubated at 27±0.5 °C for 14 days.
Formalin-sterilized plastic pots (35 cm in
diameter) were filled with autoclaved loam
soil (5.0 kg of each), infested with 150 g
inoculum of each isolate tested, and then
slightly irrigated every other day for a week.
Pots treated with the same amount of non-
inoculated sand-maize medium served as
control. Another week later, onion seedlings
were disinfected by dipping in 1% SH solution
for 3 min, rinsed three times in SDW for 10
min, and then transplanted at a rate of 6
seedlings per pot. The experiment was
performed with four pots (replicates) of each
isolate tested in a completely randomized
design. Then pots were checked daily and
irrigated when necessary. Observations of
basal rot symptoms were recorded daily and
continued with disease development until the
whole plant's complete rotting. Six months
after planting, plants were uprooted, and
percentages of disease incidence (DI) and
surviving plants (SP) were calculated
according to the following formula:
𝐷𝐼 % = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑒𝑎𝑠𝑒𝑑 𝑝𝑙𝑎𝑛𝑡𝑠
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑙𝑎𝑛𝑡𝑠 × 100
𝑆𝑃 % = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑢𝑟𝑣𝑖𝑣𝑖𝑛𝑔 𝑝𝑙𝑎𝑛𝑡𝑠
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑙𝑎𝑛𝑡𝑠 × 100
2.3 Preparation and growth conditions of
used yeast strains
Pure cultures of yeast strains were previously
isolated from different locations in Egypt and
identified according to classical methods used
in yeast taxonomy (van der Walt & Yarrow,
1984). Yeast strains which exhibit the highest
antagonistic effects against the pathogenic F.
oxysporum were selected and cultured on
glucose peptone yeast extract (GPY) medium
(Difco, 1985) by shaking on a rotary shaker at
28±0.5 °C for two days.
Ahmed Hoda et al., 2021
95
2.4 Study of antifungal activity of yeast
strains against FOC
Nineteen yeast strains were tested for the
antifungal activity against FOC using the
direct dual culture technique. Yeast strains
were initially grown on GPY broth in test tubes
by shaking on a rotary shaker at 28±0.5 °C for
2 days, as mentioned before. On the GPY
plates' surface, 0.1 ml of each aqueous yeast
suspension with a concentration of 106 cells
ml-1 were plated. Then yeasts were grown for
5-7 days as a lawn on the Sabouraud agar
surface, whereby 5 mm discs in diameter were
cut. Disks from each yeast strain were placed
on a PDA medium on one side of the Petri
plate, and the opposite side at an equal distance
was inoculated by 5 mm- disks of FOC isolate
taken from 7-days-old culture. Four plates
were used for each yeast strain tested, and the
inoculated plates with FOC discs only were
served as control. The entire experiment was
twice repeated for confirmation of the results.
After 10 days of plate incubation at 28±0.5 °C,
antifungal activity was determined by
measuring the zone of inhibition (cm)
produced by yeasts against FOC. Also, the
located mycelium inside the zones of
inhibition was microscopically examined.
Growth inhibition (%) of FOC was calculated
using the following formulae:
𝐺𝐼 % = 𝐶 − 𝑇
𝐶 × 100
Where GI = growth inhibition, C = mycelium
radial growth in control, and T = mycelium
radial growth produced by yeast strain tested.
2.5 Evaluation of antagonists under
greenhouse conditions
Yeast strains that showed the highest
suppression rate against FOC in vitro were
applied to control the disease under
greenhouse and field conditions. Pots of 35 cm
diameter were filled with sterilized soil mixed
with the FOC inoculum one week before
planting. Soil infestation was conducted 7 days
before sowing by adding 3% of the inocula
with the soil in each pot. All treatments were
applied by two methods the first was add the
pathogen and antagonistic fungus (yeasts) at
the rates of 106 CFU/g were mixed with soil
pots before sowing seedling onion, the second
methods seedling onion soaking in yeasts for
20 minutes. Seedling onion treated in
fungicide Captain (50% WP) was used as a
reference. Each pot was planted with 5
seedling onion Giza 6 cultivar. Four replicates
were used to each treatment and pots
containing inoculum of FOC only were used
as control. Plants were irrigated when
necessary and examined periodically. Data
disease incidence and plant mortality were
recorded after 6 months of seed sowing. The
formulae used to determine the diseases
incidence were followed as mentioned before.
2.6 Evaluation of antagonists under field
conditions
A field experiment was conducted to evaluate
the efficacy of biocontrol agents on onion
basal rot during 2019/2020 and 2020/2021
seasons. Seedlings of onion cv. Giza 6 were
planted in rows in plots size 5 × 4 m and
spacing 15 cm. A Randomized Block Design
(RBD) was used with three replications.
Before sowing, the treatments were applied by
two methods such as greenhouse treated, and
fungicide Captain was used for comparison.
All normal agronomical practices including
irrigation, weeding and fertilizer application
were followed at regular intervals. Natural
incidence of basal rot of onion was recorded.
At harvest time, plant samples (10 healthy
plants each) were taken at random from each
plot to determine the growth parameters, plant
Ahmed Hoda et al., 2021
96
height (cm), bulb diameter (cm), Average bulb
weight (g) and total bulb yield (ton/feddan)
were recorded (feddan = 4200 m² = 0.420
hectares = 1.037 acres).
2.7 Bulb storage
After harvest, 5 kg onion bulbs for each
replicate from treatments were placed in nylon
mesh onion bags without removing the stalks
and Store in a well-ventilated place. During
storage the air was continuously drawn over
the onions by means of a fan to remove excess
moisture. The bulbs were stored at low
temperature for 30, 60, or 90 days. After the
appropriate duration of storage, five bulbs
were removed from each replicate bag and
evaluated for severity of Enterobacter bulb
decay. Each onion bulb was sliced from the
neck to the basal plate, and the cut surface area
of the fleshy scales was rated visually for
severity of Enterobacter bulb decay
(percentage of the surface area of the fleshy
scales showing symptoms typical of this
disease) (Schroederand du Toit, 2010). A low
incidence of bulbs (1 to 5%) showed
symptoms characteristic of other storage rots
(e.g., neck rot caused by Botrytis aclada and
B. allii, black mold caused by Aspergillus
niger, Fusarium basal rot caused by Fusarium
oxysporum f. sp. cepae.
2.7 Statistical analysis
Analysis of variance (ANOVA) was carried
out using MSTAT-C program. The least
significant difference (LSD) at P≤0.05 was
applied to detect differences among treatments
(Gomez and Gomez, 1984).
3. Results and Discussion
3.1 Pathogenicity test
Nine isolates of Fusarium oxysporum f. sp.
cepae were isolated from different localities of
Assiut governorate in Egypt. Identification of
the isolates was based on spore morphology
and culture characteristics, as described by
Booth (1985) and Schwartz (2010) (Figure 1).
Figure 1: Fusarium oxysporum f. sp. cepae; A: colony on DPA after 7 days, B,
C and D: hyphae bearing short monophialides, E: micro- and macroconidia.
Pathogenicity test of isolates are presented in
Table (1) indicate that all isolates proved to be able to infect onion plants causing basal rot
symptoms. Typical symptoms observed were
Ahmed Hoda et al., 2021
97
yellowing and eventual dieback of the leaves,
drying of leaves and in advance stage, basal
portion of plants completely rotted and entire
plant got collapsed on ground, which was
noticed 15 days after transplanting in the pots.
Uninoculated plants remained healthy. These
results agree with Saxena (2007) isolated
Fusarium oxysporum f. sp. cepae from
infected bulb in USA. Davis (2008) reported
the pathogen, F. oxysporum f. sp. cepae
causing onion and garlic basal rot.
Dissanayake et al. (2009) studied the
pathogenicity of 32 isolates of Fusarium spp.
on five commercial cultivars of welsh onion
and proved that five Fusarium oxysporum
isolates had higher virulence to Allium spp.
Table 1: Pathogenic capability of F. oxysporum f. sp. cepae on onion cultivar Giza 6.
Isolates number
Disease incidence (%)
Surviving plants (%)
1
41.66
58.33
2
45.83
54.16
3
50.00
50.00
4
66.66
33.34
5
29.16
70.83
6
33.33
66.67
7
37.49
62.50
8
20.82
79.17
9
79.16
22.22
Control
0.00
100.00
L.S.D. at 5%
11.41
2.77
3.2 Evaluation of yeast isolates as biocontrol
agents against the causal pathogen in vitro
Yeast isolates from different sources were
screening for their abilities to inhibit the
growth of the plant pathogen F. oxysporum.
These isolates were Candida tropicalis,
Cryptococcus albidus, Debaryomyces
hansenii, D. pseudopolymorphus,
Galactomyces candidus, G. pseudocandidus,
Klyuveromyces marixianus, Lachancea
thermotolerans, Papiliotrema laurentii, Pichia
caribaea, Saccharomyces cerevisiae, and
Saccharomyces sp., which were identified by
using morphological and physiological
characters according to Barnett et al. (2000)
and molecular by the internal transcribed
spacer (ITS) sequences of nuclear ribosomal
DNA. The studied yeast nineteen isolates were
shown variable antagonistic impact against the
plant pathogen F. oxysporum f. sp. cepae
giving inhibition percentages of the pathogen
growth ranging from 22.28 to 57.74 (Table 2
and Figure 2). The strains Saccharomyces
cerevisiae, Candida tropicalis, Pichia
caribaea and Saccharomyces sp. were
exhibited the highest antagonistic effect.
These promising strains were selected for the
applied experimental studies in greenhouse
and field.
Ahmed Hoda et al., 2021
98
Figure 2: Antagonistic effect of different antagonistic yeasts against
Fusarium oxysporum f. sp. cepae on PDA at 28 °C after 10 days.
Results are presented in Table (3) and Figures
(3 and 4) reveals that linear growth of
Fusarium oxysporum f. sp. cepae was
significantly decreased at all the tested
treatments. The highest decreased in linear
growth was pronounced by Saccharomyces
cerevisiae and Candida tropicalis (1) by
(57.74% and 51.18 %) respectively.
Table 2: Effect of certain yeasts on inhibition growth of Fusarium oxysporum f. sp. cepae in vitro.
Inhibition growth (%)
00.00
57.74
51.18
46.29
42.59
34.81
33.33
31.85
35.19
31.85
36.96
30.37
30.37
28.89
28.89
27.41
27.41
24.44
23.70
22.22
4.21
Ahmed Hoda et al., 2021
99
Table 3: Effect of selected antagonistic yeasts against Fusarium oxysporum f. sp. cepae in vitro.
Inhibition growth (%)
Yeast
00.00
Control
51.18
Candida tropicalis (1)
46.26
Candida tropicalis (2)
42.59
Candida tropicalis (3)
36.96
Saccharomyces paradaxus
57.74
Saccharomyces cerevisiae
35.19
Pichia caribaea
3.43
L.S.D. at 5%
The Pichia caribaea gave the least decreased
by 35.19%. The mycelial growth of Fusarium
oxysporum f. sp. cepae was influenced and
much reduced by other treatments. This agreed
with data obtained by Astasa and Aliad (2005)
who reported that 4 yeast isolates showed
some inhibitory effect on the growth of F.
oxysporum in vitro.
Figure 3: A, B and C: Antagonistic effect of Saccharomyces cerevisiae
against Fusarium oxysporum after 5, 7 and 10 days on PDA medium.
D, E and F: Antagonistic effect of Candida tropicalis against Fusarium
oxysporum after 5, 7 and 10 days on PDA medium.
Figure 4: Interaction of yeast with the pathogenic Fusarium oxysporum
in dual plate confrontation. A, B and C: yeast cells attack the pathogen
hyphae. D, E and F: Papillae‐like structures.
Ahmed Hoda et al., 2021
100
Yeast isolates which were found to be strongly
antagonistic to Fusarium oxysporum f. sp.
cepae in vitro were effective producers of
antifungal metabolites (El-Mehalawy et al.,
2004). In addition, it was found that the isolates
of actinomycetes produced chitinase and β-1,
3- glucanase and caused extensive plasmolysis
and cell wall lysis of Fusarium oxysporum f.
sp. cepae in vitro. Also, a yeast’s mechanism
for biocontrol involves nutrient competition
and by-production of extracellular substances
in the wound site of the host that causes
collapse and degradation of the fungal hyphae
(Baker & Cook, 1974).
3.3 Evaluation of antagonists under
greenhouse conditions
In pot experiment, all antagonists reduced the
disease severity. Table (4) showed that under
greenhouse conditions the percentage of basal
rot disease incidence in first method recorded
between 0-26.66% but second methods in
ranged between 6.66-33.33%. Both
Saccharomyces cerevisiae and Candida
tropicalis (1) had greater decreased in diseases
caused by Fusarium oxysporum f. sp. cepae by
0.00, 6.66, 6.66 and 6.66% in two methods
respectively followed by Candida tropicalis
(3) and fungicide (Captain) by 13.33, 13.33
and 20.00%. These results agreed with El-
Mehalawy et al. (2004) found that the
production of root and attached soil particles
of 14-day-old onion seedlings were colonized
to different degrees by yeast isolates with the
frequency of colonization being significantly
(Р < 0.05) greater in the first 2 cm of root and
soil. Root colonization frequency in the
rhizosphere soil was greater in treated plants
by yeasts.
Table 4: Effect of antagonistic yeasts on the incidence of onion basal rot diseases under greenhouse
conditions.
Yeast
Disease incidence (%)
Surviving plants (%)
Add
Soaking
Add
Soaking
Candida tropicalis (1)
6.66
6.66
93.33
93.33
Candida tropicalis (2)
20.00
33.33
80.00
66.66
Candida tropicalis (3)
13.33
13.33
86.66
86.66
Saccharomyces paradaxus
20.00
20.00
80.00
80.00
Saccharomyces cerevisiae
0.00
6.66
100
93.33
Pichia caribae
26.66
40.00
73.33
60.00
Fungicide (Captain)
13.33
20.00
86.66
80.00
Control
80.00
80.00
20.00
20.00
L.S.D. at 5% (Treatments)=
17.35
22.44
(Methods) =
6.36
5.58
(Treatments × Methods) =
n.s
n.s
3.4 Evaluation of antagonists under field
conditions
Treatments that contained yeasts significantly
(Р<0.05) reduced the incidence of onion basal
rot disease. There were significant differences
in the disease index, the number of diseased
onion seedlings between two methods (add the
pathogen and antagonistic fungus in soil and
seedling onion soaking in yeasts). The
application of each antagonistic yeast using
add method increased the percentage of onion
basal rot control. Table (5) shows the effect of
antagonistic yeasts and fungicide Captain on
onion basal rot disease under field conditions
and all used treatments significantly reduced
the disease. Data also show that the highest
values of decrease occurred with fungicide
(Captain) and Saccharomyces cerevisiae,
followed by the treatments of Candida
Ahmed Hoda et al., 2021
101
tropicalis (1) and Candida tropicalis (3), while
Pichia caribae and Candida tropicalis (2)
recorded the lowest reduction compared with
untreated plants (control) in two seasons. Such
results are in accordance with that reported by
Kamel et al. (2016) found that yeast strains
isolated against Fusarium oxysporum f. sp.
cucumerinum causal agent of cucumber wilt
disease in soil. Also, antagonists were applied
by soil infestation as in a previous work
(Zeidan et al., 2018). The main mechanism
involved in late basal rot disease reduction by
the yeast fungi is the production of non-volatile
diffusible metabolites since the production of
these metabolites was related to significant in
vitro inhibition and biological control of the
pathogen. Once cell wall damage has
occurred, the pathogen is more likely to be
susceptible to attack by other biological,
physical and chemical agents. The
antagonistic yeasts in the present study were
capable of growing totally at the expense of
the hyphae of Fusarium, indicating their
potential for pathogen suppression (Joubert
and Doty, 2018) where the antagonism takes
place outside the limits of rhizosphere.
Table 5: Effect of antagonistic yeasts on the incidence of onion basal rot diseases under field
conditions.
Yeast
Disease incidence (%)
2019/2020
2020/2021
Add
Soaking
Add
Soaking
Candida tropicalis (1)
11.33
12.00
11.16
13.66
Candida tropicalis (2)
19.33
21.66
20.00
20.33
Candida tropicalis (3)
12.00
12.88
12.66
13.33
Saccharomyces paradaxus
13.5
15.33
12.66
16.00
Saccharomyces cerevisiae
10
10.16
9.66
10.66
Pichia caribae
14.66
15.66
14.16
16.83
Fungicide (Captain)
10.5
9.5
8.16
9.33
Control
78.33
79.00
L.S.D. at 5% (Treatments)=
1.64
1.78
(Methods)=
0.399
0.28
(Treatments × Methods)=
1.12
1.86
3.5 Evaluation of antagonists on yield
Data presented in Table (6) indicate that the
tested sowing dates affected, plant height (cm),
bulb diameter (cm), average bulb weight (g)
and total bulb yield (ton/feddan) in the two
tested growth seasons. Onion growth
measurements were data in first method best
than second method compared control in two
seasons. Values of parameters of onion plants
were significantly increased with the dual
inoculation each isolates yeast fungi. The
increase of plant growth could be attributed to
the role yeasts present in inocula. Soil
inoculation with Saccharomyces cerevisiae
and fungicide gave higher records of all
parameters followed by Candida tropicalis
(1), and Candida tropicalis (3). The increase
of onion resistance obtained in this study,
could be related to the role of yeasts as plant
growth promoters. The yeast fungi producing
growth. These metabolites are considered
important after being taken up by the plant or
indirectly by modifying the rhizosphere
environment. Höflish and Kühn (1996)
reported that the promotion of cruciferous oil
and intercrops and nutrient uptake was
stimulated by inoculating rhizosphere yeast
fungi. Also, rhizosphere yeast fungi promoted
plant growth by oxidizing ammonium to
nitrate, oxidizing elemental sulphur to
sulphate and solubilizing insoluble phosphate.
Ahmed Hoda et al., 2021
102
Yeasts may therefore prevent this growth
inhibition, and generally increase the plant’s
tolerance to stress. These enzymes may also
serve as a mechanism for ammonia secretion
by the yeasts, which have been reported in the
past and could serve as a way for the plant to
recycle nitrogen using its symbiotic partners
(Dewedar and Ibrahim, 2016).
Table 6: Effect of antagonistic yeasts on growth parameters of onion plants during 2019/2020 and 2020/2021 seasons.
Yeast
Methods
2019/2020
2020/2021
Plant
height
(cm)
Bulb
diameter
(cm)
Average
bulb
weight (g)
Total
bulb
yield
(ton/feddan)
Plant
height
(cm)
Bulb
diameter
(cm)
Average
bulb
weight (g)
Total
bulb
yield
(ton/feddan)
Candida tropicalis (1)
Soaking
64.66
3.90
67.50
15.83
64.83
4.10
65.33
15.00
Add
66.33
4.56
72.00
16.50
66.83
4.56
71.00
16.00
Candida tropicalis (2)
Soaking
61.00
3.63
62.00
13.16
61.16
3.76
63.00
12.83
Add
62.50
3.96
62.16
14.00
62.83
4.23
62.83
13.5
Candida tropicalis (3)
Soaking
62.16
3.70
64.33
14.50
62.33
3.93
65.5
15.16
Add
64.00
4.26
66.33
15.00
64.83
4.13
67.16
15.83
Saccharomyces paradaxus
Soaking
60.33
3.60
62.16
13.00
60.00
3.83
62.00
13.50
Add
61.00
4.30
63.66
13.00
61.50
4.53
65.16
14.83
Saccharomyces cerevisiae
Soaking
66.33
5.56
68.16
16.33
67.33
6.10
68.5
16.00
Add
68.16
6.23
74.16
16.50
68.66
6.35
75.16
17.00
Pichia caribae
Soaking
50.66
3.50
61.00
10.66
51.00
3.50
61.33
12.00
Add
55.66
3.90
62.16
11.50
57.00
3.93
63.00
12.83
Fungicide (Captain)
Soaking
57.16
5.20
66.16
15.33
57.00
5.53
65.66
14.33
Add
58.66
5.16
70.66
15.00
57.83
5.50
69.83
16.00
Control
45.33
3.10
56.33
6.50
48.00
3.36
55.16
5.66
L.S.D. at 5% (Treatments) =
2.51
0.23
1.69
1.46
1.46
0.46
1.01
0.59
(Methods) =
1.11
0.12
1.02
0.41
0.67
0.22
0.63
0.45
(Treatments × Methods)=
3.13
0.34
2.64
1.17
1.91
0.62
1.77
1.27
3.6 Bulb storage
Inoculated bulbs stored for 1 or 2 months after
curing did not differ significantly in severity of
bulb rot, but bulb rot was significantly more
severe for bulbs stored for 3 months after
curing postharvest disease incidence was
greatly effective. Under storage house
conditions, all treatments decreased the
incidence of basal rot diseases compared to
control as reported in Table (7). The results
showed which obtained by visual observation
that after storage for 3 months, the treatments
were effect on diseases.
Table 7: Effect of treatment by of yeast on fungal disease incidence of onion at storage house.
Yeast
Number of infected onions in storage house
2019/2020
2020/2021
Add
Soaking
Add
Soaking
Control
40
40
44.33
44.33
Candida tropicalis (1)
2.66
2.66
3.06
3.00
Candida tropicalis (2)
3.06
4.06
3.96
3.16
Candida tropicalis (3)
2.66
2.66
3.4
3.66
Saccharomyces paradaxus
2.13
2.33
3.33
3.16
Saccharomyces cerevisiae
2.66
3.33
2.5
3.00
Pichia caribae
3.5
3.76
3.66
3.66
Fungicide (Captain)
4.00
4.13
3.5
4.63
L.S.D. at 5% (Treatments) =
2.93
5.59
(Methods) =
0.92
0.65
(Treatments × Methods) =
2.62
1.85
Ahmed Hoda et al., 2021
103
These results confirm that Saccharomyces
cerevisiae treatment can result between in a
97.5 and 97% reduction in fungal damage on
onions during storage compared (60 and
54.66%) onions in the untreated control group
were infected by basal rot diseases. Storage is
one of the important aspects for post-harvest
handling of onion (Anbukkasari, 2013). The
storage condition extends the period of
availability of fresh onion by arresting the
metabolic breakdown and decay. It is achieved
by controlling the physiological activity,
biochemical activity, microbial invasion.
Inadequate and improper field curing after
harvest, infection by different pathogen. In
general, the losses, currently about 35-40% of
the onion is estimated to be lost as postharvest
losses during various postharvest operations
including storage.
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