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Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
1
Soil-borne plant pathogenic fungi biodiversity of sunflower
B Sodikov, A Khakimov, U Rakhmonov
*
, A Omonlikov, R Gulmatov and S
Utaganov
Tashkent State Agrarian University, University str., 2, 100140 Tashkent, Uzbekistan
E-mail:
u.rakhmonov@tdau.uz
Abstract
. Diseases caused by soil-borne phytopathogenic fungi are a serious problem
for agricultural crops, including sunflower crops. The limited possibilities of measures
to control them further increases the interest and focus on them. This article reveals data
on the species composition, occurrence rate of soil-borne plant pathogenic fungi isolated
from the soil of sunflower. Here, 11 species of true fungi and 1 species of oomycetes
have been isolated. The highest incidence rate was recorded in the
Fusarium oxysporum
fungi species. During the study, pathogenic fungi specific to sunflower have also been
isolated.
Keywords:
soil-borne fungi, diseases, sunflower, fungus, Fusarium, Sclerotinia,
Verticillium, Rhizoctonia, Pythium.
1. Introduction
The largest number of microorganisms is associated with the soil – bacteria, actinomycetes, fungi, algae,
invertebrates and others. Their total number varies in different soils, that is, ranges from a few hundred
thousand to several billion cells per 1 g of dry soil. The biomass of soil microorganisms is 1 to 8 tons or
more per 1 ha of arable land. Microorganisms living in the soil are actively involved in the processes of
mineralization of organic matter, the formation of soil humus, the movement of nutrients, and so on.
Soil fertility depends in many ways on their activity. Among the microorganisms in the soil there are a
number of pathogenic species that cause disease in plants, including root damage: rot, wilting, root
hypertrophy, "black spot" and others. Fungi are often the causative agents of root diseases. Soil is the
main source of water and the source of infection for them. The life cycle of many phytopathogenic fungi
is partially related to soil. This is typical for fungal species that cause rust,
Sclerotinia
, head rot and
other diseases [1-5].
The control of soil-borne fungal diseases depends on an understanding of the interactions of complex
species. Soil-borne pathogenic fungi are “hidden” in the soil, diversifying, causing a decline in crop
yields and damage to the agricultural economy. Thus, soil phytopathogens can adversely damage the
yield of many economically important crops. The introduction of crop rotation is one of effective ways
to stop the plant-pathogen cycle, prevent the accumulation of soil-borne phytopathogenic fungi [6-9].
In addition, various agrochemicals have been developed to accelerate plant growth and reduce the
impact of pathogenic fungi. However, due to the negative impact of many pesticides on the environment
and strict regulation of their use [10], there is a need to further reduce pesticide use and identify more
sustainable plant protection strategies [11].
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
2
Similar ideas on this regard have been studied in the development of a intercropping system in
agriculture (i.e., the cultivation of several types of crops in a field) [12]. Intercrops typically yield 20%
more than single crops grown in proportion [13]. Excessive yields may probably be partly due to better
light absorption and nutrient availability, but due to reduced diseases in intercropping when compared
potentially to monocultures As for the latter, analyzes show a reduction in soil-borne diseases such as
root rot and Fusarium wilt [14, 15]. For example, in 30 of the 36 studies on intercropping farming
systems, soil-borne diseases were reduced [16, 17].
In recent years, the quantity and quality of agricultural crops have been declining under the influence
of adverse microorganisms. This is due to the fact that pathogenic microorganisms adapt easily to
climatic conditions and effective control measures are not carried out in a timely manner. Development
and implementation of modern measures to combat pathogenic microorganisms will allow to obtain
high and quality yields of agricultural crops [18, 19].
To date, the species and biology of soil-borne phytopathogenic fungi in sunflower growing areas
have been little studied. This is because the main focus of many studies on sunflower phytopathogens
has been on terrestrial pathogens [20-22].
Increased attention to terrestrial diseases in sunflower fields is due to the fact that they are often
easier to observe and study. In addition, many terrestrial phytopathogens can cause serious epidemics
due to their rapid and long-distance (up to kilometers) spread in the air [23, 24]. In contrast, the effects
of underground soil-borne phytopathogenic fungi are mainly capable of spreading over short distances
(from cm to maximum meters per year) [25].
According to Lukomets and Piven [26], sunflowers can be returned to the previous fields for
cultivation after 8 years in crop rotation. This is primarily determined by the need to protect sunflowers
from soil pathogens, broomrape, cottony rot
and head rot, downy mildew, Fusarium wilt, as they can
persist in the soil for a long time [27].
2. Materials and methods
In 2019-2021, we conducted our experiments in the fields of "Rayim aka" and "Surantkent Orzu Invest"
farms in Kibray district of Tashkent region, on sunflower varieties "Dilbar", "Salyut" and "Jahongir"
[28, 29]. In order to fulfill the scientific tasks set, we have widely used the methods developed by
mycologists and phytopathologists and adopted for practice.
We used Waxman’s soil dilution method to isolate phytopathogenic fungi from the soil. This method
is used by most mycologists. This method is suitable for studying the fungal flora of different soils, the
description of soils planted with different plants, the effect of mineral fertilizers or other agrotechnical
measures on the species composition of fungi [30].
Analysis of soil microflora by soil dilution method was performed as follows. Soil samples taken
from the sunflower planting area were placed in sterile test tubes or paper bags made of double-layered
parchment paper. The obtained soil samples were passed through a fine sieve with a diameter of 4 mm
and weighed by 10 g 3-4 times on a technical scale, then placed on a filter paper with a spatula. For each
sample, a new filter paper was used and the spatula was washed with water, immersed in an alcohol
container, and passed through a flammable alcohol flame. The soil samples were placed in a sterile flask
containing 90 ml of sterile water and shaken for 5 min. Then the mixture was taken by 1 ml from the
flask and poured into a sterile tube with 9 ml of water inside and shaken slightly. Similarly, 1 ml of the
mixture from this tube was transferred to the next tube, and this process was repeated four times. From
the fourth test tube, 1 ml of the mixture was inoculated into sterile Petri dishes. The mixture from each
test tube were transplanted into a Petri dish in 4 replications. It was then filled with 10 ml of nutrient
medium cooled to 40 °C and placed in a thermostat. They were grown in a thermostat at a temperature
of 23–25 °C for 10–15 days (Figure 1). From the third day, they were examined and the colonies of
fungi were counted, they were transferred to test tubes containing the nutrient medium. The final
calculation was made after 15 days [31-34].
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
3
Figure 1.
Growing process in a thermostat:
1- filter paper with 1- 10 g of soil. 2- flask with 90 ml of
water in it. 3-6 – tubes filled with 9 ml of water. 7-10 – Petri dishes inoculated in different mixtures.
Species composition of isolated fungi was determined with guides for fungi identification by
Pidoplichko N.M. and Naumov N.A. et al. [35-37].
3. Results and discussion
During our research conducted in 2019-2021, we monitored the storage of phytopathogenic fungi in the
soils of sunflower planted areas.
When we analyzed the three-year data, we found that most of the phytopathogenic fungi that cause
disease in sunflowers are stored in the soil. The results of the study proved that the main source of
infection of the diseases root rot, cottony rot
and head rot, Fusarium and Alternaria leaf spot is soil.
The most common species of phytopathogenic fungi in sunflower were identified in the fields where
sunflower was planted continuously. This means that phytopathogenic fungi are stored in the soil or
plant residues and it is required proper crop rotation in this case. The largest number of identified species
(33.3%) are fungal species belonging to the genus Fusarium. Species of Fusarium oxysporum was found
in the roots, leaves, stems and head of sunflowers during the growing season (Table 1). Other
representatives of the Fusarium genus were seen to cause more root rot of young seedlings and wilting
of seedlings (Figure 2).
Table 1.
Biodiversity of soil-borne phytopathogenic fungi.
№
Identified fungi species
Plant parts under infestation
root
leaf
stem
head
1
Fusariumoxysporum
+
+
+
+
2
F. culmorum
+
3
F. graminearum
+
4
F. avenaceum
+
+
5
F. solani
+
5
Fusarium spp.
+
+
6
Sclerotinia sclerotiorum
+
+
+
7
Verticillium dahliae
+
8
Rhizoctonia solani
+
9
Pythium spp.
+
10
Alternariahelianthi
+
+
+
+
11
Alternariaalternata
+
+
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
4
12
Thielaviopsisbasicola
+
Figure 2.
Fusarium genes under microscope:
1-2- Isolation of Fusarium oxysporum fungus by the
method of soil dilution; 3-4- formation of fungus colonies; 5-
microscopic view of macro and micro
conidia
According to A.A. Vypritskaya et al. [38],
Fusarium spp
. appears in sunflowers at all stages of plant
development and causes damage to roots and all soil surface organs (rot, wilting, pink rot of the head,
and death of seedlings) [39]. The high toxicity of
Fusarium
pathogens is maintained even when they are
replanted into medium. [13, 18]. The severity of pathogens depends on their type, climatic conditions,
time of damage and the number of infected plants [38].
The fungus
Sclerotinia sclerotiorum
, which causes cottony rot, was observed to remain in the soil as
sclerotium [5, 30]. We observed that this fungus infects the root collar, stem and the head of sunflower.
The fungus
Sclerotinia sclerotiorum
forms multicellular colorless mycelium in the infected organs of
the plant. The sclerotia are round or slightly elongated and often form in the cavity of the sunflower
stem. They are white at the beginning of their appearance, and when they are mature, they turn darker.
Their size varies from 1-15 mm to 10-12 cm. The sclerotia located in the soil retain their viability for 3-
5 years, while those on the soil surface survive for 1-2 years (Figure 3).
3
4
5
1
2
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
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Figure 3.
Sclerotia under microscope:
1-
mycelium formed in the nutrient medium; 2-its microscopic
view; 3-disease pathogen on sunflower head.
The fungus penetrates into the tissues of sunflower and produces the enzymes pectinosterase and
polygalacterase, as well as oxalic acid. Under their influence, hydrolysis of pectin and destruction of
plant tissue are occurred [22].
The fungus
Sclerotinia sclerotiorum
forms mycelium, sclerotia, secondary sclerotia, microconidia
and ascosporeal apothecium in the life cycle of its development. Plant infestation usually occurs through
ascospores that rise into the air from the apothecium, or also from diseased plants nearby or through
mycelium that spreads from sclerotia [21].
The phytopathogens of
Rhizoctonia solani, Verticillium dahliae, Thielaviopsis basicola (Berk. et Br.)
Ferr.
and
Pythium spp.
fungi that cause root rot and root collar rot diseases in sunflower seedlings have
been identified in all three years of the experiment. From this result it can be understood that these
phytopathogens are pathogenic in the past, as well as in other agricultural crops.
Alternaria alternate
and
Alternaria sp.
fungi belonging to the
Alternaria
genus were identified every
three years [29]. Only
Alternaria helianthi
species were observed in sunflower replanted fields. Fungi
of the genus
Alternaria
cause spot diseases in sunflowers (Figure 4).
Figure 4.
Spot diseases in a sunflower:
1- microscopic vies of Alternaria sp.conidia; 2- sunflower leaf
infected by Alternatia leaf spot disease
1
2
1
2
3
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
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In sunflowers, the fungi belonging to the genus
Alternaria
cause leaf spot, and this disease affects
adversely the yield of sunflowers. Symptoms of the disease often appear 20–25 days after flowering.
Alternaria leaf spot disease infects the leaves, stems and head of the sunflower. But the greatest damage
of the disease is observed in the heads, that is, the quantity and quality of seeds decrease.
Alternaria helianthi
has been reported to be a major disease in Central Europe, India, Australia, South
America and in the humid regions Africa. Yield loss in these areas can range from 15% to 90% and oil
loss from 20% to 30% [3]. Yield loss due to this disease has been reported to be from 27% to 80% in
India [6, 30].
In addition,
Aspergillus nigerv.Tiegh.
and
Penicillium glaucum Link.
species from secondary
parasites that do not directly affect sunflowers were identified in sunflowers. These species were found
mostly in sunflower heads infected with cottony rot or head rot and spilled on the ground (Figure 5).
Figure-5.
Mold formation of secondary parasites in sunflower head
Consequently, our knowledge of the biology of soil-borne phytopathogenic fungi in sunflower fields
is mainly related to modern agriculture. Soil-borne phytopathogenic fungi, such as
Fusarium
oxysporum, Verticillium dahliae, Rhizoctonia solani
and
Pythium spp.
have been thoroughly studied
because they are common in many plants around the world. For example,
Fusarium
wilt has been well
studied in more than 100 different plants [2, 24].
The fungi of Fusarium genus are distributed throughout the world and contain at least 300
phylogenetically diverse complexes [25]. This group of ascomycetes is one of the most economically
adverse plant pathogens in the world that cause diseases in almost all plants of economic importance
and also cause billions of dollars in damage to agriculture each year [4, 10].
4. Conclusions
As a result of our research on soil-borne phytopathogenic fungi in sunflower fields, it became clear that
the amount of phytopathogens in sunflower replanted fields differs sharply from that in the fields with
crop rotation. That is, most soil phytopathogens are stored in the damaged plant residues or survive in
the soil. Therefore, in order to protect sunflower plants from diseases, it is necessary to pay special
Sustainable Management of Earth Resources and Biodiversity
IOP Conf. Series: Earth and Environmental Science
1068 (2022) 012018
IOP Publishing
doi:10.1088/1755-1315/1068/1/012018
7
attention to crop rotation in the cultivation of sunflower and removal of plant debris from the field after
the harvest. This measure prevents the storage of phytopathogenic fungi in the soil. Furthermore, as a
result of our research we found out that wheat and maize are good rotation crops for sunflower.
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