ПАРАЗИТОЛОГИЯ, 2020, том 54, № 5, с. 413-422.
УДК 579.64:632.651
NEMATICIDAL ACTIVITY OF NEMATODE-SYMBIOTIC BACTERIA
XENORHABDUS BOVIENII AND X. NEMATOPHILA
AGAINST ROOT-KNOT NEMATODE MELOIDOGYNE INCOGNITA
© 2020 L. G. Danilov, V. G. Kaplin*
All-Russia Institute of Plant Protection,
Pushkin, Saint Petersburg, 196608 Russia
* e-mail: ctenolepisma@mail.ru
Received 21.06.2020
Received in revised form 18.07.2020
Accepted 30.07.2020
The lethal effects of metabolic products produced by the symbiotic bacteria Xenorhabdus bovienii
from Steinernema feltiae and X. nematophila from S. carpocapsae were tested on M. incognita infec-
tive juveniles (J2). Treatments had cell titers of 2.5 × 109, 1.25 × 109 and 0.63 × 109 per ml at 20 °C,
23 °C and 26 °C. Exposure periods were 15 hr, 41 hr, 65 hr and 90 hr immediately after autoclaving
and at 23°C, and exposure periods of 5 hr, 26 hr, 50 hr and 74 hr after storage for 21 days at 4 °C.
The effectiveness of bacterial metabolic products immediately after preparation against M. incognita
(J2) depended on the titer of bacterial cells, the temperature of the culture liquid, and the duration
of its exposure to nematodes. Nematicidal activity of X. bovienii metabolic products was higher than
that of X. nematophila. Mortality of M. incognita J2 was 92-93 % after 90-hr exposure to X. bovienii
at 20 °C and cell titers of 2.5 × 109 and 1.25 × 109; also after 65 hr exposure at 23 °C, titer of 2.5 ×
109 and 95-99 % at 26 °C and all tested titers. The efficacy of cultural liquid of X. bovienii metabolic
products after storage at 4 °C for 21 days, after its 50 hr exposure to nematodes at 23 °C and cell
titers of 2.5 × 109 and 1.25 × 109 and 74 hr exposure at all tested titers remained high at 97-100 %.
The easiest way to control of plant pathogenic nematodes would be metabolic products of symbiotic
bacteria of Xenorhabdus. Our results suggest that the active metabolites of symbiotic bacteria need
to be identified for possible synthesis and use in the field.
Key words: entomopathogenic nematodes, symbiotic bacteria, metabolites, efficiency
DOI: 10.31857/S1234567806050041
Among plant-parasite nematodes (PPNs) developing on plant roots, the most economi-
cally important are Meloidogyne spp. (root-knot nematodes) and cyst nematodes in the fam-
ily Heteroderidae (Tylenchida). More than 100 species of root-knot nematodes have been
described, for which more than 5000 species of host plants are known (Karssen, Moens,
413
2006; Uribe, 2008). Four Meloidogyne spp. (M. incognita Kofoid & White, M. javanica
(Treub), M. arenaria Chitwood and M. hapla Chitwood) are widespread. These four spe-
cies account for 95 % of infestations on cultivated land and about 5 % of global crop loss.
M. incognita accounts for 52 % of reports, M. javanica 31 %, M. arenaria 8 %, M. hapla
7 %, and other species 2 %, from agricultural land areas (Hadisoeganda, Sasser, 1982).
Five species of root-knot nematodes (Meloidogyne incognita, M. javanica, M. arenaria,
M. hapla and M. chitwoodi) are common in the Russian Federation, but M. incognita,
M. javanica and M. arenaria are found only in greenhouses. Meloidogyne hapla develops in
the open ground and in greenhouses. Columbian root-knot nematode (M. chitwoodi Golden
et al.) is the object of an external quarantine. About 60 % of greenhouses in Russia are
contaminated with root-knot nematodes. Meloidigyne incognita almost everywhere dam-
ages vegetable and ornamental crops in greenhouses and its study is undoubtedly relevant.
Meloidogyne incognita is a cosmopolitan obligate plant-parasite and possesses a wide
host range of over 230 plant genera and 3000 species including cotton, tobacco, legumes,
vegetable crops, spices, and coffee in tropical and subtropical regions, in particular in the
warmer areas (CABI Data Report, CABI, 2017). Estimates of crop losses due to Meloido-
gyne species, mainly M. incognita and M. javanica, have ranged from 18 % to 33 % for
melon and from 24 % to 38 % for tomato (Sasser, 1979), and 25 % or more for potato
(Mai et al., 1981). This species is also the main pest of vegetable and ornamental crops in
greenhouses in temperate latitudes. In previous studies the minimum temperature threshold
for development of M. incognita was found to be 10.1 °C. Infective J2 of M. incognita
become active at soil temperatures of 16-20 °C (Vrain et al., 1978).
Organizational and economic, preventive, selection and seed-growing, physical, agro-
technical, biological, chemical and integrated methods are used in greenhouse management
of root-knot nematodes. Among these approaches, the most economically justified and en-
vironmentally safe are biological methods.
Entomopathogenic nematodes (EPNs) of the genera Steinernema Travassos (Steinerne-
matidae) and Heterorhabditis Poinar (Heterorhabditidae) in the order Rhabditida include
about 70 and 20 species, respectively. They are able to infect the post-embryonic stages of
more than 1000 species of pests of agricultural and ornamental crops (Nickle, 1977). Two
genera of entomopathogenic bacteria, Xenorhabdus Thomas and Poinar and Photorhabdus
Boemare et al. (Morganellaceae, Enterobacterales), are intimately associated with EPNs.
About 20 species of symbiotic gram-negative Xenorhabdus are associated with Steinernema
spp. and 2 species of Photorhabdus are associated with Heterorhabditis spp. (Poinar, Thomas,
1967; Akhurst, Boemare, 1990; Nguyen et al., 2007). In the process of pathogenesis, bacte-
ria and EPNs secrete proteolytic enzymes that can break down proteins as well as damage
components of the host immune complex, causing host death.
In addition to insects, EPNs are also able to suppress the development of phytonema-
todes (Bird, Bird, 1986; Ishibashi et al., 1986; Lewis, Grewal, 2005; Molina et al., 2007;
Kenney, Eleftherianos, 2016). Suppressive effects of EPNs have been observed on various
414
phytonematodes such as Belonolaimus longicaudatus Rau, Criconemoides spp. (Grewal et
al., 1997) and Globodera rostochiensis (Wollenweber) Behrens (Perry et al., 1998). However,
the most stable suppression was observed in species of Meloidogyne Göldi (Lewis et al.,
2005). Xenorhabdus and Photorhabdus can be successfully used to regulate the density of
root-knot nematodes. This effect was studied on culture filtrates of Xenorhabdus nematophila
(Poinar et al.) and X. bovienii Akhurst and Boemare from Steinernema carpocapsae (Weiser)
and S. feltiae Filipjev, respectively (Grewal et al., 1997). The culture fluids of these bacteria
showed nematicidal properties, causing the death of 98-100 % of M. incognita infective
juveniles (J2). The selective nematicidal ability of Xenorhabdus against root-knot nematodes
has been confirmed by many researchers (Paul et al., 1981; Burman, 1982; Richardson
et al., 1988; Pérez, Lewis, 2002). When tomato plants were immersed in culture liquid
of X. bovienii, M. incognita egg production was suppressed and plants were taller compared
to infected but untreated plants in the control (Pérez, Lewis, 2002; Kepenecki et al., 2016).
Bowen and Ensign (1998) suggested that it would be appropriate to use toxins derived from
liquid suspensions of the bacterial symbiont for plant protection. Antibiotic compounds
produced by different species and strains of Xenorhabdus can differ significantly in quality
indicators, which also depend on the nutrient medium composition, temperature and condi-
tions of their cultivation. In the process of studying the nematicidal activity of metabolites
produced by symbiotic Xenorhabdus, the prospects of work in this direction were enhanced
(Hu et al., 1999; Nour El-Din et al., 2014).
The aim of our research was to study the nematicidal activity of the symbiotic bacteria
Xenorhabdus bovienii (S. carpocapsae) and X. nematophila (S. feltiae), respectively, in
vitro at different exposure times, temperatures and densities of bacterial cells in the nutrient
medium and storage of cultural liquid, against M. incognita J2.
MATERIALS AND METHODS
The research was carried out in the Laboratory of Microbiology of the All-Russian In-
stitute of Plant Protection. Xenorhabdus nematophila and X. bovienii were obtained from
the cadavers of greater wax moth larvae (Galleria mellonella L.) infected with dauer juve-
niles of Steinernema carpocapsae strain “Agriotos” and S. feltiae strain RP18-91, respec-
tively, and stored in distilled water at 5-7 °C. Ten mature larvae were placed in a Petri dish
on two layers of filter paper, on the surface of which about 500 dauers were introduced in
1 ml of distilled water. After three days of incubation, the cadavers were superficial-
ly sterilized in 70 % ethanol for 2 min and placed for drying in a laminar air stream for
3 min. A drop of hemolymph was extracted from the larval proleg and transferred to Pe-
tri dishes on NBTA nutrient medium containing per liter: 0.5 g NH4H2PO4; 0.5 g K2HPO4; 0.2 g
MgSO4 ∙ 7 H2O; 5 g NaCl; 5 g yeast extract; 12 g agar; 25 mg bromothymol blue and 40 mg dime-
thyltetrazolium chloride. Cultures were incubated at 26 °C. After 72 hr, one pure colony of green
symbiotic bacteria was selected from colonies of the same size and morphology. The identification of
the primary forms of symbiotic bacteria was performed by the method of Akhurst (1980). Subcultiva-
tion continued until bacterial colonies of the same size and morphology were obtained. The pathoge-
nicity of isolates was confirmed by injection of bacterial cells into G. mellonella larvae and transfer
415
of hemolymph of infected larvae to NBTA in Petri dishes. Clean colonies of bacteria were transferred
to tubes on slants with NBTA nutrient medium and grown for 3-4 days at 26 °C. A smear of bacteria
was taken from the slant using a bacterial loop and transferred into flasks with 100 ml of nutrient broth
and grown on a shaker at 150 revolutions per minute for 2 days at 26 °C before a titer of ~ 2.5 × 109
bacterial cells per ml. Beginning with the initial titer of 2.5 × 109 cells, lower concentrations of cells
were obtained by doubling the culture liquid with sterile water to obtain titers of 1.25 × 109 and 0.63
× 109 cells per ml. The resulting culture liquids with titers of ~ 2.5 × 109, 1.25 × 109 and 0.63 × 109
cells per ml were autoclaved at a temperature of 121 °C, pressure of 1 atmosphere for 30 min and
used to study the pathogenicity of the metabolic products of symbiotic bacteria against M. incognita
J2. As known, Xenorhabdus nematophila and other symbiotic bacteria produce both heat-labile and
heat-stabile toxins, enzymes and antimicrobials. Their heat-stabile components are active after heart
sterilization and can be used against different species of bacteria and pests (Inman, Holmes, 2012).
Evaluation of the effectiveness of these inocula against J2 was tested immediately after preparation
at temperatures of 20 °C, 23 °C and 26 °C and at 23 °C following their storage at 4 °C for 21 days
(tables 1-3). Evaluation of the effectiveness of freshly obtained inocula was determined after 15, 41,
65 and 90 hr, and of stored inocula after 5, 26, 50 and 74 hr.
Table 1. Effect of metabolic products of Xenorhabdus bovienii on mortality
of Meloidogyne incognita J2, in vitro
The death of larvae at the exposure, hours (%)
The titer of bacterial cells
(n × ml-1)
15
41
65
90
20 °С
2.5 × 109
15.0 ± 0.7
28.3 ± 1.4
62.0 ± 1.2
92.3 ± 1.1
1.25 × 109
8.5 ± 0.6
19.8 ± 3.1
46.8 ± 2.5
93.0 ± 2.5
0.63 × 109
1.8 ± 0.6
5.0 ± 0.7
21.0 ± 3.1
65.0 ± 3.7
LSD0.05 (titer)
2.6
7.8
9.3
10.4
LSD 0.05 (titer + control)
1.1
3.4
4.1
4.6
Control (water)
0 ± 0
0.75 ± 0.25
1.75 ± 1.25
3.00 ± 0.41
23 °С
2.5 × 109
22.2 ± 1.2
63.5 ± 1.7
91.8 ± 2.8
1.25 × 109
18.2 ± 0.6
47.0 ± 1.4
82.0 ± 1.5
9
0.63 × 10
6.2 ± 0.9
24.5 ± 2.4
56.5 ± 1.3
No data
LSD0.05 (titer)
3.7
7.3
7.7
LSD 0.05 (titer + control)
1.7
3.3
3.4
Control (water)
1.25 ± 0.25
2.00 ± 0.41
2.25 ± 0.48
26 °С
2.5 × 109
2.5 ± 1.0
47.0 ± 1.5
99.5 ± 0.5
1.25 × 109
0.8 ± 0.5
37.0 ± 1.1
98.8 ± 1.3
9
0.63 × 10
1.0 ± 0.6
15.0 ± 0.8
97.5 ± 2.5
No data
LSD0.05 (titer)
2.9
4.5
6.4
LSD 0.05 (titer + control)
2.8
4.3
2.9
Control (water)
0.80 ± 0.25
1.25 ± 0.25
2.25 ± 0.25
416
Table 2. Effect of metabolic products of Xenorhabdus nematophila on the mortality
of Meloidogyne incognita J2, in vitro
The death of larvae at the exposure, hours (%)
Bacterial cell titer per ml
15
41
65
90
20 °С
2.5 × 109
11.8 ± 0.6
22.3 ± 1.7
47.8 ± 1.2
88.0 ± 2.8
1.25 × 109
11.3 ± 1.4
20.5 ± 0.9
24.8 ± 0.6
94.0 ± 1.5
0.63 × 109
1.3 ± 0.5
4.0 ± 0.4
8.3 ± 1.1
49.8 ± 3.8
LSD0.05 (titer)
3.7
4.3
3.9
11.2
LSD 0.05 (titer + control)
1.6
1.9
1.8
4.6
Control (water)
0 ± 0
0.75 ± 0.25
1.75 ± 1.25
3.00 ± 0.41
23 °С
2.5 × 109
20.2 ± 1.1
57.8 ± 1.7
81.5 ± 1.3
1.25 × 109
22.2 ± 0.6
28.8 ± 0.9
38.3 ± 1.3
0.63 × 109
4.0 ± 0.7
11.8 ± 1.3
24.5 ± 2.5
No data
LSD0.05 (titer)
3.3
5.1
7.0
LSD 0.05 (titer + control)
1.5
2.3
3.1
Control (water)
1.25 ± 0.25
2.00 ± 0.41
2.25 ± 0.48
26 °С
2.5 × 109
1.5 ± 0.6
35.5 ± 1.6
99.0 ± 0.6
1.25 × 109
1.8 ± 0.6
20.5 ± 1.0
95.3 ± 2.8
0.63 × 109
0.8 ± 0.5
12.0 ± 1.3
82.0 ± 1.5
No data
LSD0.05 (titer)
2.3
5.1
7.2
LSD 0.05 (titer + control)
2.3
5.0
3.2
Control (water)
0.80 ± 0.25
1.25 ±0.25
2.25 ± 0.25
Table 3. Effect of temperature and storage duration (21 days at 4 °C) of metabolic products
of symbiotic bacteria Xenorhabdus bovienii of entomopathogenic nematodes Steinernema feltiae
SRP18-91 on death of invasive larvae of root-knot nematode Meloidogyne incognita at 23 °C,
in vitro
The titer of bacterial cells
The death of larvae at the exposure, hours (%)
(n × ml-1)
5
26
50
74
No storage
2.5 × 109
1.2 ± 0.6
55.0 ± 5.9
100.0 ± 0.0
100.0 ± 0.0
1.25 × 109
4.2 ± 1.3
54.8 ± 2.7
97.0 ± 2.7
100.0 ± 0.0
0.63 × 109
0
16.8 ± 1.7
76.3 ± 1.7
99.8 ± 0.3
LSD0.05 (titer)
3.2
16.7
7.2
0.6
LSD 0.05 (titer + control)
1.4
7.4
3.2
1.2
With storage (21 days at 4 °C)
2.5 × 109
0.7 ± 0.8
36.0 ± 2.5
94.5 ± 2.4
99.0 ± 0.6
1.25 × 109
0
16.5 ± 2.1
82.5 ± 1.8
97.3 ± 2.8
0.63 × 109
0
13.3 ± 2.0
70.0 ± 3.9
99.8 ± 0.3
LSD0.05 (titer)
1.7
8.7
11.1
6.4
LSD 0.05 (titer + control)
0.8
3.9
4.9
3.1
Control (water)
0
0.75 ± 0.25
2.75 ± 0.25
7.5 ± 1.2
417
Root-knot J2 were obtained from a pure culture of M. incognita propagated on tomato plants.
Eggs were obtained by collecting galls from the affected tomato plants, washing them in water and
grinding them in 0.5 % sodium hypochlorite solution. Eggs were placed in Baermann funnels for
hatching and collection of J2 (Baermann, 1917).
Effects of bacterial metabolic products (three titers) on J2 were studied in Petri dish-
es. In the experiments, 2 ml of culture liquid was introduced into each Petri dish, while con-
trol dishes received 2 ml of tap water. Each dish received J2. All experiments were rep-
licated four times. Density of live and dead J2 were determined. Alive larvae actively move in
a liquid environment, the dead lie in the form of sticks and when they are touched with the tip of a
preparaval needle, they remain lying without signs of activity, while live larvae always respond with
activity when tactile action is applied to their body. Statistical treatment of the obtained data was
carried out with Microsoft Excel and Sigma Plot 12.0 programs. Biological efficiency was calculated
by Abbott’s formula: C = (A-B)*A-1*100 %, where A = J2 density before exposure, B = density of
still alive larvae after exposure, and C = biological efficiency, if their natural mortality in the control
did not exceed 5 %.
RESULTS
The metabolic products of symbiotic bacteria of the genus Xenorhabdus were obtained
by culturing them using nutrient broth with NBTA for 2 days at 26 °C before a titer of ~
2.5 × 109 bacterial cells per ml, followed by doubling the part of culture liquid with sterile
water to titers of 1.25 × 109 and 0.63 × 109 cells per ml and autoclaving all received liquids.
Regression analysis of the efficiency of the metabolic products of X. bovienii and X.
nematophila on the density of bacterial cells showed a linear or binomial dependence between
them, with an R21 of 0.48-0.97 and a correlation coefficient (r) of 0.70-0.98.
In laboratory conditions, the effectiveness of the bacterial metabolic products immedi-
ately after preparation against infective juveniles (J2) of root-knot nematode Meloidogyne
incognita depended on the titer of bacterial cells, the temperature of the culture liquid, and
the duration of its exposure to nematodes. In experiments with X. bovienii at titers of 0.63
× 109, 1.25 × 109, 2.5 × 109 bacterial cells per ml and on average, it was higher 1.4, 1.2,
1.05, and 1.2 times as in experiments with X. nematophila, respectively (tables 1-3).
Increasing the temperature and titer of the tested culture liquid contributed to faster growth
of the efficacy of bacterial metabolic products against J2 of root-knot nematode, especially
in experiments with X. bovienii. At 20 °C, the maximum increase of efficiency of metabolic
products was observed in X. bovienii at all tested titers after 65 hr, in X. nematophila with
titers of 0.63 × 109 and 1.25 × 109 cells per ml after 90 hr, and 2.5 × 109 after 65 hr. At 23
°C for all titers X. bovienii and X. nematophila showed the greatest increase of efficiency
after 41 hr, and at 26 °C after less than 40 hr.
Comparison of efficiency of products of metabolism of bacteria at 23 °C, used against
larvae of root-knot nematode directly after their production and after storage at 4 °C for 21
days showed that they differed slightly. At an exposure of 26 hr, the efficiency of the metabolic
products of bacteria stored for 21 days was of 1.5-3.3 times, 50 hr was of 1.1-1.2 times
lower, compared with the efficiency of their use immediately after production. However, at
the exposure of 74 hr, they did not differ and amounted to 97-100 % regardless of the titer.
418
The results of the research indicate the possibility of using symbiotic bacteria of EPNs in
the protection of vegetable crops in greenhouses against root-knot nematodes. Xenorhabdus
bovienii appears to be especially promising. At a temperature of 20 °C and an exposure of
90 hr, J2 mortality was more than 90 %. Increasing temperatures above 20 °C may result
in 99 % mortality after an exposure of 65 hr. Mortality of J2 was significantly increased
by metabolites of two tested species of symbiotic bacteria at temperatures of 23 °C and
26 °C. The highest efficacy was observed with X. bovienii metabolites at 26 °C for all tested
titers fluid (97.5-99.5 %).
DISCUSSION AND CONCLUSIONS
The entomopathogenic nematodes (EPN), Steinernema carpocapsae and S. feltiae
are found on all continents of the Earth, except Antarctica (CABI Data Report. CABI,
2020). They are symbiotically associated with the bacteria Xenorhabdus nematophila and
X. bovienii. These symbiotic bacterial-parasitic complexes are used as biological control
agents against a wide variety of insect pests in agriculture and horticulture. Temperature is
an important factor affecting both EPNs and their symbiotic bacteria. Optimum temperatures
for infection and reproduction of Steinernema carpocapsae and S. feltiae is ranging from
22 °C to 28 °C and from 20 °C to 25 °C, respectively. Optimal culture temperature for
both nematode species is 25 °C (Hirao, Ehlers, 2009). Steinernema carpocapsae is more
sensitive to suboptimal temperature than S. feltiae. Development of S. carpocapsae does
not occur at temperatures lower than 10 °C. Hazir et al. (2001) determined that the lowest
temperature for S. feltiae infection and reproduction was 8 °C while the highest was 25 °C.
Steinernema feltiae seems to be a better fit for temperatures expected in northern climates
(Sharmila et al., 2018). In the northern part of Russia (Yakutia) S. feltiae protense is able
to infect the insect host at a temperature of 6 °C, while the most optimal development of
this nematode in the insect host occurs at 18 °C to 23 °C (Ivanova et al., 2001).
Suppressive effects of Steinernema feltiae (strain SN) and S. riobrave (Cabanillas et al.)
(strain 7-12) applied as infective juveniles against Meloidogyne partityla Kleynhans, as well
as application of the S. feltiae bacterial symbiont Xenorhabdus bovienii, were investigated in
greenhouse trials (Shapiro-Ilan et al., 2006). Treatments were applied to pecan nut seedlings
(Carya illinoensis) that were simultaneously infested with M. partityla eggs. Four months
after initial treatment dry root weight was higher in the S. feltiae-infested host treatment
than in the control (approximately 80 % increase).
Application of Sterneinema pakistanese Shahina et al. for suppression of M. incognita
on tomato was investigated in Pakistan in a greenhouse at 27-35 °C. One-month-old tomato
plants were transplanted into soil in 200-ml plastic pots. Steinernema pakistanese was applied
at rates of 1250, 2500 or 5000 invasive juveniles per pot at the same time as M. incognita,
at a rate of 1500 J2 per pot. Root systems were harvested 35 days after infestation. Egg
mass densities per root system were decreased 29 %, 34 % and 59 % at the 1250, 2500 and
5000 S. pakistanense treatments, respectively. At the 2500 rate, of S. pakistanese root and
shoot weight increased 12.5 % and 8.5 %, respectively (Khan, Javed, 2018).
419
The first report of the possible antagonistic relationship between plant-parasite nema-
todes (PPNs) and entomopathogenic nematodes (EPNs), resulting in reduced population
densities of PPNs, was published by Ishibashi, Kondo (1986). One possible explanation
was that both EPNs and PPNs were attracted to root tips, but as EPNs are larger and more
active they could colonize them faster, preventing PPNs invasion and reproduction (Bird,
Bird, 1986). A later hypothesis was that a compound produced by symbiotic bacteria living
inside EPNs was toxic to PPNs (Lewis et al., 2001). Neither of these ideas (root surface
competition, bacterial products) proved to be correct. Application of dead EPNs along with
dead bacteria still reduced PPNs population density (Jagdale et al., 2002). The easiest way
to control PPNs would be metabolic products of symbiotic bacteria of EPNs. Our results
suggest that the active metabolites of symbiotic bacteria need to be identified for possible
synthesis and use in the field.
ACKNOWLEDGEMENTS
We thank Prof., Dr. Ernest C. Bernard from University of Tennessee (USA) for reading
and editing the article, as well as for valuable comments and suggestions when preparing
it for publication.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interest.
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НЕМАТИЦИДНАЯ АКТИВНОСТЬ СИМБИОТИЧЕСКИХ БАКТЕРИЙ
XENORHABDUS BOVIENII И X. NEMATOPHILA
ПРОТИВ КОРНЕВОЙ ГАЛЛОВОЙ НЕМАТОДЫ MELOIDOGYNE INCOGNITA
Л. Г. Данилов, В. Г. Каплин*
Ключевые слова: энтомопатогенные нематоды, симбиотические бактерии, мета-
болиты, эффективность
РЕЗЮМЕ
Эффективность продуктов метаболизма, продуцируемых симбиотическими бактериями
Xenorhabdus bovienii (Steinernema feltiae) и X. nematophila (S. carpocapsae), против инвазионных
личинок 2-го возраста M. incognita (J2) была испытана в лабораторных условиях при температуре
20 °С, 23 °С и 26 °С сразу после получения и автоклавирования с экспозицией 41, 65 и 90 ч,
а также при температуре 23 °С после хранения в течение 21 дня при 4 °С с экспозицией 26, 50
и 74 ч с титрами бактериальных клеток 2.5 × 109, 1.25 × 109 и 0.63 × 109/мл. Эффективность
продуктов метаболизма бактерий сразу после их получения против M. incognita (J2) зависела
от титра бактериальных клеток, температуры культуральной жидкости и продолжительности ее
воздействия на нематод. Нематицидная активность продуктов обмена веществ X. bovienii была
выше, чем X. nematophila. В опытах с X. bovienii гибель M. incognita (J2) составляла 92-93 %
после их 90-часового воздействия на нематод при 20 °C и титрах 2.5 × 109 и 1.25 × 109; 65-ча-
сового воздействия при 23 °C и титре 2.5 × 109; 98-99 %, при 26 °C и всех испытанных ти-
трах. Эффективность культуральной жидкости X. bovienii после хранения при 4 °C в течение
21 дня при 23 °C после ее 50-часового воздействия на нематод и титрах 2.5 × 109 и 1.25 × 109
и после 74-часового воздействия при всех испытанных титрах составляла 97-100 %. Продукты
метаболизма симбиотических бактерий рода Xenorhabdus против корневых галловых нематод
показали высокую эффективность, они нуждаются в идентификации для возможного синтеза
и использования в полевых условиях.
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