Relationships between M. enterolobii and F. solani

Relationships between M. enterolobii and F. solani: spatial
and temporal dynamics in the occurrence of guava decline
Vicente Martins Gomesa*, Ricardo Moreira Souzaa, Alexandre Macedo Almeidaa
and Claudia Dolinskia
Laboratório de Entomologia e Fitopatologia, Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF),
Campos dos Goytacazes (RJ) Brazil
*[email protected]
a
HIGHLIGTS
• A systemic factor induced by M. enterolobii, capable of deactivating the immunity of guava plants to F. solani.
• Morpho-physiological changes locally induced in the root system of guava plants by M. enterolobii, permitting F. solani to
invade and colonize the roots.
• Parasitism by the nematode alters root physiology at nearby points, canceling the resistance mechanism and making it
possible for the fungus to invade root tissues.
• Tissues that are rich in gall nutrients favor colonization by the fungus and subsequent deterioration.
• Parasitism by the nematode alters the chemical composition of root exudates, which in some way allows the fungus to
invade the roots.
• Guava decline only occurs in orchards infested with M. enterolobii with the associated presence of F. solani.
Abstract: Guava decline, caused by the interaction between the phytonematode Meloidogyne enterolobii and the
fungus Fusarium solani, has caused direct and indirect losses to the whole productive chain of guava. Aiming to
understand the interaction mechanisms between M. enterolobii and F. solani, this study carried out a bioassay
on guava plants with roots in two different treatments: inoculated separatelyor together with the fungus and/or
nematode. The nematode parasitism not triggered an systemic effect on the plant become susceptible to root rot
caused by the fungus.Therefore, it was concluded that there was a local effect of parasitism by M. enterolobii on
the pathogenicity of F. solani in guava roots, making it necessary for the two pathogens to occupy the same space
at the same time for occurrence of guava decline.
Keywords: complex disease, Fusarium solani, guava root-knot nematode, Meloidogyne enterolobii, Psidium guajava.
Cite as
Gomes VM, Souza RM, Almeida AM, Dolinski C. Relationships between M. enterolobii and F. solani: spatial and temporal dynamics
in the occurrence of guava decline. Nematoda. 2014;1:e01014. http://dx.doi.org/10.4322/nematoda.01014
Received: July 1, 2014 Accepted: Aug. 20, 2014
INTRODUCTION
In the state of Rio de Janeiro (Brazil), guava decline is the main disease that affects guava crop1. In
this complex disease, parasitism by the phytonematode Meloidogyne enterolobii predisposes guava
plants that are immune to Fusarium solani to extensive root deterioration caused by this fungus, which
leads to loss in production and to death of plants in a short period of time. The synergiceffect of this
disease is reinforced by the results of micro plot experiments that indicate that M. enterolobii is not
highly aggressive to guava when alone2, 3. Bioassays performed in a growth chamber using isolates of
fungi from different regions of Brazil, have confirmed that guava decline is the causal agent behind
the destruction of about 5,000 hectares of commercial guava. This result in huge economic impacts
for producers, once the losses are estimated to reach over $ 70 million4.
Nematoda. ISSN 2358-436X. Copyright © 2014. This is an Open Access article distributed under the terms of the Creative Commons Attribution
Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and
reproduction in any medium, provided the original work is properly cited.
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Relationships between M. enterolobii and F. solani: spatial and temporal dynamics in the occurrence of guava decline
Root diseases are among the main causes of reduction in production ofcrops5. Thiskind of disease
is less studied than those that affect the aerial part of the plants, due to the complexity of the factors
involved in the pathogen-host-environment interaction6.
In complex diseases involving soil fungi and phytonematodes, factors such as the species of fungus
and nematode, inoculum level, phenological stage of the plants, resistance and/or tolerance to any
pathogens living in the soil and other physical-chemical characteristics of the soil are some of the
components that interact7.
This work reports the first efforts to characterize the interaction between M. enterolobii and
F. solani in guava decline. Considering that the fungus is capable of attack and causes decomposition
in guavas only after they have been parasitized by M. enterolobii, this interaction may be mediated by
i) a systemic factor induced by M. enterolobii, capable of deactivating the immunity of guava plants to
F. solani and/or ii) morpho-physiological changes locally induced in the root system of guava plants
by M. enterolobii, permitting F. solanito invade and colonize the roots.
MATERIAL AND METHODS
The bipartite root technique was used in guava plants of the Paluma variety (susceptible to guava
decline). The roots were produced from cuttings and transplanted, at the stage of four pairs of leaves, to
planting plastic containerfilled with washed and autoclaved sand. After this, the root was divided into
two halves, providing plants with two distinct root systems. Five treatments were evaluated, namely:
i) the two halves of the root system were both non-inoculated; ii) one half was inoculated with 500 eggs
and second-stage juveniles (J2) of M. enterolobii and the other half remained non-inoculated; iii) one
half was inoculated with 5 g of wheat grains colonized with F. solani isolate UENF/CF 163 and the other
half remained non-inoculated; iv) one half was inoculated with the nematode (same inoculum), and
the other half was inoculated three weeks later with F. solani UENF/CF 163 (same inoculum) and v)
one half was inoculated with the nematode (same inoculum), and three weeks later the same half was
inoculated with F. solani UENF/CF 163 (same inoculum), and the other half remained non-inoculated.
The nematode inoculum was obtained from tomato plants cultivated in the greenhouse, and applied
in a suspension of 15 ml, which was mixed with sand in four points within the plastic container. The
isolate of F. solani used in this experiment was pathogenic to guava plants, in the presence of the
nematode, in micro plot experiments2 and in growth chamber conditions8. The wheat grains colonized
by the fungus were incorporated in the sand at a depth of about 10 centimeters.
These treatments were arranged in a completely randomized design, with six repetitions per
treatment. During the experiment, the plants were watered when necessary and received fertilizer
according to Pereira9. One hundred and twenty days after inoculation of the fungus the following
variables were evaluated: fresh mass of the aerial part (g) and volume of the root system (total,
healthy and necrotic) of each half of each plant. The volume (cm3) was obtained by immersing the
roots in a graduated test-tube, observing the displacement of water in the cylinder. The original data
(non-transformed) from each half of the root system were submitted to ANOVA and the means were
compared by Tukey test at 5%. This experiment was repeated once.
RESULTS AND DISCUSSION
No significant differences were observed in the variables weight, healthy volume, necrotic volume
and total volume of the root system, and in plant height in treatments 1, 2, 3 and 4 (Table 1). However,
an increase in fungal infection was observed when M. enterolobii and F.solani were inoculated into the
same root system (Figure 1E), revealing that disease development has a spatial and temporal dependence
for exposure to both pathogens. This can be seen in treatment 5, which produced similar results to
those found by Bowman & Bloom10 and Hillocks11. The studies carried out by Faulkner & Skotland12
showed that plants parasitized by nematodes positively influenced the period of incubation, as well as
increasing the incidence and severity of the wilt caused by Verticillium dahliae Kleb and Prathylenchus
vulnus, even when the two pathogens parasitized distinct root systems from the same plant.
This apparent contradiction indicates that the nematode can have two effects that favor the fungal
infection in guava plants. One effect is localized; the penetration and initial development of the fungus
are reinforced by the morphophysiological alterations caused by M. enterolobii infection in guava
plants, which increases the susceptibility to F. solani. The other is a systemic effect: the inhibition of
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Relationships between M. enterolobii and F. solani: spatial and temporal dynamics in the occurrence of guava decline
Table 1. Effect of Meloidogyne enterolobii and Fusarium solanion development of the root and aerial part of guava
plants with root system divided into two plastic container (I and II), in greenhouse, inoculated with 500 eggs and
second-stage juveniles of Meloidogyne enterolobii and/or 5 g of wheat grains colonized by Fusarium solani isolate
UENF/CF 163. The evaluation took place 120 days later.
Treatments applied to the root system
I
II
Non-inoculated
Non-inoculated
Non-inoculated
Fresh shoot
mass (g)
Root system volume
(cm3)a
Fresh mass of root
system (g)
I
II
I
II
93.6a
25.8a
24.4a
27.8a
28a
M. e.
98.9a
20.8a
20.4a
23.2a
26.9a
Non-inoculated
F. s.
95.5a
23.8a
24a
22.8a
22.5a
Non-innoculated
M. e. / F. s.
74.7b
20.4a
8,3b
21.2a
10.4b
M. e.
F. s.
92.8a
18.6a
23.6a
25.6a
28.4a
23.4
23.8
18.4
21.2
16.2
CV%
Measured by means of displacement of water in graduated test-tube in the laboratory. M.e. (Meloidogyne enterolobii) F.S. (Fusarium solani).Values
are mean of two experiments, each one with six repetitions(plants)per treatment. Values followed by the same letter in the column are not different
according to Tukey test at 5%.
a
Figure 1. Root system of guava plants in which the roots were divided into two plasticcontainerand inoculated with
500 eggs and second-stage juveniles of Meloidogyne enterolobii and/or 5g of wheat grains colonized by Fusarium
solani isolate UENF / CF 163. A) both halves of the root system non-inoculated; B) half inoculated with the fungus / and
half non-inoculated; C) half inoculated with nematode / and half non-inoculated; D) half inoculated with nematode /
and half inoculated with the fungus; E) half inoculated with nematode and 21 days later inoculated with the fungus
/ and half non-inoculated; F) detail of half of the root system inoculated only with F. solani; G) detail of half of the
root system inoculated only with M. enterolobii; H) detail of half the root system inoculated with M. enterolobii and
21 days later with F. solani.
the host’s resistance mechanisms occurs, resulting in simultaneous development of the fungus in the
tissues that were not infected by the nematode.
In micro plot experiments, Gomes et al.2 established that the parasitism of guava plants by
M. enterolobii is necessary for invasion and colonization of their roots by F. solani. Guava decline is
not observed in plants that were only parasitized by M. enterolobii, nor is it seen in plants inoculated
only with F. solani. In the present work, the experiment with bipartite roots, carried out twice, did
not present any evidence of one systemically transferred factor that could be involved in root rot
(Figure 1, Table 1).
In fact, no root deterioration took place, and there was not reduction in the root system or in
development of the aerial part of the plants inoculated with F. solani in isolation or together with
M. enterolobii in distinct halves of the root system of the same plant. This suggests the need of the
nematode and the fungus to be physically close for guava decline to take place, independently of the
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Relationships between M. enterolobii and F. solani: spatial and temporal dynamics in the occurrence of guava decline
mechanisms involved in this synergic interaction. Treatment 5 (Figure 1E) provided the spatial and
temporal proximity of M. enterolobii and F. solani, which appears to have triggered the occurrence
of guava decline.
According to Back et al.7 tissues from galls around the nematode are easily colonized by the fungus.
This suggests that histological alterations occur in the roots infected by the nematode, making them
very susceptible to subsequent fungus invasion. Based on this preliminary experiment with plants
that have a bipartite root system, there is a hypothesis that at least three mechanisms, acting locally on
their own or in combination, may be involved in guava decline. These mechanisms are: i) parasitism
by the nematode alters root physiology at nearby points, inhibiting the resistance mechanism and
making possible for the fungus to invade root tissues; ii) tissues that are rich in gall nutrients favor
colonization by the fungus and subsequent deterioration; iii) parasitism by the nematode alters the
chemical composition of root exudates, which in some way allows the fungus to invade the roots.
The majority of root rots caused by soil-borne pathogenic fungi depend on the pathogenicity of
the inoculum for the occurrence of the disease13. Studies demonstrate that the mechanisms of action
involved in guava decline are related to qualitative or quantitative alterations in the root exudates
from plants parasitized by M. enterolobii, which provide a temporary source of nutrients, allowing
the fungus to vegetate and increase its capacity to infect the guavas.Gomes et al.8 showed that F. solani
responds in the presence of these exudates with a capacity to produce a greater density of hyphae,
macro- and micro-conidia and resistance structures. Thus, the greater the number of propagules in
the soil, the greater will be the potential of the inoculum.
In studies by Gomes et al.14 and Almeida et al.15, intense decomposition was noted in the root
system of guavas parasitized by M. enterolobii in association with F. solani resident in the soil. The
pathogenesis was apparently aggravated by stress factors such as excess or lack of water or drastic
pruning, suggesting that there is a component of physiological imbalance involved in guava decline
associated with M. enterolobii.
Total root mass was reduced (P <0.05) when the two pathogens were inoculated together in the same
half of the root system, along with necrosis of about half of the root system. This strongly supports the
hypothesis that when parasitism by M. enterolobii occurs, quantitative and/or qualitative changes in
the root exudates allow the fungus to invade and induce decline in root system. In work by Nelson16,
root exudates were clearly seen to trigger and modulate fungal response to the roots. According to that
author, germination of F. solani f.sp. pisi chlamydospores and macro-conidia was favored in response
to sugars and ethanol present in the exudates of pea roots. According to Cia & Salgado17 damp sandy
soils, with low pH, fertility and potassium content, propitiate development of Fusarium wilt. Wilt is also
favored when in association with nematodes, especially from the genera Meloidogyne, Pratylenchus
and Rotylenchulus; severity increases when roots are damaged and the plant is debilitated.
These results reinforce those found in a study by Gomes et al.8, observing quantitative and/or
qualitative alterations that occur in root exudates from guava parasitized by M. enterolobii which
probably activate new biochemical pathways in the fungus. These expand propagule production and
increase inoculum potential,as a consequence this may reduce plant resistance locally.
Available evidence suggests that, despite its synergistic character, guava decline depends on a local
factor that is not translocated in the plant. Studies to elucidate how this local interaction between
pathogens should be targeted for further research is therefore an important aspect that should be
considered with due concern is the continuing and devastating effect of guava decline, not existing
yet management technologies economically viable.
CONCLUSIONS
No systemic effect of the parasitism by the nematode was detected that might have led to plant
susceptibility to thedamage caused by the fungus. It was therefore concluded that there was a local
effect of parasitism by M. enterolobii on the pathogenicity of F. solani in guava roots, making it necessary
for the two pathogens to occupy the same space at the same time for guava decline to occur.
ACKNOWLEDGMENTS
The authors are indebted to Dr. Silvaldo F. Silveira (UniversidadeEstadual do Norte Fluminense
Darcy Ribeiro) for technical advice on the growth chamber assay.
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REFERENCES
1. Gomes VM, Souza RM, Midorikawa G, Miller R, Almeida AM. Guava decline: evidence of nationwide incidence in
Brazil. Nematropica. 2012;42(1):153-62.
2. Gomes VM, Souza RM, Mussi-Dias V, Silveira SF, Dolinski C. Guava Decline: A Complex Disease Involving
Meloidogyne mayaguensis and Fusarium solani. Journal of Phytopathology. 2011;159(1):45-50. http://dx.doi.
org/10.1111/j.1439-0434.2010.01711.x.
3. Almeida AM, Gomes VM, Souza RM. Greenhouse and field assessment of rhizobacteria to control guava decline.
Bragantia. 2011;70(4):837-42. http://dx.doi.org/10.1590/S0006-87052011000400016.
4. Pereira FM, Souza RM, Souza PM, Dolinski C, Santos GK. Estimativa do impacto econômico e social direto de
Meloidogynemayaguensisna cultura da goiaba no Brasil. Nematologia Brasileira. 2009;33(2):176-81.
5. Hillocks RJ, Waller JM. Soilborne diseases of tropical crops. Wallingford: CABI; 1997.
6. Stamford NP, Rodrigues JJV, Heck RJ, Andrade DEGT. Propriedades físicas e químicas dos solos. In: Michereff SJ,
Andrade DEGT, Menezes M. Ecologia e manejo de patógenos radiculares em solos tropicais. Recife: UFRPE, Imprensa
Universitária; 2005. p. 41-60.
7. Back MA, Haydock PPJ, Jenkinson P. Disease complexes involving plant parasitic nematodes and soilbornepathogens.
Plant Pathology. 2002;51(6):683-97. http://dx.doi.org/10.1046/j.1365-3059.2002.00785.x.
8. Gomes VM, Souza RM, da Silveira SF, Almeida AM. Guava decline: effect of root exudates from Meloidogyne
enterolobii parasitized plants on Fusarium solani in vitro and on growth and development of guava seedlings
under controlled conditions. European Journal of Plant Pathology. 2013;137(2):393-401. http://dx.doi.org/10.1007/
s10658-013-0251-2.
9. Pereira FM. Cultura da goiabeira. Jaboticabal: FUNEP; 1995.
10. Bowman P, Bloom JR. Breaking the resistance of tomato varieties to Fusarium wilt by Meloidogyne incognita.
Phytopathology. 1966;56:871.
11. Hillocks RJ. Localised and systemic effects of root-knot nematode on the incidence and severity of Fusarium wilt
in cotton. Nematologica. 1986;32(2):202-8. http://dx.doi.org/10.1163/187529286X00165.
12. Faulkner LR, Skotland CB. Interactions of Verticillium dahliae and Pratylenchus minyus in Verticillium wilt of
peppermint. Phytopathology. 1965;55:583-6.
13. Ferraz JFP. Importância e dinâmica do inóculo potencial dos fungos fitopatogênicos do solo. Summa Phytopathologica.
1990;16:197-213.
14. Gomes VM, Souza RM, Corrêa FM, Dolinski C. Management of Meloidogyne mayaguensis in commercial guava
orchards with chemical fertilization and organic amendments. Nematologia Brasileira. 2010;34(1):23-30.
15. Almeida AM, Souza RM, Gomes VM, Miranda GB. Greenhouse and field assessment of different organic
compounds against guava-parasitic Meloidogyne enterolobii. Bragantia. 2012;71(1):67-74. http://dx.doi.org/10.1590/
S0006-87052012000100011.
16. Nelson EB. Exudate molecules initiating fungal responses to seeds and roots. Plant and Soil. 1990;129(1):61-73.
http://dx.doi.org/10.1007/BF00011692.
17. Cia E, Salgado CL. Doenças do algodoeiro (Gossypium spp.). In: Kimati H, Amorin L, Bergamin Filho A, Camargo
LEA, Rezende, JAM, editors. Manual de fitopatologia: doenças das plantas cultivadas. 3rd ed. São Paulo: Agronômica
Ceres; 1997. p. 33-48.
http://dx.doi.org/10.4322/nematoda.01014
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