J. Hortl. Sci.
Vol. 10(1):64-69, 2015

Survey of nematode-destroying fungi from selected vegetable-growing areas in Kenya

P.M. Wachira, J.N. Muindi and S.A. Okoth
University of Nairobi, P.O. Box 30197, Nairobi, Kenya

Email: pwachira@uonbi.ac.ke

ABSTRACT
Plant-parasitic nematodes cause severe damage to a wide range of economic crops, causing upto 5% yield losses

globally. In Kenya, vegetables are affected, among other pests, by parasitic nematodes, causing upto 80% loss in yield.
Nematode control is very difficult and relies heavily on use of chemical nematicides. Use of these chemical nematicides
leads to biological magnification, and elimination of natural enemies of other pathogens, thus creating a need for
greater application of pesticides, increased production costs, and development of insecticide-resistance. These factors
have led to a growing interest in search for alternate management strategies. The objective of this study was, therefore,
to document nematode-destroying fungi in selected, major vegetable-growing areas in Kenya as a step towards
developing a self-sustaining system for management of plant-parasitic nematodes. Soil samples were collected from
five vegetable-production zones, viz., Kinare, Kabete, Athi-river, Machakos and Kibwezi, and transported to the laboratory
for extraction of nematode-destroying fungi. The soil-sprinkle technique described by Jaffee et al (1996) was used for
isolating the nematode-destroying fungi from soil, while, their identification was done using identification keys
described by Soto Barrientos et al (2001). From this study, a total of 171 fungal isolates were identified as nematode-
destroying. The highest population was recorded in Kabete, at 33.9% of the total, followed by Machakos, Kibwezi,
Athi-river, with the least in Kinare, at 24.6, 22.2, 11.7 and 7.6% of the total population, in that order. Arthrobotrys was
the most frequent genus, with mean occurrence of 7.3, followed by Monacrosporium with 6 and Stylophage with 5.2.
A. dactyloides was significantly (P=0.002) affected by the agro-ecological zone, with the highest occurrence recorded
in Kabete, and the least in Athi-river. Kibwezi recorded highest diversity index, with a mean of 1.017, while, Athi-river
recorded the least, with a mean of 0.333. Kibwezi had the highest species richness, recording a mean of 3.4, while, the
least mean of 1.6 was recorded in Athi-river. Mean species richness of 2.2 was recorded for both Kabete and Machakos,
and 1.8 for Kinare. From the three genera recorded, Arthrobotrys was more effective at trapping nematodes compared
to Monocrosporium and Stylopage. The genus Arthrobotrys had the highest number of trapped nematodes, with a
total population of 57, followed by Monacrosporium, the least being Stylopage, with 45 and 36, respectively, in a period
of 104 hours. From the study, it is evident that agricultural practices affect occurrence and diversity of nematode-
destroying fungi, and, Arthrobotrys can be used as a bio-control agent for managing plant-parasitic nematodes.

Key words: Artabotrys, biological control, plant-parasitic nematodes

INTRODUCTION
Horticultural crops, both for local consumption and

export, are important in Kenya. One-tenth of the vegetables
in Kenya are grown for export. They are recognized for
their health and nutritional benefits, and provide cash income
and employment for close to two million people in Kenya
(Dobson et al, 2004). Production of vegetables in Kenya,
especially for an expanding domestic market, is even now
limited by major pests and diseases (Dobson et al, 2004).
Plant-parasitic nematodes have been identified as a major
production constraint, affecting vegetable production,
resulting in reduced yield quality and quantity (Nchore et
al, 2010). They are responsible for upto 80%, on vegetable

production (Kaskavalci, 2007). Vegetable production in
Kenya is characterized by high chemical input for pest and
soil fertility management (Mutsotso et al, 2005). These
practices have been associated with increase in soil-borne
diseases and decline in beneficial soil micro-organisms
(Wachira et al, 2008). Specifically, vegetable damage by
root-knot nematode has been reported in Kenya, with
infected plants rendered unacceptable to international
markets (Nchore et al, 2010). The root knot nematode
increases wounding of the root system, thus providing points
of ingress of the pathogen. The nematode may also modify
the tissue in a way that it becomes more amendable to
bacterial colonization (Hayward, 1991). Globally, it is



65

Nematode-destroying fungi in vegetable farms in Kenya

estimated that US $ 500 million is spent on root-knot
nematode control strategy (Keren-Zur et al, 2000; Pinkerton
et al, 2000), including use of nematicides, organic-manure
amendment and use of resistant cultivars (Akhtar & Malik,
2000). Overall, though nematicides are effective in managing
root-knot nematode and other plant-parasitic nematodes, they
are expensive and become environmental pollutants when
not applied at the right time, in the right manner and in the
right dosage. This increases cost of production to the farmers,
reducing their profit (Republic of Kenya, Taita District
Development Strategies 2002-2006). Use of nematicides is
also curtailed by their threat to groundwater, soil biodiversity,
as well as long waiting-periods between use, harvesting and
marketing of a crop (Bridge, 1996).

Alternatively, soil beneficial microorganisms can be
used as an alternative, thereby helping reduce application
of chemicals to the soil. This entails the use of natural
enemies to control nematode pests. Beneficial micro-
organisms are non-polluting and, thus, environmentally safe
and acceptable. Usually, these are species-specific to the
target pest, therefore with no chances of affecting non-
target species (unlike chemicals, which are broad-spectrum
in their action (Hein et al, 2007). Nematode-destroying fungi
are one such group of beneficial microorganisms for use in
control of plant-parasitic control of plant-parasitic
nematodes. These micro-fungi are natural enemies of the
nematodes. They naturally capture, kill and digest nematodes
present in the soil (Rodrigues et al, 2001; Nordbring-Hertz
et al, 2002). They comprise three main groups: the nematode
trapping fungi, the endoparasitic fungi, and the egg-and cyst-
parasitic fungi (Nordbring-Hertz et al, 2002; Masoomeh et
al, 2004). After trapping the nematodes, the fungi penetrate
their cuticle, invade their entire body-cavity and, then, digest
them completely. This group of fungi has drawn much
attention due to their potential as biological control agents
for plant-parasitic nematodes (Jansson et al, 2000; Sanyal,
2000; Masoomeh et al, 2004). About 70% of the fungal
genera and 160 species are associated with nematodes, but,
only a few can be used as biological control agents for
nematodes (Elshafie et al, 2006). This study was, therefore,
aimed at documenting occurrence and diversity of nematode-
destroying fungi and testing their efficacy on plant-parasitic
nematodes, to harness their potential as bio-control agents
against plant-parasitic nematodes.

MATERIAL AND METHODS
Soil samples were collected from five different

vegetable-growing areas in Kenya, viz., Kinare, Kabete,

Athi-river, Machakos and Kibwezi, in the order of altitude
and temperature. Kinare was a high-altitude area and the
coldest, with Kibwezi being the lowest and hottest. Vegetable
gardens in each zone were dominated mainly by spinach,
kale, tomato, cabbage and pepper, among other vegetables.
From each of the study areas, five farms under intensive
vegetable-production were selected randomly for this study.
From each of the farms, five different vegetable gardens
were sampled. From each vegetable garden in turn, five
soil samples were collected and mixed together in a bucket
to make a composite sample. One kilogram of soil was then
re-sampled from the composite sample in the bucket, put
into plastic bags, labelled and placed in a cool box. Soil
sampling was done using a soil auger sterilized using ethanol
after every sampling, to avoid cross-contamination. All the
samples were later transported to the laboratory for isolating
nematode-destroying fungi.

Isolation of nematodes-destroying fungi was done
using the soil-sprinkle technique described by Jaffee et al
(1996) where, tap water agar (TWA) was prepared by
dissolving 20g agar in one litre of tap water. The medium
was autoclaved and cooled before use after amending it
with 0.1g per litre of streptomycin sulfate under a laminar
air flow cabinet. One gram of soil sample was sprinkled on
the medium in the Petri dish, and a suspension of
Meloidogyne species consisting of approximately 1000
nematodes, was added to the Petri dishes as bait (Christina
et al, 1999). The plates were then incubated at room
temperature and observed daily from the third week, up to
the sixth week, under a dissecting microscope. The
examination was focussed on trapped nematodes, trapping
organs and conidia of the nematode-destroying fungi
(Wachira et al, 2008).

Taxonomic classification of the nematode-destroying
fungi was done using the ‘slide culture technique’ where
slides were observed under a microscope, while identification
of the genus was done using identification keys described
by Soto Barrientos et al (2001). After identification of
nematode-destroying fungi, pure cultures of the three most-
frequent fungal isolates were made for the experiment on
efficacy. A 5mm mycelial block was inoculated into PDA in
a Petri dish and allowed to grow for five days, before
approximately 50 plant-parasitic nematodes were added.
Efficacy of the fungal isolates was monitored for a period
of 3-6 weeks. Trapped nematodes were counted for five
days after 3 weeks of incubation. All the data in this study
was analyzed by Analysis of Variance (Kindt & Coe, 2005)

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66

RESULTS AND DISCUSSION
From this study, 171 fungal isolates were identified

as nematode-destroying. They grouped into three genera
and five taxa. The three genera were: Arthrobotrys,
Monacrosporium and Stylopage. Arthrobotrys was a
frequently-encountered genus. The genus Arthrobotrys was
represented by A. oligospora, A. dactyloides and A.
longispora, the genus Monocrosporium was represented
by M. cionopagium, while the genus Stylopage was
represented by S. grandis. A. oligospora had the highest
frequency of occurrence, followed by A. dactyloides, M.
cionopagium, S. grandis; the least frequent was A.
longispora with occurrence of 46.20, 45.61, 5.85, 1.17 and
1.17%, decreasing in that order (Fig. 1).

Fungal isolates were recovered from all the vegetable-
production zones. Excepting A. dactyloides, all the isolates
were not significantly (P> 0.05) affected by the agro-
ecological zone. Frequency of occurrence of A. dactyloides
was significantly (P=0.002) affected by the agro-ecological
zone. The highest occurrence of A. dactyloides was
recorded in Kabete, while the least was recorded in Athi-
river, with a total record of 40 and 4, respectively. The
species was also recorded in Machakos, Kibwezi and Kinare,
with occurrence of 19, 10 and 5, respectively, in decreasing

order. Among the isolates, only A. oligospora and A.
dactyloides were found to occur in all the agro-ecological
zones. M. cionopagium occurred in all the zones except
Kinare, while, S. grandis was present in both Kibwezi and
Kinare. A. longispora was recorded in Kibwezi only
(Table 1).

The highest number of nematode-destroying fungi
was recorded in Kabete, followed by Machakos, Kiwezi,
Athi-river and, finally Kinare, with total mean abundance
of 11.6, 7.6, 7.4, 4.0, and 2.6 in that (decreasing) order.
Kibwezi recorded the highest diversity index, with a mean
of 0.930, followed by Machakos with 0.637, while Kabete
recorded the least diversity index mean of 0.411. Mean
richness and abundance varied between vegetable-
production zones. The highest mean species richness was
recorded in Kibwezi, while the least was recorded in Athi-
river. All the agro-ecological zones differed significantly (P
= 9.587 x 10-4) in terms of species abundance. Kabete
had the highest species abundance with a mean of 11.6,
and, the least was seen in Kinare with species mean
abundance of 2.6 (Table 2).

More nematode-destroying fungi were detected with
increase in the number of the soil samples under study. It is
evident that all the possible isolates of nematode-destroying
fungi were recorded in this study, from the samples collected.
Collecting and processing additional samples may not have
significantly increased the number of isolates (Fig. 2).

There was a significant (P=0.003) difference on
efficacy between the three most-frequent nematode-
destroying fungal species. Arthrobotryrs oligospora was
the most efficient nematode-destroying fungus, with a mean
of 7.3, followed by Monacrosporium; the least was
Stylopage, with mean records of 5.9 and 5.1, respectively.

Nematode-destroying fungi were isolated from all the
selected vegetable-production zones. These occurred at
different frequencies and diversity. The study demonstratedFig. 1. Percentage occurrence of nematode-destroying fungi in

some vegetable-producing areas of Kenya

Table 1. Occurrence of nematode-destroying fungi in major agro-
ecological zones of Kenya
Zone A. A. A. M. S. Total

dactyloides oligospora longispora cionopagium grandis
Kabete 20 17 0 1 0 58
Machakos 19 22 0 1 0 42
Kinare 5 7 0 0 1 13
Kibwezi 10 20 2 5 1 38
Athi-river 4 13 0 3 0 20
P value 0.002 0.395 0.062 0.165 0.062

Table 2: Mean shannon, species richness and abundance of
nematode-destroying fungi in different vegetable-growing areas
in Kenya
Zone N Mean Mean Mean

shannon richness abundance
Kibwezi 5 0.930 3.4 7.6
Machakos 5 0.637 2.2 7.4
Athi-river 5 0.483 1.6 4.0
Kinare 5 0.482 1.8 2.6
Kabete 5 0.411 2.2 11.6
P value 9.587 x 10-4

Wachira et al

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67

the occurrence of diverse nematode-destroying fungi in
nature, especially, in vegetable-production zones. These
findings agree with previous reports on nematode-destroying
fungi that indicate that these are wide-spread in all habitats,
but, at different densities and diversities (Birgit et al, 2002;
Wachira et al, 2008).

Arthrobotrys oligospora was the most abundant
species of nematode-destroying fungi in the area under study.
Other studies on nematode-destroying fungi report the same
observation. It has never been clear why this is the most
frequently encountered fungus. Wachira et al (2008) had
suggested that farming practices like weeding could be the
cause of such high occurrence. It has also been suggested
that it is due to the ability of the fungus to exist both as a
saprophyte and a plant-parasitic nematode feeder (Sobita
and Anamika, 2011). Due to this high occurrence, this fungus
has attracted several other interesting studies (Niu and
Zhang, 2011).

It was expected that the highest divergence of fungi
would be isolated from areas under low temperature
(Kinare). However, this was not the case. Kinare had the
least variety of fungi. This was attributed to the high use of
chemical fertilizers and pesticides, since, all the vegetables
were aimed for the market. In a study on long-term effects
of manures and fertilizers on soil productivity and quality, it
was reported that chemically fertilized soils had lower content
of organic matter and fewer numbers of microfauna than
manured soils (Edmeades, 2003). The highest number of
nematode-destroying fungi was recovered from Kabete.
Soils in this area had been collected from the farm at
University of Nairobi to which animal manure had been
frequently applied. This may explain the high number of
nematode-destroying fungi here, since, these are associated

with increase in beneficial micro-organisms in the soil
(Wachira and Okoth, 2009). In our study, a high fungal
population was found in areas where manure had been
applied, and low fungal population in areas where chemical
fertilizer was applied.

Temperature is an important factor in regulating
microbial activity and shaping soil microbial communities. It
determines moisture level in the soil, which is key to fungal
spore germination and growth. High temperatures lead to
low soil-moisture, which leads to low fungal-spore
germination. A study by Haugen and Smith (1992) reported
that at high temperatures, there was low germination of
fungal spores, leading to low fungal population, while, under
low temperatures there was high fungal germination, leading
to a high fungal population. This was found to be in reverse
in our study. Although Machakos and Kibwezi experience
high temperatures, a high population of nematode-destroying
fungi was seen here by us. This could be attributed to the
irrigation activities undertaken at the farm which ensured
moist conditions throughout the growth season. This soil
enhanced moisture, coupled with high temperature, improved
fungal spore germination (as, fungal spores germinate better
under moist and warm conditions).

Efficacy test showed that the genus Arthrobotrys
was most effective in trapping plant-parasitic nematodes.
Previous studies on fungi of this genus have consistently
showed that it is able to trap 90% of all the nematodes in
Petri dishes and liquid cultures in 16-40 hours (Rajeswari
and Sivakumar, 1999). Therefore, due to its high occurrence,
this fungus can be used in management of plant-parasitic
nematodes, and its potential for this ability should be
investigated. The investigation should focus on finding
suitable carrier/s for the fungus and its mode of application.
This would reduce over-reliance on chemical nematicides
and help develop a self-regulating system in the soil for control
of soil borne pests.
CONCLUSION

Additional evidence has been provided by this study
that nematode-destroying fungi naturally occurr in
agricultural habitats. It is also evident that agricultural
activities targeting high crop-production, like, application of
chemical fertilizers and pesticides, directly affect soil
biodiversity adversely. Results from this study can be used
in further research for establishing the potential of nematode-
destroying fungi in regulation of plant-parasitic nematode
population.

Fig. 2. A total-species cumulative curve for nematode-destroying
fungi in some vegetable production zones of Kenya

Number of samples

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68

ACKNOWLEDGEMENT
University of Nairobi is acknowledged for providing

laboratory equipment and space. We also wish to thank the
small scale farmers of five different vegetable-production
zones under study for their cooperation and for providing
free access to their farms.

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(MS Received 29 June 2013, Revised 17 March 2015, Accepted 25 March 2015)

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Nematode-destroying fungi in vegetable farms in Kenya