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Vol.21 No.9 September 2003
Using fungi and yeasts to manage
vegetable crop diseases
Zamir K. Punja1 and Raj S. Utkhede2
1
Center for Environmental Biology, Dept of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby,
British Columbia, Canada V5A 1S6
2
Pacific Agri-Food Research Center, Agriculture and Agri-Food Canada, PO Box 1000, Agassiz, British Columbia, Canada V0M 1A0
Vegetable crops are grown worldwide as a source of
nutrients and fiber in the human diet. Fungal plant
pathogens can cause devastation in these crops under
appropriate environmental conditions. Vegetable producers confronted with the challenges of managing fungal pathogens have the opportunity to use fungi and
yeasts as biological control agents. Several commercially available products have shown significant disease
reduction through various mechanisms to reduce
pathogen development and disease. Production of
hydrolytic enzymes and antibiotics, competition for
plant nutrients and niche colonization, induction of
plant host defense mechanisms, and interference with
pathogenicity factors in the pathogen are the most
important mechanisms. Biotechnological techniques
are becoming increasingly valuable to elucidate the
mechanisms of action of fungi and yeasts and provide
genetic characterization and molecular markers to
monitor the spread of these agents.
Since the domestication of crop plants by humans first
began , 10 000 years ago, diseases caused by plant
pathogenic fungi have continued to inflict considerable
losses in harvestable yield and have reduced the aesthetic
value and storage life of agricultural crops. These
pathogenic fungi have caused considerable economic
losses for producers; on average, annual losses in North
America can be up to 10% and are higher in less
industrialized regions of the world. Even with recent
technological advances in the development of resistant
varieties of crop plants using genetic engineering
approaches [1], and with new discoveries of novel, sitespecific fungicides [2] and continually evolving crop
production practices, fungal plant pathogens continue to
find opportunities to destroy crop plants.
Management strategies for vegetable crop diseases
Vegetable crops are grown and consumed worldwide and
leafy vegetables and fruits in particular provide a source of
nutrients and fiber in the human diet. These crops might
be consumed fresh or after processing and are produced
either on farms with conventional or organic agricultural
production methods, or under intensively managed environmentally controlled glasshouses. These vegetable crops
Corresponding author: Zamir K. Punja ([email protected]).
are not spared from destruction by fungal pathogens,
which infect roots, stems, leaves, flowers and fruits. The
challenges for producers in managing these diseases are
ever-increasing, as consumer demand for year-round
production of fresh vegetables with reduced or no pesticide
residues continues to grow. Concerns over the potential
impact of disease management practices – including the
use of fungicides – on the environment or on consumer
health have prompted producers to examine alternative
methods to combat fungal diseases. In this review, we
discuss the use of fungi and yeasts to manage fungal
diseases on vegetable crops, and highlight recent developments in this area.
Emergence of fungi and yeasts as potential disease
management agents
The plant pathogenic fungi attacking vegetable crops that
have been studied from the perspective of using fungi and
yeasts for control, range from biotrophs to necrotrophs.
Biotrophic fungi, such as powdery mildew fungi, only grow
and reproduce on the living host plant (obligate parasites)
(Fig. 1), whereas necrotrophs, such as Botrytis cinerea,
which causes gray mold disease, are opportunistic fungi
that grow and reproduce on plant debris or organic matter
but can rapidly invade wounded or senescing plant tissues.
In addition, fungi can infect the roots and colonize the
vascular tissues of the plant, causing root rots and wilt
diseases (Pythium spp. and Fusarium spp., respectively)
(Fig. 1). An understanding of the disease cycle (events
leading from initial infection to colonization and reproduction of the pathogen) (Fig. 2) and life cycle of the pathogen
are crucial to the successful use of any disease management strategy. Most plant pathogens affecting vegetable
crop species have been reasonably well-studied and
information on their biology is available [3]. The use of
fungi and yeasts to manage these diseases requires
disruption of some stage of the disease- or life-cycle of
the pathogen (Fig. 2) and this has been achieved through
several different mechanisms (Fig. 3). Prevention of
infection, reduction in colonization of host tissues, or
reducing sporulation or survival of the pathogen, can each
provide a level of disease control using biological control
agents (Fig. 2).
Many of these fungi and yeasts exist naturally on or
near plant leaves, roots and other structures as epiphytes
or saprophytes, using nutrients available in various
http://tibtec.trends.com 0167-7799/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0167-7799(03)00193-8
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(a)
(b)
401
Vol.21 No.9 September 2003
Pathogen development and biocontrol activity
Survival
Germination
and infection
(c)
Tissue
colonization
(d)
Biocontrol agent
Growth
and sporulation
Fig. 1. Using fungi and yeasts to control fungal pathogens on cucumber. (a) Blastospores of the yeast Tilletiopsis pallescens from a 72-h-old liquid broth culture.
Scale bar, 20 mm. (b) Cucumber leaf heavily infected with powdery mildew [Podosphaera (Sect. Sphaerotheca) xanthi ] growth and sporulation. (c). Two applications – made one-week apart – of the yeast suspension shown in (a) to leaves
shown in (b) provided a significant reduction in growth and development of the
mildew pathogen. This was caused, in part, by the production of antifungal compounds by the yeast [10]. Photograph taken one week after the second application
of yeast spores. (d) Application of the biocontrol agent Gliocladium catenulatum
(Prestop Mix) to cucumber seed at the time of planting followed by inoculation 10
days later with Pythium aphanidermatum provided significant protection and
improved growth (plant on left) compared with the control plant (plant on right),
which did not receive the biocontrol agent. Photograph taken three weeks after
seeds were planted.
niches. Research to elucidate whether these organisms
could potentially be used as biological control agents to
combat diseases has intensified over the past 20 years, and
this has led to the commercial development of several
registered microbial agents for vegetable crop disease
management, as well as for diseases on other crops
(Table 1). Following their initial discovery, the development
Spread
and infection
TRENDS in Biotechnology
Fig. 2. The various stages of the development of a pathogen and resulting plant
disease can be reduced by the application of fungi and yeast biological control
agents. Different agents can target single or multiple stages of pathogen development as indicated.
of these biological control agents from a research laboratory to a commercial product is quite a daunting task.
Information needs to be gathered on the efficacy and
mode(s) of action of the agent, as well as on the survival
and spread and potential toxicity to non-target species
[4– 6]. Furthermore, formulation, product stability and
shelf-life studies are also required [4– 6]. The quest to
identify biological control agents for plant diseases has,
however, provided tremendous opportunities for plant
pathologists, mycologists, geneticists, biochemists and
Table 1. Commercially available fungi and yeast biological control products to manage vegetable crop diseasesa
Product trade name
Microorganism(s) contained
Fungal disease target
Manufacturer or distributor
AQ 10
Binab
Biofox C
Ampelomyces quisqualis M-10
Trichoderma spp.
Fusarium oxysporum
(non-pathogenic)
Trichoderma spp.
Coniothyrium minitans
Fusarium oxysporum
(nonpathogenic)
Coniothyrium minitans
Pythium oligandrum
Gliocladium catenulatum
Trichoderma harzianum
T. harzianum T-22
Powdery mildews
Root rot, wilt
Wilt
Ecogen, USA
Binab, Sweden
S.I.A.P.A., Italy
Root rot, wilt
Root rot
Wilt
Bioplant, Denmark
Prophyta Biologischer, Germany
Natural Plant Protection, France
Root rot
Root rot
Root rot, wilt
Root rot
Root rot
Bioved, Hungary
Biopreparaty, Czech Republic
Verdera Oy, Finland
Efal Agri, Israel
Bioworks, USA
Root rot
Certis, USA
Powdery mildews
Grey mold
Root rot
Root rot, wilt
Plant Products, Canada
Makhteshim Chemical Works, Israel
Agrimm Technologies, New Zealand
Ecosense Laboratories, India
Biofungus, Superesivit
Contans WG, Intercept WG
Fusaclean
KONI
Polyversum
Primastop (Prestop Mix)
Root Pro
Root Shield, Plant Shield,
T-22 Planter box
Soil Gard
Sporodex
Trichodex
Trichopel
Trieco
a
Trichoderma (Gliocladium)
virens GL-21
Pseudozyma flocculosa
T. harzianum
Trichoderma spp.
Trichoderma viride
For more details, visit http://www.oardc.ohio-state.edu/apsbcc/productlist.htm. See also [76].
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Fungal or yeast biological control agent
Production of
antibotic
compounds
Secretion of
enzymes
Parasitism of
pathogen
Competition
for nutrients
and infections
sites
Interference
with
pathogenicity
factors
Induced
resistance in
host plant
Inhibition of fungal pathogen growth, destruction of
hyphae and spores and reduced development of disease
TRENDS in Biotechnology
Fig. 3. Mechanisms by which fungi and yeasts reduce growth and development of fungal plant pathogens and reduce disease.
molecular biologists to interact, work together, and gain a
better understanding of how these microbes can reduce
fungal pathogen development and disease. Here, we
summarize recent scientific developments and illustrate
how modern research techniques are being applied to
better understand the way in which biological control of
vegetable diseases using fungi and yeasts is achieved.
Efficacy data on these biocontrol agents are summarized
elsewhere [7]. There is no single unifying feature that can
be identified among the biological control agents listed in
Table 1 that would explain how they manifest themselves
as antagonists to disease-causing fungi. However, several
important features have emerged from scientific investigations concerning their modes of action (Fig. 3), and these
are discussed later.
Role of mycoparasitism in pathogen biocontrol
Reports dating back to the 1930s first showed that fungal
pathogens could be infected or parasitized by other fungi
(mycoparasites) [8]. The most widely studied fungi in this
regard were different species of Trichoderma. In the late
1980s, yeasts were discovered that could reduce the
growth and spore production of plant pathogenic fungi
[9,10]. These interactions between plant pathogen and
mycoparasite require that they be in close physical
proximity to each other. As a result, most observations
have been made from Petri dishes or detached plant
tissues under controlled conditions. For example, Ampelomyces quisqualis (AQ 10) was shown to be parasitic on
powdery mildew hyphae and conidia [11], whereas Coniothyrium minitans (Contans) is mycoparasitic on sclerotia of Sclerotinia spp. [12,13], and Pythium oligandrum
(Polyversum) is mycoparasitic on other Pythium spp. and
some other fungi [14,15]. These findings have now been
extended outside the confines of the laboratory to
vegetable crops grown under glasshouse and field conditions, and these specific microbial agents have been
shown to reduce disease development significantly and are
now registered products (Table 1).
In many cases, however, the importance of mycoparasitism is difficult to demonstrate conclusively in situ,
even though it is evident under experimental conditions.
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For example, although Trichoderma spp. were among the
first mycoparasites to be described, their role in reducing
infection and colonization of host tissues through
mycoparasitism has been difficult to confirm [8]. There
are technical difficulties in making microscopic observations to demonstrate mycoparasitic activity in situ, such
as at the soil – root interface, even with the availability of
fluorescence imaging and differential staining methods.
The recent development of a monoclonal antibody,
prepared against a b-1, 3-glucanase enzyme, specific
to the genus Trichoderma and related species, showed
use in staining the cell walls of the mycoparasite but
not the fungal pathogen Rhizoctonia solani, and could
therefore be used to study dual interactions [16]. The
antibody could also be used in a combined baitingELISA technique to detect Trichoderma spp. in composts. Such techniques should significantly facilitate an
understanding of the role of mycoparasitism in biological control studies.
Production of antibiotic compounds by fungi and yeasts
The production of antibiotic compounds is characteristic of
many effective fungal and yeast biocontrol agents, and can
be shown both in vitro and in vivo. Species of Trichoderma
and Gliocladium, as well as the yeast Pseudozyma, which
are currently all registered biological control products
(Table 1), are known to produce several secondary
metabolites with broad-spectrum antimicrobial activity.
For example, gliotoxin and gliovirin are well-described
antibiotics (among others) produced by Trichoderma
(Gliocladium) virens [8]. The antibiotics produced by
Pseudozyma flocculosa are a mixture of fatty acid-containing derivatives that affect membrane permeability of the
target organisms, thereby inhibiting their growth [9].
Conclusive evidence for the role of antibiotics in biocontrol-mediated disease suppression has required the
development of antibiotic-minus mutant strains with a
subsequent evaluation of their efficacy. Mutants of T. virens
unable to synthesize gliotoxin and gliovirin were shown to
have lost their capacity to control root-infecting fungi such
as Pythium [8]. In some instances, disease-suppressive
activity was directly correlated with the timing and
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TRENDS in Biotechnology
amount of antibiotic produced [17]. However, not all
studies aimed at generating antibiotic-minus mutants
have provided clear results, as there are reports of T. virens
mutants lacking gliotoxin production, which provided
significant control of Rhizoctonia root rot [8]. Therefore,
other attributes of the biological control agent Trichoderma clearly also play a significant role. A recent report
by Cheng et al. [18] using insertional mutagenesis showed
that strains of Pseudozyma that lacked production of the
glycolipid flocculosin had significantly reduced biocontrol
activity against powdery mildew.
Role of extracellular enzyme production by fungi and
yeasts
Secretion of hydrolytic enzymes, particularly chitinases
and glucanases, is a feature common to many effective
biological control agents. Strains of Trichoderma, for
example, are efficient producers of lytic enzymes, and
many are used in commercial enzyme manufacturing.
Using molecular biology techniques, the genes encoding
chitinases, glucanases and proteinases have been cloned
and sequenced from Trichoderma species. Mutant strains
with disrupted activity of ech 42, a chitinase-encoding
gene, were shown to be less effective as biocontrol agents
against Rhizoctonia solani and Botrytis cinerea compared
with wild-type strains [19,20]. Conversely, the overexpression of several genes encoding enzymes such as chitinase
(ech 42, chit 33) [19,21], endoglucanase (egl1) [22], and
proteinase ( prb1) [23], in transformed Trichoderma spp.
improved the antagonistic potential of the agent against
pathogens such as Rhizoctonia and Pythium, both in vitro
and in vivo.
A mutant strain of T. harzianum with an enhanced
ability to hydrolyze pustulan (a polymer of b-1, 6-glucans)
showed enhanced production of chitinase and b-1, 3- and
b-1, 6-glucanases, and produced more extracellular proteins and other compounds [24]. This strain provided a
significantly increased inhibitory activity against Botrytis
cinerea in vitro. There is probably a complex sequential
time-course of induction of these enzymes, and interactions with other compounds are possible (e.g. with
antibiotics to achieve optimal biological activity). In
T. harzianum, differential expression of a series of
chitin-degrading enzymes was reported during mycoparasitism, which varied with time and the fungal pathogen
host [25]. Specificity of hydrolytic enzyme activity was also
suggested in a study by Woo et al. [20], where an
endochitinase-deficient mutant displayed differing levels
of biocontrol activity against different pathogens.
Secretion of an exo- b-1, 3-glucanase by Ampelomyces
quisqualis was found to play a role during the later stages
of hyperparasitism of powdery mildew [11].
The importance of hydrolytic enzyme production in the
biocontrol activity of yeasts can vary with the organism,
with Candida producing biologically relevant levels for
Botrytis control [26] and Tilletiopsis spp. producing
insignificant enzyme activity against powdery mildews
[10]. In situ localization of various lytic enzymes during
interactions between a specific biocontrol agent and
pathogen remains a challenge, but microscopic observations have revealed that pathogen hyphae – in addition
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to other pathogen structures – were disintegrated and
collapsed [11,27– 29]. The attachment of yeasts to pathogen hyphae is an important factor for biocontrol activity
[30], enabling cell wall degrading enzymes to have an
effect. Taken together, recent research on extracellular
enzyme production by fungal and yeast biocontrol agents
convincingly demonstrate their involvement in reducing
pathogen growth and infection. Predictably, synergies
between these enzymes and antibiotic compounds have
also been reported. For example, hydrolytic enzymes in the
presence of gliotoxin, peptaibols or other antifungal
compounds significantly suppressed the growth of
B. cinerea and Fusarium oxysporum compared with either
one alone [31,32].
Biocontrol agents can affect pathogenicity of fungal
pathogens
There are several pathogenicity factors that influence the
degree and extent to which a fungal organism can invade
host plant tissues [33]. Disruption of any of these through
site-directed mutagenesis, for example, can render a plant
pathogen unable to infect. One interesting aspect of
biocontrol agent-induced suppression of disease is the
reported affect of T. harzianum on development of gray
mold disease caused by B. cinerea through a reduction in
its pathogenicity [34,35]. Production of cystein protease
enzymes by Trichoderma was reported to inhibit the
activities of hydrolytic enzymes – especially polygalacturonases – in the pathogen, which are important pathogenicity factors in Botrytis and many other fungi [34,35]. The
proteases inactivated the pathogen enzyme by cleaving
the molecule. Reduction in disease was also demonstrated with extracts containing proteases from Trichoderma culture filtrates and from infected bean leaves,
and was reversed by adding protease inhibitors [35].
For such an interaction to be evoked on the plant leaf
surface infected with B. cinerea, the interacting
organisms must spatially and temporally occupy the
same niche and be in close proximity to one another,
providing localized protection.
Induction of host plant defenses by fungi and yeasts
Higher plants are able to defend themselves against
potential pathogens through the induction of a diverse
array of chemical compounds whose production is triggered by elicitor molecules or inducing agents [36]. An
interesting area of biocontrol agent-induced suppression
of plant diseases is the induction of host defense responses
(Fig. 4). Following their application to plants, Trichoderma
spp., Pythium oligandrum and nonpathogenic Fusarium
oxysporum (Table 1) have all been reported to enhance
structural and biochemical changes, which increased
resistance to disease [14,37 – 40]. These changes included
enhanced deposition of plant cell wall materials
(e.g. callose) at the infection site, as well as increased
activity of several enzymes (e.g. peroxidase and chitinases)
and other pathogenesis-related proteins [14,38 – 42]. In
some of these reports, however, the biochemical changes
might provide only correlative and not confirmatory
evidence for their role in induced resistance. In one report,
biocontrol activity of T. virens was highly correlated with
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Vol.21 No.9 September 2003
Fungal or yeast biological control agent
Production of elicitors
Production of signaling
compounds
Colonization of
tissues
Induction of defense
responses in the plant
Production of growthpromoting substances
Stimulation of growth
of plant
Reduced pathogen development
TRENDS in Biotechnology
Fig. 4. Induction of plant host responses by fungal and yeast biological control agents that can lead to biological control of disease.
induction of terpenoid synthesis and peroxidase activity in
plant roots, which were shown to be inhibitory to R. solani
[43]. Yeast biocontrol agents have also been reported to
induce host defense responses following their application
to plant tissues [44]. A transposon-mediated insertional
mutagenesis approach has been used to create mutants of
nonpathogenic F. oxysporum Fo47 that were altered in
their biocontrol activity [45] and could be used to further
study the mechanism of action.
Induction of plant defense responses through signaling
pathways is well-described for plant growth-promoting
rhizobacteria, which use several mechanisms to achieve
induced systemic resistance in the plant [46]. However, it
is unclear whether specific or general elicitors are
produced by the fungal and yeast biocontrol agents, and
whether a host recognition system is triggered to initiate
the defense mechanism similar to that occurring in
incompatible pathogen – host interactions [1]. Interestingly, as all of these inducing biocontrol agents have
been reported to colonize root tissues internally (mainly
epidermal and cortical cells) without causing noticeable
cell damage [14,40 – 42], host plant defenses could have
been induced as a result (Fig. 4). The release of fungal
pathogen elicitor molecules (e.g. oligosaccharides) is
known to trigger host defense responses against pathogens
[46] and biocontrol agents could potentially act in the same
way. In addition, T. harzianum has been reported to
produce growth-promoting substances that enhanced root
and shoot growth following application in the absence
of pathogens [4,47]. Production of diffusible metabolites
capable of solubilizing phosphates and micronutrients was
demonstrated [48], and enhanced micronutrient levels in
plants treated with T. harzianum was reported [49].
Competition for nutrients and niche colonization by
fungi and yeasts
Fungal pathogens require entry points to gain access into
plant tissues. For obligate parasites, this is usually
achieved by direct penetration of hyphae through the
cuticle and epidermis of the plant. For facultative
parasites that are mostly saprophytic, entry can be
through wounds, senescing host tissues, or natural openings such as stomates and lenticels. These areas are
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generally nutrient-rich owing to exudation of sugars and
amino acids. Biological control agents that can compete
effectively with the pathogen to occupy these infection
sites and use the nutrients can effectively displace the
pathogen by preventing germination of propagules or
infection (Fig. 2). Biocontrol agents such as Trichoderma
and Gliocladium spp. can outgrow and outcompete the
pathogen, especially if applied before pathogen arrival.
Colonization of roots by Trichoderma (rhizosphere competence) is an important aspect contributing to its biocontrol
efficacy [4]. Nonpathogenic F. oxysporum strains can also
compete with pathogenic strains for infection sites and
nutrients (e.g. carbon on the roots) [50]. Competition for
nutrients is also a mechanism by which many yeast
biocontrol agents that colonize wounds or senescing
tissues can prevent infection by pathogens [51]. Treatment
of wounds, germinating seeds, or flower blossoms can
therefore provide opportunities to establish biocontrol
agents that can then outcompete pathogens. There is some
evidence that biocontrol fungi such as Clonastachys
(Gliocladium) roseum can enter the host tissues and
reside as an endophyte [52], subsequently colonizing the
tissues or potentially inducing host defenses to reduce
further development of the pathogen. Such endophytes are
receiving increasing interest from the perspective of their
role(s) in plants [53].
Other fungi and yeasts show biocontrol potential
Many reports have described the biocontrol potential of
other saprophytic fungi and yeasts to reduce diseases on
vegetable crops; this information is summarized elsewhere
[7]. The mechanisms of action of these agents fall into the
same categories as those described here. Further research
on these organisms and their advancement through the
microbial registration process should increase their
chances of being used as biocontrol agents in the future,
thereby adding to the list of current products summarized
in Table 1.
Applications of molecular methods to biocontrol fungi
and yeasts
Several fungi and yeasts that have the potential to reduce
the development of vegetable crop diseases have recently
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TRENDS in Biotechnology
been characterized using molecular methods. Mitochondrial DNA, internal transcribed spacers of rDNA (ITS1
and ITS2 regions), and nuclear DNA have been evaluated
using techniques such as restriction fragment length
polymorphisms (RFLP), arbitrarily primed polymerase
chain reaction (AP-PCR), random amplified polymorphic
DNA (RAPD), sequence-characterized amplified region
(SCAR) and other molecular approaches. These studies
were used to distinguish between species and among
strains of the biocontrol fungi Trichoderma [54 – 59],
Gliocladium [60], Ampelomyces [61], and the yeasts
Pseudozyma [62] and Tilletiopsis [63]. In addition to
resolving taxonomic affinities, the molecular tools provided strain-specific markers to track the movement of
strains [57,64,65] and to test the genetic stability over
successive generations of propagation [66]. Molecular tools
will prove to be valuable in monitoring the survival and
environmental fate following release of these biocontrol
agents as well as in ensuring product quality and stability
during large-scale production of inoculum.
Genetic transformation techniques have been applied to
Trichoderma and nonpathogenic F. oxysporum. Transformation of T. harzianum with the b-glucuronidase (uid
A, gus) gene and the hygromycin B (hyg B) gene provided
markers for use in population dynamic studies [67– 69].
Co-transformation with genes encoding b-glucuronidase
and green fluorescent protein (GFP) has also been
described [70]. Similar markers (gus, hyg B) were
developed for nonpathogenic F. oxysporum strains
[42,50,71] and used to study the role of competition for
infection sites on plant roots and to estimate fungal
biomass on roots in relation to the pathogenic strains.
Techniques of protoplast fusion were used to create strain
T-22 of T. harzianum by fusing a mutant strain capable of
colonizing plant roots with a strain able to compete with
bacteria under iron-limiting conditions [4]. This new
strain had the enhanced ability to colonize the root system
of host plants, resulting in greater efficacy as a biological
control agent for long-term root protection [4]. Yeasts with
biocontrol potential have also been transformed with the
GFP, which was used to track movement [72]. Transformation of Saccharomyces to express a cecropin-A based
peptide with antifungal activity was recently described
[73] that enhanced the ability of the strain to reduce decay
when applied to tomato fruits. Expression of novel
antimicrobial compounds in biological control agents
through genetic transformation provides a new approach
for disease control. Finally, the use of antimicrobial genes
from biocontrol fungi, such as Trichoderma, when
expressed in transgenic plants, has also opened up new
opportunities to enhance resistance to pathogens [74,75].
Several crop species have now been engineered with
genes expressing chitinases; these transgenic plants
were shown to express resistance to many different
fungal pathogens [1].
Concluding remarks
Techniques in biotechnology are becoming increasingly
applicable to studies on the biological control of plant
diseases using fungi and yeasts. These techniques have
helped to elucidate mechanisms of action and have
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Vol.21 No.9 September 2003
405
provided methods to evaluate the extent to which these
agents can spread and survive. Biological control agents
provide viable alternative options to vegetable producers
in the management of fungal diseases and in reducing the
frequency of fungicide applications. The registration of
additional effective biological control agents should materialize with continuing research at appropriate levels of
funding as well as with expedited regulatory approval of
these microbes.
Acknowledgements
Funding for this work was provided by the Natural Sciences and
Engineering Research Council of Canada through the NSERC Biocontrol
Network.
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