Nematode-Trapping Fungi

400 Pages·2014·16.568 MB·English

by  Ke-Qin Zhang, Kevin D. Hyde (eds.)

Nematode-Trapping Fungi
Fungal Diversity Research Series
Volume 23
Series Editor: Kevin D. Hyde
For further volumes:
http://www.springer.com/series/10408
Ke-Qin Zhang • Kevin D. Hyde
Editors
Nematode-Trapping Fungi
1 3
Editors Kevin D. Hyde
Ke-Qin Zhang Institute of Excellence in Fungal Research,
Laboratory of Conservation and Utilization and School of Science
of Bio-Resources Mae Fah Luang University
Yunnan University Chiang Rai
Kunming Thailand
China
ISSN 1608-6791 ISSN 2212-6236 (electronic)
ISBN 978-94-017-8729-1 ISBN 978-94-017-8730-7 (eBook)
DOI 10.1007/978-94-017-8730-7
Springer Dordrecht Heidelberg New York London
Library of Congress Control Number: 2014935064
© Mushroom Research Foundation 2014
Co-published by Springer Science+Business Media B.V., Dordrecht, The Netherlands
and Kevin D. Hyde, Chiang Rai, Thailand
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Preface
Nematophagous fungi are an important, fascinating group of soil microorganisms
that can suppress the populations of plant-parasitic nematodes. They have been
studied over several decades and the beautiful micrographs of these fungi trapping
nematodes have marveled scientists and students alike. These remarkable fungi are
also important potential biocontrol agents of nematodes diseases of plants and ani-
mals, they produce a swathe of natural chemicals and are model organisms for gene
functional studies. The research team of Zhang Ke-Qin and colleagues has been
working on many aspects of nematode-trapping fungi for more than 20 years. These
studies have resulted in a wealth of information and it is now considered timely to
bring all this information together into a book so that everyone who is interested can
read about the amazing fungi.
The book comprises eight chapters, Chapter 1 is an overview of the data on
nematode-trapping fungi presented in this book, including their taxonomy, phy-
logeny and evolution. Four general groups of nematophagous fungi are general ac-
cepted and are based on the mechanisms by which they attack nematodes. These
consist of (1) nematode-trapping fungi using adhesive or mechanical hyphal traps,
(2) endoparasitic fungi using their spores, (3) egg parasitic fungi invading nema-
tode eggs or females with their hyphal tips, and (4) toxin-producing fungi immo-
bilizing nematodes before invasion. The nematode-trapping fungi with adhesive or
mechanical hyphal traps are the main focus of this book, while the other types of
fungi are discussed but in less detail. Chapter 2 deals with the methodology to study
nematode trapping fungi. Although there has been a huge increase in our knowledge
of nematophagous fungi, the methodology used to study these organisms are unique
and have changed little over the years. These methods are detailed in Chapter 2 and
include techniques for obtaining mixed cultures of the fungi from nature, for isolat-
ing taxa into pure culture, for observing living material and for making permanent
microscope preparations. Chapter 3 deal with history and taxonomy of orbiliaceous
nematode-trapping fungi, the filamentous species forming trapping devices to prey
nematodes. The taxonomic history of predatory orbiliaceous fungi is reviewed and
the system of using trapping devices as the primary morphological criterion for ge-
neric delimitation is advocated. Following this taxonomic concept, keys for genera
of Arthrobotrys, Drechslerella and Dactylellina, which include all reported species
v
vi Preface
of predatory orbiliaceous fungi are presented. Totally, 54, 14 and 28 species from
Arthrobotrys, Drechslerella and Dactylellina respectively, are morphologically de-
scribed and illustrated. Known asexual-sexual connections (14 pairs) of predatory
orbiliaceous fungi are summarized and their taxonomic descriptions and illustra-
tions presented.
Chapter 4 deals with the ecology of nematode–trapping fungi. These fungi have
extensively been studied both because of their unique predatory life history and
because they are potential biocontrol agents of economically important plant- and
animal- parasitic nematodes. Fundamental knowledge of the ecology of these fungi
is therefore essential before the value of such biocontrol methods can be assessed.
Topics dealt with in Chapter 4 include occurrence and habitats, geographical and
seasonal distribution, quantification of abundance, and effects of soil conditions
and nematode density on their distribution. Competition between nematodes and
nematophagous fungi, the effect of fungistasis and extreme ecological factors such
as heavy metals and salinity on these fungi, and their genetic diversity and specia-
tion are included in this chapter.
In Chapter 5 the use of nematode trapping fungi in biological control is dis-
cussed. Plant-parasitic nematodes cause severe damage to world agriculture each
year. Environmental and health concerns over the use of chemical pesticides has
increased the need for alternative measures to control plant-parasitic nematodes.
Nematophagous fungi, a natural enemy of nematodes, have received most atten-
tion in biological control of plant-parasitic nematodes. This is due to their specific
ability to capture and kill nematodes. Nematophagous fungi are divided into four
groups according to their mode of action against nematodes, and several fungi such
as Pochonia chlamydosporia and Paecilomyces lilacinus have been developed as
commercial biological nematicides. In Chapter 5, important nematode parasitic and
antagonistic fungi, and their taxonomy, biology and their mode of action are dis-
cussed. Progress in the study of highly virulent fungal strains for nematode biologi-
cal control, and application of nematode-antagonistic agents are also discussed.
In Chapter 6 we describe the characterization of extracellular enzymes from
nematophagous fungi, the expression and regulation of serine protease prC in Clo-
nostachys rosea, and the genome and proteomic analyses of the nematode-trapping
fungus Arthrobotrys oligospora. At present, the detailed molecular pathogenic
mechanisms against nematodes by nematophagous fungi have not yet been fully
elucidated. However, increasing evidence show that extracellular hydrolytic en-
zymes including proteases, collagenase, and chitinase may be involved in nema-
tode-cuticle penetration and host-cell digestion. Recently, the crystal structures of
proteases (Ver112 and PL646) and chitinase CrChi1 from nematophagous fungi
were resolved, which can help us to identify the active site residues and to elucidate
the catalytic mechanism of these enzymes involved in infection against hosts. The
expression and regulation of protease PrC from Clonostachys rosea by different en-
vironmental conditions has also been reported. The genome of Arthrobotrys oligos-
pora has been sequenced, and a model of nematode trap formation in A. oligospora
suggested; thus the genome data may serve as a roadmap for further investigations
Preface vii
into the interaction between nematode-trapping fungi and their host nematodes, pro-
viding broad foundations for research on the biocontrol of pathogenic nematodes.
Nematode-trapping fungi having proven to be a treasure house of novel chemi-
cals. Chapter 7 summarizes more than 200 compounds from fungi that have been
shown to possess nematicidal activities. These compounds belong to diverse chemi-
cal groups including alkaloid, quinone, isoepoxydon, pyran, furan, peptide, macro-
lide, terpenoid, fatty acid, diketopiperazine, aphthalene and simple aromatics. They
have mainly been isolated from a variety of ascomycetous and basidiomycetous
fungal taxa. Their nematicidal activities are described and their potential roles in the
biocontrol of nematodes are discussed.
Previous studies based on traditional techniques have revealed much about
nematophagous fungi. Modern techniques however, can now help to elucidate the
molecular mechanisms underlying infection of nematodes by the nematophagous
fungi, and help us to understand virulent factors, the role of proteases, chitinases
and small chemical molecules, and the regulation of trap formation. Further studies
using modern molecular techniques are needed to better understand these important
mechanisms and the overall functioning of nematode trapping fungi and the future
studies needed are addressed in Chapter 8.
It has been a privilege to participate in the compilation of this book on nema-
tode-trapping fungi. Although I have barely studied the nematode-trapping fungi
through one student, Aung Swe, I believe these fungi to be truly amazing and I have
enjoyed editing the writings of the various authors of the world experts at the Yun-
nan University nematode-trapping fungi laboratory. A huge amount of work on this
organisms has come out the laboratories of Zhang Ke-Qin as well as other labora-
tories and it has been an honour to help put this data together in a modern book on
nematode-trapping fungi. I hope the readers will find as much enjoyment in reading
the book as I have in editing it.
Chiang Rai Kevin D. Hyde
September 2013
Abstract
Nematophagous fungi are an important, fascinating group of soil microorganisms
that can suppress the populations of plant-parasitic nematodes. They have been
studied over several decades and the beautiful micrographs of these fungi trapping
nematodes have marvelled scientists and students alike. This book comprises eight
chapters providing data on nematode-trapping fungi, particularly those of the Orbili-
aceae whose asexual states produce nematode- trapping devices. Chapter 1 provides
an overview of nematode-trapping fungi, including their taxonomy, phylogeny and
evolution. The nematode-trapping fungi with adhesive or mechanical hyphal traps
are the main focus of this book, while the other types of fungi are discussed but in
less detail. Chapter 2 deals with the methodology to study nematode trapping fungi.
These methods include techniques for obtaining mixed cultures of the fungi from
nature, for isolating taxa into pure culture, for observing living material and for mak-
ing permanent microscope preparations. Chapter 3 deal with history and taxonomy
of orbiliaceous nematode-trapping fungi, the filamentous species forming trapping
devices to prey nematodes. The taxonomic history of predatory orbiliaceous fungi
is reviewed and the system of using trapping devices as the primary morphological
criterion for generic delimitation is advocated. Following this taxonomic concept,
keys for genera of Arthrobotrys, Drechslerella and Dactylellina, which include
all reported species of predatory orbiliaceous fungi are presented. Totally, 54, 14
and 28 species from Arthrobotrys, Drechslerella and Dactylellina respectively, are
morphologically described and illustrated. Known asexual-sexual connections (14
pairs) of predatory orbiliaceous fungi are summarized and their taxonomic descrip-
tions and illustrations presented. Chapter 4 deals with the ecology of nematode–
trapping fungi. Topics dealt with include occurrence and habitats, geographical and
seasonal distribution, quantification of abundance, and effects of soil conditions and
nematode density on their distribution. Competition between nematodes and nema-
tophagous fungi, the effect of fungistasis and extreme ecological factors such as
heavy metals and salinity on these fungi, and their genetic diversity and speciation
are also. In Chapter 5 the use of nematode trapping fungi in biological control is dis-
cussed. Nematophagous fungi are divided into four groups according to their mode
of action against nematodes, and several fungi such as Pochonia chlamydosporia
and Paecilomyces lilacinus have been developed as commercial biological nemati-
ix
x Abstract
cides. In Chapter 5, important nematode parasitic and antagonistic fungi, and their
taxonomy, biology and their mode of action are discussed. Progress in the study
of highly virulent fungal strains for nematode biological control, and application
of nematode-antagonistic agents are also discussed. In Chapter 6 we describe the
characterization of extracellular enzymes from nematophagous fungi, the expres-
sion and regulation of serine protease prC in Clonostachys rosea, and the genome
and proteomic analyses of the nematode-trapping fungus Arthrobotrys oligospora.
At present, the detailed molecular pathogenic mechanisms against nematodes by
nematophagous fungi have not yet been fully elucidated. However, increasing evi-
dence show that extracellular hydrolytic enzymes including proteases, collagenase,
and chitinase may be involved in nematode-cuticle penetration and host-cell diges-
tion. The expression and regulation of protease PrC from Clonostachys rosea by
different environmental conditions has also been reported. The genome of Arthro-
botrys oligospora has been sequenced, and a model of nematode trap formation in
A. oligospora suggested; thus the genome data may serve as a roadmap for further
investigations into the interaction between nematode-trapping fungi and their host
nematodes, providing broad foundations for research on the biocontrol of patho-
genic nematodes. Nematode-trapping fungi having proven to be a treasure house
of novel chemicals. Chapter 7 summarizes more than 200 compounds from fungi
that have been shown to possess nematicidal activities. These compounds belong
to diverse chemical groups including alkaloid, quinone, isoepoxydon, pyran, furan,
peptide, macrolide, terpenoid, fatty acid, diketopiperazine, aphthalene and simple
aromatics. Their nematicidal activities are described and their potential roles in the
biocontrol of nematodes are discussed. Previous studies based on traditional tech-
niques have revealed much about nematophagous fungi. Modern techniques how-
ever, can now help to elucidate the molecular mechanisms underlying infection of
nematodes by the nematophagous fungi, and help us to understand virulent factors,
the role of proteases, chitinases and small chemical molecules, and the regulation
of trap formation. Further studies using modern molecular techniques are needed
to better understand these important mechanisms and the overall functioning of
nematode trapping fungi and the future studies needed are addressed in Chapter 8.