Introduction

In recent decades, concerns about the environmental hazards of using chemical nematicides and limited alternative crops for rotation have led to the development of biological control agents as a component of crop protection. Biological control is now a key strategy used for controlling pests worldwide. Eilenberg et al. [1] defined biological control (or biocontrol) as follows: "The use of living organisms to suppress the population density or impact of a specific pest organism, making it less abundant or less damaging than it would otherwise be".

Department of Plant Pathology, Marvdasht Branch, Islamic Azad University, P.O. Box 465, Marvdasht, Fars, Iran e-mail: [email protected]

R. Zare

Department of Botany, Iranian Research Institute of Plant Protection, P.O. Box 1454-19395, Tehran, Iran e-mail: [email protected]

J.M. Merillon and K.G. Ramawat (eds.), Plant Defence: Biological Control, Progress in Biological Control 12, DOI 10.1007/978-94-007-1933-0_4, © Springer Science+Business Media B.V. 2012

Four basic strategies can be used in biological control (i) Introduction: which is considered as a classical technique whereby an exotic helpful organism is introduced into a new region and become fully established. This strategy is usually used against introduced pests that have no indigenous antagonists. (ii) Augmentation: in this method laboratory-bred individuals can be released to compensate the inefficiency of present microbial agents. The inadequate level of control can be driven by low number of native natural enemies. (iii) Inoculation: when an indigenous antagonist is not present or an introduced one cannot survive permanently, an inoculative release is made at the beginning of planting season. This process may need to be repeated for each following crop. (iv) Inundation: in this technique the mass culture of a pathogen is carried out for urgent use at critical periods when rapid suppression of pest population is necessary [2].

Biological control agents have an important effect in the regulation of plant-parasitic nematode populations, and numerous organisms including fungi, bacteria, viruses, nematodes and other invertebrates have antagonistic activity against plant parasitic nematodes [3]. Various aspects of biological control of nematodes using microbial control agents have been already reviewed [3-11].

The developmental process of progressing biological agents include the isolation and identification of microbial agents associated with plant parasitic nema-todes especially in suppressive soils (a soil that completely suppresses nematode reproduction); examination of their potential ability in controlling nematodes; changing the soil environment in favor of antagonistic agents; understanding the mechanisms of parasitism and pathogenicity; and development of commercial product. Investigating nematode-suppressing soil demonstrated that their controlling activity is due to egg-parasitizing fungi, generalized fungal antagonists, mutualistic fungal endophytes, rhizobacteria and obligate parasitic bacteria [12]. Comprehending the mechanisms of suppressiveness can be useful in plant-parasitic nematode control by helping in manipulating these mechanisms.

Lots of natural enemies attack nematodes and decrease their populations, but the number of organism which could be employed for biocontrol is restricted. In other words many soil types all around the world show biological control activity but their effect on nematodes can range from insignificant to complete suppression. In this section the biological control of plant parasitic nematodes by fungal agents will be emphasized according to recent research progresses.

Fungal biological control is an exciting and rapidly developing research area and there is growing attention in the exploitation of fungi for the control of nematodes. The relationship between nematodes and fungi that infect them has been the subject of widespread mycological studies. Our information about fungal biological control agents has originally been based on the voluminous and detailed work by Charles Drechsler [284-287]. Different aspects of fungal biological control of nematodes have been reviewed by Jaffee [13], Siddiqui and Mahmood [14], Kerry [15], Kerry and Hominick [2], Lopez-Llorca et al. [16]. Hallmann et al. [17] classified these fungi into three large groups: nematophagous fungi, saprophagous fungi, and endophytic fungi; however we do not follow this classification here. We consider all nematode parasitic and antagonistic fungi as: (i) nematophagous fungi and (ii) endophytic fungi, and their taxonomy and mode of action are briefly shown in Table 4.1.

Table 4.1 Taxonomy of some nematode parasitic and antagonistic fungi and their infection mechanism

Fungal group

Phyllum

Anamorph

Teleomorph

Infection structures

Nematophagous fungi

Nematode-trapping

Endoparasitic

Toxin-producing Endophytic fungi

Zygomycota Ascomycota

Basidiomycota

Oomycota

Chytridiomycota

Blastocladiomycota

Ascomycota

Basidiomycota Egg- and female-parasitic Oomycota Ascomycota

Basidiomycota

Arthrobotrys

Dactylellina

Drechslerella

Gamsylella

Nematoctonus

Harposporium

Drechmeria

Haptocillium

Hirsutella

Nematoctonus

Pochonia

Paecilomyces

Lecanicillium

Acremonium spp. Nonpathogenic F. oxysporum Neotyphodium spp.

Stylopage Adhesive hyphae

Cystopage Adhesive hyphae

Orbilia Adhesive networks

Orbilia Adhesive knobs and/or nonconstricting rings

Orbilia Constricting rings

Orbilia Adhesive branches or unstalked knobs

Hohenbuehlia Adhesive "hour-glass" knobs

Myzocytiopsis Zoospores

Haptoglossa "Gun cells", injection

Catenaria Zoospores

Podocrella Ingested conidia

? Adhesive conidia

Cordyceps? Adhesive conidia

? Adhesive conidia

Hohenbuehelia Adhesive spores

Nematophthora Zoospores

Metaordyceps Appressoria

Cordyceps Appressoria

Cordyceps Appressoria

Pleurotus Toxic droplets

Coprinus Toxin, "spiny structures"

? Unknown3

? Unknown3

? Unknown3

Glomus spp. Unknown3

3See text for possible mode of action

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