TABLE CONTENTS

Genetic Improvement for Enhanced Efficacy of Entomopathogenic
Nematodes
Tomalak, M. (1) & Grewal, P.S. (2)
(1) Department of Biological Pest Control and Quarantine, Institute of Plant Protection, Wladyslawa Wegorka
20, 60-318 Poznan, Poland; (2) Center for Urban Environment and Economic Development, The Ohio State
University, 1680 Madison Avenue, Wooster, OH 44691, USA.
Growing economic importance of entomopathogenic nematodes (EPNs) as biocontrol agents
generates a strong demand for strains with the highest reproductive potential, storage
stability, and field efficacy. Initiated over 20 years ago, research on genetic improvement of
EPNs has employed a range of approaches, including strain hybridization, genetic selection
and mutagenesis. Hybridization of geographically distant strains helped to widen genetic and
phenotypic variation within the resulting populations, which could be used subsequently in
selection processes. Attempts to improve both relatively well-defined traits (e.g. ability to
disperse in the soil and host finding, infectivity at lower temperatures, or desiccation
tolerance) as well as highly complex qualities (e.g. overall efficacy in controlling pest
populations in particular environments) with the aid of artificial selection have been
successfully conducted in several laboratories worldwide. Relatively little attention has been
paid so far to mutagenesis as a source of new and valuable phenotypes in EPNs. Although the
process of mutagenesis can produce a wide range of changes in individual genes, it is very
unpredictable and requires proper screening for the mutant phenotypes. Moreover, not all
nematode species respond equally to mutagens. Our earlier study on a series of mutagens
applied to Heterorhabditis bacteriophora was discouraging, while the same agents produced
many point mutations affecting morphology and/or behavior of infective juveniles in
Steinernema feltiae. Of this material, mutations in at least two genes (Sfrol-1, Sflon-1)
improved the nematode performance in soil penetration and infectivity.
Although all the tested methods revealed some potential for genetic improvement of EPNs,
the populations obtained have had rather limited impact on the use of nematodes in
agricultural practices, so far. Poor understanding of the genetic background responsible for
the observed phenotypic changes, lengthy breeding procedures, and potential reversion of the
improved characters to their wild type are most probable explanations for this situation.
Recent advances in research conducted at the genomic level, particularly of H. bacteriophora
suggest, however, that hitherto missing genetic information as well as more precise and
predictable methods may soon be available for further works on improvement of EPNs.
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