Abstract
Entomopathogenic nematodes are effective biocontrol agents against arthropod pests. However, their efficacy is limited due to sensitivity to environmental extremes. The objective of the present study was to establish a foundation of genetic-based selection tools for beneficial traits of heat and desiccation tolerance in entomopathogenic nematodes. Screening of natural populations enabled us to create a diverse genetic and phenotypic pool. Gene expression patterns and genomic variation were studied in natural isolates. Heterorhabditis isolates were phenotyped by heat- and desiccation-stress bioassays to determine their survival rates compared to a commercial line. Transcriptomic study was carried out for the commercial line, a high heat-tolerant strain, and for the natural, low heat-tolerant isolate. The results revealed a higher number of upregulated vs. downregulated transcripts in both isolates vs. their respective controls. Functional annotation of the differentially expressed transcripts revealed several known stress-related genes and pathways uniquely expressed. Genome sequencing of isolates with varied degrees of stress tolerance indicated variation among the isolates regardless of their phenotypic characterization. The obtained data lays the groundwork for future studies aimed at identifying genes and molecular markers as genetic selection tools for enhancement of entomopathogenic nematodes ability to withstand environmental stress conditions.
Highlights
Domestication and improvement of crop plants and animals have been part of agriculture for thousands of years
The occurrence of natural populations of entomopathogenic nematodes (EPNs) was assessed as recovery frequency and abundance expressed as percentage[30]
The two isolates from non-cultivated soils were identified as Steinernema feltiae, whereas, all other six isolates were identified as Heterorhabditis spp. (Table 1, Fig. 1C)
Summary
Domestication and improvement of crop plants and animals have been part of agriculture for thousands of years. Based on the screening of natural populations, the leading approach to EPN enhancement seems to be a genetic one, through selective breeding of strains with beneficial traits, genetic manipulation (mutagenesis) and genetic engineering[18,27,28]. Advanced genetic techniques, such as gene transformation and induction of mutations using RNA silencing have been studied, and enhancement of beneficial traits for environmental stress tolerance has been reported[25]. Further transcriptomic and genomic studies under stress conditions are expected to reveal specific genes involved in the stress response, and enable the establishment of expression markers for the enhancement or degradation of beneficial traits
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