Heat tolerance among different strains of the entomopathogenic nematode Heterorhabditis bacteriophora
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Quality of biological control products based on entomopathogenic nematodes can be severely damaged due to exposure to high temperature surpassing 40°C. The study screened 36 natural populations and 18 hybrid or inbred strains of Heterorhabditis bacteriophora for their response to high temperature. Nematodes were tested with or without prior adaptation to heat at 35°C for 3 h. Five strains of H. indica and one of H. megidis were also included. Molecular identification using nuclear ribosomal DNA sequences confirmed the designation to the three Heterorhabditis spp. The mean tolerated temperature ranged from 33.3°C to 40.1°C for non-adapted and from 34.8°C to 39.2°C for adapted strain populations. H. indica was the most tolerant, followed by H. bacteriophora and H. megidis. No correlation was recorded between tolerance assessed with and without adaptation to heat, implying that different genes are involved. Correlation between heat tolerance and mean annual temperature at place of origin of the strains was weak. A high variability in tolerance among strains and the relatively high heritability (h² = 0.68) for the adapted heat tolerance recorded for H. bacteriophora provide an excellent foundation for future selective breeding with the objective to enhance heat tolerance of H. bacteriophora.
KeywordsBiological control Adaptation H. indica H. megidis Selective breeding Enhanced heat tolerance
Thanks are due to all colleagues, who kindly provided nematode strains and to Berhanu Hunegnaw Kassahun for technical support with the molecular identification. The scholarship to the first author by the German Academic Exchange Service (http://www.daad.de) is highly appreciated.
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