Genetic Selection for Heat Tolerance and Low Temperature Activity of the Entomopathogenic Nematode–bacterium Complex Heterorhabditis Bacteriophora–Photorhabdus Luminescens

Abstract

The entomopathogenic nematode–bacterium complex Heterorhabditis bacteriophora–Photorhabdus luminescens is used in commercial biocontrol of insect pests. Tolerance and activity of the nematodes at extreme environmental conditions can limit the shelf life, quality and field performance of nematode-based products. To overcome these limitations, the potential for genetic improvement of the heat tolerance and the activity at low temperature was investigated. Heat tolerance and cold activity are quantitative traits, influenced by several genes and environmental factors. The breeding success for such traits depends on the genetic proportion on the phenotypic variability, the heritability, which was determined by recording the variability within and between homozygous inbred lines. The heritability for heat tolerance was 0.68 and for activity at low temperature 0.38. To increase heat tolerance, 4 selection steps were carried out, which increased the mean tolerated temperature from 38.5 to 39.2 °C. The mean temperature at which the dauer juveniles of H. bacteriophora were active, could be reduced from 7.3 to 6.1 °C during the first 5 selection steps. However, for unknown reasons, it increased during the following 5 steps to 7.1 °C. A screening among different P. luminescens isolates for growth at low temperature resulted in several cold-adapted strains from North America, which reached considerable cell density at 6 °C.