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.

The Role of Root-Produced Volatile Secondary Metabolites in Mediating Soil Interactions

“…In that perspective, entomopathogenic nematodes appear as good candidates. Several studies have succeeded in selecting beneficial traits such as host finding (Gaugler and Campbell 1991;Gaugler, Campbell, and McGuire 1989), virulence (Peters and Ehlers 1998;Tomalak 1994) and tolerance to temperature (Ehlers et al 2005;Grewal, Gaugler, and Wang 1996;Griffin and Downes 1994) or desiccation (Strauch et al 2004). …”

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…This heterogeneity in lipid utilisation, where a few individuals remain visibly dark and rich in reserves when others of the population are completely transparent and close to death by starvation, may be indicative of a "bet-hedging" strategy, where parents spread the risk so that at least some offspring survive (Fenton & Hudson, 2002). Apart from genetic variation (Ehlers, Oestergaard, Hollmer, Wingen, & Strauch, 2005;Shapiro, Glazer, & Segal, 1997;Wang, Jung, Son, & Choo, 2013), differences between individuals may arise due to varied conditions experienced during development. IJs emerging from a host at different times differ in size, infectivity and other behaviours Nguyen & Smart, 1995;Ryder & Griffin, 2003), presumably due to differing conditions of nutrition experienced.…”

“…Both Heterorhabditis and Steinernema species have responded to artificial selection (e.g. Ehlers et al, 2005;Gaugler & Campbell, 1991) and the short lifecycle of EPN means that adaptation may be rapid. Traditional views of ecological communities assume that they are full or saturated with species, but this may be less general than was previously thought, and even species-rich communities can still accept new-comers, resulting in increased species diversity (Sax et al, 2007).…”

Comparison of virulence of hybridized entomopathogenic nematode Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) strains and their parents

“…The IJs were placed into BSA, being inoculated with bacteria, and incubated at 25±1.5 ˚C in orbital shaker at 200 rpm in the dark, as well (Lunau et. al., 1993;Ehlers et. al., 1998;Ehlers, 2001).…”