Phenotyping dauer juvenile oxidative stress tolerance, longevity and persistence within wild type and inbred lines of the entomopathogenic nematode Heterorhabditis bacteriophora

The commercial use of the entomopathogenic nematode Heterorhabditis bacteriophora as a biocontrol agent against noxious insects is limited due to its relatively short shelf-life. Longevity of dauer juveniles (DJ) during storage and in transit to end users is considerably restricted by environmental stresses. As a derivative stress triggered by environmental factors, oxidative stress causes a strong internal metabolic imbalance leading to lifespan reduction. In this study, the relation between DJ oxidative stress tolerance and longevity in H. bacteriophora was investigated at 25 and 7°C. A strong and significant correlation between DJ oxidative stress tolerance and longevity during storage in Ringer's solution (R=0.802 at 7°C; R=0.604 at 25°C) was recorded. Phenotyping of these traits was performed for 40 H. bacteriophora wild type strain and inbred line collections. At 25°C, the mean time survived in Ringer's by 50% of the DJ (MTS₅₀) ranged from 21 to 57 days, whereas under oxidative stress, survival was from 3 to 22 days. At 7°C, a maximum MTS₅₀ of 94 days was assessed when DJ were stored in Ringer's, while the maximum MTS₅₀ was only 25 days with oxidative stress induction. The heritability of DJ tolerance to oxidative stress, determined by using homozygous inbred lines, is high (h²>0.9), an indication of a high probability for successful selective breeding. In a subset of preselected H. bacteriophora inbred lines, DJ oxidative stress tolerance correlated with the DJ survival (persistence) after application to sand (R = 0.719). The study provides fundamental data required for a genetic breeding programme to produce hybrids with improved stress tolerance and prolonged shelf-life and soil persistence.