High level of genetic diversity among Steinernema monticolum in Korea revealed by single-enzyme amplified fragment length polymorphism

Single nucleotide polymorphism markers in Heterorhabditis bacteriophora associated with virulence at low temperature

The entomopathogenic nematode (EPN), Heterorhabditis bacteriophora, is an important biological control agent worldwide. Industrially produced EPN need to meet the climatic requirements for the control of pests in field agriculture in autumn and spring when temperatures are low. For this trait (virulence at low temperature), previous EPN improvement attempts relied on phenotypic selection and the selected trait had low stability. The use of molecular markers can increase the efficacy of EPN breeding by tracking traits associated with specific genotypes. To date, fewer than 200 polymorphic and reproducible sequence-tagged molecular markers in H. bacteriophora have been reported. Here, we enhanced the palette of highly polymorphic genetic markers for this EPN by applying genotyping by sequencing (GBS). By analysing 48 H. bacteriophora homozygous wild-type inbred lines from different origins, we determined 4894 single nucleotide polymorphisms (SNPs) with at least one polymorphism along the tested set. For validation, we designed robust PCR assays for seven SNPs, finding 95% correspondence with the expected genotypes along 294 analysed alleles. We phenotyped all lines for their virulence at low temperature (15°C) against mealworm and observed infectivity ranging from 38 to 80%. Further, we carried out association analyses between genotypic and phenotypic data and determined two SNPs yielding potential association with H. bacteriophora virulence at low temperature. The use of these candidate SNPs as breeding markers will speed up the generation of strains better adapted to low temperature in this species. The generated set of lines and SNP data are a versatile tool applicable for further traits in this EPN.

Identification and bacterial characteristics of Xenorhabdus hominickii ANU101 from an entomopathogenic nematode, Steinernema monticolum

An entomopathogenic nematode, Steinernema monticolum, was collected in Korea. Its identity was confirmed by morphological and molecular characters. Its symbiotic bacterium, Xenorhabdus hominickii ANU101, was isolated and assessed in terms of bacterial characteristics. Sixty-eight different carbon sources were utilized by X. hominickii ANU101 out of 95 different sources from a Biolog assay. Compared to other Xenorhabdus species, X. hominickii ANU101 was relatively susceptible to high temperatures and did not grow above 34°C. Furthermore, its growth rate was much slower than other Xenorhabdus species. X. hominickii exhibited insecticidal activities against coleopteran, dipteran, and lepidopteran insect pests. The bacterial virulence was not correlated with its host nematode virulence with respect to relative insecticidal activity against target insects. X. hominickii ANU101 exhibited antibiotics tolerance. The bacterium possesses four different plasmids (Xh-P1 (104,132bp), Xh-P2 (95,975bp), Xh-P3 (88,536bp), and Xh-P4 (11,403bp)) and encodes 332 open reading frames. Subsequent predicted genes include toxin/antitoxins comprising a multidrug export ATP-binding/permease. This study reports bacterial characters of X. hominickii and its entomopathogenicity.