Genetic Improvement of Heat Tolerance inHeterorhabditis bacteriophorathrough Hybridization

A trait for heat tolerance was transferred from the IS5 strain to the HP88 strain ofHeterorhabditis bacteriophoraPoinar. The transfer was accomplished by allowing the heat tolerant strain (IS5) to mate with the commercial strain (HP88). The hybrid nature of the progeny was confirmed using a marker mutant of the HP88 strain (Hp-dpy-2) and by backcrossing. Progeny from the cross were screened for heat tolerance by measuring survival after 2 h exposure to 40°C. After three and six passages throughGalleria mellonella(L.), survival of hybrid nematodes was significantly greater than survival of the HP88 strain and was similar to the survival of the IS5 strain. Fitness, in terms of virulence, reproduction and storage capacity was compared among the IS5, hybrid, and HP88 strains. At 32°C, the IS5 and hybrid strains caused mortality ofG. mellonellaat a faster rate than the HP88 strain. Similar to the IS5 strain, the hybrids exhibited sensitivity to cold. After 1 week of storage at 10°C, the survival of the hybrid and IS5 strains was significantly reduced relative to the HP88 strain. No differences were detected in reproductive potential among the strains. This study demonstrates the potential of using hybridization to genetically improve entomopathogenic nematodes and illustrates the advantages of using marker mutations in this endeavor.