Screening of Verticillium lecanii (Lecanicillium spp.) hybrid strains based on evaluation of pathogenicity against cotton aphid and greenhouse whitefly, and viability on the leaf surface

In a previous study, protoplast fusion was performed among 3 strains of the entomopathogenic fungi Verticillium lecanii, as a result of which 174 hybrid strains were obtained. The aim of the present study was to screen desirable hybrid strains that have a wide host range or durable effects. Initially, 43 hybrid strains were used in bioassays against the cotton aphid. Of these strains, 30 induced equal or higher mortality as compared to Vertalec (41.9%). Secondly, 50 hybrid strains were used in bioassays against the greenhouse whitefly. Of these strains, 37 exhibited an equal or higher infection rate as compared to that of Mycotal (36.2%). Finally, 50 hybrid strains were applied to cucumber leaves in order to test strain viability under low humidity conditions (ca. 13% RH). Two weeks after strain application, 17 hybrid strains exhibited equal or higher viability as compared to B-2 (1.5E+03 cfu/square cm). These results indicated some hybrid strains whose parental characteristics had not only recombined but also whose pathogenicity or viability had improved. Finally, we selected 13 candidate hybrid strains that exhibited high values in each experiment, and these hybrid strains can be expected to be highly effective as biological control agents.