Effects of Cryopreservation at -80oC on the Formulation and Pathogenicity of the Obligate Aphid Pathogen Pandora nouryi

Abstract

Cryopreservation at -80 degrees C is an alternative to liquid nitrogen storage for Entomophthorales. However, detailed studies about its effects on fungal pathogenicity and formulation are very limited. In the present study, the obligate aphid pathogen Pandora nouryi was formulated as mycelia grown on millet-gel granules after preservation as primary spores at -80 degrees C for 3-18 months, although its ability to produce infectious conidia gradually diminished. The sporulation capacity of this granular formulation was reduced to 18.5 x 10(4) conidia/mg after 18 months of storage, which was still higher than that of mycotized aphids. The half-decline time of sporulation capacity was computed as 13.6 months. The infectivity to the green peach aphid Myzus persicae had no significant decline in 12 months. The ability to yield resting spores within host carcasses remained unchanged, and the probability of resting spore formation increased with the conidial concentrations that infect aphids. Therefore, cryopreservation at -80 degrees C exerted a marginal impact on formulation and pathogenicity of P. nouryi and can substitute for costly liquid nitrogen storage in routine laboratory studies. The potential of the formulation in aphid biocontrol can be maintained although there is a risk of losing fungal sporulation ability in long-term preservation.