Potential use of seeds for long-term cryopreservation of oomycete cultures

Abstract

Oomycetes are difficult to preserve in culture using ordinary slow freezing on agar disks. Here we tested a vitrification method as an alternative approach for long-term preservation of oomycete strains. Selected seeds were used as a culture substrate before preservation at ultra-low temperature. Rape or sesame seeds were inoculated with oomycete strains, then vitrified and cryopreserved in liquid nitrogen. Thirteen out of 20 strains tested were successfully revived from the cryopreserved infested seeds with a viability of >50%. Viability was better on sesame seeds than on rape seeds. The possibility of cryopreservation using seeds was also investigated for the ordinary slow freezing method. Though viability was not stable among the conditions tested and varied among isolates, the oomycete strains examined were well preserved and showed higher viability when seeds were used rather than agar-culture disks. Also, when infested seeds were used, viability was higher for the slow freezing method than for the vitrification method in most cases. These results suggest that seeds after infestation can be a useful substrate for long-term cryopreservation of oomycetes.