STORAGE OF PHYTOPHTHORA CULTURES IN LIQUID NITROGEN ULTRA LOW TEMPERATURE

68 strains of 15 species of Phytophthora and two strains of Peronophythora litchii were successfully preserved in liquid nitrogen ultra low temperature.The effects of freezing rate,cryoprntectants and thawing rate on the viability of fungi were examined.It is essential for Phytophthora and Peronophythora that crucially controlling of freezing rate by lowering temperature 1 centigrade degree per minute to -40℃ and then removing to liquid nitrogen.This procedure could be manipulated with a simple devised equipment easily.Whe- reas directly removing from room temperature to ultra low temperature caused serious damage and death of fungi.The protectants used either 10% glycerol or 5—15% dimethyl sulfoxide could prevent fungi from damage.No preference of which protectants was shown in tested, therefore either one could be used.The thawing condition either rapid thawing by removing vials from liquid nitrogen to 38℃ water bath or moderate rate by thawing in 20℃ water bath did not show significant influence on the viability of Phytophthora and Peronophythora.Our results confirm that with suitable protective agent and slow freezing rate Phytophthora species and Peronophythora litchii can be preserved in liquid nitrogen.