Simple and inexpensive long-term preservation methods for Phytophthora infestans.

Phytophthora infestans is one of the most notorious pathogen among Phytophthora species causing potato late blight disease. Stable and long-term preservation of this pathogen is essential for biological research and fungicide screening. The aim of this study was to find a suitable long-term preservation method for P. infestans. We adjusted the storage temperature, made a slight modification to the rye seed method, and compared the influence of four preservation methods (the mineral oil method, the sterile water method, the rye seed method, and the modified rye seed method) on survival, growth and virulence of four isolates of P. infestans. The results showed that all four methods maintained high viability of the tested P. infestans isolates, but the two rye seed methods were the best ways to maintain 100% viability of the P. infestans isolates without contamination. The four preservation methods did not significantly influence growth or morphological characteristics of the P. infestans isolates. The impacts of the four methods on the virulence of the four P. infestans isolates were isolate-specific. For isolates YF3 and 64093, all four methods were suitable for maintaining their virulence. Whilst for isolate HQK8-3, the rye seed and sterile water methods were more suitable to maintain its virulence than the other two methods. For isolate 32835, storage under mineral oil was the best method for maintaining its virulence. In view of these results, it is recommended P. infestans should be stored by several different storage methods to ensure the safety and stability of the isolates.