An approach for long-term preservation of Blumeria graminis f. sp. tritici

Blumeria graminis f. sp. tritici (Bgt) is an obligate parasite that only infects living tissues of wheat (Triticum aestivum L.). Long term preservation of Bgt is useful for genetic studies but it is challenging due to difficulty of artificial cultivation. In this study a simple protocol was developed in which desiccating the conidia using crystals (3–6 mm in diameter) of silica gel allowed viable storage for 12 months. The conidia were mixed with silica gel, dried for 5 h at 23 °C, and then stored at −80 °C. The preserved Bgt isolates still maintained their viability after 12 months and successfully infected detached leaves of wheat seedlings. Analysis of 20 Bgt isolates revealed that the cryopreservation process had no effect on two key phenotypic variants: virulence against 12 near-isogenic wheat cultivars and their sensitivity to the fungicide triadimefon. DNA sequencing analysis confirmed that the nucleotide sequences of the 1.4 α-demethylase inhibitor (cyp51), chitin synthase 1 (chs1), and β-tubulin (tub2) genes had not changed and still contained the corresponding single nucleotide mutations. These results indicate that the silica gel-based desiccation protocol is suitable for the long term preservation of large numbers of Bgt isolates.