LOW-TEMPERATURE STORAGE OF MONOSPORIDIAL CULTURES OF THE WHEAT BUNT FUNGI

Collections of Tilletia species are commonly maintained in the form of sori harvested from smutted heads. This has been a convenient and eff ective storage method because teliospores enclosed in a sorus remain v iable for over 20 years. However, mycelial cultures derived from germi nated teliospores are genetically mixed because of meiotic segregation among sporidia. For the purposes of genetic analysis and establishing strain identity, it is necessary to maintain haploid sporidial cultur es that can be readily retrieved for manipulations. We found that spor idial cultures of Tilletia tritici and Tilletia controversa can be pre served for at least 1 year by suspending a mixture of mycelia and spor idia in 15% glycerol and storing at -70 degrees C. Approximately 80% o f the stored cultures were viable after 12 months in storage. Five out of nine monosporidial cultures of T. tritici and T. controversa teste d retained their sexual fertility in interspecific crosses. The glycer ol storage method has advantages over serial transfer in the maintenan ce of monosporidial cultures by reducing the accumulation of somatic m utations; however, the technique should be used cautiously until great er infectivity of stored cultures is demonstrated.