Preservation of Phakopsora pachyrhizi Uredospores

This study compared different temperatures and dormancy-reversion procedures for preservation of Phakopsora pachyrhizi uredospores. The storage temperatures tested were room temperature, 5 C, )20 C and )80 C. Dehydrated and non-dehydrated uredospores were used, and evaluations for germination (%) and infectivity (no. of lesions⁄cm2) were made with fresh harvested spores and after 15, 29, 76, 154 and 231 days of storage. The dormancy-reversion procedures evaluated were thermal shock (40 C⁄5 min) followed or not by hydration (moist chamber⁄24 h). Uredospores stored at room temperature were viable only up to a month of storage, regardless of their hydration condition. Survival of uredospores increased with storage at lower temperatures. Dehydration of uredospores prior to storage increased their viability, mainly for uredospores stored at 5 C, )20 C and )80 C. At 5 C and )20 C, dehydrated uredospores showed increases in viability of at least 47 and 127 days, respectively, compared to non-dehydrated spores. Uredospore germination and infectivity after storage for 231 days (7.7 months), could only be observed at )80 C, for both hydration conditions. At this storage temperature, dehydrated and non-dehydrated uredospores exhibited 56 and 28% of germination at the end of the experiment, respectively. Storage at )80 C also maintained uredospore infectivity, based upon levels of infection frequency, for both hydration conditions. Among the dormancyreversion treatments applied to spores stored at )80 C, those involving hydration allowed recoveries of 85 to 92% of the initial germination.