Métodos de preservação in vitro de urediniósporos de Puccinia kuehnii

With the aim of evaluating preservation methods of Puccinia kuehnii urediniospores, two bioassays were conducted: the first one (B1) with different methods of dehydration and the second one (B2) with different methods rehydration. B1 and B2 differed in the inclusion of silica gel granule in B1 for preservation in microcentrifuge tubes. Leaves with symptoms of orange rust were harvested from the sugarcane cultivar SP89 1115. P. kuehnii urediniospores were extracted from the leaves with the aid of a vacuum bomb. Later, they were placed in microcentrifuge tubes. Treatments for B1 were: l: dehydration in silica gel, lyophilization and without dehydration, ll: room temperature (20oC), refrigerator (5oC), freezer (-20oC) and deep-freezer (- 80oC). Treatments for B2 were: l: dehydration in silica gel and without dehydration, ll: room temperature (20oC), refrigerator (5oC), freezer (-20oC) and deep-freezer (-80oC), lll: with and without rehydration in the evaluations. The initial germination was carried out for both experiments, other assessments were made at 15 and 30 days of storage and then at every 30 days until 180 days. Urediniospore suspensions were prepared in water and a 0.1-mL aliquot was transferred to Petri dishes containing agar-water (15 g L-1). They remained at 20oC in the dark. To assess viability, the count of 200 urediniospores/plate was performed. The data were subjected to nonparametric Kruskal-Wallis analysis of variance and complemented by Dunn's test. Results showed that viability decreased with time, and the best treatments reached 27.6% and 6.6% at 30 days, and 12.0% and 1.9% at 60 days for B1 and B2, respectively. Dehydration method in silica gel followed by storage at -80oC was the only treatment that presented viable urediniospores (1.2%) at 180 days for B1. For B2, the best method was preservation with dehydration, followed by storage at 5oC, without rehydration. This method showed the best germination percentage at 120 days (0.4%). Influence of the factor thermal shock was not observed in the recovery of viable urediniospores in B2. Inclusion of silica gel granules in the microcentrifuge tube allowed the recovery of viability of urediniospores at 180 days.