Puccinia kuehnii urediniospores viability and its germination influenced by aqueous extracts of leaves of sugarcane

Abstract

Rusts contribute to yield losses in crops of sugarcane. The present study was to evaluate the viability urediniospores of Puccinia kuehnii over time and the influence of aqueous extracts in vitro germination. Leaves with symptoms orange rust, cultivar SP89 1115 and RB72 454, were collected for the first bioassay (B1). These were stored in a humid chamber, to date evaluations. Urediniospores were collected from the leaves, and suspended in distilled water 0.1 ml was prepared they were transferred to Petri dishes containing agar-water, maintained at 20°C in the dark for 24 hours. Evaluations were made at 0, 1, 2, 4, 8 and 16 days after harvest of the sheets, with five replicates for evaluation. In the second bioassay (B2) the urediniospores were collected from leaves with symptoms of orange rust cultivar SP89 1115 of sugarcane. Suspension was prepared in distilled water, aliquot of 0.1 ml were transferred to Petri dishes containing agar-water, and 1 ml of aqueous extract of leaves of sugarcane. Treatments consisted of two aqueous extracts of leaves of sugarcane: susceptible RB72 454 and resistant RB86 7515 in dilutions of 1:1, 10-1, 10-2, 10-3, with four replications. For both bioassays were evaluated germination of 200 urediniospores/plate. The results showed that B1 for variety SP89 1115 germination percentage was significantly lower than the RB72 454, respectively 26.4% and 93.1% at the time of collection of the field and 24.8% and 32.4% to 16 days after collection. In B2 the germination of urediniospores receiving the aqueous suspension of the resistant variety, was on average 7.6 percentage points lower than those who received the aqueous suspension of susceptible variety.