Inhibition of urediniospore germination in Puccinia hemerocallidis by Bacto Agar and changes in percent germination and germ-tube elongation on agarose over time

Abstract

Agar is a commonly used gelling agent and a raw material used in other gelling agents. The effects of five gelling agents and potato dextrose agar on urediniospore germination, and changes in percent urediniospore germination and germ-tube elongation in Puccinia hemerocallidis over time were investigated in vitro. Percent urediniospore germination differed significantly between the tested gelling agents. Urediniospores germinated well on Gelrite, agarose, Phytagar, and Oxoid No. 3 agar in decreasing order, and percent urediniospore germination was negatively correlated with the concentration of gelling agent. Urediniospores germinated poorly on the substrates containing more than 0.5% Bacto Agar. The concentration of Bacto Agar that caused 50% inhibition of urediniospore germination was 18.2 µg/mL in 1% agarose substrate. However, there were no significant differences in germ-tube elongation between the concentrations of Bacto Agar water extract tested. Unidentified inhibitory compounds from Bacto Agar water extract were adsorbed on a C18 column and the effluent water did not affect spore germination. However, the methanol-eluted solution from the C18 column completely inhibited urediniospore germination when the solution was evaporated and reconstituted with water. Changes in percent urediniospore germination and germ-tube length on 1% agarose water substrate over time fitted well with negative exponential models. The time to the half-asymptote of percent urediniospore germination and germ-tube length was 1.4 and 6.0 h, respectively, and the time to 95% of the asymptote was 6.1 and 30.9 h for spore germination and germ-tube elongation, respectively.

Keywords:

• gelling agent
• urediniospore
• daylily rust
• Hemerocallis
• inhibition