Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/7/2009
Publication Date: 8/1/2009
Citation: Li., Y., Trigiano, R.N., Windham, M.T., Vito, L.M., Fare, D., Spiers, J.M., and Copes, W.E. 2009. Inhibition of urediniospore germination Puccinia hemerocallidis by Bacto Agar and changes in percent germination and germ-tube elongation on agarose over time. Canadian Journal of Plant Pathology 31:163-168. Interpretive Summary: Agar is a common gelling agent used in media to grow microorganisms, including fungi and bacteria. Fungal spores of Puccinia hemerocallidis, which causes daylily rust disease, do not germinate well on standard agars, so agar components were evaluated. The fungal spores germinated but elongated poorly on media containing gelling agents with more than 0.5% Bacto agar, but germinated and elongated normally on media containing a highly refined form of agar (agarose) or no agar (Gelrite®). Poor growth responses also occurred when the fungus was grown on Gelrite containing a water extract of Bacto agar and decreased as the concentration of agar-based product was increased. Growth of rust spores was also affected by pH, with optimal spore germination and elongation at pH 5.9 and 5.8, respectively. This information will be useful to scientists who perform research with Puccinia hemerocallidis.
Technical Abstract: The effects of some gelling agents and pH on urediniospore germination and germ tube elongation of Puccinia hemerocallidis were investigated in vitro. Gelling agents significantly affected urediniospore germination. Very few urediniospores germinated on the substrates containing more than 0.5% Bacto agar, and percent urediniospore germination was negatively correlated with the concentration of the agar-based products. Percent urediniospore germination was significantly greater on Gelrite® and agarose than on Bacto agar in all concentrations tested. A water extract of Bacto agar added into a substrate of 1% agarose caused 50% inhibition of urediniospore germination at 1.8 µg/ml. However, there were no significant differences in germ tube elongation among Bacto agar water extract concentrations 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. Urediniospore germination decreased as the concentrations of agar-based products increased. Changes of percent urediniospore germination and germ tube length on 1% agarose water substrate vs. time fit well to negative exponential models. The time to the half-asymptote of percent urediniospore germination and germ tube length was 1.4 h and 6.0 h, respectively, and the time to 95% of asymptote was 6.1 h for spore germination and 30.9 h for germ tube elongation. Quadratic regression equations described the changes of urediniospore germination and germ tube elongation as affected by pH. The optimum pH for urediniospore germination and germ-tube elongation was similar, which was estimated as pH 5.9 and 5.8 by using empirically derived quadratic equations, respectively.