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Etiology

Production, Storage, Germination, and Infectivity of Uredospores of Uredo eichhorniae and Uromyces pontederiae. R. Charudattan, Associate professor, Plant Pathology Department, University of Florida, Gainesville 32611; D. E. McKinney(2), and Karen T. Hepting(3). (2)(3)Former graduate research assistants, Plant Pathology Department, University of Florida, Gainesville 32611. Phytopathology 71:1203-1207. Accepted for publication 12 March 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1203.

Uredo eichhorniae and Uromyces pontederiae are pathogens of aquatic plant genera in the family Pontederiaceae. Usually less than 20% of freshly harvested uredospores of these fungi germinated on water at suitable temperatures, but more than 70% germinated when also exposed to optimal concentrations of β-ionone, 2-hexanone, 2-heptanone, α-ionone, 5-methyl-2-hexanone, 1-octanol, retinol, retinal, 1-nonanol, or n-nonanal (in order of decreasing efficacy). The spores could be stimulated to germinate on water, water agar, or leaf surfaces at temperatures from 10 to 30 C (optimum 20 C). The uredospores lost germinability within 4 wk when stored in ambient air at 20, 5, –5, or –12C; at 20 C in vacuum; or with anhydrous calcium sulfate, silica gel, or phosphorus pentoxide. At 5 C, relative humidity (RH) of 35, 52, or 61% in storage was more conducive to spore germinability than 0, 82, or 100% RH. Spores stored in liquid nitrogen remained germinable for more than 18 mo and did not require heat shock to activate germination. Consistent host infection occurred and uredia were formed only when newly inoculated plants were incubated with 500 μl of gaseous 2-heptanone, 5-methyl-2-hexanone, or 2-hexanone per milliliter of air in a dew chamber. Spraying leaves with water agar-based inoculum containing 1–100 μl of α-ionone per milliliter was less effective in promoting infection. Uredospores of U. pontederiae infected Pontederia lanceolata leaves at 15, 20, and 25 C, but uredosori were formed only at 20 and 25 C. Spores germinated but did not form appressoria on the host at 30 C; they failed to germinate at 35 C. No cross-infection occurred with the two rusts on P. lanceolata and Eichhornia crassipes.