Analysis of Factors Governing in Vitro Accumulation of Zoospores of Pythium Aphanidermatum on Roots: I. Behavior of Zoospores

Abstract

Zoospores of Pythium aphanidermatum in distilled water suspension responded to intact pea roots by massing in large numbers at the sites of elongation behind the root tips. They showed preferential attraction to wounds made by puncturing the epidermis, and to the stele exposed at the cut ends of roots. Massing of zoospores was followed, almost immediately, by encystment and early germination, the germ tubes being directed towards the source of stimulation. The phenomenon was non-specific over a wide range of plants examined. Root exudate and extract, diffusing from the ends of capillary tubes containing these materials in agar, caused identical zoospore responses. Analysis of zoospore movement under stimulation revealed a sequence of responses—initial disruption of the typical course of movement, attraction, trapping, and early cessation of movement by encystment. Attraction was equated with chemotaxis, whilst trapping showed features of kineses.

The microclimate inhabited by macroalgal propagules

“…Surface cues for larvae can also be diffusible chemicals (Hadfield, 1977;Hirata & Hadfield, 1986). Similarly, diffusible chemical cues are used by heterotrophic dinoflagellates to find prey species or decomposing macroalgae (Hauser etal., 1975;Spero, 1985) and by zoospores of parasitic fungi to find host species (e.g., Royle & Hickman, 1964;Machlis, 1969;Khew & Zentmyer;. While such behaviours have not been reported in macroalgal propagules, they could be particularly adaptive for species which are found exclusively or nearly so as epiphytes, endophytes, or parasites of particular species (e.g., Goff, 1982;Apt, 1984;Correa & McLachlan, 1991).…”

Zoospore Homing and Infection Events: Effects of the Biocontrol Bacterium Burkholderia cepacia AMMDR1 on Two Oomycete Pathogens of Pea ( Pisum sativum L.)

“…The zoospore attraction assay was based on the capillary root model, in which zoospore attraction to glass capillaries that are loaded with a test compound is evaluated (48). The assay used was a modification of the agar-free version involving quantification of zoospores in open-ended capillaries (2).…”

“…If the lack of zoospore attraction towards seed exudates in which the bacteria grew was due to metabolism of attractants and not due to production of a repellent, then diluting regular exudates with exudates in which the bacteria grew should not have resulted in a reduction in zoospore attraction. To test the effect of bacterial incubation on zoospore attraction over time, B. cepacia AMMDR1 was incubated in seed exudates as described above and samples were taken at zero time and after 4,8,12,24,48, and 72 h. The samples were treated as described above, and samples that were diluted 50-fold were evaluated to determine their attractiveness to Pythium zoospores. There were four replicates per time period.…”

<i>Rosa multiflora</i> with Root Rot Tolerance Has No Tolerance Mechanism on the Root Surface during the Early Infection Process

“…After heating medium at 40°C, the capillary tube was filled with agar medium with root extract and it was put on a slide glass and covered with a cover glass. A zoospore suspension of 3.0 × 10 3 zoospores/mL was dropped around the capillary tube (Royle and Hickman, 1964). After inoculation for 30 min, zoospores were stained with aceto-carmine and observed under an optical microscope.…”