Effects of calcium on germination and further zoospore release from zoospore cysts of Phytophthora parasitica

doi:10.1016/S0953-7562(96)80085-2

Mycological Research

Volume 100, Issue 12, 1996, Pages 1498-1504

https://doi.org/10.1016/S0953-7562(96)80085-2 Get rights and content

Cysts of Phytophthora parasitica, induced by vortex treatment of zoospore suspensions, germinated poorly when held in Eppendorf tubes but germinated well when transferred to glass slides within the first few minutes of encystment. The responsiveness to a surface, or to other treatments where tested, was lost after 12-15 min in the Eppendorf tubes. Slides pretreated with silicone (hydrophobic) were as effective as untreated slides in promoting germination. Dilution of cyst suspensions with distilled water or with the liquid into which zoospores were released caused a consistent decrease in germination. Dilution with CaCl₂ (50 mm) or with supernatant from centrifuged cysts gave germination equivalent to control (undiluted) cysts. Lower concentrations of CaCl₂ were less effective, and there was no response to calcium by older (20 min) cysts. Dilution with zoospore lysate (caused by filtering zoospore suspensions through a Nucleopore filter) or with water passed through glass microfibre filters gave significant stimulation of cyst germination, above the undiluted control levels. Cysts that did not germinate within 2 h in response to treatments could release a further zoospore (diplanetism) by 8 h, but calcium suppressed this in a concentration-dependent manner.

The findings support a previous model that encysting zoospores release a substance (probably calcium) that must be reabsorbed for germination, and that this reabsorption is facilitated when cysts are on a surface. However, other factors provide the germination trigger, because calcium added to diluted cyst suspensions only restored germination to the initial (undiluted) level. The loss of germination responsiveness within a few minutes of encystment is suggested to involve a loss of signal transduction, consistent with the reported microtubular rearrangements in young cysts. Release of a further zoospore from non-germinated cysts is a default mechanism that requires no specific trigger, but it is suppressible by external calcium, with potential for control of P. parasitica in recirculating irrigation systems in glasshouses.

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There was wide variation in Ca content in the soils studied here and the occurrence of Aphanomyces root rot was found to be negatively related to soil Ca content. A number of studies have indicated that Ca has an impact on sensitive stages such as zoospore release, movement and cyst germination of the life cycles of many soilborne oomycetes, including Aphanomyces, Pythium and Phytophthora (Lewis, 1977; Kao and Ko, 1986; Deacon and Donaldson, 1993; Broembsen and Deacon, 1996, 1997; Heyman et al., 2007). The study of Heyman et al. (2007) on pea root rot caused by A. euteiches Drechs.
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^*: Permanent address: Plant Pathology Department, Oklahoma State University, 110 Noble Research Center, Stillwater, OK 74078-9947, U.S.A.; research was conducted while on sabbatical leave at the University of Edinburgh.

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Effects of calcium on germination and further zoospore release from zoospore cysts of Phytophthora parasitica

Mycological Research

Physiological and Molecular Plant Pathology

Physiological and Molecular Plant Pathology

Experimental Mycology

Cell Biology International Reports

Experimental Mycology

Cell Calcium

Physiological and Molecular Plant Pathology

Mycological Research

Transactions of the British Mycological Society

Physiological and Molecular Plant Pathology

Experimental Mycology

Experimental Mycology

Phytochemistry

Molecules of the Cytoskeleton

The effect of organic compounds on the encystment, viability and germination of Phytophthora cinnamomi

Journal of General Microbiology

Motility, taxis and tropism in Phytophthora

Repeated zoospore emergence as a possible adaptation to parasitism in Aphanomyces

Experimental Mycology