Zoospore chemotaxis in Australian isolates of <i>Phytophthora</i> species

Halsall, DM

doi:10.1139/m76-062

Cited by 27 publications

(11 citation statements)

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“…For example, taxis occurs towards root difFusates and mixtures of nutrients, and, depending on the fungus, towards individual sugars and amino aeids (e.g. Royle & Hiekman, 1964i;Ho & Hickman, 1967;Chang-Ho & Hiekman, 1970), ethanol (Allen & Newhook, 1973;Halsall, 1976) and other volatile compounds (Cameron & Carlile, 1978). It occurs also in response to eleetrieal or ionic fields (Troutman & Wills, 1964;Khew & Zentmyer, 1974;Miller, Shand & Gow, 1988).…”

Section: Introductionmentioning

confidence: 99%

Behaviour of zoospores and zoospore cysts in relation to root infection by Pythium aphanidermatum

1991

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The pre-penetration sequence involving zoospore taxis, encystment, cyst germination and germ-tube orientation was studied by video microscopy when roots of wheat, cress or tomato were placed in suspensions of zoospores of Pythium aphanidermatum (Edson) Fitzp. The sequence was also studied in vitro, to identify the responsible factors.Several amino acids, sugars or volatile compounds elicited one of more stages of the sequence, but only glutamic acid and aspartic acid elicited all stages and thus could account for the observed behaviour on roots. Polyuronates of root surface slime also may be needed for encystment and orientation of spores, because germ-tubes emerged towards roots from a fixed point near the former position of the water-expulsion vacuole. However, identical patterns of zoospore accumulation and encystment on untreated roots and roots encased in alginate gel indicated that neither polyuronates nor specific sugar residues of root slime caused localized encystment on roots.Based on these results, a 'simplest case' model of the pre-penetration sequence on roots is proposed.

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Section: Introductionmentioning

confidence: 99%

Behaviour of zoospores and zoospore cysts in relation to root infection by Pythium aphanidermatum

1991

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“…Simulated root models, complex mixtures such as V8 broth, and some pure compounds and defined mixtures have been used to demonstrate various parts of the sequence in vitro (Dukes & Apple, 1961;Royle & Hickman, 1964a, b ;Zentmyer, 1966;Bimpong & Clerk, 1970;Ho & Hickman, 1967;Khew & Zentmyer, 1973;Halsall, 1976). In general no pure compound approached the activity of root exudate and most were only effective at high concentrations.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Organic Compounds on the Encystment, Viability and Germination of Zoospores of Phytophthora cinnamomi

1982

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A number of organic compounds were tested to determine their ability to induce encystment or germination of zoospores of the fungus, Phytophthora cinnamomi. The basic amino acids, lysine and arginine, induced encystment at concentrations in the millimolar range. Pectin (500 pg ml-l) also induced encystment and in addition stimulated the encysted cells to germinate. A wide range of carbohydrates and the amino acids, glutamate and aspartate, stimulated cysts to germinate although they did not themselves induce encystment.The polypeptide, polyc-lysine and the basic proteins, histone 1, histone 4 and lysozyme together with the lectin, concanavalin A, immobilized swimming zoospores at concentrations between 0.3 and 10 pg ml-l. At concentrations below 1 pg ml-1 cysts were formed but at higher concentrations cells lysed and the viability of the population was reduced. These compounds did not induce germination of the encysted zoospores. Ethanol, isovaleraldehyde and hexanal also induced encystment but only at concentrations in the millimolar range.These data, together with previous work on cations show that the triggering of motile cells to encyst does not in this species invariably result in the cells being committed to germination.

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“…Zoospores are chemotactically attracted to root tips (Halsall, 1976) and to points where lateral roots are about to emerge: on root tips they attach and encyst mainly in the zone of elongation just behind the root cap. Germ tubes from the encysted spores then penetrate the root tissue.…”

Section: Dna-based Detectionmentioning

confidence: 99%

“…In water, sporangia from oospores are small and release 8-16 zoospores (Duncan, 1975); larger sporangia (on average 50 × 30 µm (Bain and Demaree, 1945)) are produced on infected roots and can release 40-50 zoospores, perhaps more. Zoospores are chemotactically attracted to root tips (Halsall, 1976) and to points where lateral roots are about to emerge: on root tips they attach and encyst mainly in the zone of elongation just behind the root cap. Germ tubes from the encysted spores then penetrate the root tissue.…”

Section: Figurementioning

confidence: 99%

Scientific Opinion on the risks to plant health posed by Phytophthora fragariae Hickman var. fragariae in the EU territory, with the identification and evaluation of risk reduction options

2014

EFS2

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The Panel on Plant Health assessed the risk to plant health from Phytophthora fragariae for the European Union and evaluated the current EU legislation and possible risk reduction options. The pest is present in most areas of Europe except southern Mediterranean regions. Entry through the plants for planting, but not seeds, pathway, is assessed as a major pathway, with the probability of entry rated as unlikely and the uncertainty as high. The probability of establishment is likely in the absence of existing disease control practices with low uncertainty. The probability of spread in the absence of a scheme for the production of certified plants for planting is considered to be very likely. With certification, spread is considered to be unlikely to moderately likely, depending on the inclusion of testing for the pathogen as part of certification. These ratings have medium uncertainty. Potential impact is rated as minor with medium uncertainty. The Panel evaluated the effectiveness of current EU legislation regarding the introduction and spread of P. fragariae. According to the regulation the import of Fragaria plants for planting, other than seeds, is prohibited from specified countries, whereas for import of these plants from other countries and for movement of these plants within the EU special requirements with respect to P. fragariae must be fulfilled. If the current legislation specific to P. fragariae were removed, no major consequences would be expected, unless the industry simultaneously ceased its voluntary certification activity. This is largely because of the important level of protection afforded to the industry by the widely used certification schemes for Fragaria, which significantly reduce the risks of entry, establishment, spread and impact. Certification schemes for the movement of Fragaria plants for planting offer the greatest efficiency and feasibility and the least uncertainty, especially if effective detection is incorporated into them. SUMMARYFollowing a request from the European Commission (EC), the EFSA Panel on Plant Health (PLH) was asked to deliver a scientific opinion on the pest risk of Phytophthora fragariae Hickman var. fragariae for the European Union (EU) territory and to identify risk reduction options and evaluate their effectiveness in reducing the risk to plant health posed by the organism. In particular, the Panel was asked to provide an opinion on the effectiveness of the current EU requirements against this organism, which are laid down in Council Directive 2000/29/EC, in reducing the risk of introduction of this pest into, and its spread within, the EU territory.The Panel conducted the pest risk assessment following the general principles of the -Guidance on a harmonised framework for pest risk assessment and the identification and evaluation of pest risk management options‖ (EFSA PLH Panel, 2010) and of the -Guidance on evaluation of risk reduction options‖ (EFSA PLH Panel, 2012). As Phytophthora fragariae Hickman var. fragariae is already present in some EU Me...

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Zoospore chemotaxis in Australian isolates of Phytophthora species

Cited by 27 publications

References 0 publications

Behaviour of zoospores and zoospore cysts in relation to root infection by Pythium aphanidermatum

Behaviour of zoospores and zoospore cysts in relation to root infection by Pythium aphanidermatum

The Effect of Organic Compounds on the Encystment, Viability and Germination of Zoospores of Phytophthora cinnamomi

Scientific Opinion on the risks to plant health posed by Phytophthora fragariae Hickman var. fragariae in the EU territory, with the identification and evaluation of risk reduction options

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