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All 170 Pythium isolates from carrot cavity spot lesions from a field in Western Australia were found to belong to either P. coloratum or P. sulcatum. All isolates of P. coloratum produced large, brownish-black, water-soaked and depressed lesions on mature carrots inoculated with agar plugs colonized by the pathogen. In comparison, only a few isola...
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Context 1
... Zoospores were produced at all the temperatures tested ( Table 2). The isolates did not produce any hyphal swellings. They were homothallic and oospores were produced on all agar media except PDA. The oogonia were smooth and globose (28 m average diameter). Antheridia, one to three per oogonium, were monoclinous and diclinous with straight necks (Fig. 1). Oospores were aplerotic (25 m average diameter) with yellow contents (Table 2, Fig. 1). The fast growing isolates were identified as P. coloratum according to Plaats-Niterink ...
Context 2
... produce any hyphal swellings. They were homothallic and oospores were produced on all agar media except PDA. The oogonia were smooth and globose (28 m average diameter). Antheridia, one to three per oogonium, were monoclinous and diclinous with straight necks (Fig. 1). Oospores were aplerotic (25 m average diameter) with yellow contents (Table 2, Fig. 1). The fast growing isolates were identified as P. coloratum according to Plaats-Niterink ...
Citations
... Some of these cases appear to be quite temperature dependent (Baptista et al. 2011;Kageyama et al. 2002;Parkunan and Ji 2013;Petkowski et al. 2013;Weiland et al. 2013). P. coloratum is pathogenic on some root crops (El-Tarabily et al. 1996;Vincelli and Lorbeer 1990). The lab test we employed using fertilizer-moistened filter paper is a very simplified environment for Pythium disease development. ...
Two commercial greenhouses producing potted plants in Pennsylvania using recycled irrigation water in an ebb-and-flood system have incurred significant crop losses due to Pythium aphanidermatum. In cooperation with the greenhouses, one or more of their water tanks was monitored continuously (128 tank samplings) for Pythium spp. by baiting. Nine species of Pythium and three species of Phytopythium were recovered, representing clades A, B, E, and K, but none was P. aphanidermatum. The recovered Pythium spp. were (i) P. rostratifingens, (ii) isolates identical to Pythium sp. nov. OOMYA1702-08 (Glade B2), (iii) P. coloratum, (iv) P. middletonii, (v) and (vi) two new species in Glade E2, (vii) a new species in Glade B2, (viii) isolates very similar to Pythium sp. nov. OOMYA1646-08 (Glade E2), and (ix) a new species in Glade A. The Phytopythium spp. recovered were (i) Phytopythium litorale, (ii) P. helicoides, and (iii) P. chamaehyphon. This article illustrates the different communities of Pythium and Phytopythium spp. found in each greenhouse over 10 months. Some of the baited species display resistance to the oomycete fungicide active ingredient, mefenoxam. P. helicoides and the new species in Glade B2 were pathogenic on seedlings in potting mix with fertilizer added.
... Most of the carrot cultivars are orange pigmented but cultivars with other pigments and colors, such as purple, red, dark orange, yellow, and white, are being gradually introduced into local markets, with high consumer acceptance. Cavity spot (CS) is an important limiting factor in carrot production worldwide, including Ontario (11,13,18,28,38). Although the disease does not reduce harvested tonnage, carrot roots with more than a few superficial cavities are not accepted for fresh market or for processing, which results in reduced marketable yield (28). ...
... The marketable portion of the carrot root develops within the top 20 cm of soil and the expansion of the tap root begins between M2 and M3. This is also the period of high susceptibility of carrot to root infection (11,28). The relationship of weather parameters to CS will allow growers to plan disease management strategies such as modifying irrigation or harvest dates to limit CS and increase the volume of marketable carrot roots. ...
Field trials to determine the effect of carrot pigmentation and weather parameters on cavity spot (CS) of carrot were conducted in the Holland/Bradford Marsh region of Ontario between 2002 and 2009. In all, 23 colored carrot cultivars from the United States Department of Agriculture (USDA) Agricultural Research Service breeding program at the University of Wisconsin (n = 5) and commercial seed companies (n = 18) were seeded in organic soil (pH 6 to 7, 45 to 75% organic matter) in late May to early June and harvested in late October or early November. Carrot roots were assessed for CS severity midseason and postharvest. Evaluations postharvest indicated that the purple pigmented carrot from breeding line 'USDA 106-3' and cultivars 'Purple Rain' and 'Purple Haze' consistently had low CS severity. The orange-pigmented 'USDA 101-23', 'Cellobunch', 'YaYa', and 'Envy' had moderate CS; and the red-pigmented carrot breeding line 'USDA 104-3' and cultivars 'Atomic Red', 'Proline Red', 'Dragon', and an unnamed line from India had high CS. Differences In CS severity in carrot cultivars between evaluations at midseason and postharvest suggest that some carrot cultivars are more susceptible to Pythium spp. inoculum in soil (alloinfection) and others to secondary infection (autoinfection) that can be attributed to the Pythium sp. involved in CS. CS severity was positively correlated with total rainfall 2 and 3 months after seeding, and was negatively correlated with number of days with air temperature >= 30 degrees C 3 and 4 months after seeding. Soil temperature and total rainfall were the best predictors of CS incidence and severity. These results could allow a forecast of disease incidence and severity at harvest.
... Accepted December 16, 1997. 5045, 34032, Montpellier, France. the role of several fast-growing Pythium species was also demonstrated (Guérin et al. 1994; El-Tarabily et al. 1996 ), including P. ultimum, which is one of the cavity spot-causing agents in the United States (Vivoda et al. 1991). Although superficial, cavity spot symptoms vary, depending on the Pythium species group involved in their development . ...
The process of infection of carrots by Pythium violae and Pythium ultimum, two causes of cavity spot, is described. The first species causes limited root necrosis, the second progressive root rot. Colonization by both species was intracellular and limited within the tissues. Modes of cell wall degradation were studied by staining (PATAg test) and labeling techniques. Pectins were labeled with monoclonal antibodies and cellulose with an exoglucanase-gold complex. Cell wall polysaccharides were degraded differently by the two species. Pythium violae was responsible for degradations, which could be noticeable, especially for high methylesterified pectins, but which occurred after colonization and were localized near the hyphae. The conservation of integrity of diseased tissue was apparently due to the absence of degradation away from the hyphae. In contrast, P. ultimum was responsible for more extensive degradation of pectins and cellulose, which occurred at a relatively greater distance from the hyphae. Degradation of pectins was always more rapid in the cell walls than in the intercellular junctions. This phenomenon led to loss of tissue integrity and could explain the tissue maceration caused by P. ultimum infection. These differences in infection process are discussed in connection with the enzymic potential for degradation of cell wall polysaccharides.Key words: Daucus carota L., Pythium, pectin, cellulose, cytochemistry.
... In Europe, White (1986) and Guerin et al. (1994) demonstrated the role of the slow-growing P. sulcatum as well as of the fast-growing P. ultimum, P. irregulare, P. intermedium, and P. sylvaticum. Another fast-growing species, P. coloratum, has been isolated from CCS lesions in Western Australia (El-Tarabily et al., 1996) and more recently in south-western France (Breton, unpubl.). ...
... In artificial inoculations, symptoms caused by P. violae and P. sulcatum are well-delimited and oriented across the breadth of the root (Groom and Perry, 1985;Montfort and Rouxel, 1988), while P. ultimum and P. coloratum cause maceration of tissues and more progressive lesions (Campion et al., 1997;El-Tarabily et al., 1996). However, it is not possible to diagnose visually which Pythium species is responsible for a CCS lesion in naturally infected roots. ...
... Therefore, results cannot be directly extrapolated to other regions. White (1986), Liddell et al. (1989), and El-Tarabily et al. (1996) described the composition of Pythium complexes by isolation from lesions and concluded that the effects of environmental conditions on CCS development differed between Pythium species. White (1988) found for example that P. sulcatum was less sensitive than P. violae to metalaxyl, a standard fungicide for CCS control. ...
Carrot cavity spot (CCS) is characterised by the appearance of small sunken elliptical lesions on the tap root. It is caused by a complex of Pythium species, but the species diversity and interactions within the complex have never been studied for modelling CCS epidemics. The diversity of a pathogenic Pythium community was assessed during 3 consecutive years in a field experiment after an initial artificial soil infestation with P. violae. 1241 lesions were examined, yielding 728 Pythium isolates. Conventional microbiological methods and restriction polymorphism of the internal transcribed spacer regions of the rDNA of 209 representative Pythium isolates allowed us to identify 655 isolates as belonging to six Pythium species, including P. violae and five indigenous species (P. sulcatum, P. intermedium, P. sylvaticum/irregulare, P. coloratum, and P. ultimum). Biological traits, such as pathogenicity, optimum temperature for mycelial growth and saprophytic survival of the inoculum, explained the fluctuations in the composition of the complex over 17 successive samplings during the 3-year period, most notably the prevalence of first P. violae and then P. sulcatum. P. violae and P. sulcatum were occasionally isolated in mixture from single lesions (10.4% and 9.6%, respectively). Other species were more frequently isolated in mixture: 30.8% for P. intermedium, 33.8% for P. sylvaticum/irregulare, 42.9% for P. ultimum, and 66.7% for P. coloratum. A contingency analysis allowed us to define ‘major’ and ‘minor’ species on both pathological and ecological criteria (frequency of occurrence in the complex, pathogenicity and ability to induce lesions by themselves), and demonstrated that infection by one ‘major’ pathogen species (P. violae or P. sulcatum) is not positively correlated with the presence of a second Pythium species. The ratio between ‘observed’ and ‘expected’ mixed infection frequency under the assumption of independent infection (mir) was less than 1 for P. violae, P. sulcatum, P. intermedium, and P. sylvaticum/irregulare (P
... ultimum, a été soulignée par différents travaux Briard, 1990), en particulier aux Etats-Unis, où elle cause les plus gros dégâts avec P. violae . Quatre autres espèces à croissance rapide, P. intermedium de Bary, P. irregulare Buisman, P. sylvaticum Campbell & Hendrix et P. coloratum Vaartaja sont aussi associées au cavity spot El-Tarabily et al., 1996). Au total, ce sont 11 espèces de Pythium qui seraient impliquées dans la maladie en France (Guerin, 1993 ;Rouxel & Breton, 1998 ;Villeneuve et al., 2001), d'où la nécessité d'introduire la notion de « complexe parasitaire » et de « complexe d'espèces ». ...
... b El-Tarabily et al. (1996) rapportent avoir isolé P. coloratum en Australie alors que cette espèce n'a jamais été mise en évidence par -Boulé et al., 2004a-Boulé et al., , 2004b. Le pouvoir pathogène de ces espèces n'a pas été formellement établi. ...
... Certains champignons, tels que P. oligandrum (Martin & Hancock, 1987 ;White, 1992 ;Petch & White, 1995) et Trichoderma harzianum (Nelson et al., 1988 ;, sont des parasites indigènes de différentes espèces de Pythium, dont plusieurs responsables du cavity spot. El-Tarabily et al. (1996) ont isolé des actinomycètes de la rhizosphère de carottes, produisant des composés antifongiques particulièrement actifs contre P. coloratum. P. oligandrum est capable de limiter la croissance mycélienne et la formation d'oogones de P. violae et P. sulcatum (White, 1992), et le développement au champ de P. ultimum sur des résidus de culture (Martin & Hancock, 1986). ...
version n°4, février 2009
imprimable en recto verso
... The pathogen of particular concern to the Australian carrot industry is Pythium, the causative agent of cavity spot (El-Tarabily et al., 1996;68 JOURNAL The whiskers indicate the 10th and 90th percentiles, and data lying beyond these limits are marked as dots. Davison and MacKay, 1998). ...
The Australian vegetable production industry has the potential to substantially reduce its water consumption by reusing water from the post-harvest washing process for irrigation or further washing, but the water must be of sufficient quality to prevent detrimental agricultural and environmental effects. We conducted a broad survey of microbial, chemical and physical characteristics of water entering (sourcewater) and exiting (wastewater) carrot-washing operations across Australia. In addition to describing differences in water quality from the perspective of reuse options, we also briefly considered some potential issues associated with the discharge of the wastewater to the environment. Agrochemical concentrations were generally low, and chlorpyriphos and linuron were the only agrochemicals found in significantly higher concentrations in the wastewater than the sourcewater. In some cases, the potential plant toxicity effects arising from high concentrations of linuron in the wastewater would have precluded it from being used for irrigation of certain vegetable crops. These chemicals also have the potential to cause environmental damage, as does the high level of turbidity of the wastewater. Several potentially pathogenic fungi were isolated, and in many cases disinfection systems may need to be considered. A fecal contamination indicator bacterium, Escherichia coli(Migula) Castellani & Chalmers, was found in significantly higher concentrations in wastewater than sourcewater, and concentrations of up to 2,800 cfu.mL were detected. This indicates a potential hazard to the consumer if the water is to be reused, but the standard industry practice of passing the product through a final chlorine rinse could reduce this risk.
... Definitive evidence for the biological origin of this soil-borne disease was provided by Groom and Perry (1985) and then by White (1988), who established that two slow-growing Pythium species, P. violae (Chesters and Hickman) and P. sulcatum (Pratt and Mitchell), were the most important causal organisms in countries where cavity spot occurred. Several fast-growing Pythium species including P. ultimum (Trow) (Vivoda et al. 1991) and P. coloratum (Vaartaja) (El-Tarabily et al. 1996) have also been demonstrated to cause cavity spot. ...
... Within 24 h of sampling, the carrots were cleaned under running water for 4 h to remove soil particles and surface microorganisms (El-Tarabily et al. 1996). Two hundred pieces (ca. ...
... The pieces were surface-disinfested by immersion in 70% ethyl alcohol for 3 min followed by immersion in 1.05 % sodium hypochlorite for 4 min. Surface-disinfested pieces were then rinsed 10 times (5 min for each rinse) with sterile, distilled water to remove residual hypochlorite, and then dried on sterile filter paper for 30 min in a laminar flow cabinet (El-Tarabily et al. 1996). Tissues from the lesion margins were then excised aseptically and plated with the internal tissue facing down, on a modified selective medium (Jeffers and Martin 1986) for the isolation of Pythium species. ...
In a survey of carrot diseases of the Nile delta region of northern Egypt, Pythium sulcatum (Pratt and Mitchell) and P. ultimum (Trow) were isolated from 74 and 26%, respectively, of carrot roots showing cavity spot disease. In laboratory and glasshouse pathogenicity tests, P. sulcatum caused significantly (P < 0.05) more severe damage than P. ultimum. The greater level of pathogenicity of P. sulcatum was associated with its ability to produce a wider array of cell-wall-degrading enzymes with significantly (P < 0.05) higher enzymatic activities compared to P. ultimum. Polygalacturonase, pectin lyase, pectate lyase and cellulase were detected in cavity spot lesions induced by both P. sulcatum and P. ultimum. Pectin methylesterase was detected in tissues invaded by P. sulcatum and not by P. ultimum. This is the first record of cavity spot disease of carrots in Egypt and indicates P. sulcatum and P. ultimum as the causal agents of this disease in the region surveyed.
... Both species are important in North America and Europe (Benard and Punja 1995;Kalu et al. 1976;White 1986), whereas only P. sulcatum has been reported from Japan (Kaygeyama et al. 1996;Nagai et al. 1986). P. violae (Dewan and Sivasithamparam 1989;Vaartaja 1967) and P. sulcatum occur in Australia (El-Tarabily et al. 1996), but until this survey, only P. sulcatum had been isolated from carrots (Davison and McKay 1998;El-Tarabily et al. 1996). This is the first record of P. violae from carrots in Australia. ...
... Both species are important in North America and Europe (Benard and Punja 1995;Kalu et al. 1976;White 1986), whereas only P. sulcatum has been reported from Japan (Kaygeyama et al. 1996;Nagai et al. 1986). P. violae (Dewan and Sivasithamparam 1989;Vaartaja 1967) and P. sulcatum occur in Australia (El-Tarabily et al. 1996), but until this survey, only P. sulcatum had been isolated from carrots (Davison and McKay 1998;El-Tarabily et al. 1996). This is the first record of P. violae from carrots in Australia. ...
A survey of Pythium spp. from carrot-growing regions of Australia showed that P. sulcatum was the most common pathogenic species and occurred in all Australian states. It was isolated from carrots with a range of
symptoms including cavity spot, and brown, discoloured, forked or hairy roots. Hordeum murinum P. violae was also isolated from tissue with cavity spot symptoms, but only from South Australia and from properties along the Murray
River in Victoria. All P. violae isolates tested were pathogenic. This is the first record of P. violae from Australian carrots. Some isolates of P. irregulare, P. ultimum, Pythium HS-group and Pythium ‘D’ were also pathogenic in in vitro tests. RAPD analysis of a subset of Australian P. sulcatum isolates showed that they clustered into two clades. The type and isotype formed a third clade. Isolates from Tasmania were
in clade 1, isolates from Queensland and southern Victoria were in clade 2; isolates from New South Wales, Western Australia
and the Murray River basin were in both clades. Comparisons between RAPD clades showed that isolates differed in growth rate
and oospore diameter but not in oogonium diameter. Australian isolates of P. sulcatum are plerotic, whereas the type is aplerotic. The restricted host range of P. sulcatum, its genetic diversity, together with the small number of sites where carrots are grown, indicate that it may be a pathogen
of native Apiaceae that has become a pathogen of carrots.
Additional keywords
Pythium sulcatum
–
Pythium violae
–
Daucus carota var. sativa
... The slow-growing species P. violae and P. sulcatum are the most important causal organisms in Europe, Japan and North America (Nagai et al., 1986;White, 1986;Montfort & Rouxel, 1988;Vivoda et al., 1991;Breton & Rouxel, 1993;Benard & Punja, 1995). In WA, P. sulcatum is the most important species (Davison & McKay, 1998), although P. coloratum has also been implicated (El-Tarabily et al., 1996). ...
Metalaxyl was used to control Pythium diseases of carrots in experiments on farms with a history of cavity spot. The first experiment compared the method of application (sprayed, banded or broadcast) and rate (0, 1.5, 3 or 6 kg a.i. ha−1) one week after sowing. Three additional experiments compared the rate (0, 0.75, 1.5 or 3 kg a.i. ha−1) and time (sowing, 1- to 2- or 4- to 5-true-leaf stage) of application. In expt 1, the application of metalaxyl, but not the method by which it was applied, increased yield by 20% and significantly reduced the incidence of cavity spot, forking and misshapen carrots. In expts 2, 3 and 4, neither the rate nor time of application affected yield or reduced the incidence of Pythium diseases. Comparison of the sites showed that they differed in past metalaxyl usage. Metalaxyl had not been used on the site of expt 1, but had been used previously at sites 2, 3 and 4. Laboratory experiments were conducted to determine whether these differences in efficacy resulted from reduced sensitivity of Pythium isolates to metalaxyl, or reduced persistence of metalaxyl in soil. ED50 values showed that there was no reduction in metalaxyl sensitivity. The half-life of metalaxyl was 82 days in soil from expt 1, but was 10 days or fewer in soils from expts 2, 3 and 4. Thus the failure of metalaxyl to control Pythium diseases was associated with reduced persistence in soil, not reduced sensitivity of the target fungi.
... Evidence for biological origin then by White (1988) w60 established that two slow-Lowing Pythiuin species, P. violae and P. sukataun, were the major h g a l species responsible for the disease in Europe. Recently, the role of several fast-growing Pvthizini species was also demonstrated (Guérin et al. 1994;El-Tarabily et al. 1996), including P. adtimum, which is one of the cavity spot-causing agents in the United States Wivoda et al. 1991). ...
The process of infection of carrots by Pythium violae and Pythium ultimum, two causes of cavity spot, is described. The first species causes limited root necrosis, the second progressive root rot. Colonization by both species was intracellular and limited within the tissues. Modes of cell wall degradation were studied by staining (PATAg test) and labeling techniques. Pectins were labeled with monoclonal antibodies and cellulose with an exoglucanase-gold complex. Cell wall polysaccharides were degraded differently by the two species. Pythium violae was responsible for degradations, which could be noticeable, especially for high methylesterified pectins, but which occurred after colonization and were localized near the hyphae. The conservation of integrity of diseased tissue was apparently due to the absence of degradation away from the hyphae. In contrast, P. ultimum was responsible for more extensive degradation of pectins and cellulose, which occurred at a relatively greater distance from the hyphae. Degradation of pectins was always more rapid in the cell walls than in the intercellular junctions. This phenomenon led to loss of tissue integrity and could explain the tissue maceration caused by P. ultimum infection. These differences in infection process are discussed in connection with the enzymic potential for degradation of cell wall polysaccharides.
