Pythium splendens-suppressive soils from different islands of Hawaii
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Abstract Carrot roots with cavity spot lesions from eight different counties in Norway were sampled and Pythium species were isolated on selective medium. Pythium spp. were characterised morphologically and by species‐specific PCR. Laboratory experiments with inoculations of carrot roots were performed. A total of 130 isolates out of 230 Pythium ‐like isolates tested with PCR were identified as pathogenic species of Pythium. These were P. intermedium (29%), P. sulcatum (23%), P. sylvaticum (16%), P. violae (15%) and a possible new Pythium species designated P . ‘ vipa ’ (18%). There were some differences between geographical regions and ages of cavities regarding the frequency of the different species isolated. When rating sunken lesions in the laboratory inoculation experiments, P. ‘ vipa ’ was the most aggressive and P. violae the least aggressive species. P. intermedium and P. ‘ vipa ’ caused more discolouration of the infected carrot tissue than the other species. The importance of the different Pythium spp. as agents of cavity spot in Norway is discussed.
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SUMMARY The possibility of an association between cavity spot and root dieback of carrots has been demonstrated, along with control of both disorders by soil sterilisation with methyl bromide or seed and soil treatment with metalaxyl. When carrots were grown in sterilised soil into which five Pythium spp. were introduced individually, cavity spot occurred and the Pythium spp. were re‐isolated from cavities. The relatively slow growing Pythium violae gave the highest percentage of carrots with cavities. In a laboratory test a range of Pythium spp. produced cavities on carrots previously grown in sterilised soil, and with one exception were re‐isolated from those cavities.
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Metalaxyl
Root rot
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Abstract The potential of anthranilate in the control of Pythium-induced damping-off in horticultural crops was investigated under gnotobiotic conditions. Mutational studies of P. aeruginosa PNA1 led us to identify anthranilate as an antifungal compound active against Pythium species. Anthranilate inhibited growth of the Pythium species in vitro and a 50% growth inhibition was observed at the concentration of 30 μg/ml of anthranilate in GCY medium. The addition of anthranilate at 50 μg/g of potting mix protected lettuce, tomato and beans in vivo against Pythium-induced damping-off. In view of rapid germination of Pythium sporangia in response to seed or root exudates and followed by immediate infection, the use of anthranilate in the suppression of damping-off was investigated.
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Damping off
Pythium aphanidermatum
Potting soil
Pythium ultimum
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Some Pythium spp. cause damping off and root rot in soybeans and other crop species. One of the most effective management tools to reduce disease is host resistance; however, little is known about resistance in soybean to Pythium spp. The soybean nested associated mapping (SoyNAM) parent lines are a set of germplasms that were crossed to a single hub parent to create recombinant inbred line populations for the purpose of mapping agronomic traits. The SoyNAM parents were screened for resistance to Pythium lutarium, Pythium oopapillum, Pythium sylvaticum, and Pythium torulosum in separate assays to evaluate seed and root rot severity. Of the 40 SoyNAM parents, only 'Maverick' was resistant to the four species tested; however, 13 were resistant to three species. Other lines were resistant to two, one, or none of the species tested. Correlations between seed and root rot severity for the lines assessed were weak or insignificant. Results indicate that mechanisms of resistance to seed and root rot caused by Pythium spp. may not necessarily be the same.
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Root rot
Damping off
Pythium ultimum
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Abstract Pythium root rot (PRR), caused by various Pythium species, is a major disease of creeping bentgrass in the transition zone of the United States. Characterization of various Pythium species associated with PRR was determined by identifying 106 Pythium isolates from samples of symptomatic turfgrass cores. Pathogenicity assays were conducted on post‐emergent (7‐day old) seedlings and mature (5‐week old) creeping bentgrass plants that were inoculated with four different Pythium spp. and incubated at 34 ℃/28 ℃ for 1 to 5 weeks. The results demonstrated that pathogenicity on post‐emergent seedlings may not correlate with pathogenicity on mature plants. The sensitivity of various Pythium spp. to ten commercially available fungicides was determined through in vitro mycelial growth assays. Isolates ( n = 20) varied in sensitivity to fungicides across and within species of Pythium . Management of PRR was determined through field experiments, revealing that cyazofamid‐based treatments were most effective when applied preventatively in the early summer, and were able to reduce disease severity when applied curatively.
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Pythium species attack various vegetable crops causing seed, stem and root rot, and 'damping-off' after germination. Pythium diseases are prevalently controlled by two classes of fungicides, QoIs with azoxystrobin and phenlyamides with mefenoxam as representatives. The present study aimed to test the sensitivity of six Pythium species from different vegetable crops to azoxystrobin and mefenoxam and differentiating species based on ITS, cytochrome b and RNA polymerase I gene sequences.The inter- and intra-species sensitivity to azoxystrobin was found to be stable, with the exception of one Pythium paroecandrum isolate, which showed reduced sensitivity and two cytochrome b amino acid changes. For mefenoxam, the inter-species sensitivity was quite variable and many resistant isolates were found in all six Pythium species, but no RNA polymerase I amino acid changes were observed in them. ITS and cytochrome b phylogenetic analyses permitted a clear separation of Pythium species corresponding to globose- and filamentous-sporangia clusters.The results document the necessity of well-defined chemical control strategies adapted to different Pythium species. Since the intrinsic activity of azoxystrobin among species was stable and no resistant isolates were found, it may be applied without species differentiation, provided it is used preventatively to also control highly aggressive isolates. For a reliable use of mefenoxam, precise identification and sensitivity tests of Pythium species are crucial because its intrinsic activity is variable and resistant isolates may exist. Appropriate mixtures and/or alternation of products may help to further delay resistance development. © 2018 Society of Chemical Industry.
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Root rot
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Seedling blights and root rots caused by Pythium species account for almost US$25 million in annual losses to corn (Zea mays) production in the United States and Ontario. Variations in annual rainfall and increasing use of no-till agriculture can favor soilborne pathogens like Pythium. To date, 44 species have been reported as pathogenic to corn in the United States. The average annual corn planting date in the United States has shifted approximately 1 week earlier in the past decade, exposing young corn plants to longer germination periods of generally cooler temperatures, favoring attack by Pythium. Optimal temperatures, aggressiveness, and response to chemical and biological treatment options vary by species. This review consolidates the species of Pythium reported as corn pathogens in literature to date. It also provides an insight into management strategies and discusses variations in fungicide sensitivity observed in corn-related Pythium species.
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Damping off
Metalaxyl
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The carrot which is important in our nutrition, exposed to many pathogenic microorganisms in field and storage. There are many fungal pathogens cause problems in carrot production. This study purposed to give information about Pythium species that cause root disease and symptoms, in our country and the world. Pythium species cause significant economic losses in carrots fungal diseases. The most important Pythium species known asdamping-of disease Pythium irregulare and Pythium ultimum , cavity spot disease agents; Pythium sulcatum , Pythium violae , Pythium irregulare, Pythium sylvaticum , Pythium ultimum , Pythium colaratum , root dieback; Pythium irregulare and Pythium ultimum , among these.
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Pythium ultimum
Root rot
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