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Pythium dissotocum. A, B. hyphal tip forming filamentous sporangium; C. zoospores in a vesicle at the tip of an exit tube; D. Empty cyst with an exit tube after the cyst has germinated by repeated emergence of zoospore; E. Cyst germinates by a germ tube; F–J. oogonia with short stalked monoclinous antheridia; K, L. oogonia with aplerotic to nearly plerotic oospores Scale bar: 20 μm (all at the same magnification except A)
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A diagnostic key has been developed to facilitate the identification of 48 species of Pythium recorded in Taiwan so far. Photomicrographs are provided for the 10 most common or economically important species to highlight their major morphological characteristics.
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... All steps were conducted at room temperature in light. Morphological identification of isolates was achieved using taxonomic keys for Pythium (Ho 2011;Van der Plaats-Niterink 1981). ...
Orange (Citrus sinensis), a major crop in Vietnam, has been suffering from a disease with symptoms of leaf yellowing, gummosis, and root rot. This study identified the associated microorganism of the disease and evaluated its pathogenicity to citrus species. In 2021, two Pythium isolates, assigned as VN-Oo16 and VN-Oo29, were isolated from the rhizosphere soil of symptomatic orange plants in Tuyen Quang province in northern Vietnam, and were identified as Pythium deliense based on morphological and molecular characteristics. The two isolates formed numerous inflated, lobulate, and toruloid sporangia, smooth oogonia, and aplerotic, thick-walled oospores. In the phylogenetic trees based on the Internal Transcribed Spacers (ITS) and cytochrome c oxidase subunit 1 (cox1) sequences, these two isolates and other GenBank P. deliense isolates formed a distinct species cluster. Pathogenicity assays of P. deliense (VN-Oo29 isolate) were conducted by inoculation of mycelium plugs or zoospore suspension on the detached fruits, stems of grafted seedlings, and roots of seedlings grown from seeds. In pomelo and orange, P. deliense produced typical brown rot on wounded fruits and gummosis on wounded stems. P. deliense was not able to infect the roots of pomelo, orange, and lime seedlings. To our knowledge, this is the first report of P. deliense in association with citrus in the world as well as in Vietnam.
... Pythium identification has conventionally been done by examining morphological characteristics in conjunction with the keys developed by either Plaats-Ninterink (1981) or Dick (1990). For specific countries, researchers can refer to keys of Robertson (1980) for species in New Zealand, Ali-Shtayeh (1986) for species in Israel, Watanabe (2010) for species recorded in Japan or Ho (2011) for species recorded in Taiwan. Although Pythium spp. ...
Amongst the 1,400 species within the Zingiberaceae, ginger (Zingiber officinale Roscoe) is believed to be the most commonly used spice for cooking, medicine and confectionery purposes. Following more than a thousand years of domestication and development in the East, ginger is now grown worldwide throughout the tropics and subtropics. Ginger has drawn great attention from scientists over the years for its antibacterial and antifungal chemicals; nonetheless, ginger is a host for many bacteria, fungi, oomycetes and viruses. Among these phytopathogens, Pythium, an oomycete that causes Pythium soft rot (PSR) disease is of the most concern and is widely distributed throughout ginger growing regions. Losses due to PSR in pre- and post-harvested ginger are generally from 5-30%, but losses up to 100% have been recorded in India and Australia. Pythium myriotylum was believed to be the causal pathogen for the PRS disease outbreaks recorded on the two oldest ginger farms in Australia in 2007. However, P. myriotylum isolated from ginger exhibited differences in pathogenicity on ginger compared with P. myriotylum isolated from other crops in Australia. In addition, from 2007 onwards, PSR was observed on many other farms. A three-year-project (2012 to 2015) was initiated to assess the diversity within P. myriotylum occurring on Australian ginger farms as well as to study the presence of other Pythium spp. occurring on these ginger farms.
The species status of P. myriotylum recovered from ginger with PSR symptoms in Queensland had been previously called into question since numerous PSR isolates exhibited morphological features which had been believed to be unique to P. zingiberis. Although the species status of P. myriotylum and P. zingiberis has been discussed, no comprehensive and comparative assessment has been made to date. International reference isolates of these two species, P. myriotylum CBS254.70 and P. zingiberis NBRC30817 were imported for exclusive re-examination along with samples of P. myriotylum from the collection of the University of Queensland. Since the reference isolate of P. zingiberis NBRC30817 showed minor divergence (less than 1%) in gene sequences (20 gene regions analysed) and very similar morphology, it was proposed to be reunited with the taxon P. myriotylum. The identification of P. myriotylum as a pathogen of PSR disease of ginger in Australia was confirmed.
A collection of Pythium spp. (173 isolates) was isolated from diseased ginger rhizomes and soils collected around diseased ginger. Eleven distinct Pythium spp. were identified based on morphology and molecular sequences. Pathogenicity assays confirmed that P. myriotytlum isolates recovered from PSR ginger were pathogenic on ginger rhizomes and plants at a wide temperature range from 20 - 35 °C. Pythium aphanidermatum was pathogenic on ginger at 30 - 35 °C. Nine other species assessed were either non-pathogenic or pathogenic on the ginger rhizome only. Subsequent sequence assessments showed that P. myriotylum isolates from different farms were genetically uniform and had a host preference to ginger.
Isolates of P. myriotylum derived from different hosts and origins showed differences in pathogenicity to ginger. Sequence diversity based on single nucleotide polymorphism (SNP) was investigated for these isolates of P. myriotylum. Overall, within 22 nuclear and mitochondrial genes studied, a higher number of true and unique SNPs were discovered in P. myriotylum isolates obtained from PSR ginger in Australia compared with other P. myriotylum isolates. Additionally, the use of the enzyme HinP1I in a PCR-RFLP of the CoxII gene successfully discriminated P. myriotylum isolates from PSR ginger from other P. myriotylum and Pythium spp. Using the same PCR-RFLP of the CoxII gene, P. myriotylum was also detected directly from PSR infected ginger; thus providing a potential diagnostic tool.
The recovery of Pythium oligandrum, a well-known mycoparasitic oomycete, from soils around PSR ginger led to an investigation of antagonism and mycoparasitism of P. oligandrum against an isolate of the PSR pathogen, P. myriotylum Gin1. It was apparent that P. oligandrum did not produce substances toxic to P. myriotylum Gin1, but it did parasitize and compete against P. myriotylum Gin1 in vitro assays. Disease indices recorded in pathogenicity assays in Petri plates containing dual cultures of P. oligandrum and the target pathogen were reduced significantly compared with those recorded with single cultures of P. myriotylum Gin1. However, subsequent pot trials with co-inoculation of these two Pythium species showed no significant difference from control inoculations with P. myriotylum Gin1 only.
The symptoms of soft rot on ginger were not only induced by Pythium, but were also found to be induced by Pythiogeton (Py.) ramosum, a less studied oomycete. This reports Py. ramosum as a pathogen of ginger occurred at high temperatures (30 – 35 °C), and is the first record of its pathogenicity on ginger. It also was confirmed to be pathogenic on excised ginger, carrot and potato roots/tubers and other tested crop species in Petri plate assays. Py. ramosum also exhibited intraspecific variation within the ITS and CoxI genes.
Damping-off disease caused by multiple species of soilborne pathogens causes severe economic losses to sugar beet production. Thus, identifying the causal agent is important to formulating effective disease management. During a July 2021disease survey in a sugar beet field at Grand Forks, North Dakota, we observed that approximately 15% of plants located in low areas of a commercial field showed wilting leaves that were pale green and slightly blight in color, and the roots were dark brown to black along with irregular necrotic lesions. The isolated pathogen had the characteristic morphology of Pythium deliense. The sequence of the internal transcribed spacer (ITS) region and the cytochrome c oxidase subunit 1 mitochondrial (cox1) genes were 100% homologous with corresponding sequences in the NCBI database confirmed its P. deliense identity. Moreover, the ITS phylogeny confirmed its identity as P. deliense, and its close relationship with P. aphanidermatum. A disease screening trial with four sugar beet varieties was done. Growers and breeders could benefit from information about accurate sugar beet pathogen in a given field to formulate effective disease management practices.
Pythium sp. was isolated from the roots, crowns and rhizosphere soil of Catharanthus roseus (L.) G. Don. (common name; vinca) showing symptoms of root and crown rot disease in plantation areas in Chiang Mai Thailand. The pathogen was studied by morphological and molecular analysis based on internal transcribed spacer (ITS) sequence. The Pythium isolate was confirmed as Pythuim deliense. The pathogenicity of the isolate was tested by inoculating with an agar disc containing mycelium of the fungus on detached C. roseus leaves compared with an agar disc alone as the control. It was found that P. deliense infected the vinca leaves causing a brown rot. Moreover, P. delicense infected and caused rot symptoms on plant crowns 5 d after inoculation with a mycelial suspension. This is the first report of P. deliense as pathogenic to C. roseus in Thailand.
Pythium myriotylum and P. zingiberis have both been implicated in soft rot of ginger (Zingiber spp.). The status of these two taxa as distinct species follows original descriptions of physiology, morphology and pathogenicity. However, their status has been questioned by phylogenetic analyses. In this study, putative P. zingiberis isolates recovered from edible ginger (Z. officinale) rhizomes with Pythium soft rot (PSR) disease sampled from Queensland, Australia, were compared with reference isolates of P. myriotylum from peanut in Israel (CBS254.70) and P. zingiberis from ginger in Japan (NBRC30817). All isolates differed slightly in temperature optima for growth and produced similar sizes of oogonia and oospores. The sequence homology of 20 gene fragments retrieved from nuclear and mitochondrial genomes ranges from over 99 to 100% to each other. In vitro pathogenicity assays were conducted on excised carrot, ginger, potato, radish and sweet potato tuber/root sections and on seeds and seedlings of cucumber, cauliflower, millet, rye, sweet corn, tomato and wheat with each of the isolates. The reference isolate P. zingiberis NBRC30817, which was previously believed to have a narrow host range, was pathogenic on a number of tested plant species. Analysis of this comprehensive set of data allowed us to assign all tested isolates, including the isolate P. zingiberis NBRC30817, to the taxon P. myriotylum, thus confirming that the causal pathogen of PSR disease of ginger in Australia is P. myriotylum.
During the period 2003-2009 a comprehensive study of Pythium species in soil and water samples collected from various habitats on Hainan Island was conducted using conductedusing a combination of baiting and selective agar medium technique. A total of 2348 isolates were identified into 29 species: P. acanthicum, P. acanthophoron, P. aphanidermatum, P. aristosporum, P. arrhenomanes, P. carolinianum, P. catenulatum, P. cucurbitacearum, P. deliense, P. dissotocum, P. graminicola, P. helicoides, P. hydnosporum, P. indigoferae, P. inflatum, P. intermedium, P. irregulare, P. marsipium, P. middletonii, P. monospermum, P. myriotylum, P. oedochilum, P. paroecandrum, P. pulchrum, P. spinosum, P. splendens, P. sylvaticum, P. ultimum and P. vexans. Except for P. acanthicum, P. aphanidermatum, P. catenulatum, P. deliense, P. dissotocum, P. indigoferae, P. marsipium, P. myriotylum and P. splendens, the remaining 20 species are new records for Hainan. Pythium cucurbitacearum is the first record in China. Several species of Pythium which are either terrestrial or occasionally found in fresh water were isolated for the first time from fallen leaves submerged in sea water in or near mangrove habitats: P. vexans, P. aphanidermatum, P. cucurbitacearum, P. helicoides and P. middletonii. It remains to be determined whether they should be treated as halotolerant strains or marine species of Pythium but their repeated isolation pointed out their significance in litter decomposition in the marine habitat. By far, P. vexans is the most widespread and abundant species followed by P. deliense, P. acanthicum, P. aphanidermatum, P. helicoides and P. splendens. Of the 23 sampling sites, the greatest diversity of Pythium species was found in the cities of Wenchang, Haikao, Wuzhishan, Ledong and their vicinity.
Ginger is considered by many people to be the outstanding member among 1400 other species in the family Zingiberaceae. Not only it is a valuable spice used by cooks throughout the world to impart unique flavour to their dishes but it also has a long track record in some Chinese and Indian cultures for treating common human ailments such as colds and headaches. Ginger has recently attracted considerable attention for its anti-inflammatory, antibacterial and antifungal properties. However, ginger as a crop is also susceptible to at least 24 different plant pathogens, including viruses, bacteria, fungi and nematodes. Of these, Pythium spp. (within the kingdom Stramenopila, phyllum Oomycota) are of most concern because various species can cause rotting and yield loss on ginger at any of the growth stages including during postharvest storage. Pythium gracile was the first species in the genus to be reported as a ginger pathogen, causing Pythium soft rot disease in India in 1907. Thereafter, numerous other Pythium spp. have been recorded from ginger growing regions throughout the world. Today, 15 Pythium species have been implicated as pathogens of the soft rot disease. Because accurate identification of a pathogen is the cornerstone of effective disease management programs, this review will focus on how to detect, identify and control Pythium spp. in general, with special emphasis on Pythium spp. associated with soft rot on ginger.
