Pathogenicity Of Pythium Species Research Articles

Comparative genomics reveals the presence of simple sequence repeats in genes related to virulence in plant pathogenic Pythium ultimum and Pythium vexans

In this study, we evaluated the occurrence, relative abundance (RA), and density (RD) of simple sequence repeats (SSRs) in the complete genome and transcriptomic sequences of the plant pathogenic species of Pythium to acquire a better knowledge of their genome structure and evolution. Among the species, P. ultimum had the highest RA and RD of SSRs in the genomic sequences, whereas P. vexans had the highest RA and RD in the transcriptomic sequences. The genomic and transcriptomic sequences of P. aphanidermatum showed the lowest RA and RD of SSRs. Trinucleotide SSRs were the most prevalent class in both genomic and transcriptomic sequences, while dinucleotide SSRs were the least prevalent. The G + C content of the transcriptomic sequences was found to be positively correlated with the number (r = 0.601) and RA (r = 0.710) of SSRs. A motif conservation study revealed the highest number of unique motifs in P. vexans (9.9%). Overall, a low conservation of motifs was observed among the species (25.9%). A gene enrichment study revealed P. vexans and P. ultimum carry SSRs in their genes that are directly connected to virulence, whereas the remaining two species, P. aphanidermatum and P. arrhenomanes, harbour SSRs in genes involved in transcription, translation, and ATP binding. In an effort to enhance the genomic resources, a total of 11,002 primers from the transcribed regions were designed for the pathogenic Pythium species. Furthermore, the unique motifs identified in this work could be employed as molecular probes for species identification.

Pathogenic and molecular characterisation of <i>Pythium spp.</i> inducing root rot symptoms in other crops intercropped with beans in Southwestern Uganda

Objective: In Southwestern Uganda, bean root rot epidemics associated with Pythium species are frequent despite the use of various management methods. This study set out to determine whether other crops in bean cropping systems of Southwestern Uganda are affected by Pythium root rots and to characterise the Pythium species using Internal transcribed sequence (ITS) DNA primers. Methodology and Results: Root rots were found to occur on maize, sorghum, peas and potato sampled from farmer’s fields where they were found to be intercropped with beans affected by root rot. Pythium species were isolated using Corn meal agar (CMA).DNA was subsequently extracted and polymerase chain reaction ( PCR) analysis carried out using ITS DNA region primers and then the PCR products were sequenced. Twenty-one Pythium species were isolated. Cross pathogenicity tests were done in a screen house using bean pathogenic Pythium species and Pythium , species derived from other crops intercropped with beans. The Pythium species were moderately to non-pathogenic in maize and millet while those in sorghum and peas were highly pathogenic. Conclusion and application of results: This study found that other crops intercropped with beans in Southwestern Uganda were affected by Pythium root rots. Peas and sorghum were highly susceptible to the pathogenic Pythium species and could therefore be contributing to the continuous bean root rot epiphytotics in the region. On the other hand, maize and millet were non pathogenic to the Pythium species. This knowledge could be used to advice farmers not to include sorghum and peas when intercropping with beans, as they seem to be contributing to the Pythium inoculum load. They could alternatively use maize and millet, as they are not susceptible to the pathogenic Pythium species. Keywords: Pythium , root rots, Southwestern Uganda, ITS DNA, pathogenic

Pathogenicity of Pythium species causing seed rot and damping-off in soybean under controlled conditions

Pythium species cause seed rot (SR) and damping-off (DO) in soybean worldwide. In a previous study, a number of Pythium species were isolated from infected soybean plants across Ontario and Quebec, but their comparative pathogenicities to soybean were not examined. In the present research, 24 isolates from eight Pythium spp. were evaluated for their pathogenicity in causing soybean SR and DO in a greenhouse environment. The effect of temperature on the ability of these isolates to cause SR was also studied. There were significant differences among the eight Pythium spp. for both SR and DO. When tested at 25°C, Pythium ultimum was the most pathogenic species, causing 97.0% SR and 46.4% DO, on average, in the two soybean cultivars used. Pythium aphanidermatum was the second most pathogenic species, resulting in 88.5% SR and 41.8% DO. The two species resulted in significantly greater SR and DO than the other six species tested and were considered highly pathogenic. Of the two cultivars used in these trials, ‘Beechwood’ was significantly more susceptible than ‘Nattawa’ to both SR and DO. Temperature had a significant influence on SR caused by Pythium spp. At all four temperatures tested (4°C, 12°C, 20°C and 28°C), P. ultimum was highly pathogenic, while P. arrenomanes, P. coloratum and P. dissotocum were the least pathogenic. The interactions between temperature and Pythium spp. were more pronounced for P. aphanidermatum, which showed an increased percentage of SR with an increase in temperature, and for P. irregulare, P. macrosporum and P. sylvaticum, which showed a decreased percentage of SR with an increase in temperature.

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean.

A case study of infection of rice roots by deleterious fungi and minor pathogenic Pythium species in a paddy field

Roots of rice plants grown in paddy fields in a transplant culture system were collected seven times between 8 and 22 weeks after transplanting, for two crop seasons. Rice seedlings grown in a potting medium amended with the collected roots were significantly shorter than those grown in the same medium either without the addition of the roots or amended with pasteurized, collected roots indicating that seedlings were inhibited by heat-labile microorganisms on the collected rice roots. Ninety-five and 172 pure cultures of Pythium spp. and fungi, respectively, were isolated from the rice roots collected 5 or 7.5 weeks after transplanting in the fields. Among these microorganisms, Pythium aristosporum inhibited seedling growth in greenhouse experiments, and Acremonium sp., Alternaria sp., Epicoccum nigrum, Fusarium sp., Massarina sp., Penicillium spp., Rhinocladiella sp., Stemphylium sp., Trichocladium sp., and several unidentified fungi inhibited seminal root growth in in vitro experiments. These microorganisms might be involved in the inhibition of seedling growth in soils amended with the rice roots collected from the paddy field. Thus, roots of rice plants at the middle stage of growth transplanted into paddy fields can harbor pathogenic or deleterious fungi or Pythium sp(p). The effects of these microorganisms on rice growth in paddy fields are discussed.

Kinds, Abundance and Pathogenicity of Pythium Species Isolated from Maize Rhizosphere of Various Habitats in El-Minia Governorate, Egypt

A total of 374 Pythium isolates were isolated and identified from the rhizosphere soils of maize plants grown in 100 different agricultural fields in nine provinces at El-Minia Governorate, Egypt. Five Pythium spp. of P. defense, P. graminicola, P. irregulare, P. oligandrum and P. splendens were obtained. P. deliense and P. oligandrum were predominant in all of the locations with 48.1% and 41.4% of total counts, respectively. P. graminicola, P. irregulare and P. splendens were not isolated in 4, 2 and 4 provinces out of 9 provinces with 5.3%, 3.5%, and 1.6% of isolation percentage from total counts, respectively. Number of Pythium isolates in each were 34, 31, 34, 33, 34, 96, 37, 37 and 38 out of 374, for locations of El-Edwa, Maghagha, Beni-Mazar, Matai, Samalout, El-Minia city, Abou-Querquas, Mallawi and Der Mawas, respectively. Pre- and post-emergence pathogenicity tests indicated that only P. deliense was highly pathogenic to germinating grains and seedlings of maize whereas P. oligandrum was non-pathogenic.

Identification and pathogenicity of Pythium species causing damping-off in sugarbeet in northwest Iran

Seventy-eight Pythium isolates were obtained from diseased sugarbeet seedlings that were planted in soil samples collected from different sugarbeet fields in northwest Iran. P. ultimum var. ultimum was the dominant species, representing 52.6% of isolates, and P. aphanidermatum, P. deliens, P. oligandrum, P. ostracodes, Pythium group HS and Pythium group T were the other species identified. Five other isolates could not be identified and were designated as Pythium sp. In the greenhouse pathogenicity test, P. ostracodes and two isolates of P. oligandrum and Pythium sp. were non-pathogenic and four isolates belonging to P. aphanidermatum, P. ultimum var. ultinmum and Pythium group HS were very highly pathogenic. The remaining 24 isolates were weakly, moderately or highly pathogenic. This is the first report of isolation of Pythium group T and P. ostracodes from sugarbeet and the pathogenicity of the Pythium group T on sugarbeet. It is also the first report of P. paroecandrum and Pythium group HS being isolated from sugarbeet and their pathogenicity on sugarbeet in Iran. Pythium group T is a new record for Iran.

The effect of dairyshed effluent irrigation on the occurrence of plant pathogenic <i>Pythium</i> species in pasture

A preliminary survey of pastures sprayirrigated with dairyshed effluent revealed a significant increase in the population of plant pathogenic Pythium species isolated from both soil and roots In vitro pathogenicity tests showed the majority of these isolates to be pathogenic when inoculated onto the seedlings of white clover subterranean clover and perennial ryegrass although both clover species were more susceptible to Pythiuminduced disease than ryegrass

Suitability of Ten Plant Baits for the Rapid Detection of Pathogenic Pythium Species in Hydroponic Crops

Ten types of plant baits were tested in the laboratory to assess their capacity to detect pathogenic Pythium species. These were orange tree leaves, tomato leaves, pepper leaves, geranium leaves, Bermuda grass leaves, pine needles, immature carnation petals, hemp-seed cotyledons, pepper and cucumber fruits. The Pythium spp. tested were P. aphanidermatum, P. irregulare and Pythium ‘group F’ from hydroponic market garden crops in the Poniente region of Almeria (south-east Spain). The test consisted of observing the velocity at which five baits were colonized and the day of colonization of the first bait. Results indicated that the slowest baits to be infected were immature carnation petals and pine needles. These two, together with Bermuda grass leaves, were also the baits infected in lowest number, such that practically no further infection was produced in the baits after the fifth day of contact with the inoculated water. The other plant baits tested were equally suitable for detection of Pythium spp. over the first two days, although only orange leaves and hemp-seed cotyledons were infected on the first day.

Soilborne Plant Diseases Caused by Pythium spp.: Ecology, Epidemiology, and Prospects for Biological Control

Soilborne root diseases caused by plant pathogenic Pythium species cause serious losses in a number of agricultural production systems, which has led to a considerable effort devoted to the development of biological agents for disease control. In this article we review information on the ecology and biological control of these pathogens with the premise that a clear understanding of the ecology of the pathogen will assist in the development of efficacious biocontrol agents. The lifecycles of the pathogens and etiology of host infection also are reviewed, as are epidemiological concepts of inoculum-disease relationships and the influence of environmental factors on pathogen aggressiveness and host susceptibility. A number of fungal and bacterial biocontrol agents are discussed and parallels between their ecology and that of the target pathogens highlighted. The mechanisms by which these microbial agents suppress diseases caused by Pythium spp., such as interference with pathogen survival, disruption of the process of plant infection, and induced host resistance, are evaluated. The possibilities for enhancement of efficacy of specific biological control agents by genetic manipulation or deployment tactics are discussed, as are conceptual suggestions for consideration when developing screening programs for antagonists.

Soilborne Plant Diseases Caused by Pythium spp.: Ecology, Epidemiology, and Prospects for Biological Control

Soilborne root diseases caused by plant pathogenic Pythium species cause serious losses in a number of agricultural production systems, which has led to a considerable effort devoted to the development of biological agents for disease control. In this article we review information on the ecology and biological control of these pathogens with the premise that a clear understanding of the ecology of the pathogen will assist in the development of efficacious biocontrol agents. The lifecycles of the pathogens and etiology of host infection also are reviewed, as are epidemiological concepts of inoculum-disease relationships and the influence of environmental factors on pathogen aggressiveness and host susceptibility. A number of fungal and bacterial biocontrol agents are discussed and parallels between their ecology and that of the target pathogens highlighted. The mechanisms by which these microbial agents suppress diseases caused by Pythium spp., such as interference with pathogen survival, disruption of the...

Inoculation of cucumber roots with zoospores of mycoparasitic and plant pathogenic Pythium species: Differential zoospore accumulation, colonization ability and plant growth response

Hydroponically grown cucumber (Cucumis sativus) seedlings were inoculated with zoospores of 1 mycoparasitic (Pythium oligandrum) and 2 pathogenic (Pythium aphanidermatum and Pythium ‘group F’) Pythium spp. During the first 2 days after inoculation, all the Pythium spp. caused reduction in the root length. However, roots treated with Pythium oligandrum quickly reached the length of the control and on the 8th day, and for the rest of the experimental period, stimulation of root elongation was noted. Pythium oligandrum was not pathogenic on cucumber and no differences in the fresh weights of control and Pythium oligandrum inoculated plants were observed in the course of the experiment. Pythium ‘group F’ and Pythium aphanidermatum were pathogenic on cucumber seedlings, but their pathogenicities differed. Thus, while Pythium ‘group F’ had a constant, negative influence on root length and plant growth, measured as fresh weight, Pythium aphanidermatum caused generalized necroses of the root system, inhibiting consistently root elongation and plant growth and finally causing plant death. Moreover, the zoospores of 2 mycoparasitic species, Pythium oligandrum and Pythium periplocum, were not attracted to roots of cucumber and accumulated on the roots in very low numbers compared to those of the pathogenic species, Pythium aphanidermatum, which were strongly attracted and accumulated in large numbers. Finally, it was also found that Pythium oligandrum colonized the roots very poorly, while Pythium ‘group F’ and Pythium aphanidermatum were significantly better root colonizers. The significance of these findings is discussed in relation to the ecology of Pythium species and biocontrol.

Pathogenicity ofPythium species on cucumber in peat-sand, rockwool and hydroponics

Pythium spp. that cause damping-off of seedlings also can cause root rot of older plants and lead to yield reductions. This can be especially severe in soilless cultures where the fungus can spread easily with the nutrient solution. 39Pythium isolates obtained from discolored roots were assayed for their ability to cause damping-off on cucumber seedlings in sand-peat and for their pathogenicity in soilless culture of cucumber in rockwool or hydroponic solution. Isolates ofPythium aphanidermatum, P. irregulare, P. sylvaticum andP. ultimum were highly pathogenic in sand-peat, but onlyP. aphanidermatum strains were pathogenic in soilless conditions and led to root decay, plant death in rockwool culture and growth reduction in hydroponic culture. One strain ofP. aphanidermatum significantly reduced the yield of cucumber grown in rockwool under conditions similar to those of commercial cultures.

Effect of partial sterilization by steam or formalin on damping-off of sitka spruce

Three species of Pythium isolated from alkaline soil of an old established nursery at Ampthill were found to be parasitic to Sitka spruce seedlings. Symptoms varied from typical damping-off to a slow root-rot. Not all infected seedlings died, some surviving as stunted plants with partly diseased root systems. Pathogenic Pythium species were common in nursery soil at Ampthill, but absent from forest soil there, while pathogenic and non-pathogenic species were more abundant in the old than in the newer sections of the Kennington nursery. P. ultimum was abundant in soil from three alkaline nurseries (pH 6·8–7·2) and rare or absent in soil from two acid nurseries (pH 5·3–5·5). The effect of partial sterilization of nursery soil at Ampthill was, in part, to destroy pathogens. Pythium did not survive either the initial steam or formalin treatment, and subsequent recolonization of treated soil was slow. Formalin was highly toxic to Pythium species in agar cultures and in soil. Trichoderma viride , which is more tolerant of formalin than most other soil fungi, was often the dominant recolonizer of formalin-treated soil. Steam or formalin treatment markedly improved numbers and height of Sitka spruce seedlings in the first year after treatment and showed a moderate residual effect in the second year, but gave little improvement in the third year.