Comparative Physiology and Behaviour of the Mycoparasites Pythium acanthophoron, P. oligandrum and P. mycoparasiticum

Pythium acanthophoron (two isolates) was as aggressive as P. oligandrum in hyphal interactions with Fusarium oxysporum on water agar films. It caused rapid post-contact lysis or cytoplasmic coagulation of the host, and often branched and penetrated the host at contact points. P. acanthophoron grew across a range of fungi on pre-colonized agar plates; the range was narrower than for P. oligandrum but broader than for P. mycoparasiticum. In chemically defined liquid media, P. acanthophoron was unique among the six known mycoparasitic Pythium spp. in requiring organic nitrogen but not thiamine. It also grew on mannitol as the sole carbon source in the presence of calcium or sterols or both. However, individual isolates of the three mycoparasitic species showed different responses to calcium and the sterols ergosterol, cholesterol and beta-sitosterol when grown on mannitol. All three mycoparasites required components of molasses, carrot extract or sunflower seed extract to produce oogonia in culture; they formed few oogonia on potato extract, with or without dextrose, even when supplied with sterols. The three mycoparasites were less tolerant of high NaCl levels in culture than were three phytopathogens (P. aphanidermatum, P. ultimum, P. graminicola), in contrast to a previous report for P. oligandrum and P. ultimum. These in vitro studies suggest that P. acanthophoron has potential for use as a biocontrol agent instead of, or in addition to, P. oligandrum.     

First records of Pythium aquatile and P. macrosporum isolated from soils in Japan

Pythium aquatile and P. macrosporum were isolated from the soil of a cultivated field in Gunma Prefecture and a forest in Nagano Prefecture for the first time in Japan. Their morphological characteristics are described, and their pathogenicity and taxonomy are discussed.     

Materials forPythium flora of Japan VIII Two species ofPythium:P. pyrilobum andP. oligandrum

Two species ofPythium (P. pyrilobum, P. oligandrum) having spherical sporangia with complex subglobose elements were isolated from the crown of creeping bentgrass [Agrostis palustris (cv. Penncross)] and from vegetable field soil, respectively. They are reported for the first time in Japan.     

Interaction of the mycoparasite Pythium oligandrum with other Pythium species

Interactions of Pythium oligandrum and four plant‐pathogenic Pythium spp. (P. ultimum, P. vexans, P. graminicola and P. aphanidermatum,) were studied in vitro by (i) video microscopy of hyphal interactions on water agar films, (ii) counting of host and mycoparasite propagules in different regions of opposing colonies on sunflower‐seed extract agar films and (Hi) ability of P. oligandrum to overgrow plates of potato‐dextrose agar previously colonized by Pythium spp. Pythium oligandrum typically coiled round the hyphae of Pythium hosts and penetrated the host hyphae after approximately 50 min from the hyphal coils, causing disruption of host hyphal tips up to 1.2 mm ahead of contact points. The relative growth rates of mycoparasite and host hyphae, timing of penetration and distance (sub‐apical) at which penetration led to host tip disruption were used to assess the potential of mycoparasitism by P. oligandrum to prevent the growth of Pythium hosts. P. aphanidermatum was unique among the ‘host’ Pythium spp. in being largely unaffected by P. oligandrum and in antagonizing the mycoparasite by coiling and penetrating the mycoparasite hyphae. Other host Pythium spp. apparently differed in susceptibility, the most susceptible being P. vexans and P. ultimum, whereas P. graminicola was more resistant. The results are discussed in relation to the role of P. oligandrum as a biocontrol agent, especially for limiting the ability of other Pythium spp. to increase their propagule populations in crop residues.     

Isolation of Pythium oligandrum from Egyptian soil and its mycoparasitic effect on Pythium ultimum var. ultimum the damping-off organism of wheat

Pythium oligandrum Drechsler bearing spherical sporangia with complex subglobose elements was isolated for the first time in Egypt from agricultural field soil cultivated with alfalfa (Trifolium alexandrinum) in El-Minia, Egypt. This fungus was found to be an active bio-control agent against P. ultimum var. ultimum, the damping-off organism of wheat. In agar plates, P. oligandrum parasitized P. ultimum var. ultimum hyphae with the aid of thin haustorial branches or infection pegs, eventually leading to host destruction. Incorporation of P. oligandrum into carboxymethylcellulose seed coating successfully eliminated pre-emergence damping-off of wheat caused by P. ultimum var. ultimum, whereas Post-emergence damping-off was prevented by adding inocula of P. oligandrum to the soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

腐霉属的两个新种*

新种镰雄腐霉Pythium falciforme sp. nov.和南宁腐霉P. nanningense sp. nov.分离自中国广西地区土壤。新种提供了拉丁文、中文描述和形态图,并讨论。模式标本保藏于广西大学植物病理教研室(GUPL)。     

Isolation of Pythium Acanthicum,P. oligandrum,and P. periplocum from Soil and Evaluation of Their Mycoparasitic Activity and Biocontrol Efficacy Against Selected Phytopathogenic Pythium Species

Mycoparasitic Pythium species with spiny oogonia were surveyed in 50 Palestinian agricultural fields subject to different cropping practices using the Sclerotia Bait Technique (SBT) and the Surface-Soil-Dilution-Plate method (SSDP) with the selective VP3 medium. The mycoparasitic Pythium species were obtained from 21 (42%) soils using the SSDP method and from 37 (74%) soils using SBT. Pythium acanthicum and P. oligandrum were isolated by both methods, whereas P. periplocum was isolated only by the SBT. Using a newly modified dual plate culture method (MDPCM), the three mycoparasites showed varying antagonistic performance against several Pythium host species under a range of in vitro conditions. However, P. periplocum and P. oligandrum were found to be active biocontrol agents against P. ultimum, the damping-off organism of cucumber. This pathogen was antagonized, on thin films of water agar, by the three mycoparasites, and was moderately susceptible to P. periplocum while slightly susceptible to P. acanthicum and P. oligandrum. In direct application method in which antagonistic mycoparasites were incorporated into peat/sand mixture artificially infested with P. ultimum under growthroom conditions, Pythium oligandrum and P. periplocum (at 500 CFUg⁻¹) significantly improved seedling emergence and protected seedlings from damping-off. In the seed coating method, biocontrol by two types of seed dressing (homogenate- or oospore coated seeds), was comparable to that achieved by direct application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of Sugar Beet Seed Treatment with Pseudomonas fluorescens and Low Fungicide Doses on Infection with Pythium and Plant Yield and Quality

The effect of sugar beet seed inoculation with the bacterium Pseudomonas fluorescens and treatment with the fungicides Thiram 42‐S and Dithane S‐60 with and without seed inoculation aiming to control the root decay agents Pythium ultimum and Pythium debarianum was studied during a 2‐year trial on two soil types (Mollic Gleysols and Eutric Cambisols). The influence of the treatments on parameters of sugar beet yield and quality such as root yield, sugar content, sugar in molasses, sugar yield as well as percentage of the infected and decayed plants as a consequence of parasitic oomycete infestation will be described.     

Pythium species associated with cavity spot on carrots in Norway

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.     

Red rot resistance in interspecific protoplast fusion product progeny of Porphyra yezoensis and P. tenuipedalis (Bangiales, Rhodophyta)

Nine primary regenerants were recovered by interspecific protoplast fusion of Porphyra yezoensis Ueda T‐14 (Py) (cultivated Porphyra) and Porphyra tenuipedalis Miura (Pt). This combination is difficult to achieve with conventional sexual hybridization, yet is important in that non‐cultivated P. tenuipedalis is partially resistant (PR) to red rot disease, caused by the microbial pathogen, Pythium porphyrae Takahashi et Sasaki. Out of the nine primary regenerants, two strains (Py‐Pt‐4 and Py‐Pt‐7) were like the parent, P. tenuipedalis, while the rest were like the other cultivated parent P. yezoensis T‐14 in their life cycle. Red rot resistance was assessed in parents and interspecific fusion product progeny (FPP) by exposing the foliose thalli to equivalent infection and measuring two parameters of the host‐pathogen interactions: supported fungal biomass and amount of disease produced. Intermediate resistance between P. yezoensis T‐14 (1.00) and P. tenuipedalis (0.13) was observed in two of the Py‐type FPP, Py‐Pt‐2F₂ (0.25) and Py‐Pt‐5F₂ (0.23). Stable inheritance of resistance was observed through two subsequent generations. The morphologic and reproductive characteristics of the regenerated foliose thalli, and nature of host‐pathogen interactions were used to further verify the hybrid origin of the FPP. Host‐pathogen interactions were followed using epi‐fluorescence and scanning electron microscopy (SEM). The zoospores encysted at higher rates on the susceptible cultivated parent (P. yezoensis T‐14) germinated immediately and the short germ tubes formed appres‐soria and penetrated the algal cells near the site of encystment. While on the PR parental (P. tenuipedalis) and partially resistant FPP (PRFPP) progeny (Py‐Pt‐2F₂ and Py‐Pt‐5F₂) the low rate of zoospore encystment was followed by cyst germination, but only a few of the germ tubes formed appressoria and penetrated the thallus surface. Long germ tubes (with no appressoria) were seen growing on the thallus surface without host penetration. The minimal rate of encystment concomitant with low rate of appressorium formation on the PR parent and PRFPP was observed as the major factor responsible for the partial resistance in these thalli.     

Long-term changes in frequencies ofPythium iwayamai andP. paddicum in upland- and paddy-field soils

The long-term changes in the frequencies ofPythium iwayamai andP. paddicum in upland- and flooded paddy-field soils were compared. The frequencies of both species fell in both soils within the first 6 months after they had been buried. After 36 and 48 months,P. iwayamai showed higher frequency thanP. Paddicum in upland-field soil, whileP. paddicum showed higher frequency thanP. iwayamai in paddy-field soil. These findings indicate respectively higher colonization ability to organic matters ofP. iwayamai in upland-field soil andP. paddicum in paddy-field soil.This study was partly supported by a Grant-in-Aid (no. 63560048) from the Ministry of Education, Science and Culture, Japan.     

凝胶电冰与腐霉属的分类

用聚丙烯酰胺凝胶电泳技术分析27株计23种腐霉的菌体蛋白,结果表明:蛋白带型在种内表现出一致性,在种间则差异显著。     

Effect of Storage on the Survival and Biocontrol Activity of Pythium oligandrum in Pelleted Sugar Beet Seed

Seeds of sugar beet were pelleted with oospores of Pythium oligandrum and stored for 6 years at 8 20IC. Mycelium of P. oligandrum grew from pelleted seed when plated on cornmeal agar (CMA) within 48 h from 100% of seeds stored for 0, 2 and 4 years, and from 93% of seeds stored for 6 years. The germination of oospores removed from pelleted seed immediately after pelleting was 30% on CMA after 18 h of incubation, but storage gradually reduced germination to only 16% after 48 h of incubation for oospores removed from seed stored for 6 years. The biocontrol activity of P. oligandrum -pelleted seed was also tested after 6 years of storage in mixes of soil naturally infested with Pythium spp. and Aphanomyces cochlioides , and sand. P. oligandrum -pelleted seed had no effect in reducing damping-off due to the combined effect of Pythium spp. and A. cochlioides in 5 and 1% (v/v) soil-sand mixtures. However, in the 1% (v/v) soil-sand mixture, P. oligandrum significantly reduced Pythium spp.-induced damping-off from 33 to 26%.     

中国腐霉属的水生种类

腐霉属是一个世界广布分类群,迄今为止已报道约100种.它们主要分布于土坡中,条件适合时侵染植物引起病害,造成多种经济植物的重大损失.腐霉也见水中,它们既可寄生于藻类及一些小动物上,也可腐生于动植物残骸上.在研究微生物与水质关系时,腐霉的作用是不可忽视的.在发酵工业上,腐霉可望用于生产多种酶类及转化街族化合物,所以它是一个经济意义较重要的类群.     

Intraspecific and within-isolate sequence variation in the ITS rRNA gene region of Pythium mercuriale sp. nov. (Pythiaceae)

Sixteen Pythium isolates from diverse hosts and locations, which showed similarities in their morphology and sequences of the internal transcribed spacer (ITS) region of their rRNA gene, were investigated. As opposed to the generally accepted view, within single isolates ITS sequence variations were consistently found mostly as part of a tract of identical bases (A-T) within ITS1, and of GT or GTTT repeats within the ITS2 sequence. Thirty-one different ITS sequences obtained from 39 cloned ITS products from the 16 isolates showed high sequence and length polymorphisms within and between isolates. However, in a phylogenetic analysis, they formed a cluster distinct from those of other Pythium species. Additional sequencing of two nuclear genes (elongation factor 1 alpha and beta-tubulin) and one mitochondrial gene (nadh1) revealed high levels of heterozygosity as well as polymorphism within and between isolates, with some isolates possessing two or more alleles for each of the nuclear genes. In contrast to the observed variation in the ITS and other gene areas, all isolates were phenotypically similar. Pythium mercuriale sp. nov. (Pythiaceae) is characterized by forming thin-walled chlamydospores, subglobose to obovoid, papillate sporangia proliferating internally and smooth-walled oogonia surrounded by multiple antheridia. Maximum likelihood phylogenetic analyses based on both ITS and beta-tubulin sequence data place P. mercuriale in a clade between Pythium and Phytophthora.     

Prof. Dr. Lothar Behr

A damping-off disease of wheat was shown in a wheat field in Kidwan village, El-Minia city, Egypt, during December, 2000. Pythium diclinum was the causal agent of such disease and this is the first reported work of its isolation as a disease to wheat. Wheat seedlings collected from that field showed browning lesions at the basal part and wilting followed by damping-off. Examination of root pieces and other infected parts yielded only Pythium diclinum. The pathogen was characterized by its typically filamentous zoosporangia, diclinous antheridia and aplerotic thick-walled oospores. Pathogenicity of this fungus was determined on wheat under greenhouse conditions and P. diclinum was proved to be pathogenic on wheat. Two isolates of each of Gliocladium roseum and Trichoderma harzianum were tested for their bio-control activity against damping-off disease of wheat caused by P. diclinum. Incorporation of G. roseum or T. harzianum isolates into carboxymethylcellulose seed coating successfully eliminated pre-emergence damping-off of the wheat caused disease, whereas post-emergence damping-off was prevented by adding inocula of each of the two fungi separately to the infested soil with P. diclinum.     

New Pythium Taxa Causing Root Rot on Mediterranean Quercus Species in South-west Spain and Portugal

Pythium spiculum, a recently described new taxon, has been frequently isolated from declining Quercus rotundifolia and Q. suber roots and rhizosphere since 2003 in southern Iberia. In soils of declining Quercus forests this species was found as frequently as Phytophthora cinnamomi which, until now, was the only oomycete described as a Quercus root rot pathogen in the region. Inoculation tests conducted on young Q. rotundifolia plants showed that Py. spiculum is an aggressive root pathogen, although producing severities of symptoms significantly lower than those of P. cinnamomi. This new pathogen could play a role as decline factor in southern Iberia. Another new species, Py. sterilum, was also found to be pathogenic to Quercus roots but there are presently only few records of this organism isolated from rhizosphere of declining oaks in central Spain. More than an active decline factor, this species should be considered as a potential risk for Quercus forests.