Polymorphisms and Evolution of Solanum bulbocastanum Genes for Broad-Spectrum Resistance to Phytophthora infestans

Russian Journal of Plant Physiology - For two decades, Solanum bulbocastanum Dun. has been challenging potato geneticists with its durable resistance to Phytophthora infestans Mont. de Bary, the...     

Effect of Bacillus Bacteria on Hydrogen Peroxide Content and Gene Expression of Hydrolase Inhibitors in Potato Plants Infected with Phytophthora infestans (Mont.) de Bary

Russian Journal of Plant Physiology - Late blight of potato (Solanum tuberosum L.) caused by the oomycete Phytophthora infestans (Mont.) de Bary was studied in respect to the disease resistance...     

Specificity of cytoplasmic and cell-wall antigens from four species of Phytophthora.

Cytoplasmic and cell-wall antigens and antisera were prepared from four Phytophthora species, and cell-wall antigens were prepared from two Pythium species. Immunodiffusion of the Pythium and Phytophthora cell-wall antigens showed that the two Pythium species did not cross-react with the Phytophthora cell-wall antisera. Immunodiffusion analysis of both cell-wall and cytoplasmic antigens of Phytophthora revealed some degree of specificity between species but not between A1 and A2 mating types in Phytophthora cinnamomi. Species specificity was improved by using indirect fluorescent antibody techniques and by the use of cross-absorbed sera. Agglutination and quantitative precipitation techniques did not significantly improve specificity. It was possible to distinguish serologically between Phytophthora cinnamomi and Phytophthora cambivora and the Phytophthora cryptogea-Phytophthora drechsleri group. The absence of consistent serological variation between P. cryptogea and P dreschsleri is consistent with the suggestion (Bumbieris, 1974) that P. cryptogea and P. drechsleri should be considered as one species.     

Differential uptake and metabolism of sitosterol and cholesterol by Achlya, Pythium, and Phytophthora species.

The relative ability of isolates of Achlya bisexualis and A. ambisexualis and isolates of Pythium and Phytophthora to take up and metabolize sitosterol and cholesterol was studied. Species of Pythium and Phytophthora took up cholesterol and sitosterol efficiently, whereas Achlya species took up booth sterols inefficiently. Species of Pythium and Phytophthora produced a polar metabolite and esters from sitosterol as they did from cholesterol. Achlya species did not produce the polar metabolite from either sterol. In these experiments Achlya species produced esters only from cholesterol; however, their failure to produce esters from sitosterol may have been due to the higher sitosterol than cholesterol concentration.     

基于rDNA ITS序列探讨部分腐霉种的系统发育与其形态特征

基于对73株计58种腐霉和6种疫霉的核糖体DNA的ITS序列分析,以海生疫霉为外围群,按邻接法构建系统发育树,对腐霉的系统发育关系进行了研究。结果表明:在58种腐霉中,Pythium ostracodes,P.chamaehyphon,P.carbonicum,P.montanum和P.vexans归为同一组,介于其它腐霉和疫霉之间,这5种腐霉的孢子囊均为球形;现已归为疫霉属的P.undulatum 单独为一组,它与腐霉的亲缘关系比疫霉更近;其余52种腐霉聚成一大组,这52种腐霉基本上按孢子囊或菌丝膨大体形态分成Ⅰ、Ⅱ两组:第1组31种腐霉, 其中30种腐霉的孢子囊或菌丝膨大体为球形;第Ⅱ组21种腐霉,其中19种腐霉的孢子囊为丝状、瓣状或裂片状。基于ITS序列分析,腐霉属的其它性状如藏卵器壁是否光滑、卵孢子是否满器、雄器的着生方式和数量、异宗配合等呈多元演化。     

Two Widely Accessible Media for Growth and Reproduction of Phytophthora and Pythium Species

Tomato agar and soybean agar were found to be comparable to or in some cases better than the popular V8 vegetable juice agar in supporting linear growth of Phytophthora cactorum, Phytophthora capsici, Phytophthora parasitica, Pythium aphanidermatum, and Pythium splendens; sporangium production of P. capsici, P. palmivora, and Pythium splendens; and oospore formation of P. cactorum, P. parasitica, Pythium aphanidermatum and Pythium splendens. These two media with readily accessible ingredients can be used to substitute for V8 juice agar in pathological and physiological studies of these two important groups of fungi in countries where V8 vegetable juice is not available or difficult to obtain.     

Potassium homeostasis influences the locomotion and encystment of zoospores of plant pathogenic oomycetes

Zoospores of plant pathogenic oomycetes exhibit distinct swimming speeds and patterns under natural conditions. Zoospore swimming is influenced by ion homeostasis and changes in the ionic composition of media. Therefore, we used video microscopy to investigate swimming patterns of five oomycete species in response to changes in potassium homeostasis. In general, zoospore speed tended to be negatively correlated with zoospore size. Three Phytophthora species (Phytophthora palmivora, Phytophthora megakarya, and Phytophthora infestans) swam in straight patterns with speeds ranging from 50 to 250 microm/s whereas two Pythium species (Pythium aphanidermatum and Pythium dissotocum) swam at similar speeds ranging from 180 to 225 microm/s with a pronounced helical trajectory and varying amplitudes. High external concentrations of potassium salts reduced the swimming speed of Ph. palmivora and induced encystment. This was not observed for Py. aphanidermatum. Application of the potassium ionophores gramicidin, nigericin and valinomycin resulted in reduced swimming speeds and changes in the swimming patterns of the Phytophthora species. Therefore, potassium ions play a key role in regulating zoospore behavior.     

Phylogenetic relationships of Pythium and Phytophthora species based on ITS rDNA, cytochrome oxidase II and beta-tubulin gene sequences

Fifty-eight isolates representing 39 Pythium species and 17 isolates representing nine Phytophthora species were chosen to investigate intra- and intergeneric relationships with sequence analysis of three genomic areas. The internal transcribed spacer regions (ITS1 and ITS2), including the 5.8S gene of the ribosomal DNA were PCR amplified with the universal primers ITS1 and ITS4. On the other hand 563 bp of the cytochrome oxidase II (cox II) gene was amplified with the primer pair FM66 and FM58 for Pythium and FM75 and FM78 for Phytophthora. The 658 bp partial beta-tubulin gene was amplified with the forward primer BT5 and reverse primer BT6. Maximum parsimony analysis of the three DNA regions revealed four major clades, reflective of sporangial morphology. Clade 1 was composed of Pythium isolates that bear filamentous to lobulate sporangia. Clade 2 represents Pythium isolates that bear globose to spherical zoosporangia or spherical hyphal swellings. Meanwhile Phytophthora isolates were lumped into Clade 3 wherein the papillate, semipapillate and nonpapillate species occupied separate subclades. Lastly, Clade 4 was composed of Pythium species that bear subglobose sporangia resembling the papillate sporangia observed in Phytophthora. Hence a number of species (Ph. undulata, P. helicoides, P. ostracodes, P. oedochilum and P. vexans) have been proposed to be the elusive intermediate species in the Pythium-to-Phytophthora evolutionary line.     

Paenibacillus polymyxa antagonizes oomycete plant pathogens Phytophthora palmivora and Pythium aphanidermatum

Aim:  To find sustainable alternatives to the application of synthetic chemicals for oomycete pathogen suppression.
Methods and Results:  Here, we present experiments on an Arabidopsis thaliana model system in which we studied the antagonistic properties of rhizobacterium Paenibacillus polymyxa strains towards the oomycete plant pathogens Phytophthora palmivora and Pythium aphanidermatum . We carried out studies on agar plates, in liquid media and in soil. Our results indicate that P. polymyxa strains significantly reduced P. aphanidermatum and P. palmivora colonization in liquid assays. Most plants that had been treated with P. polymyxa survived the P. aphanidermatum inoculations in soil assays.
Conclusions:  The antagonistic abilities of both systems correlated well with mycoidal substance production and not with the production of antagonistic substances from the biocontrol bacteria.
Significance and Impact of the Study:  Our experiments highlight the need to take biofilm formation and niche exclusion mechanisms into consideration for biocontrol assays performed under natural conditions.     

A molecular phylogeny of Phytophthora and related oomycetes

Phylogenetic relationships among 50 Phytophthora species and between Phytophthora and other oomycetes were examined on the basis of the ITS sequences of genomic rDNA. Phytophthora grouped with Pythium, Peronospora, and Halophytophthora, distant from genera in the Saprolegniales. Albugo was intermediate between these two groups. Unlike Pythium, Phytophthora was essentially monophyletic, all but three species forming a cluster of eight clades. Two clades contained only species with nonpapillate sporangia. The other six clades included either papillate and semipapillate, or semipapillate and nonpapillate types, transcending traditional morphological groupings, which are evidently not natural assemblages. Peronospora was related to P. megakarya and P. palmivora and appears to be derived from a Phytophthora that has both lost the ability to produce zoospores and become an obligate biotroph. Three other Phytophthoras located some distance from the main Phytophthora-Peronospora cluster probably represent one or more additional genera.     

Direct observation of the structure of mycelial cell walls from the potato blight fungus Phytophthora infestans by solid-state 13C NMR

Mycelial cell walls from the potato blight fungus ( Phytophthora infestans ) (Mont.) de Bary were examined in the solid state by ¹³C nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning. The spectrum was free from interference by spinning sidebands. The main component of the cell walls had the spectral properties of a β -(1,3')-glucan. Protein appeared to be present also. The presence of β -(1,6')-linked glucose residues, cellulose or chitin was not ruled out, but there was no evidence for these as major components of the cell walls.     

Late blight on potato is suppressed by the biosurfactant-producing strain Pseudomonas koreensis 2.74 and its biosurfactant

Potato late blight disease caused by the zoospore-producing pathogen Phytophthora infestans (Mont.) de Bary is one of the most destructive plant diseases world-wide and currently its management mainly relies on the frequent use of fungicides. This study investigated the possibility of reducing potato late blight by biocontrol with the biosurfactant-producing strain Pseudomonas koreensis 2.74. Significant disease reduction with the biosurfactant-producing strain and its biosurfactant was observed in greenhouse trials using a detached-leaf assay. A direct effect of the biosurfactant on zoospores of P. infestans was also observed, whereas the biosurfactant only caused a minor reduction in mycelial growth rate and had no effect on the rate of sporangia production in pure culture.     

Exoproteinases of the oomycete Phytophthora infestans

When grown in a medium containing heat-stable potato tuber proteins, the oomycete Phytophthora infestans (Mont.) de Bary produces a set of exoproteinases active at neutral and mildly basic pH values. These extracellular proteinases have been shown by SDS-PAGE with the presence of gelatin to include at least six components differing in molecular weight. Inhibitory analysis and study of the effects of the enzymes on various synthetic substrates show that the culture liquid of P. infestans contains mainly serine proteinases specific to trypsin and subtilisin and metalloproteinases. Their activity is suppressed by proteinase-inhibitor proteins from potato tubers. It is suggested that P. infestans exoproteinases may be the metabolic target for natural proteinase inhibitors from potato.     

Activation of elicitor defensive properties by systemic signal molecules during the interaction between potato and Phytophthora

The elicitor arachidonic acid in combination with jasmonic acid (JA) induced a higher level of defense against the late blight agent in potato (Solanum tuberosum L.) tissues than in combination with salicylic acid (SA). On the contrary, the elicitor chitosan displayed a higher inductive effect in combination with SA as compared with JA. The optimal concentrations of tested compounds were selected for designing the compositions activating wound repair, induction of proteinase inhibitors, and resistance to the biotrophic pathogen Phytophthora infestans (Mont.) de Bary. It was demonstrated that the compositions of elicitor and systemic signal molecules provided a faster spreading of an inducing effect in the potato tissues.     

Occurrence of Pythium spp. and Phytophthora spp. in Norwegian Greenhouses and their Pathogenicity on Cucumber Seedlings

Samples of tomato, lettuce and cucumber submitted for diagnosis to the Plant Protection Centre at the Norwegian Crop Research Institute and samples of soil, water and cucumber collected from greenhouses employing hydroponic cultures were examined for the occurrence of Pythium spp. and Phytophthora spp. Two species of Phytophthora and 16 species of Pythium were identified. Phytophthora cryptogea was found on tomato and lettuce. Phytophthora nicotianae was found on tomato fruit. Phytophthora was not found on cucumbers. Pythium irregulare and Pythium group F were the two most commonly found Pythium species in hydroponically cultivated cucumbers. A pathogenicity test with 56 isolates was performed on cucumber seedlings. The most aggressive species were Pythium aphanidermatum, P. irregulare, Pythium paroecandrum and Pythium ultimum.     

Pythium vexans Causing Stem Rot of Dendrobium in Yunnan Province,China

Since 2002 a severe root and stem disease of Dendrobium has occurred periodically each year in the plantations of Simao City, Yunnan Province, China. Symptoms included water‐soaked and brown lesions, and rot of tissues. Based on the morphological characteristics and the internal transcribed spacer‐1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2 and β‐tubulin gene sequences, the pathogen was identified as Pythium vexans de Bary. The pathogenicity of the fungus was confirmed by satisfying Koch’s postulates. This is the first world record of stem rot of Dendrobium caused by P. vexans.     

马铃薯非共生血红蛋白基因StHb1的克隆及表达

采用RT-PCR技术成功分离了马铃薯StHb1基因序列.经半定量RT-PCR分析表明,StHb1基因的表达在抗性品种(陇薯三号)和感性品种(荷兰十五)块茎中均受致病疫霉的侵染所抑制;StHb1基因在正常生长的马铃薯块茎组织中表达量最高;外源NO和H2O2的作用可明显地抑制StHb1基因的表达,但在抗性品种中该基因受抑制的程度低于感性品种.上述试验结果暗示了StHb1基因与马铃薯对致病疫霉侵染的抗性应答具有一定的相关性.     

Boosting the Immune System of Solanaceous Plants by Lysophosphatidylcholine

An in vitro treatment of solanaceous plants, viz. potato (Solanum tuberosum L.) and tobacco (Nicotiana tabacum L.), with lysophosphatidylcholine promoted their resistance to phytopathogens, such as Phytophthora infestans (Mont.) de Bary and potato virus Y. The systemic and long-term lysophospholipid-induced response was independent of the phytopathogen type. It was concluded that lysophosphatidylcholine, a product of phosphatidylcholine hydrolysis with phospholipase A₂, plays an important role in the regulation of plant immune system.     

一种土壤中大豆疫霉菌分离新方法*

由于腐霉菌的干扰,土壤中大豆疫霉菌的分离十分困难。利用大豆疫霉菌的致病性和大豆对病原菌的选择作用排除腐霉菌,我们建立了一种简单、有效的土壤中大豆疫霉菌的分离方法。该方法用不含抗大豆疫霉根腐病基因的大豆叶碟诱钓大豆疫霉菌的游动孢子,将诱钓叶碟直接接种不含抗大豆疫霉菌基因的大豆植株,再对病株进行选择性或非选择性分离获得大豆疫霉菌。此方法能十分有效地排除腐霉菌干扰和细菌的污染,直接获得纯化菌株。应用该方法我们在以前未报道有大豆疫霉根腐病发生的山东、河南、安徽、江苏和浙江分离到大豆疫霉菌。