Soft Rot Pathogen Research Articles

Green Synthesis of Silver Nanoparticles with Culture Supernatant of a Bacterium Pseudomonas rhodesiae and Their Antibacterial Activity against Soft Rot Pathogen Dickeya dadantii.

Bacterial stem and root rot disease of sweet potato caused by Dickeya dadantii recently broke out in major sweet potato planting areas in China and calls for effective approaches to control the pathogen and disease. Here, we developed a simple method for green synthesis of silver nanoparticles (AgNPs) using bacterial culture supernatants. AgNPs synthesized with the cell-free culture supernatant of a bacterium Pseudomonas rhodesiae displayed the characteristic surface plasmon resonance peak at 420–430 nm and as nanocrystallites in diameters of 20–100 nm determined by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. Functional groups associated with proteins in the culture supernatant may reduce silver ions and stabilize AgNPs. The AgNPs showed antibacterial activities against D. dadantii growth, swimming motility, biofilm formation, and maceration of sweet potato tubers whereas the culture supernatant of P. rhodesiae did not. AgNPs (12 µg∙ml−1) and AgNO3 (50 µg∙ml−1) showed close antibacterial activities. The antibacterial activities increased with the increase of AgNP concentrations. The green-synthesized AgNPs can be used to control the soft rot disease by control of pathogen contamination of sweet potato seed tubers.

A Flavor Lactone Mimicking AHL Quorum-Sensing Signals Exploits the Broad Affinity of the QsdR Regulator to Stimulate Transcription of the Rhodococcal qsd Operon Involved in Quorum-Quenching and Biocontrol Activities.

In many Gram-negative bacteria, virulence, and social behavior are controlled by quorum-sensing (QS) systems based on the synthesis and perception of N-acyl homoserine lactones (AHLs). Quorum-quenching (QQ) is currently used to disrupt bacterial communication, as a biocontrol strategy for plant crop protection. In this context, the Gram-positive bacterium Rhodococcus erythropolis uses a catabolic pathway to control the virulence of soft-rot pathogens by degrading their AHL signals. This QS signal degradation pathway requires the expression of the qsd operon, encoding the key enzyme QsdA, an intracellular lactonase that can hydrolyze a wide range of substrates. QsdR, a TetR-like family regulator, represses the expression of the qsd operon. During AHL degradation, this repression is released by the binding of the γ-butyrolactone ring of the pathogen signaling molecules to QsdR. We show here that a lactone designed to mimic quorum signals, γ-caprolactone, can act as an effector ligand of QsdR, triggering the synthesis of qsd operon-encoded enzymes. Interaction between γ-caprolactone and QsdR was demonstrated indirectly, by quantitative RT-PCR, molecular docking and transcriptional fusion approaches, and directly, in an electrophoretic mobility shift assay. This broad-affinity regulatory system demonstrates that preventive or curative quenching therapies could be triggered artificially and/or managed in a sustainable way by the addition of γ-caprolactone, a compound better known as cheap food additive. The biostimulation of QQ activity could therefore be used to counteract the lack of consistency observed in some large-scale biocontrol assays.

Emergence of apple bacterial quick decline caused by Dickeya dadantii in Japan

Since 2014 in some parts of Iwate Prefecture in Japan, an apple disease called quick decline (QD) has been reported. The causal agent was isolated from tissues with visible QD symptoms and identified as the soft-rot pathogen Dickeya dadantii by morphological, physiological, biochemical, phenotypic and genetic characterizations. To the best of our knowledge, this is the first report of apple QD disease caused by D. dadantii in Japan and in the world. Here, we propose calling this disease apple bacterial quick decline to distinguish from other diseases and physiological disorders.

Ochrobactrum quorumnocens sp. nov., a quorum quenching bacterium from the potato rhizosphere, and comparative genome analysis with related type strains.

Ochrobactrum spp. are ubiquitous bacteria attracting growing attention as important members of microbiomes of plants and nematodes and as a source of enzymes for biotechnology. Strain Ochrobactrum sp. A44T was isolated from the rhizosphere of a field-grown potato in Gelderland, the Netherlands. The strain can interfere with quorum sensing (QS) of Gram-negative bacteria through inactivation of N-acyl homoserine lactones (AHLs) and protect plant tissue against soft rot pathogens, the virulence of which is governed by QS. Phylogenetic analysis based on 16S rRNA gene alone and concatenation of 16S rRNA gene and MLSA genes (groEL and gyrB) revealed that the closest relatives of A44T are O. grignonense OgA9aT, O. thiophenivorans DSM 7216T, O. pseudogrignonense CCUG 30717T, O. pituitosum CCUG 50899T, and O. rhizosphaerae PR17T. Genomes of all six type strains were sequenced, significantly expanding the possibility of genome-based analyses in Ochrobactrum spp. Average nucleotide identity (ANIb) and genome-to-genome distance (GGDC) values for A44T and the related strains were below the single species thresholds (95% and 70%, respectively), with the highest scores obtained for O. pituitosum CCUG 50899T (87.31%; 35.6%), O. rhizosphaerae PR17T (86.80%; 34.3%), and O. grignonense OgA9aT (86.30%; 33.6%). Distinction of A44T from the related type strains was supported by chemotaxonomic and biochemical analyses. Comparative genomics revealed that the core genome for the newly sequenced strains comprises 2731 genes, constituting 50–66% of each individual genome. Through phenotype-to-genotype study, we found that the non-motile strain O. thiophenivorans DSM 7216T lacks a cluster of genes related to flagella formation. Moreover, we explored the genetic background of distinct urease activity among the strains. Here, we propose to establish a novel species Ochrobactrum quorumnocens, with A44T as the type strain (= LMG 30544T = PCM 2957T).

Genomic characterisation of the new Dickeya fangzhongdai species regrouping plant pathogens and environmental isolates

BackgroundThe Dickeya genus is part of the Pectobacteriaceae family that is included in the newly described enterobacterales order. It comprises a group of aggressive soft rot pathogens with wide geographic distribution and host range. Among them, the new Dickeya fangzhongdai species groups causative agents of maceration-associated diseases that impact a wide variety of crops and ornamentals. It affects mainly monocot plants, but D. fangzhongdai strains have also been isolated from pear trees and water sources. Here, we analysed which genetic novelty exists in this new species, what are the D. fangzhongdai-specific traits and what is the intra-specific diversity.ResultsThe genomes of eight D. fangzhongdai strains isolated from diverse environments were compared to 31 genomes of strains belonging to other Dickeya species. The D. fangzhongdai core genome regroups approximately 3500 common genes, including most genes that encode virulence factors and regulators characterised in the D. dadantii 3937 model strain. Only 38 genes are present in D. fangzhongdai and absent in all other Dickeyas. One of them encodes a pectate lyase of the PL10 family of polysaccharide lyases that is found only in a few bacteria from the plant environment, soil or human gut. Other D. fangzhongdai-specific genes with a known or predicted function are involved in regulation or metabolism.The intra-species diversity analysis revealed that seven of the studied D. fangzhongdai strains were grouped into two distinct clades. Each clade possesses a pool of 100–150 genes that are shared by the clade members, but absent from the other D. fangzhongdai strains and several of these genes are clustered into genomic regions. At the strain level, diversity resides mainly in the arsenal of T5SS- and T6SS-related toxin-antitoxin systems and in secondary metabolite biogenesis pathways.ConclusionThis study identified the genome-specific traits of the new D. fangzhongdai species and highlighted the intra-species diversity of this species. This diversity encompasses secondary metabolites biosynthetic pathways and toxins or the repertoire of genes of extrachromosomal origin. We however didn’t find any relationship between gene content and phenotypic differences or sharing of environmental habitats.

Threat of establishment of non-indigenous potato blackleg and tuber soft rot pathogens in Great Britain under climate change.

Potato blackleg and soft rot caused by Pectobacterium and Dickeya species are among the most significant bacterial diseases affecting potato production globally. In this study we estimate the impact of future temperatures on establishment of non-indigenous but confirmed Pectobacterium and Dickeya species in Great Britain (GB). The calculations are based on probabilistic climate change data and a model fitted to disease severity data from a controlled environment tuber assay with the dominant potato blackleg and soft rot-causing species in GB (P. atrosepticum), and three of the main causative agents in Europe (P. carotovorum subsp. brasiliense, P. parmentieri, Dickeya solani). Our aim was to investigate if the European strains could become stronger competitors in the GB potato ecosystem as the climate warms, on the basis of their aggressiveness in tubers at different temperatures. Principally, we found that the tissue macerating capacity of all four pathogens will increase in GB under all emissions scenarios. The predominant Pectobacterium and Dickeya species in Europe are able to cause disease in tubers under field conditions currently seen in GB but are not expected to become widely established in the future, at least on the basis of their aggressiveness in tubers relative to P. atrosepticum under GB conditions. Our key take-home messages are that the GB potato industry is well positioned to continue to thrive via current best management practices and continued reinforcement of existing legislation.

Short Communication: Isolation and identification of actinomycetes potential as the antagonist of Dickeya zeae pineapple soft rot in Lampung, Indonesia

Aeny TN, Prasetyo J, Suharjo R, Dirmawati SR, Efri, Niswati A. 2018. Isolation and Identification of actinomycetes potential as the antagonist of Dickeya zeae pineapple soft rot in Lampung, Indonesia. Biodiversitas 19: 2052-2058. This study was aimed to collect and identify actinomycetes from the rhizosphere of pineapple with the potency as a biocontrol agent of Dickeya zeae, the pathogen of pineapple soft rot. Soil samples were collected from four different pineapple plantations in Lampung Province, in December 2016. Samples were air-dried, serially diluted, and plated on modified ISP2 medium and several single characterized colonies were sub cultured and purified. The growing colonies were grouped into different colour series based on their aerial-mycelia and substrate-mycelia colors. Antagonistic activity of the actinomycetes isolates were evaluated against Dickeya zeae by agar diffusion method using the same medium agar lawn with the bacterial cultures. Selected antagonistic actinomycete isolates with the biggest clear zone formation were further characterized and identified molecularly based on 16S rDNA sequences. The results showed that as many as 34 actinomycete isolates collected from pineapple rhizosphere produced clear zones. Two isolates, namely GGF2-i5 and GGF4-i18, presented the biggest clear zone were proposed as the potential antagonist strains against D. zeae and identified as Streptomyces parvulus and Streptomyces hygroscopicus subsp. hygroscopicus, respectively. Both of the 16S rRNA gene sequences from those strains were deposited in the GenBank with the accession number MH170279 and MH170280, respectively.

Pectobacterium zantedeschiae sp. nov. a new species of a soft rot pathogen isolated from Calla lily (Zantedeschia spp.)

Four Gram-negative, rod-shaped pectinolytic bacterial strains designated as 2M, 9M, DPMP599 and DPMP600 were subjected to polyphasic analyses that revealed their distinctiveness from the other Pectobacterium species. Strains 2M and 9M were isolated from Calla lily bulbs cultivated in Central Poland. DPMP599 and DPMP600 strains were isolated from Calla lily leaves from plants grown in Serbia. Phylogenetic analyses based on nine housekeeping genes (gapA, gyrA, icdA, pgi, proA, recA, recN, rpoA, and rpoS), as well as phylogeny based on the 381 most conserved universal proteins confirmed that Pectobacterium zantedeschiae strains were distantly related to the other Pectobacterium, and indicated Pectobacterium atrosepticum, Pectobacterium betavasculorum, Pectobacterium parmentieri and Pectobacterium wasabiae as the closest relatives. Moreover, the analysis revealed that Pectobacterium zantedeschiae strains are not akin to Pectobacterium aroidearum strains, which were likewise isolated from Calla lily.The genome sequencing of the strains 2M, 9M and DPMP600 and their comparison with whole genome sequences of other Pectobacterium type strains confirmed their distinctiveness and separate species status within the genus based on parameters of in silico DNA–DNA hybridization and average nucleotide identity (ANI) values. The MALDI-TOF MS proteomic profile supported the proposition of delineation of the P. zantedeschiae and additionally confirmed the individuality of the studied strains. Based on of all of these data, it is proposed that the strains 2M, 9M, DPMP599, and DPMP600 isolated from Calla lily, previously assigned as P. atrosepticum should be reclassified as Pectobacterium zantedeschiae sp. nov. with the strain 9MT (PCM2893=DSM105717=IFB9009) as the type strain.

Bioinformatic analysis of the complete genome sequence of Pectobacterium carotovorum subsp. brasiliense BZA12 and candidate effector screening

Pectobacterium carotovorum subsp. brasiliense (Pcb) is a gram-negative, plant pathogenic bacterium of the soft rot Enterobacteriaceae (SRE) family. We present the complete genome sequence of Pcb strain BZA12, which reveals that Pcb strain BZA12 carries a single 4,924,809 bp chromosome with 51.97% GC content and comprises 4508 predicted protein-coding genes. Gene annotation of these genes utilized GO, KEGG, and COG databases. In comparison with three closely related soft-rot pathogens, strain BZA12 has 3797 gene families, among which 3107 gene families are identified as orthologous with those of both P. carotovorum subsp. carotovorum PCC21 and P. carotovorum subsp. odoriferum BCS7, as well as 36 putative Unique Gene Families. We selected five putative effectors from the BZA12 genome and transiently expressed them in Nicotiana benthamiana. Candidate effector A12GL002483 was localized in the cell nucleus and induced cell death. This study provides a foundation for a better understanding of the genomic structure and function of Pcb, particularly in the discovery of potential pathogenic factors and for the development of more effective strategies against this pathogen.

The Changing Face of Bacterial Soft-Rot Diseases.

Bacterial soft rot is a disease complex caused by multiple genera of gram-negative and gram-positive bacteria, with Dickeya and Pectobacterium being the most widely studied soft-rot bacterial pathogens. In addition to soft rot, these bacteria also cause blackleg of potato, foot rot of rice, and bleeding canker of pear. Multiple Dickeya and Pectobacterium species cause the same symptoms on potato, complicating epidemiology and disease resistance studies. The primary pathogen species present in potato-growing regions differs over time and space, further complicating disease management. Genomics technologies are providing new management possibilities, including improved detection and biocontrol methods that may finally allow effective disease management. The recent development of inbred diploid potato lines is also having a major impact on studying soft-rot pathogens because it is now possible to study soft-rot disease in model plant species that produce starchy vegetative storage organs. Together, these new discoveries have changed how we face diseases caused by these pathogens.

Efficiency of Vegetable Soft Rot Pathogen Pectobacterium carotovorum subsp. carotovorum(Pcc21) as a Host Cell for Foreign Gene Expression

외래유전자 형질발현을 증폭하기 위해 형질발현 벡터의 개발뿐만 아니라 박테리아, 곰팡이, 효모, 곤충, 식물 및 동물세포와 같은 다양한 숙주세포의 개발이 시도되어 왔다. 특히 DH5α, XL1-blue, Top10 및 BL21과 같은 대장균(Escherichia coli)는 단백질 생산과 형질전환에 가장 널리 사용되고 있는 숙주 중 하나이며, LBA4404, GV3101 및 EHA105와 같은 아그로박테리움(Agrobacterium tumefaciens)은 식물 형질전환에 흔히 사용되고 있다. 그러나 여전히 의학 및 생명공학 분야에서는 단백질 생산을 위한 새로운 숙주세포 개발에 대한 요구가 있다. 최근 감자 무름병균인 펙토박테리아(Pectobacterium carotovorum subsp. carotovorum)는 사용의 편리함 때문에 새로운 숙주세포로써의 가능성에 대한 관심을 얻게 되었다. 이번 연구에서 E. coli(DH5α), A. tumefaciens(LBA4404) 및 P. carotovorum(Pcc21)을 포함하는 다양한 숙주세포에서 GFP 단백질생산 효율을 조사하였다. GFP 전사량은 RT-PCR로 확인하였고 단백질은 Western blot 분석으로 분석하였다. 그 결과 Pcc21은 DH5α와 LBA 4404와 비교했을 때 30% 정도 더 높은 GFP 단백질을 생산하였고 전사량 또한 증가하였다. 따라서 펙토박테리아 Pcc21이 외래 단백질 발현을 위한 새로운 숙주세포로써의 가능성이 높은 것으로 생각된다. 더 나아가 펙토박테리아는 쉽게 식물에 감염되기 때문에 A. tumefaciens 대신 식물의 일시적, 영구적 형질전환을 위한 숙주세포로 사용할 수 있을 것이라 생각된다.

Calcium soil amendment increases resistance of potato to blackleg and soft rot pathogens

Dickeya and Pectobacterium species cause blackleg / soft rot disease complex on potato in Zimbabwe. The disease is seedborne and difficult to control. This research focused on ways of increasing the inherent resistance of potato plants and tubers to blackleg and soft rot. Two field experiments were conducted at the University of Zimbabwe campus plots in 2008/9 and 2009/10 seasons in order to determine reproducibility of the results. Sprouted tubers of cv. BP1 were inoculated with a mixture of Pectobacterium atrosepticum, Pectobacterium carotovorum subsp. brasiliense and Dickeya dadantii. The inoculated tubers were planted in plots treated with different fertilizer combinations. The treatments were: 1) compound S (7N: 21P: 8K) + ammonium nitrate (34 %N); 2) compound D (7N: 14P: 7K) + calcium nitrate (19 Ca: 15.5N); 3) compound S + calcium nitrate and 4) compound D + ammonium nitrate. Blackleg disease incidence and severity were recorded fortnightly starting from 2 weeks after crop emergence (WACE) while soft rot disease was assessed at physiological maturity. Blackleg incidences and severity were significantly lower (P < 0.05) in the plots where calcium nitrate was applied for both experiments. Blackleg disease incidence was reduced by more than 20% in both experiments 1 and 2. Soft rot incidence in the progeny tubers was also significantly reduced by the calcium treatment. In addition, calcium amendment significantly reduced (P < 0.05) soft rot losses of tubers in storage. Calcium nitrate was effective in reducing blackleg and soft rot diseases in combination with either compound D or compound S. The yield was significantly higher in plots where compound S was applied as a basal fertilizer than that recorded in plots treated with compound D fertilizer. This study shows that calcium soil amendments reduce blackleg and soft rot diseases under Zimbabwe’s growing seasons in red fersiallitic soils. Compound S produces better results in potato production than compound D and farmers should be encouraged to use compound S when growing potatoes. Key words : potato, disease resistance, blackleg, soft rot, storage losses, calcium: potato, disease resistance, blackleg, soft rot, storage losses, calcium

Effect of ginger endophyte Rhizopycnis vagum on rhizome bud formation and protection from phytopathogens

Abstract Most of the microorganisms residing within the plants are likely to be beneficial to the host plants as they either inhibit phytopathogens or promote plant growth. In the current study, endophytic fungal isolate from Zingiber officinale Rosc. with antagonism to soft rot pathogen Pythium myriotylum was investigated for its broad antiphytopathogenic properties. The crude extract prepared from the organism was found to have activity against various phytopathogens which was confirmed by scanning electron microscopic analysis. The isolate was identified as Rhizopycnis vagum by ITS sequencing. Remarkably, during the rhizome protection studies, the organism was found to prevent P. myriotylum infection in ginger with associated enhancement in germination and bud development. Hence the result is indication of role of endophytic fungi as highly promising and broad spectrum plant probiotic agent.

Chemical composition, antioxidant capacity and antibacterial activity against some potato bacterial pathogens of fruit extracts from Phytolacca dioica and Ziziphus spina-christi grown in Egypt

Abstract In the present study, the effects of n-hexane extracts from Phytolacca dioica L. and Ziziphus spina-christi L. fruits were evaluated against the growth of potato brown and soft rot bacterial pathogens, namely, Ralstonia solanacearum, Dickeya solani, Pectobacterium carotovorum subsp. carotovorum, Enterobacter cloacae, and Bacillus pumilus. The chemical components of the oils were analyzed using GC/MS, and the antioxidant activity was determined using 2,2-dipheny-1-picrylhydrazyl radical-scavenging (DPPH) and β-carotene-linoleic acid assays. Aromatic hydrocarbons such as 6-phenyl-dodecane and 7-phenyl-tridecane were the most abundant compounds identified in n-hexane from both fruits. Also, some volatile compounds such as α-citronellol (2.46%), and dodecane (2.27%) were found in P. dioica and m-cymene (1.95%), crypton (1.58%), and α-pinene (1.20%) found in Z. spina-christi fruit extracts. Z. spina-christi fruit extract showed antioxidant activity, with IC50 values of 5.5 ± 0.1 and 4.1 ± 0.1 μg/mL, while P. dioica fruit extract showed values of 5.2 ± 0.1 and 6.3 ± 0.1 μg/mL, as measured by DPPH and β-Carotene-linoleic acid, respectively. The minimum inhibitory concentration values for Z. spina-christi fruit extract ranged from 32 to 125 μg/mL against the studied bacteria. For P. dioica, the MIC values ranged from 32 to 64 μg/mL. The extracts from P. dioica and Z. spina-christi fruits exhibited different levels of activities against the growth of potato brown rot, soft rot and blackleg bacterial pathogens.

Exogenous application of phenylacetic acid promotes root hair growth and induces the systemic resistance of tobacco against bacterial soft-rot pathogen Pectobacterium carotovorum subsp. carotovorum.

Phenylacetic acid (PAA) was evaluated for its capability to promote plant growth and induce systemic resistance in tobacco (Nicotianum tabacum L cv. Xanthi) against the bacterial soft rot pathogen Pectobacterium carotovorum subsp. carotovorum (PCC). Exogenous application of PAA influenced root formation, the activities of defence-related enzymes and the expression of defence and growth-related genes. Increased formation of lateral roots can be observed in tobacco treated with higher PAA concentrations. The highest elicitation of induced systemic resistance (ISR) was found in plants treated with 0.5mM PAA, where the phytotoxic effect was minimal. The activities of the defence enzymes phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphnenoloxidase (PPO) were modulated upon treatment with different PAA concentrations. Reverse transcription-PCR analyses showed that 0.5mM PAA modulated the expression of the growth-related genes NtEXP2 and NtEXP6, and the defence-related genes Coi1, NPR1, PR-1a and PR-1b. These results showed that different concentrations of PAA can elicit different responses and effects on tobacco growth and resistance. This study presents the important role of PAA not only on plant growth but also for plant immunity against phytopathogens.

Metabolite analysis of endophytic fungi from cultivars of Zingiber officinale Rosc. identifies myriad of bioactive compounds including tyrosol

Endophytic fungi associated with rhizomes of four cultivars of Zingiber officinale were identified by molecular and morphological methods and evaluated for their activity against soft rot pathogen Pythium myriotylum and clinical pathogens. The volatile bioactive metabolites produced by these isolates were identified by GC–MS analysis of the fungal crude extracts. Understanding of the metabolites produced by endophytes is also important in the context of raw consumption of ginger as medicine and spice. A total of fifteen isolates were identified from the four varieties studied. The various genera identified were Acremonium sp., Gliocladiopsis sp., Fusarium sp., Colletotrichum sp., Aspergillus sp., Phlebia sp., Earliella sp., and Pseudolagarobasidium sp. The endophytic community was unique to each variety, which could be due to the varying host genotype. Fungi from phylum Basidiomycota were identified for the first time from ginger. Seven isolates showed activity against Pythium, while only two showed antibacterial activity. The bioactive metabolites identified in the fungal crude extracts include tyrosol, benzene acetic acid, ergone, dehydromevalonic lactone, N-aminopyrrolidine, and many bioactive fatty acids and their derivatives which included linoleic acid, oleic acid, myristic acid, n-hexadecanoic acid, palmitic acid methyl ester, and methyl linoleate. The presence of these varying bioactive endophytic fungi may be one of the reasons for the differences in the performance of the different ginger varieties.

Characterization of the rcsA Gene from Pantoea sp. Strain PPE7 and Its Influence on Extracellular Polysaccharide Production and Virulence on Pleurotus eryngii.

RcsA is a positive activator of extracellular polysaccharide (EPS) synthesis in the Enterobacteriaceae. The rcsA gene of the soft rot pathogen Pantoea sp. strain PPE7 in Pleurotus eryngii was cloned by PCR amplification, and its role in EPS synthesis and virulence was investigated. The RcsA protein contains 3 highly conserved domains, and the C-terminal end of the open reading frame shared significant amino acid homology to the helix-turn-helix DNA binding motif of bacterial activator proteins. The inactivation of rcsA by insertional mutagenesis created mutants that had decreased production of EPS compared to the wild-type strain and abolished the virulence of Pantoea sp. strain PPE7 in P. eryngii. The Pantoea sp. strain PPE7 rcsA gene was shown to strongly affect the formation of the disease symptoms of a mushroom pathogen and to act as the virulence factor to cause soft rot disease in P. eryngii.

Putative new species of the genus Dickeya as major soft rot pathogens in Phalaenopsis orchid production

Bacterial soft rots are a serious limitation to the production of orchids and other horticultural plants. Here, the characterization of causative bacteria isolated from Phalaenopsis orchids showing symptoms, from a commercial production site, is reported. The most commonly isolated bacteria were identified as Dickeya spp. Partial sequencing of 16S rDNA, fliC and dnaX showed diversity among the isolates and divided the isolates into two groups, with greatest similarity to previously reported undefined Dickeya lineages from orchids (UDL‐3 and UDL‐4). Two isolates (B16, S1) were sequenced using next‐generation sequencing, which has provided draft genomes of these two isolates for further studies (Alič et al., ). Newly developed fliC‐based lineage‐specific quantitative real‐time PCR assays were used to distinguish among the lineages and to assess their relative abundances in diseased tissues. Virulence and aggressiveness comparison tests in vivo on Phalaenopsis orchids, potato plants and witloof chicory leaves indicated high virulence and extreme maceration potential of these novel Dickeya isolates, compared to a reference panel of other Dickeya spp. Pantoea cypripedii (formerly Pectobacterium cypripedii), which has previously been reported as a soft rot pathogen of orchids, was not detected, and isolates obtained from culture collections did not cause symptoms on artificially infected Phalaenopsis orchids.

Characterization of Dickeya and Pectobacterium strains obtained from diseased potato plants in different climatic conditions of Norway and Poland

Soft rot and blackleg of potato caused by pectinolytic bacteria lead to severe economic losses in potato production worldwide. To investigate the species composition of bacteria causing soft rot and black leg of potato in Norway and Poland, bacteria were isolated from potato tubers and stems. Forty-one Norwegian strains and 42 Polish strains that formed cavities on pectate medium were selected for potato tuber maceration assays and sequencing of three housekeeping genes (dnaX, icdA and mdh) for species identification and phylogenetic analysis. The distribution of the species causing soft rot and blackleg in Norway and Poland differed: we have demonstrated that mainly P. atrosepticum and P. c. subsp. carotovorum are the causal agents of soft rot and blackleg of potatoes in Norway, while P. wasabiae was identified as one of the most important soft rot pathogens in Poland. In contrast to the other European countries, D. solani seem not to be a major pathogen of potato in Norway and Poland. The Norwegian and Polish P. c. subsp. carotovorum and P. wasabiae strains did not cluster with type strains of the respective species in the phylogenetic analysis, which underlines the taxonomic complexity of the genus Pectobacterium. No correlation between the country of origin and clustering of the strains was observed. All strains tested in this study were able to macerate potato tissue. The ability to macerate potato tissue was significantly greater for the P. c. subsp. carotovorum and Dickeya spp., compared to P. atrosepticum and P. wasabiae.

Analyses between Reproductive Behavior, Genetic Diversity and Pythium Responsiveness in Zingiber spp. Reveal an Adaptive Significance for Hemiclonality.

Mode of reproduction is generally considered to have long-range evolutionary implications on population survival. Because sexual reproduction produces genetically diverse genotypes, this mode of reproduction is predicted to positively influence the success potential of offspring in evolutionary arms race with parasites (Red queen) whereas, without segregation and recombination, the obligate asexual multiplication may push a species into extinction due to the steady accumulation of deleterious mutations (Muller’s ratchet). However, the extent of linearity between reproductive strategies, genetic diversity and population fitness, and the contributions of different breeding strategies to population fitness are yet to be understood clearly. Genus Zingiber belonging to the pan-tropic family Zingiberaceae represents a good system to study contributions of different breeding behavior on genetic diversity and population fitness, as this genus comprises species with contrasting breeding systems. In this study, we analyzed breeding behavior, amplified fragment length polymorphism diversity and response to the soft-rot pathogen Pythium aphanidermatum in 18 natural populations of three wild Zingiber spp.: Z. neesanum, Z. nimmonii, and Z. zerumbet, together with the obligately asexual cultivated congener, ginger (Z. officinale). Ginger showed an exceptionally narrow genetic base, and adding to this, all the tested cultivars were uniformly susceptible to soft-rot. Concordant with the postulates of Muller’s ratchet, the background selection may be continuously pushing ginger into the ancestral state, rendering it inefficient in host-pathogen coevolution. Z. neesanum and Z. nimmonii populations were sexual and genetically diverse; however, contrary to Red Queen expectations, the populations were highly susceptible to soft-rot. Z. zerumbet showed a hemiclonal breeding behavior. The populations inhabiting forest understory were large and continuous, sexual and genetically diverse, but were susceptible, whereas populations inhabiting the revenue land were fragmented and monoclonal, but were resistant. It may be possible that, when genetic recombination becomes at a premium due to the genetic constraints imparted by habitat fragmentation or pathogen pressure, Z. zerumbet