Epidemiological evidence for the emergence of a new pathogenic variant of Ralstonia solanacearum in Martinique (French West Indies)

The emergence of a new genotype and pathogenic variant of Ralstonia solanacearum in Martinique is described. Bacterial wilt of solanaceous crops caused by phylotype‐I and ‐II strains (‘historical strains’), was reported in Martinique in the 1960s. From 1999, Anthurium and cucurbit production was strongly affected by strains described as a new pathogenic variant genotyped phylotype IIB/sequevar4NPB (phIIB/4NPB). The following questions concerning these strains were investigated: (i) were they introduced or endemic, (ii) was their distribution widespread in Martinique, and (iii) which factors could explain this emergence? This study examined 221 isolates collected from 1989 to 2003 after several surveys. The main survey (2002–03) included 115 vegetable and ornamental crop farms. From 1999 to 2001, these phIIB/4NPB strains were initially described as the ‘Anthurium‐cucurbit’ strain. In 2003, they made up one‐third of the isolates recovered from solanaceous hosts, particularly tomato. This pathogenic variant of R. solanacearum was consistently recovered from wild species and several weeds throughout Martinique, suggesting that these strains were well established in Martinique. Data reported are consistent with the emergence of a new population of R. solanacearum in Martinique, which has spread rapidly across the entire island and may overtake the previously established population, particularly on tomatoes. Evidence is presented which suggests that the emergence of these new strains is more frequent on vegetable crops when cucurbitaceous and musaceous plants are grown in succession.     

Characterization of Erwinia sp. causing black rot of papaya (Carica papaya) first recorded in Okinawa Main Island,Japan

Since 2002, papaya black rot has been spreading over several islands of Okinawa Prefecture, Japan. To devise a prevention strategy for the disease, microbiological research on the pathogen was conducted. Twelve strains were isolated from papaya infected with black rot showing symptoms such as water-soaked lesions on stems and petioles, black spots on fruits, and rotted leaves turning yellow with necrotic spots. Through Koch's postulates, we confirmed that the isolated strains caused papaya black rot. Bacteriological assays showed that the strains have characteristics different from the type strains of Erwinia mallotivora, E. papayae, and E. psidii. Moreover, 16S rDNA sequence similarity searches showed that the isolated strains had less than 98.6% similarity with type strains. Additionally, phylogenetic analysis of 16S rDNA sequences suggested that the isolated strains were possibly a novel species belonging to the genus Erwinia, as the strains formed an independent cluster and had low sequence similarity with the type strains. Earlier studies indicated that papaya black rot is caused by E. cypripedii. Therefore, we propose to add the Erwinia sp. isolated in this study to the list of papaya black rot pathogens.     

湖南水稻上1种新矮缩病的病原研究

 Summer rice was suffered extensive damage from a new dwarf disease in Hunan Province in year 2009. In this study, the causal agent of this disease was confirmed as Southern rice black-streaked dwarf virus (SRBSDV) by nested RT-PCR, RT-PCR and PCR product sequencing.     

Resistance in water yam (Dioscorea alata) cultivars in the French West Indies to anthracnose disease based on tissue culture-derived whole-plant assay

Reactions of 60 water yam ( Dioscorea alata ) cultivars to three isolates of the yam anthracnose fungal pathogen ( Colletotrichum gloeosporioides ) were evaluated using tissue culture-derived whole-plant assay. Three disease parameters: single score on a scale of 0–6 at the seventh day after inoculation (SD7); area under the disease progress curve (AUDPC); and disease progress rate ( R _d) were compared, and cultivars were classified into disease-response groups using a rank-sum method based on AUDPC scores for the two most virulent isolates. A wide range of variation in resistance of the D. alata cultivars, and significant effects of pathogen isolate and isolate–cultivar interactions, were observed for all disease parameters. The three disease parameters were positively correlated; however, four cultivars showed great dispersions from the regression lines for comparisons of SD7 with the multiple assessments based AUDPC and R _d. The 60 cultivars were separated into resistant ( n  = 12), moderately resistant ( n  = 19), moderately susceptible ( n  = 18) and susceptible ( n  = 11) groups. The potential of the tissue culture-derived whole-plant assay to resistance breeding programmes and further understanding of the yam anthracnose pathosystem is discussed.     

Studies on the interaction between the biocontrol agent,Serratia plymuthica A30, and blackleg‐causing Dickeya sp. (biovar 3) in potato (Solanum tuberosum)

Interactions between Serratia plymuthica A30 and a blackleg‐causing biovar 3 Dickeya sp. were examined. In a potato slice assay, S. plymuthica A30 inhibited tissue maceration caused by Dickeya sp. IPO2222 when co‐inoculated at a density at least 10 times greater than that of the pathogen. In glasshouse experiments, population dynamics of the antagonist and of the pathogen in planta were studied by dilution plating and confocal laser scanning microscopy (CLSM) using fluorescent protein‐tagged strains. Pathogen‐free minitubers were vacuum‐infiltrated with DsRed‐tagged Dickeya sp. IPO2222 and superficially treated during planting with a water suspension containing GFP‐tagged S. plymuthica A30. A30 reduced the blackleg incidence from 55% to 0%. Both the pathogen and the antagonist colonized the seed potato tubers internally within 1 day post‐inoculation (dpi). Between 1 and 7 dpi, the population of A30 in tubers increased from 10¹ to c. 10³ CFU g^?1 and subsequently remained stable until the end of the experiment (28 dpi). Populations of A30 in stems and roots increased from c. 10² to c. 10⁴ CFU g^?1 between 7 and 28 dpi. Dilution plating and CLSM studies showed that A30 decreased the density of Dickeya sp. populations in plants. Dilution plating combined with microscopy allowed the enumeration of strain A30 and its visualization in the vascular tissues of stem and roots and in the pith of roots, as well as its adherence to and colonization of the root surface. The implications of these finding for the use of S. plymuthica A30 as a biocontrol agent are discussed.     

Identification and characterization of a novel etiological agent of mango malformation disease in Mexico, Fusarium mexicanum sp. nov

The primary objective of this study was to characterize Fusarium spp. associated with the economically devastating mango malformation disease (MMD) in Mexico. In all, 142 Fusarium strains were isolated from symptomatic mango inflorescences and vegetative tissues in eight geographically diverse Mexican states from 2002 through 2007. Initially, all the Mexican isolates were screened for genetic diversity using appolymerase chain reaction and random amplified polymorphic DNA markers and were grouped into seven distinct genotypes. Based on results of these analyses, evolutionary relationships and species limits of the genetically diverse MMD-associated Fusarium spp. were investigated using multilocus DNA sequence data and phylogenetic species recognition. Maximum parsimony analyses of a five-locus data set comprising 5.8 kb of aligned DNA sequence data indicated that at least nine phylogenetically distinct Fusarium spp. within the Gibberella fujikuroi species complex are associated with MMD, including one species within the African clade (Fusarium pseudocircinatum), two species within the Asian clade (F. mangiferae and F. proliferatum), and at least six species within the American clade (F. sterilihyphosum and five undescribed Fusarium spp.). Molecular phylogenetic analyses indicate that a novel genealogically exclusive lineage within the American clade was the predominant MMD associate in Mexico. This new Fusarium sp. caused MMD and could be distinguished from all other known species morphologically by the production of mostly sterile, coiled hyphae which are typically associated with sporodochial conidiophores together with unbranched or sparsely branched aerial conidiophores. Koch's postulates were completed for isolates of the new species on nucellar seedlings of mango cv. Ataulfo. This pathogen is formally described herein as F. mexicanum.     

A new Fusarium lineage within the Gibberella fujikuroi species complex is the main causal agent of mango malformation disease in Brazil

Mango malformation is a serious disease in tropical and subtropical areas of the world and has been attributed to various Fusarium spp., including F. mangiferae , F. proliferatum , F. sacchari , F. sterilihyphosum and F. subglutinans . Isolates of Fusarium associated with mango malformation from Brazil, Egypt, India, South Africa and the United States were evaluated through amplified fragment length polymorphisms (AFLPs) and partial DNA sequences of the genes encoding β-tubulin ( tub2 ) and translation elongation factor 1-α ( tef1 ). These techniques were used to delimit species and to estimate the genetic and phylogenetic relatedness of the isolates. In the AFLP analysis, most of the Brazilian isolates formed a unique cluster. Additionally, one small cluster was formed by isolates of F. sterilihyphosum from Brazil and South Africa, and another by isolates of F. mangiferae from Egypt, India, South Africa and the United States. In the phylogenetic analysis, most of the Brazilian isolates represented a new phylogenetic lineage in the Gibberella fujikuroi species complex, where they formed a sister clade to F. sterilihyphosum. Representatives of both clades were pathogenic to mango (cv. Tommy Atkins) and Koch's postulates were completed for isolates belonging to the new lineage and to F. sterilihyphosum . Thus, most of the mango malformation disease in Brazil is due to a distinct phylogenetic lineage of Fusarium , and to a lesser extent by F. sterilihyphosum. The new phylogenetic lineage identified in this study, together with F. mangiferae and F. sterilihyphosum , are the only known taxa of Fusarium proven to be capable of causing mango malformation.     

Phytophthora obscura sp. nov., a new species of the novel Phytophthora subclade 8d

A new Phytophthora species was detected (i) in the USA, infecting foliage of Kalmia latifolia, (ii) in substrate underneath Pieris, and (iii) in Germany in soil samples underneath Aesculus hippocastanum showing disease symptoms. The new species Phytophthora obscura sp. nov. is formally named based on phylogenetic analysis, host range, Koch’s postulates and morphology. Phytophthora obscura is homothallic with paragynous antheridia and semipapillate sporangia. It is genetically closely related to P. syringae and P. austrocedrae and together these three species define a new Phytophthora subclade 8d, with significant support for all genetic loci analysed including seven nuclear genes and the mitochondrial gene coxII. The morphological and ecological characteristics are very similar to P. syringae, and it is likely that P. obscura was not described earlier because it was identified as P. syringae. Artificial inoculations indicated that horse chestnut, kalmia, pieris and rhododendron might be hosts, and Koch’s postulates were confirmed for kalmia from which it was isolated. This pathogen was named after its elusive nature since it has to date rarely been detected in the US and Germany.     

Pewenomyces kutranfy gen. nov. et sp. nov. causal agent of an important canker disease on Araucaria araucana in Chile

Araucaria araucana, (commonly referred to as araucaria, pewen, or monkey puzzle tree) is an ancient conifer endemic to the Chilean and Argentinian mountain ranges where it has a sacred relevance to indigenous communities. During 2015, a serious disease was noticed on trees of all ages in most of the natural distribution of this iconic tree. Four areas were surveyed, and the most important symptoms of the disease were cankers on branches and stems resulting in copious resin exudation. Trees were monitored for a period of two years and isolations were made from the cankers. Field observations showed that the disease typically begins on the leaves or at the leaf bases and progresses downwards to initiate cankers that can girdle branches or stems within a two-year period. Black ascomata, resembling those of Caliciopsis species previously described from A. araucana, were consistently found developing in the cankers from which isolations were made. Phylogenetic analyses of the ITS, nucSSU, and nucLSU gene regions showed that the fungus resides in the Coryneliaceae but is distinct from other genera in that family. The morphological characteristics and phylogenetic position of the fungus show that it represents a new genus and species, described here as Pewenomyces kutranfy gen. nov. et sp. nov. Pathogenicity trials on trees under field conditions confirmed that this newly described fungus is able to cause cankers on A. araucana similar to those found under natural conditions.     

Overwintering of Erwinia carotovora subsp. carotovora in Diseased Tissues in Soil and Its Role as Inoculum for Soft Rot of Chinese Cabbage (Brassica campestris, Pekinensis Group)

To examine whether the pathogenic bacterium, Erwinia carotovora subsp. carotovora, causal agent of soft rot of Chinese cabbage (Brassica campestris L., pekinensis group), can overwinter in plant debris and soil and serve as inoculum the following year, we monitored field populations of rifampicin-resistant, phage-sensitive strains of the bacterium. Chinese cabbage (cv. Matsushima Kohai W1116) were planted in field soil in pots that were sunk into the field on Aug. 2, 1996 and eventually reduced to one plant per pot. Outer petioles of the plants were inoculated with mixture of 13 bacterial strains of E. carotovora subsp. carotovora on Sept.5, 1996. After the soft rot spread throughout the plant, the diseased plant was buried in the potted soil. New seeds were sown in the pots on April 30, 1997, and the disease was observed in June and July. The bacterial strains were re-isolated from the potted soil, diseased tissue and rhizosphere soil by the dilution plating method on modified Drigalski's medium containing 100 ppm rifampicin and by the enrichment technique. In addition to rifampicin resistance, phage sensitivities of some of the re-isolated strains were identical to those of the strains buried in the soil with the diseased plant in the previous year. From these results, some of the 13 strains overwintered in the soil and infested plant tissue and acted as primary inoculum the following year. The frequency of re-isolation varied among the strains, perhaps because of competition among the strains, differences in epidemiological behavior and stabilizing selection among the strains, and the presence of different ecotypes of the organism. Received 21 July 2000/ Accepted in revised form 19 September 2000     

Preliminary investigation of the causal agent(s) of a disease causing leaf curl of tobacco in South Africa

A high incidence (86%) of potyvirus infection was noted in tobacco plants exhibiting a form of leaf curl in South Africa. Despite leaf curl being reported in the literature to be of geminiviral aetiology, no geminiviruses were detected. Furthermore, no other virus particles were detected by virus purification, TEM and serology. Twelve species of dsRNA were consistently isolated from these tobacco plants, but were absent from other forms of leaf curl-affected and healthy tobacco. Aphid and mechanical inoculation demonstrated that the purified potyvirus(es) did not cause leaf curl symptoms, but rather mild mottle and mosaic symptoms in tobacco. Partial characterization of the potyvirus preparation showed a possible relationship to a South African strain of potato virus Y. Because potyvirus-inoculated plants did not manifest leaf curl symptoms, and because leaf curl symptoms were noted in some plants not infected with a potyvirus, it was concluded that the potyvirus is not involved in the leaf curl aetiology, but causes a latent infection, the symptoms of which are masked. The pattern of the dsRNA banding, induction of enations and lack of mechanical and seed transmission are common to plant reoviruses. The possibility of a phytoreovirus involvement in this form of leaf curl is currently being investigated. The results from this study suggest that tobacco leaf curl disease worldwide, with regard to geminiviruses, be re-evaluated.     

Development of a PCR-based diagnostic test for Spongospora subterranea f.sp. nasturtii, the causal agent of crook root of watercress (Rorippa nasturtium-aquaticum)

The polymerase chain reaction (PCR) technique was utilized to obtain internal transcribed spacer ribosomal DNA (ITS rDNA) and small-subunit (18S) rDNA sequences from UK isolates of Spongospora subterranea f.sp. nasturtii , a plasmodiophorid pathogen of watercress ( Rorippa nasturtium-aquaticum ). ITS sequence data obtained from S. subterranea isolated from a range of UK sites were found to be identical. PCR primers were designed using these sequences and were shown to be capable of specific amplification of S. subterranea f.sp. nasturtii DNA from plant tissue and from water samples containing zoospores of the pathogen. As little as 5 ng total genomic DNA from infected plant material, or 1000 zoospores, was required for consistently successful amplification of DNA. A filtration-based method for obtaining pathogen DNA for PCR from watercress-bed water was developed.     

Resistance in Australian barley (Hordeum vulgare) germplasm to the exotic pathogen Puccinia striiformis f. sp. hordei,causal agent of stripe rust

Eighty‐eight Australian and 10 international barley cultivars were assessed for resistance to the barley stripe (yellow) rust pathogen, Puccinia striiformis f. sp. hordei (Psh). All cultivars were tested for seedling resistance to two UK‐derived isolates of Psh (11.01 and 83.39) that were shown to differ in virulence based on responses on 16 differential barley genotypes. The 98 barley cultivars differed substantially in stripe rust response; 45% were susceptible to Psh 11.01, 53% to Psh 83.39 and 44% to both isolates. The observed diverse infection types (ITs) suggest the presence of both known and uncharacterized resistance. However, further multipathotype tests are required for accurate gene postulation. The Yerong × Franklin (Y×F) doubled haploid (DH) population was phenotypically assessed as seedlings using both Psh isolates. Yerong and Franklin were immune and highly resistant, respectively, to both isolates used in this study. Marker‐trait and QTL mapping identified a major effect on the long arm of chromosome 7H contributed by Franklin in response to all isolates. The resistance of Yerong was mapped to 113·96 and 169·38 cM on chromosome 5HL in response to Psh 11.01 and 83.39, respectively. The Psh resistance sources identified in this study can be used for further genetic analysis and introgression for varietal improvement.     

Acolpenteron australe sp. n. (Dactylogyridae:Dactylogyrinae), a new species from the ureters of Percichthys trucha (Perciformes:Percichthyidae) in Patagonia (Argentina)

Acolpenceron australe sp. n. (Dactylogyridae, Dactylogyrinae) is described from ureters and renal tubules of Percichthys trucha (Cuvier et Valenciennes) (Perciformes, Percichthyidae) from Andean Patagonian lakes. The new species has a haptor with 14 hooks, with shanks comprised of two subunits. It has overlapped intercaecal gonads, male copulatory organ as a sclerotized tube with one counterclockwise coil and a J-shaped accessory piece. It differs from the other species of Acolpenteron by having a non-forked accessory piece. This is the first monogenean species described from a percichthyid host in South America.     

Phytophthora bilorbang sp. nov., a new species associated with the decline of Rubus anglocandicans (European blackberry) in Western Australia

A new homothallic Phytophthora species, isolated from rhizosphere soil and roots of declining or dead Rubus anglocandicans (European blackberry) in south-west Western Australia, is described as Phytophthora bilorbang sp. nov. It produces non-papillate sporangia, smooth-walled oogonia containing thick-walled oospores, and paragynous antheridia. Although morphologically similar to several species within ITS Clade 6 and sub-clade II, namely P. gibbosa, P. gregata and P. megasperma, phylogenetic analyses of the ITS, cox1, HSP90, BT and NADH gene regions demonstrate that P. bilorbang sp. nov. is a distinct species. Additionally, P. bilorbang differs from these species in its growth and colony morphology on several media. Pathogenicity tests indicate that P. bilorbang could be responsible for the decline syndrome of blackberry within the Warren and Donnelly River catchments in the south-west of Western Australia.     

Identification of a genetic lineage within Xanthomonas arboricola pv. juglandis as the causal agent of vertical oozing canker of Persian (English) walnut in France

A new bacterial disease of Persian (English) walnut (Juglans regia) has been observed in France. This disease, called vertical oozing canker (VOC), is characterized by vertical cankers on trunks and branches of affected walnut trees with oozing exudates. To determine the aetiology of the disease, a study was carried out in 79 walnut orchards and nurseries located in southeastern and southwestern France. Bacterial analysis from diseased samples yielded 36 strains identified as Xanthomonas arboricola and 32 strains identified as Brenneria nigrifluens on the basis of biochemical tests. The causal agent of VOC was identified as X. arboricola by pathogenicity tests on walnut. Fluorescent amplified fragment length polymorphism (F‐AFLP) was carried out on 36 strains of X. arboricola collected in this study, 24 strains of X. arboricola pv. juglandis isolated from walnut blight symptoms and one strain of X. arboricola pv. corylina included as an outgroup. Based on cluster analysis of F‐AFLP data, most X. arboricola strains responsible for main VOC outbreaks showed a high degree of similarity, forming a cluster clearly separate from strains of X. arboricola pv. juglandis isolated from walnut blight symptoms. It is suggested that VOC is caused by a distinct genetic lineage within the pathovar juglandis of X. arboricola that is also able to cause classical bacterial blight symptoms on walnut leaves and fruits.     

进境木质包装中检出线虫新种--新加坡伞滑刃线虫

从新加坡进境阔叶木质包装中分离到伞滑刃属松材线虫组新种——新加坡伞滑刃线虫。该线虫雌虫和雄虫体长分别为850（690～961）肿和792（553．950）μm，身体较粗壮，口针15～16μm，侧区有4条侧线，雌虫后阴子宫囊较长（平均102μm），尾部圆锥形（c=20），略向腹面弯曲，末端钝圆，或有极短的尾尖突（1～2μm），雄虫交合刺长（41～48μm），喙突显著，远端有盘状突。该线虫与松材线虫组的B．conicaudatus、B．luxuriosae、B．fraudulentus、B．kolymensis、B．baujardi、B．xylophilus、B．mucronatus及B．abruptus形态上近似，但可从较大的交合剌及雌虫尾部形态来区分。另外用ITS-RFLP方法也可将该线虫区分出来。