Assessment of recent outbreaks of Dickeya sp (syn. Erwinia chrysanthemi) slow wilt in potato crops in Israel

Suspected Dickeya sp. strains were obtained from potato plants and tubers collected from commercial plots. The disease was observed on crops of various cultivars grown from seed tubers imported from the Netherlands during the spring seasons of 2004-2006, with disease incidence of 2-30% ( 10% in average). In addition to typical wilting symptoms on the foliage, in cases of severe infection, progeny tubers were rotten in the soil. Six strains were characterised by biochemical, serological and PCR amplification. All tests verified the strains as Dickeya sp. The repPCR and the biochemical assays showed that the strains isolated from blackleg diseased plants in Israel were very similar, if not identical to strains isolated from Dutch seed potatoes, suggesting that the infection in Israel originated from the Dutch seed. The strains were distantly related to D. dianthicola strains, typically found in potatoes in Western Europe, and were similar to biovar 3 D. dadanti or D. zeae. This is the first time that the presence of biovar 3 strains in potato in the Netherlands is described. One of the strains was used for pathogenicity assays on potato cvs Nicola and Mondial. Symptoms appeared 2 to 3 days after stem inoculation, and 7 to 10 days after soil inoculation. The control plants treated with water, or plants inoculated with Pectobacterium carotovorum, did not develop any symptoms with either method of inoculation. The identity of Dickeya sp. and P. carotovorum re- isolated from inoculated plants was confirmed by PCR and ELISA

The Role of Host Genetics in Susceptibility to Influenza: A Systematic Review

Background: The World Health Organization has identified studies of the role of host genetics on susceptibility to severe influenza as a priority. A systematic review was conducted to summarize the current state of evidence on the role of host genetics in susceptibility to influenza (PROSPERO registration number: CRD42011001380). Methods and Findings: PubMed, Web of Science, the Cochrane Library, and OpenSIGLE were searched using a pre-defined strategy for all entries up to the date of the search. Two reviewers independently screened the title and abstract of 1,371 unique articles, and 72 full text publications were selected for inclusion. Mouse models clearly demonstrate that host genetics plays a critical role in susceptibility to a range of human and avian influenza viruses. The Mx genes encoding interferon inducible proteins are the best studied but their relevance to susceptibility in humans is unknown. Although the MxA gene should be considered a candidate gene for further study in humans, over 100 other candidate genes have been proposed. There are however no data associating any of these candidate genes to susceptibility in humans, with the only published study in humans being under-powered. One genealogy study presents moderate evidence of a heritable component to the risk of influenza-associated death, and while the marked familial aggregation of H5N1 cases is suggestive of host genetic factors, this remains unproven. Conclusion: The fundamental question ‘‘Is susceptibility to severe influenza in humans heritable?’ ’ remains unanswered. No

First report of potato blackleg caused by a biovar 3 Dickeya sp. in Georgia

In Western and Northern Europe, Dickeya species are causing increasingly severe economic losses in potato (Solanum tuberosum) crops. The costs of seed potato production resulting from Dickeya spp. infection are high due to rejection and declassification of seed tubers (Slawiak et al., 2009). Potato blackleg caused by Dickeya spp. is primarily a seed tuber-borne disease (Tsror et al., 2009). Symptoms including blackening of the stem base, wilting of plants and rotten seed tubers are observed. Recently, outbreaks of potato blackleg were recorded in Georgia on three cultivars, in Samtskhe-Javakheti region, Akhalkalaki district, in an area in excess of 100 hectare

First report of latent infection of Cyperus rotundus caused by a biovar 3 Dickeya sp. (Syn. Erwinia chrysanthemi) in Israel

Recent outbreaks of potato blackleg in Israel, caused by Dickeya spp., on plants grown from seed tubers imported from Northern Europe, are of a great concern. The warm climatic conditions during the growing season favour disease expression, and may result in the establishment of the pathogen in the potato ecosystem and a spread to weeds and other crops (Tsror et al., 2009). Until recently, most of Dickeya spp. strains found in association with potato blackleg in Europe were characterised as D. dianthicola (biovars 1 or 7). These strains have a relatively lowgrowth temperature compared with other Dickeya spp. and seem to be more adapted to cool European climate conditions. However, during the last three years, Dickeya spp. strainsbelonging to a new biovar 3 clade, probably constituting a newspecies, have been isolated from potato tubers inseveral countries in Northern Europe (Slawiak et al., 2009 and references therein). To study dissemination to weeds, surveys were conducted in potato fields where Dickeya-infected potato plants were detected during two consecutive spring seasons (2009 and 2010). Symptomless plants of 12 species of local weeds were randomly collected: Cyperus rotundus,Orobanche aegyptiaca, Amaranthus spinosus, Polygonum equisetiforme, Chenopodium sp., Heliotropium sp., Centaurea iberica, Sorghum haepense, Malva nicaeensis, Cynodon dactylon, Amaranthus blitum and Solanum elaeagnifolium. Roots or tubers (in the case of C. rotundus)of 15 plants of each weed were washed, surface sterilised and then sample homogenates were plated on crystal violet pectate medium (CVP). Cavity forming bacteria were transferred to nutrient agar and analysed. Dickeya spp. were isolated only from the perennial weed C. rotundus.Incidence of infected plants was 6.7 and 14.3% in 2009 and 2010, respectively). DNA extracted from the bacteria isolated from C. rotundus was positive in a PCR amplification procedure using pelADE specific primers which are specific for E. chrysanthemi (Nassar et al., 1996).Isolates were identified by biochemical assays as biovar 3 (Palacio-Bielsa et al., 2006). They were characterised as the new genetic clade, using dnaX sequence (Slawiak et al., 2009) and REP-PCR analyses (Tsror et al.,2009). These isolates caused maceration of potato tubers at 30°C (Laurila et al., 2008) and formed clear haloes on a polygalacturonic acid medium (Collmer et al.,1988). This is the first report of Dickeya spp. latent infection in one of the most prevalent weeds in potato fields in Israel. C. rotundus is difficult to control because of resistance to most herbicides. Therefore, it may serve as an alternative host for Dickeya spp. allowing the pathogen to survive in the absence of a host crop

First report of latent infection of Cyperus rotundus caused by a biovar 3 Dickeya sp. (Syn. Erwinia chrysanthemi) in Israel

Recent outbreaks of potato blackleg in Israel, caused by Dickeya spp., on plants grown from seed tubers imported from Northern Europe, are of a great concern. The warm climatic conditions during the growing season favour disease expression, and may result in the establishment of the pathogen in the potato ecosystem and a spread to weeds and other crops (Tsror et al., 2009). Until recently, most of Dickeya spp. strains found in association with potato blackleg in Europe were characterised as D. dianthicola (biovars 1 or 7). These strains have a relatively lowgrowth temperature compared with other Dickeya spp. and seem to be more adapted to cool European climate conditions. However, during the last three years, Dickeya spp. strainsbelonging to a new biovar 3 clade, probably constituting a newspecies, have been isolated from potato tubers inseveral countries in Northern Europe (Slawiak et al., 2009 and references therein). To study dissemination to weeds, surveys were conducted in potato fields where Dickeya-infected potato plants were detected during two consecutive spring seasons (2009 and 2010). Symptomless plants of 12 species of local weeds were randomly collected: Cyperus rotundus,Orobanche aegyptiaca, Amaranthus spinosus, Polygonum equisetiforme, Chenopodium sp., Heliotropium sp., Centaurea iberica, Sorghum haepense, Malva nicaeensis, Cynodon dactylon, Amaranthus blitum and Solanum elaeagnifolium. Roots or tubers (in the case of C. rotundus)of 15 plants of each weed were washed, surface sterilised and then sample homogenates were plated on crystal violet pectate medium (CVP). Cavity forming bacteria were transferred to nutrient agar and analysed. Dickeya spp. were isolated only from the perennial weed C. rotundus.Incidence of infected plants was 6.7 and 14.3% in 2009 and 2010, respectively). DNA extracted from the bacteria isolated from C. rotundus was positive in a PCR amplification procedure using pelADE specific primers which are specific for E. chrysanthemi (Nassar et al., 1996).Isolates were identified by biochemical assays as biovar 3 (Palacio-Bielsa et al., 2006). They were characterised as the new genetic clade, using dnaX sequence (Slawiak et al., 2009) and REP-PCR analyses (Tsror et al.,2009). These isolates caused maceration of potato tubers at 30°C (Laurila et al., 2008) and formed clear haloes on a polygalacturonic acid medium (Collmer et al.,1988). This is the first report of Dickeya spp. latent infection in one of the most prevalent weeds in potato fields in Israel. C. rotundus is difficult to control because of resistance to most herbicides. Therefore, it may serve as an alternative host for Dickeya spp. allowing the pathogen to survive in the absence of a host crop

Erwinia chrysanthemi in Israel - epidemiology and monitoring in seed tubers

In recent years, Erwinia chrysanthemi (Ech) on potato in Israel, in plants grown from imported Dutch seed tubers has been occurring more frequently causing economic damage. Disease symptoms first appear as wilt of the top leaves, which then spreads to the lower ones, followed by desiccation. Discoloration of the vascular system in the stem base is usually observed, followed by external darkening. In severe infections, the stem, and even the whole plant can dry out. Symptoms are usually associated with soft rot of the mother tuber, and sometimes (depending on level of infection) of the daughter tubers as well. The objectives of the present study were: a) to assess the impact of Ech-infected seed tubers imported from The Netherlands on disease expression in Israel, b) to develop a protocol for the detection of latent Ech infection in seed tubers. In spring 2004, disease was observed in several plots on imported cvs. Desirée and Mondial. In 2005, disease incidence on various imported cultivars ranged from 5 to 30% (8.2% on average) on more than 200 ha. In the autumn crop where domestic tubers harvested from an infested field were used disease incidence was 10-15%. In 2006, the disease was observed on more than 260 ha in various cultivars with disease incidence ranging from 2 to 30% (10% on average). Seed tubers sampled from commercial lots imported from Holland were tested for latent Ech infection, based on bio-PCR or enrichment ELISA. Out of 36 tested lots 24 were Ech-positive. Disease levels recorded in the fields in these lots ranged from 3% to 35% (10% on average), with only one exceptional case, where a low incidence of diseased plants was observed in a field originated from a Ech-negative seed lot. A protocol for detection of Ech in seed tubers was developed. A sample comprised of 200 tubers per 25 tons per lot divide into four or 10 replicates (50/20 tubers each), surfacesterilize with 0.5% NaOCl for 1 min, and the stolon end of each tuber was cut and placed in enrichment medium. After incubation of 48h, 0.2-ml aliquot was used for ELISA analysis or DNA extracted from the supernatant was used for PCR analysis. Our findings so far demonstrated the higher sensitivity of the bio PCR in comparison with the ELISA. This protocol is being tested also in spring 2007 with a large number of seed lots. Samples from these lots were planted in the field and Ech incidence is being recorded. Correlations between latent infections in the seed tubers and disease expression will be further studied, in order to evaluate the accuracy of the suggested protocol, and/or to improve it.vokMyynti MTT Tietopalvelut 31600 Jokioine

Why have Colletotrichum and Helminthosporium become such a problem for fresh and ware potato quality - pathogen change or climate change

Both black dot and silver scurf caused by Colletotrichum coccodes and Helminthosporium solani, respectively, cause blemishes on the potato periderm. These diseases often occur together and frequently confused, cause reductions in fresh and ware potato production potential and damage value of seed potatoes. These diseases are largely distributed in all potato growing regions of the world, but black dot is most important in areas with dry and hot conditions, such as the Mediterranean regions, western USA, South Africa and southern Australia, although it is also well established in more temperate areas, such as UK, France, the Netherlands and Germany. Both diseases became a major problem in potato production over the past decade due to an increased demand for washed potatoes with a high-quality appearance. C. coccodes appears as a highly diverse species morphologically, physiologically and genetically; the existence of vegetative compatibility groups might explain this diversity, despite the fact that no sexual stage is known for the pathogen. C. coccodes is also diverse from a pathological point of view: it infects a range of plant species within and outside the Solanaceae, and shows some specific interactions with individual potato cultivars. In contrast, with H. solani there are no alternative hosts except to tuber-bearing Solanum species. Changes in cropping systems and in consumer dictate a reassessment of the economic importance of the skin blemish diseases, that severely affects the economic value of fresh market and seed potato production in regions of the world where external appearance is an essential driver of market access. An integrated disease management approach that includes cultural, biological and chemical control methods, in the field and in storage, is necessary for long-term control of skin blemish diseases. The fungicide TBZ was used for silver scurf control until the 1980 s, but due to high frequency of resistance imazalil has become the main fungicide used on seed tubers in Europe. However, C. coccodes is not sufficiently controlled by imazalil, suggesting another reason why black dot became a major pathogen on potato. Additional fungicides e.g. prochloraz, fludioxonil and azoxystrobin that control both pathogens are being introduced, however resistance to fludioxonil in H. solani was recently reported. Adequate control of the skin blemish diseases with very low tolerance for market access is highly problematic, and will require integrated strategies combining all currently available control methods.vokMyynti MTT Tietopalvelut 31600 Jokioine

Characterization of Dickeya strains isolated from potato grown under hot-climate conditions

Dickeya strains isolated in Israel in 2006–2010 were characterized by dnaX sequence analysis, pulsed-field gel electrophoresis (PFGE), biochemical assays and pectolytic activity, and found to be homogeneous: most of them could be classified as ‘Dickeya solani’. Of the 34 strains isolated from imported seed tubers or potato plants grown from imported seed, 32 were typed as ‘D. solani’ and only two were characterized as Dickeya dianthicola. Biovar typing indicated that all ‘D. solani’ strains were biovar 3. ‘Dickeya solani’ strains were most closely related to Dickeya dadantii subsp. dieffenbachiae according to PFGE and dnaX analyses and both species exhibited high pectolytic activity. Expression levels of two putative virulence genes, pelL (encoding a pectic enzyme) and dspE (encoding a type III effector) were significantly induced in ‘D. solani’ strains isolated from potato plants or tubers grown in hot climates such as the Negev region in Israel, compared to those isolated from seed tubers imported from the Netherlands, France or Germany. Results of this study support the hypothesis that ‘D. solani’ strains isolated in Israel are also clonal; however, they appear to be more virulent than strains isolated in Europ

Assessment of recent outbreaks of Dickeya sp (syn. Erwinia chrysanthemi) slow wilt in potato crops in Israel

Suspected Dickeya sp. strains were obtained from potato plants and tubers collected from commercial plots. The disease was observed on crops of various cultivars grown from seed tubers imported from the Netherlands during the spring seasons of 2004-2006, with disease incidence of 2-30% ( 10% in average). In addition to typical wilting symptoms on the foliage, in cases of severe infection, progeny tubers were rotten in the soil. Six strains were characterised by biochemical, serological and PCR amplification. All tests verified the strains as Dickeya sp. The repPCR and the biochemical assays showed that the strains isolated from blackleg diseased plants in Israel were very similar, if not identical to strains isolated from Dutch seed potatoes, suggesting that the infection in Israel originated from the Dutch seed. The strains were distantly related to D. dianthicola strains, typically found in potatoes in Western Europe, and were similar to biovar 3 D. dadanti or D. zeae. This is the first time that the presence of biovar 3 strains in potato in the Netherlands is described. One of the strains was used for pathogenicity assays on potato cvs Nicola and Mondial. Symptoms appeared 2 to 3 days after stem inoculation, and 7 to 10 days after soil inoculation. The control plants treated with water, or plants inoculated with Pectobacterium carotovorum, did not develop any symptoms with either method of inoculation. The identity of Dickeya sp. and P. carotovorum re- isolated from inoculated plants was confirmed by PCR and ELISA