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

Exome sequencing and disease-network analysis of a single family implicate a mutation in KIF1A in hereditary spastic paraparesis

Whole exome sequencing has become a pivotal methodology for rapid and cost-effective detection of pathogenic variations in Mendelian disorders. A major challenge of this approach is determining the causative mutation from a substantial number of bystander variations that do not play any role in the disease etiology. Current strategies to analyze variations have mainly relied on genetic and functional arguments such as mode of inheritance, conservation, and loss of function prediction. Here, we demonstrate that disease-network analysis provides an additional layer of information to stratify variations even in the presence of incomplete sequencing coverage, a known limitation of exome sequencing. We studied a case of Hereditary Spastic Paraparesis (HSP) in a single inbred Palestinian family. HSP is a group of neuropathological disorders that are characterized by abnormal gait and spasticity of the lower limbs. Forty-five loci have been associated with HSP and lesions in 20 genes have been documented to induce the disorder. We used whole exome sequencing and homozygosity mapping to create a list of possible candidates. After exhausting the genetic and functional arguments, we stratified the remaining candidates according to their similarity to the previously known disease genes. Our analysis implicated the causative mutation in the motor domain of KIF1A, a gene that has not yet associated with HSP, which functions in anterograde axonal transportation. Our strategy can be useful for a large class of disorders that are characterized by locus heterogeneity, particularly when studying disorders in single families

Joubert Syndrome 2 (JBTS2) in Ashkenazi Jews Is Associated with a TMEM216 Mutation

Patients with Joubert syndrome 2 (JBTS2) suffer from a neurological disease manifested by psychomotor retardation, hypotonia, ataxia, nystagmus, and oculomotor apraxia and variably associated with dysmorphism, as well as retinal and renal involvement. Brain MRI results show cerebellar vermis hypoplasia and additional anomalies of the fourth ventricle, corpus callosum, and occipital cortex. The disease has previously been mapped to the centromeric region of chromosome 11. Using homozygosity mapping in 13 patients from eight Ashkenazi Jewish families, we identified a homozygous mutation, R12L, in the TMEM216 gene, in all affected individuals. Thirty individuals heterozygous for the mutation were detected among 2766 anonymous Ashkenazi Jews, indicating a carrier rate of 1:92. Given the small size of the TMEM216 gene relative to other JBTS genes, its sequence analysis is warranted in all JBTS patients, especially those who suffer from associated anomalies. © 2010 The American Society of Human Genetics

Characterization of Pectobacterium brasiliense strains from potato and vegetables in Israel

International audiencePectobacterium brasiliense (Pbr) infects a wide range of crops worldwide, causing potato blackleg and soft rot and vegetable soft rots. This study aimed to characterize the genetic diversity and virulence variability among 68 Pbr strains isolated from either symptomless potato progeny tubers, diseased potato plants, ware potatoes wash water, or vegetables grown in Israel, as well as strains isolated from symptomless seed tubers grown in Europe, or diseased potato plants grown in France. The collection was typed using PCR and TaqMan real-time PCR analyses, dnaX sequence analysis, pulsed-field gel electrophoresis (PFGE), and pectolytic activity. dnaX phylogeny grouped almost all strains in a common genetic clade related to Pbr, which was distinct from the other Pectobacterium species. PFGE analysis identified two main clusters, including one major group of 47 strains with 95%-100% similarity. Maceration assays on two potato cultivars showed significant differences between strains but with no correlations with the source of the strains nor the status of the host (with/without symptoms). Molecular (dnaX sequences and PFGE profiles) and phenotypic analyses (tuber maceration tests) showed that the tested Pbr strains are not a homogeneous group. Analysis of the tested Pbr strains isolated from potato and vegetables grown in fields with a history of potato cultivation suggests that seed tubers imported from Europe may be the main source for Pbr in Israel. To the best of our knowledge, this is the first study that describes biodiversity and population structure of P. brasiliense isolated from potato and vegetables under hot climate condition