Genetic variability and virulence among Verticillium albo-atrum isolates from hop

Verticillium wilt, caused by Verticillium albo-atrum or V. dahliae, is an important disease of many worldwide crop species. In Europe, V. albo-atrum isolates infecting hop express different levels of virulence, inducing mild or lethal disease syndromes, and it is therefore an attractive model for studying the virulence of this pathogen. In this work, eleven amplified fragment length polymorphism (AFLP) primer combinations were used to analyze genetic variability among 55 V. albo-atrum hop isolates from four European hop growing regions, as well as isolates from other hosts and V. dahliae isolates. Cluster analysis divided V. albo-atrum and V. dahliae isolates into two well-separated groups. Within the V. dahliae cluster, isolates were separated without host specific grouping, although no host adapted isolates were included. In V. albo-atrum, the alfalfa isolates were distinct from isolates of other hosts, where a high association with virulence was observed in hop and tomato isolates. All lethal hop isolates were genetically different from mild hop isolates. The lethal hop isolates from England and Slovenia expressed the same virulence phenotype, although they showed a different AFLP pattern. The mild hop isolates formed two subgroups, to which isolates clustered irrespective of geographical location. These data suggest multiple origins of V. albo-atrum hop isolates, and the possible appearance of new virulent isolates in the future in other hop growing regions.     

Genetic diversity and relationships among cultivated and wild accessions of tartary buckwheat (Fagopyrum tataricum Gaertn.) as revealed by RAPD markers

The methodology of sampling and the selection of a proper marker systemfor the analysis of accessions are major concerns in the evaluation of gene bank material. In our study the RAPD analysis of bulked DNA samples and single seedsDNA was successfully employed to evaluate intra- and inter-population geneticvariability of cultivated and wild tartary buckwheat accessions. The bulkingapproach enabled the distinction of all 40 analysed accessions and theirseparation into geographically well defined clusters. Three wild populations,two from Sichuan and one from Qinghai, formed a group that was geneticallyrelatively distant from wild populations from Tibet and all cultivatedlandraces which, on the other hand, exhibited very close relationships. Thesingle seed study that was used after bulked DNA analysis provided detailedinformation of the genetic variation present within some accessions of specialinterest. A moderate level of genetic variability was detected betweenaccessions and the variability was partitioned into between- andwithin-population components. On average, most of the detected variation ispresent between F. tataricumpopulations. The genetic and geographic distribution of variability is furtherdiscussed. We demonstrated the usefulness of combining bulking and single seedstudy approaches for the effective evaluation of genetic variability inF. tataricum accessions that couldalso have wider applicability in the management of plant genetic resources andphylogenetic studies.     

Disseminated tuberculosis in hyrax (Procavia capensis) caused by Mycobacterium africanum

Tuberculosis due to Mycobacterium africanum was diagnosed in an adult female hyrax (Procavia capensis). Pathologic examination revealed disseminated tuberculous lesions. The same pathologic changes were also found in a male hyrax that died a year later. Both animals were imported from the United Arab Emirates and were held in captivity at the Zagreb Zoo in Croatia. The source of infection remains unknown. The acid-fast bacteria isolated from the lungs of the female hyrax were identifyed by polymerase chain reaction as Mycobacterium tuberculosis complex and Geno Type MTBC test confirmed the strain to be M. africanum I.     

The combined effects of multiple diseases and climatic conditions on thousand kernel weight losses in winter wheat

Thousand kernel weight (TKW) is a yield component associated with grain quality. It is reported in the literature that TKW is significantly influenced by varieties, agro-ecological conditions and disease indices, but the influence of their interactions on TKW loss has rarely been taken into consideration. The main objective of this study was to examine the combined effects of multiple diseases and climatic conditions on TKW losses in winter wheat. Leaf rust, powdery mildew, and Septoria tritici blotch were considered biotic predictor variables in regression models explaining TKW losses. Monthly averages of temperature, relative humidity and total rainfall in May and June in the 2006–2013 growing seasons were used as abiotic predictor variables. The results of this study indicated a significant low positive correlation between yield loss and TKW loss in the two varieties. TKW losses were less influenced by leaf rust, powdery mildew, and Septoria tritici blotch than yield losses. The significant influence of the interaction between variety and the environmental conditions on TKW loss was confirmed from the general linear model function. The results of this study indicated that factors influencing yield and yield component losses are part of the complex environment, and the relationship between them should be investigated with respect to their interactions.     

Deep‐sequencing revealed Citrus bark cracking viroid (CBCVd) as a highly aggressive pathogen on hop

Newly emerging or re‐emerging diseases are a constant and significant threat to agricultural production, so prompt and accurate identification of the causative agents is required for rapid and appropriate disease management. Classical methods of pathogen detection can be successfully supplemented by next‐generation sequencing (NGS), whereby sequence analysis can help in the discovery of new or emerging diseases. In 2007, hop growers in Slovenia reported the appearance of severely stunted hop plants, a phenomenon that spread rapidly within hop gardens and among farms. Classical diagnostic methods were unable to detect a new pathogen; therefore, single step high‐throughput parallel sequencing of total RNA and small RNAs from plants with and without symptoms was employed to identify a novel pathogen. The sequences were assembled de novo and also mapped to reference genomes, resulting in identification of a novel sequence of Citrus bark cracking viroid (CBCVd) in the stunted hop plants. Furthermore, the presence of this novel pathogen on hop was confirmed by RT‐PCR analysis of 59 plants with symptoms from 15 hop gardens, representing the main outbreak locations identified by systematic disease monitoring, and small RNA Illumina sequencing of the bulked RNA sample. The high infectivity of the newly identified CBCVd was also confirmed by biolistic inoculation of two hop cultivars, which developed aggressive symptoms in controlled conditions. This study shows the feasibility of deep sequencing for the identification of causative agents of new diseases in hop and other plants.     

Diagnostic techniques for viroids

The fast growth of the human population forces us to produce more food, but higher crop production also leads to the fast spread of diseases. Plant pathology deploys a wide range of methods that do not provide an adequate solution to all disease losses. In the case of viroids, therapeutic means of control are not available; therefore control strategies are more focused on the development of reliable detection methods to quickly exclude the infected plant material. Although viroids are the smallest and simplest plant pathogens, their identification and detection is not straightforward. Each viroid–host combination is specific, and for reliable identification, all steps from sampling to final detection must be performed accurately. In this review, several methods for viroid detection in various host plants are discussed, including their advantages and disadvantages. Even though relatively new molecular methods enable fast and sensitive detection of viroids, a combination of different methods gives the most reliable identification. Techniques based on nucleic acids may be the future for viroid detection but they still cannot replace biological indexing, which is usually essential in epidemiological and aetiological studies.     

38–48 kDa subunits of buckwheat 13S globulins are controlled by a single locus

The inheritance of buckwheat (Fagopyrum esculentum Moench) seed storage proteins was investigated by control crosses between accessions containing different SDS‐PAGE protein patterns in the range of 38–48 kDa. Analysis of segregation of individual F₁ and F₂ seeds obtained by 17 crosses showed segregation of eight electrophoretic bands, from which 12‐banding variants were inferred. Two variants contained one band, nine contained two bands and one variant contained three bands and behaved as a single co‐dominant unit. The segregation of banding variants fits the expected ratios and thus supports the hypothesis of single Mendelian gene inheritance and that alleles are co‐dominant. The results therefore suggest that the genes controlling globulin subunits are tightly linked and inherited as a single locus. The locus was designated Glob‐1 and the twelve segregated protein variants as alleles a‐l. This is the first buckwheat globulin locus identified with multiple alleles, phenotypically expressed as groups of protein bands and thus applicable as a functional marker in buckwheat genomic studies.