No abstract

This research was carried out to study the levels of bacterial wilt resistance and genetic diversity of (near) pentaploid sexual hybrids between S. commersonii (2n=2x= 24, 1EBN) and cultivated S. tuberosum. Following artificial inoculations with Ralstonia solanacearum, wilting degree was estimated on a scale from 0 to 4, and seven genotypes of 26 (27%) displaying a S. commersonii like behavior were identified. Latent bacterial colonizations were detected in roots of symptomless S. commersonii and hybrids, whereas no bacterial populations were detected within stems. This suggests that the movement and/or growth of the bacterium in the aerial part were strongly inhibited. A molecular study with AFLP markers clustered hybrids into nine groups and provided evidence that resistant hybrids were slightly more similar to cultivated S. tuberosum than to the wild parent. This is important in view of the re-establishment of the cultivated genetic background through backcrosses. Hybrids displayed good fertility and are being used for further breeding efforts.Resumen Esta investigación fue realizada para estudiar los niveles de resistencia a la marchitez bacteriana y la diversidad genética de híbridos sexuales (casi) pentaploides entre S. commersoni y S. tuberosum cultivado. Después de las inoculaciones artificiales con Ralstonia solanacearum, la marchitez fue estimada en una escala de 0 a 4 y se identificaron siete genotipos de 26 (27%) que se comportaron como S. commersoni. Se detectaron colonizaciones bacterianas latentes en raíces que no presentaban síntomas de S. commersoni e híbridos mientras que no se detectó población bacteriana dentro de los tallos. Esto sugiere que el movimiento y/o crecimiento de la bacteria en la parte aérea fue fuertemente inhibido. Un estudio molecular con marcadores AFLP agrupó los híbridos en nueve grupos y dio la evidencia de que los híbridos fueron ligeramente más similares al S. tuberosum cultivado que sus progenitores silvestres. Esto es importante en vista del restablecimiento de los antecedentes genéticos de la especie cultivada por medio de retro cruzamientos. Los híbridos mostraron buena fertilidad y están siendo usados para mejoramiento.

Since gene expression approaches constitute a starting point for investigating plant–pathogen systems, we performed a transcriptional analysis to identify a set of genes of interest in tomato plants infected with F. oxysporum f. sp. lycopersici (Fol) and Tomato Mosaic Virus (ToMV). Differentially expressed tomato genes upon inoculation with Fol and ToMV were identified at two days post-inoculation. A large overlap was found in differentially expressed genes throughout the two incompatible interactions. However, Gene Ontology enrichment analysis evidenced specific categories in both interactions. Response to ToMV seems more multifaceted, since more than 70 specific categories were enriched versus the 30 detected in Fol interaction. In particular, the virus stimulated the production of an invertase enzyme that is able to redirect the flux of carbohydrates, whereas Fol induced a homeostatic response to prevent the fungus from killing cells. Genomic mapping of transcripts suggested that specific genomic regions are involved in resistance response to pathogen. Coordinated machinery could play an important role in prompting the response, since 60% of pathogen receptor genes (NB-ARC-LRR, RLP, RLK) were differentially regulated during both interactions. Assessment of genomic gene expression patterns could help in building up models of mediated resistance responses.

No abstract

Efficient control of Xanthomonas axonopodis pv. dieffenbachiae, the causal agent of anthurium bacterial blight, requires sensitive and reliable diagnostic tools. The European standard EN ISO 16140:2003 has been followed to compare a nested PCR assay (N-PCR) to a reference method (isolation and serological identification of bacterial colonies) and to other alternative serological detection methods. The evaluation was performed in two steps: a comparative study and a collaborative study involving 15 European laboratories. Although inclusivity was maximal (100%) for all methods, a maximal exclusivity was obtained only with N-PCR followed by an enzymatic restriction digestion of the amplicons. Exclusivity indices of 90Á6, 88Á7 and 47Á2% were found for indirect ELISA, immunofluorescence and double antibody sandwich ELISA, respectively. An exclusivity of 92Á5% was obtained with the reference method, further increased to 100% if pathogenicity tests were performed as a supplemental assay. The best level of sensitivity (relative detection level) was obtained with the reference method followed by the N-PCR assay. The N-PCR performance in terms of relative accuracy, accordance and concordance was very similar to that of the reference method. Moreover, N-PCR had undeniable advantages compared to the reference method (less labour-intensive and less time-consuming). In addition, post-test probabilities of infection were calculated to select the most appropriate detection scheme related to the prevalence of the pathogen. The N-PCR assay has since been included in a revised version of the EPPO detection protocol.