Agrobacteria Enhance Plant Defense Against Root-Knot Nematodes on Tomato.

The increased incidence of the crown gall disease caused by Agrobacterium tumefaciens has long been associated with activities of root-knot nematodes (Meloidogyne spp.). Pot experiments on tomato were designed to assess plant vitality, nematode reproduction, and crown gall incidence in combined infection with Agrobacterium and Meloidogyne spp. on tomato roots. Results suggest that tomato plants infected with pathogenic A. tumefaciens 2 days before the nematodes show enhanced plant defense against M. ethiopica resulting in lower egg and gall counts on roots 45 and 90 days postinoculation (dpi); no significantly enhanced defense was observed when the plant was inoculated with bacteria and nematodes at the same time. Split-root experiments also showed that the observed interaction was systemic. Reverse-transcription quantitative polymerase chain reaction analysis that targeted several genes under plant hormonal control suggests that the suppression was mediated via systemic acquired resistance by the pathogenesis-related protein 1 and that M. ethiopica did not enhance the defense reaction of tomato against Agrobacterium spp. Nematodes completely inhibited tumor growth in a 45-day experiment if inoculated onto the roots before the pathogenic bacteria. We conclude that the observed antagonism in the tested pathosystem was the result of initially strong plant defense that was later suppressed by the invading pathogen and pest.

Complete genome sequences of blueberry red ringspot virus (Caulimoviridae) isolates from the Czech Republic and Slovenia.

Genomic DNA of blueberry red ringspot virus (genus Soymovirus, family Caulimoviridae) from highbush blueberry plants growing for years in the Czech Republic and Slovenia was sequenced. The circular dsDNA genomes consist of 8,303 and 8,299 nt, respectively, and contain eight open reading frames (ORFs) longer than 100 amino acids. The European isolates are 90% to 99% identical in aa sequences of distinct proteins. In contrast to the American New Jersey isolate, in-frame initiation codons have been found upstream from AUG codons of ORFs I, IV and V in the European isolates. These and other differences resulted in a longer capsid protein, reverse transcriptase, movement protein and protein the encoded by ORF VII and reduced (75.4% to 93.7%) amino acid identity with corresponding proteins of the New Jersey isolate.

Development and inter-laboratory evaluation of real-time PCR assays for the detection of pospiviroids.

Assays based on real-time PCR (TaqMan) that can detect a number of viroids in the genus Pospiviroid have been developed and evaluated. The assays are designed for detecting viroids from tomato leaf material but detection from other solanaceous hosts of these viroids has been confirmed. These methods have been validated by nine laboratories and comprise a reliable set of assays for the detection of CEVd, TASVd, CLVd and a generic assay which will detect the six viroids of concern to European tomato growers: PSTVd, TCDVd, CEVd, CLVd, TASVd and CSVd.