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The Ralstonia solanacearum species complex (RSSC) can cause bacterial wilt in a wide variety of plant species, including a number of ornamental glasshouse crops. Recently in Europe, ornamental rose plants for the production of cut flowers and propagation materials have been strongly affected by Ralstonia pseudosolanacearum , phylotype I, biovar 3. To test for the presence of the pathogen in the glasshouse, sampling of water from a drainage gutter or well may be an efficient strategy since it is known that RSSC can be released from infected root systems in the water. A protocol was developed to detect low densities of R. pseudosolanacearum in drain water collected from rose growers. Drain water was filtered through a bacterial filter, the filtrate was collected and target bacteria enriched for 48 h in Semi‐selective Medium South Africa (SMSA) broth supplemented with sterilized tomato plant extracts. DNA extracted from the enrichment broth was analysed using a TaqMan test in a duplex format, based on specific egl sequences of RSSC and the use of an extraction and amplification control. The optimized protocol had a detection level of ≤1–10 colony forming units of R. pseudosolanacearum in drain water.

The virulence of Meloidogyne hapla, M. chitwoodi, and M. fallax was studied on genotypes of Solanum spp. in a greenhouse. Juveniles of 11 M. hapla race A isolates, 3 M. hapla race B isolates, and 5 mono-female lines of a M. hapla race A isolate were inoculated on S. chacoense, S. hougasii, and S. sparsipilum. Juveniles of eight M. chitwoodi isolates, five M. fallax isolates, and six mono-female lines of a M. chitwoodi isolate were inoculated on S. bulbocastanum, S. chacoense, S. hougasii, S. stoloniferum, and S. tuberosum. Virulence was expressed as nematode reproduction 8 weeks after inoculation. Nematode reproduction was estimated by the number of egg masses and, in one experiment, by the number of hatched second-stage juveniles per inoculated juvenile. Considerable variation in virulence and resistance was observed among M. hapla isolates and plant genotypes, respectively. The M. hapla isolate-plant species interaction was highly significant. The response to M. chitwoodi ranged from susceptible (S. tuberosum and S. chacoense) to highly resistant (S. bulbocastanum and S. hougasii). S. tuberosum was susceptible to M. fallax, whereas all four wild species were resistant. In contrast to M. hapla, no significant isolate-plant genotype interaction was obtained for M. chitwoodi or M. fallax, indicating no or little intraspecific variation in virulence. M. chitwoodi juveniles in species mixtures with M. fallax isolates appeared to be able to break the resistance of S. bulbocastanum and S. hougasii. Significant differences among mono-female lines of M. hapla and M. chitwoodi were observed, indicating heterogeneity of pathogenicity within meiotic parthenogenic Meloidogyne populations.

To study virulence and aggressiveness in root-knot nematodes on cultivars of potato (Solanum tuberosum L., four isolates of Meloidogyne hapla Chitwood race A, one of M. hapla race B, three of Meloidogyne chitwoodi Golden et al., and two of Meloidogyne fallax Karssen were evaluated on 10 commercial potato cultivars under semisterile conditions in Petri dishes. Virulence and aggressiveness were assessed in terms of nematode reproduction by egg-mass index and reproduction factor, estimated by the number of egg masses and juveniles produced, respectively, divided by the number of juveniles inoculated. Significant interaction for both parameters was revealed between species of Meloidogyne and potato cultivars. Only M. hapla showed significant isolate-by-cultivar interaction, which was predominantly caused by the M. hapla race B isolate Hh. This indicates variation in virulence and suggests the occurrence of different genetic factors for virulence and resistance in M. hapla isolates and potato cultivars, respectively. Despite large differences, the observed levels of resistance were too low to be of practical meaning for breeding, with the exception of resistance to isolate Hh. No significant differences were obtained between isolates of M. chitwoodi and M. fallax or isolate-by-cultivar interaction, indicating neither variation in aggressiveness nor in virulence in the isolates used. A comparative greenhouse experiment gave comparable results for egg-mass index but contradicting results for reproduction factor, most likely because of differences in life cycle, which appeared to be shorter in M. fallax than in M. hapla and M. chitwoodi. The Petri-dish method proved to be accurate for virulence studies of root-knot nematodes on potato culitvars. Meloidogyne fallax was most aggressive on potato, followed by M. chitwoodi, M. hapla race A, and finally by M. hapla race B. Key words: aggressiveness, biadditive model, biplot, plant breeding, resistance, virulence.