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The identification and detection of Pseudomonas syringae pv. papulans, the causal agent of blister spot of apple, on apple leaves and fruit was achieved by polymerase chain reaction amplification of a specific DNA fragment of the hrpL sequence. The consensus primers hrpL(1) and hrpL(2) were designed based on the alignment of pseudomonad hrpL gene sequences available in nucleic acid data banks. This primer set produced a 631-bp amplicon from 37 of the 57 pseudomonads strains tested. These strains belonged to genomospecies 1 and 2, as described by Gardan et al. (8). The amplicon obtained from 30 of these strains was digested with eight restriction enzymes. Three different restriction patterns were produced from strains belonging to genomospecies 1, resulting in A1 and A2 patterns, while strains belonging to genomospecies 2 were characterized by a B pattern. Patterns A1 and A2 differed at only two sites, a Bsp 143I site located at nucleotide 360 and a MseI site located at nucleotides 22-24. Group A2 consisted solely of P. syringae pv. papulans strains. The hrpL gene in P. syringae pv. papulans strain CFBP3323 was sequenced. Two primer sets, Pap1/Pap2 and Pap1/Pap3, were designed and tested for specificity to P. syringae pv. papulans. These primers amplified expected fragments of 242 and 303 bp, respectively. Pap1/Pap2 amplified a fragment only with P. syringae pv. papulans DNA, while Pap1/Pap3 amplified all tested strains belonging to genomospecies 1. A diagnostic procedure using the Pap1/Pap2 primer set was successful for the detection of P. syringae pv. papulans in diseased fruit and artificially inoculated leaves.

A technique based on the use of specific primers for polymerase chain reaction (PCR) was developed for the identification of the stem and bulb nematode belonging to the Ditylenchus dipsaci species complex. The internal transcribed spacer region ITS1 and ITS2, the gene 5.8 S and part of genes 18 S and 26 S of twenty populations of the D. dipsaci species complex belonging to both D. dipsaci sensu stricto and Ditylenchus sp. B (corresponding to populations of giant individuals associated to Vicia faba) and three congeneric species were amplified with two universal ribosomal primers. PCR-amplified DNA samples were digested with five restriction enzymes in order to reveal some polymorphism allowing the identification of D. dipsaci populations associated with Fabaceae seeds. The polymorphism among species was confirmed by the sequencing of the PCR products. A primer (DdpS2) was designed in a region conserved in all populations of both D. dipsaci sensu stricto and D. sp. B studied in the present work. The other Anguinidae species (except a few species from Central Asia associated to Astereaceae and D. sp. G associated to Plantago maritima) differ in two to four nucleotides at the 3 0 extremity of this region. This sequence portion coincides with a TspEI restriction site. In combination with a primer located in the ribosomal region, this first primer is a good candidate for identification by PCR of populations of the D. dipsaci species complex found in Fabaceae seeds. A second primer (DdpS1) was designed in a similar way and was specific to D. dipsaci sensu stricto. The utility of these two sets of primers is discussed against the background of quarantine regulation.

Xanthomonas campestris pv. campestris (Xcc) causes the black rot of cruciferous plants. This seed-borne bacterium is considered as the most destructive disease to cruciferous crops. Although sources of contamination are various, seeds are the main source of transmission. Typical symptoms of black rot were first observed in 2011 on cabbage and cauliflower fields in the main production areas of Algeria. Leaf samples displaying typical symptoms were collected during 2011 to 2014, and 170 strains were isolated from 45 commercial fields. Xcc isolates were very homogeneous in morphological, physiological and biochemical characteristics similar to reference strains, and gave positive pathogenicity and molecular test results (multiplex PCR with specific primers). This is the first record of Xcc in Algeria. Genetic diversity within the isolates was assessed in comparison with strains isolated elsewhere. A multilocus sequence analysis based on two housekeeping genes (gyrB and rpoD) was carried out on 77 strains representative isolates. The isolates grouped into 20 haplotypes defined with 68 polymorphic sites. The phylogenetic tree obtained showed that Xcc is in two groups, and all Algerian strains clustered in group 1 in three subgroups. No relationships were detected between haplotypes and the origins of the seed lots, the varieties of host cabbage, the years of isolation and agroclimatic regions.

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