Bacterial Wilt of Artichoke caused by Ralstonia Solanacearum in Egypt

Much attention has been paid to increasing the yield of artichoke (Cynara scolymus) in Egypt in recent years. During an extension program, a wilt disease was first observed to cause considerable losses in some fields of the main production areas (Kafr Eddoar and Bosaly in Behara and Etfeeh in Giza) during the 1998-99 growing season. Disease incidence ranged from 5-20% with symptoms appearing 6-8 weeks after transplanting. Affected plants were pale and stunted. Petioles of lower leaves were water-soaked whilst the leaves themselves were purplish with a yellow margin, later becoming necrotic and dropping off. Subsequent leaves also developed the same symptoms. The growing apex collapsed, stunted side shoots appeared but then wilted and died. Transverse sections of roots and stems of affected plants showed browning of the vascular bundles on which ooze soon appeared.

Isolations were performed on triphenyl tetrazolium salt (TTC) medium (Kelman, 1954), according to Adhikari (1993). Six samples, each of four plants, from three fields in the two main production areas were used for isolation. Bacteria with similar characteristics were isolated from all samples and produced fluidal colonies which were either entirely white or white with a red centre after incubation for 72 h at 28°C on TTC medium. They were positive for poly-b -hydroxybutyrate, oxidase, gelatin hydrolysis, nitrate reductase, levan formation, utilisation of L-histidine, L-asparagine and sucrose and negative for arginine dihydrolase, starch hydrolysis, utilisation of D-alanine, glycerol and glucose (Palleroni, 1984). A positive reaction was obtained in immunofluorescence antibody staining (IFAS) as described by Janse (1988). Isolates were therefore identified as Ralstonia (Pseudomonas) solanacearum.

Two isolates were each inoculated into twenty plants using the method of Adhikari (1993), together with 20 control plants. Typical symptoms were seen on the inoculated plants within four weeks of inoculation and by eight weeks all plants had wilted and died. Bacteria with the same characteristics as those inoculated were successfully re-isolated. Uninoculated control plants remained healthy. This is thought to be the first report of Ralstonia solanacearum causing a wilt disease in artichoke.