Second International Bacterial Wilt Symposium
The Second International Bacterial Wilt Symposium took place in Gosier, Guadeloupe, on 1997-06-22/27. Many papers and posters were presented on the following subjects: diversity, diagnosis, pathogenicity, host resistance, biological control and epidemiology, disease management. The EPPO Secretariat has extracted the following information.
1) Genetic diversity of Ralstonia solanacearum (EPPO A2 quarantine pest) race 3 in Western Europe was determined with molecular techniques. 22 strains from the Netherlands, 4 from United Kingdom, 1 from Sweden and 3 from France were examined. In addition, three race 3 strains and three race 1 strains from outside Europe were included in the study for comparison. Race 1 could clearly be separated from race 3. But within race 3, only a small variation was observed. No relation was found between geographical origin of race 3 strains and their profiles. The existence of a small variation could indicate that the potato material which has been responsible for the introduction of the pathogen into various European countries contained several clonal lines of race 3. (van der Wolf, J.M. et al. Genetic diversity of Ralstonia solanacearum race 3 in Western Europe determined by AFLP, RC-PFGE and PCR with repetitive sequences. p 15).
2) In Japan, the genetic diversity of R. solanacearum was studied. The bacterium was isolated from various host plants (pumpkin, Perilla, Strelitzia, strawberry, statice (Limonium sinuatum) and solanaceous crops). Two races and four biovars have been identified. Race 1 (biovars 1 and 4) is the most common race, race 3 (biovar 2) has been found in potatoes in Nagasaki. (Tsuchiya, K.; Horita, M. Genetic diversity of Ralstonia solanacearum in Japan. p 17)
3) In Pakistan, 40 isolates of R. solanacearum were isolated in various provinces from wilted chilli, tomato, potato plants and diseased potato tubers. Preliminary studies showed that 37 isolates from the semi-tropical tomato, chilli and potato-growing areas belonged to biovar 3, and that 3 isolates from potatoes grown in the north West Frontier Province (cool, humid and hilly area ) belonged to biovar 2. (Burney, K.; Ahmad, I. Biovars of Ralstonia solanacearum in Pakistan. p 21)
4) Bacterial wilt in Réunion island is caused by strains of either race 1 (biovar 3) or race 3 (biovar 2) of R. solanacearum. Symptoms caused by strains of race 1 are exclusively observed in lowlands (at altitudes lower than 1000 m). Race 3 (biovar 2) strains are recovered from almost all wilted potato plants growing on the hills (at altitudes over 1000 m). ;(Nicole, J.F. et al. A tentative explanation of the geographical distribution, on Réunion island of bacterial wilt caused by either biovar 2 or biovar 3 of Ralstonia solanacearum. p 62)
5) In 1991-93, fields surveys were done in Sri Lanka on potato, tomato, capsicum and aubergine (Solanum melongena) grown at 28 locations in the hilly part of the island, to detect R. solanacearum. Biovar 2 was only found on potatoes grown in the wet areas at 1860 m altitude. Biovar 3 was found in potato, tomato, aubergine and capsicum in both highlands and lowlands. Biovar 4 was observed only in potato fields where biovar 3 was also detected. (Kelaniyangoda, D.B. Field survey and identification of biovar type of Ralstonia solanacearum in solanaceous crops grown in the hill country of Sri Lanka. p 95.)
6) Field experiments were conducted in Nepal in 1995 and 1996 to determine the effects of latent tuber infection and soil infestation by R. solanacearum race 3 on the incidence of potato brown rot. Two sources of seed potatoes were used: pre-basic seed potatoes (free from the pathogen); and farm-saved seed potatoes (15 to 19 % were latently infected). Three different soils were compared: a non-infected soil, and 2 naturally infected soils where potatoes (affected by the disease) had been grown 7 or 18 months prior to the experiment. Differences in disease incidence with seed-health status were highly significant for 1995 and 1996. In infested plots with a 7-month break between successive potato crops (irrespective of seed-health status), differences in disease incidence (average 48.2 % in 1995 and 63.2 % in 1996) with different levels of soil infestations were significant. However, in plots where an 18-month break between potato crops was in place, there was no significant difference in disease incidence (average 32.5 %) between non-infested and infested soils. (Pradhanang, P.M.; Elphinstone, J.G. The relative importance of latent tuber and soil infestation by Ralstonia solanacearum on the incidence of bacterial wilt of potato. p 114.)
Sources
Abstracts of papers presented at the Second International Bacterial Wilt Symposium, Gosier, Guadeloupe, 1997-06-22/27.