Activity 11.2, Biotechnology project: characterization of Ralstonia solanacearum strains from eggplant

Bacterial wilt caused by Ralstonia solanacearum, is a limiting factor on eggplant production throughout Asia. Race 1 Strains are generally associated with bacterial wilt in eggplant. Of the 289 R.solanacearum strains classified into biovars, 16(8%) out of 200 isolated from Pangasinan belonged to biovar 3 while 184 (92%) were biovar 4 out of 43 Quezon isolates 20 (46.5%) were biovar 3 and 23 (53.5%) were biovar 4. For the Batangas isolates, 12(38.7%) were biovar 3 and 19(61.3%) belonged to biovar 4. Most of the Nueva Ecija isolates (12/15 = 80%) were biovar 3, while the remaining strains were biovar 4. During the 2003 dry season, 505 eggplant samples from 48 fields were collected and tested for R. solanacearum by culturing and immunoassay (Rs BID ELISA and Rs Immuno Strip, Agolia Inc., Elkhart, IN USA). Results were the same for ELISA and culturing for 69.5% of the samples (55% both positive, 15.5% both negative). For 28.3% of the samples, ELISA was positive but R. solanacearum was not recovered; in 1.2% of the samples of R. solanacearum was recovered by culturing but ELISA was negative. Both ELISA and culturing were negative for all samples taken from three fields in which no bacterial wilt was observed. ELISA and ImmunoStrip results were the same for 91% of the samples. For the remaining 9%, ImmunoStrip results were positive while ELISA results were negative. Of the 59 R. solanacearum isolates evaluated for aggressiveness using eggplant. Eg 203, Abar and Casino cultivars, 5 isolates had 33% bacterial wilt infection to the resistant cultivar Eg 203. SAS cluster analysis grouped the isolates into 9 clusters. Most of the virulent isolates belonged to cluster 1 to 5 while the less virulent were in clusters 6 to 9. No correlation was observed between aggressiveness, biovar and origin.