Evaluation of immunoassays for detection of Ralstonia solanacearum, causal agent of bacterial wilt of tomato and eggplant in the Philippines

Bacterial wilt, caused by Ralstonia solanacearum, is a limiting factor in tomato and eggplant production throughout Asia. Race I strains are generally associated with bacterial wilt in both crops. 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 ImmunoStrip, Agdia 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 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. Two hundred eighty nine strains of R. solanacearum isolated in the survey were identified to biovar level: all were biovars 3 or 4. In a second immunoassay evaluation subsequently carried out in eggplant in the 2003 wet season, ELISA and culturing results were the same in 96.2% of 105 samples.