The Effect of Composts on Field Soils Affected by Bacterial Wilt of Edible Ginger in Hawaii

Bacterial wilt caused by Ralstonia solanacearum is the most important disease affecting edible ginger (Zingiber officinale) in Hawaii.  Serious outbreaks began occurring in 1993 and large losses continue every year.  Ralstonia solanacearum is persistent in soil and following crop failure, fields are abandoned and left unsuitable for ginger production for many years.  A reliable and sensitive method utilizing enrichment followed by PCR was developed for detecting the pathogen in soil. This methodology proved to be a useful diagnostic tool in testing environmental samples and has become the method of detection for R. solanacearum testing on the Big Island of Hawaii at the University of Hawaii–Manoa College of Tropical Agriculture and Human Resources’ Agricultural Diagnostic Service Center (ADSC). This method was used in a 10-week pot study to determine the effect of soil amendments on the survival of R. solanacearum in naturally infested Hawaiian soils.  The soil amendments used included an initial application of vermicompost, vermitea, and IMOlizer at high, mid, and low rates.  At the end of the 10-week period none of the treatments showed an ability to significantly reduce bacterial abundance over time.  Some treatments showed an initial decline in bacterial abundance between 0–4 weeks but were followed by a sharp increase at the 6-week time point.  A future experiment using repeated applications of these amendments may address the loss of suppression over time.  A website explaining bacterial wilt, its symptoms, our method for detection, as well as management strategies, are now available at http://www.ctahr.hawaii.edu/dnn/gingerwilt for growers and the public to visit.