ARS | Publication request: Susceptibility of Geranium Cultivars (Pelargonium spp.) to Ralstonia solanacearum

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 2009
Publication Date: August 16, 2009
Citation: Norman, D.J., Huang, Q., Yuen, J.M.F., Mangravita-Novo, A., Byrne, D. 2009. Susceptibility of Geranium cultivars to Ralstonia solanacearum. HortScience. 44(5):1-5.

Interpretive Summary: Geraniums (Pelargonium spp.) have been cultivated for more than 350 years and are one of the most popular bedding plants worldwide. Geraniums are suseptible to bacterial wilt caused by Ralstonia solanacearum that is distributed worldwide and attacks over 450 plant species. R. solanacearum contains many strains that differ in host range, geographical distribution, pathogenicity and biochemical properties, and are generally classified into five races based on host range and five biovars according to their biochemical properties. In our study, we tested sixty-one cultivars of geranium including zonal, regal, ivy, and scented for their susceptibility to three different strains of Ralstonia solanacearum found in the United States or imported from infected plant propagative material. We found that the two race 1 biovar 1 (R1B1) strains were more virulent on most cultivars of zonal, regal and ivy geraniums than the race 3 biovar 2 (R3B2) strain. The R3B2 strain had a much narrower host range and was not able to infect most regal geranium cultivars when applied as a soil drench. Many of the scented cultivars were found to be resistant to all three strains of R. solanacearum. Our study will be of value primarily to geranium breeders and growers, as well as plant pathologists interested in bacterial wilt caused by R. solanacearum.

Technical Abstract: Sixty-one cultivars of geraniums including zonal, regal, ivy, and scented were tested for susceptibility to three strains of Ralstonia solanacearum: a Race 1 Biovar 1 (R1B1) strain P597 isolated from tomato in Florida, a R1B1 strain P673 obtained from pothos originating in Costa Rica, and a Race 3 Biovar 2 (R3B2) strain UW551 isolated from geranium imported from Kenya. These three strains represent populations of R. solanacearum found in the United States or imported from infected plant propagative material. A genetic comparison of the geranium cultivars was also done using amplified fragment length polymorphisms. Both R1B1 strains were more virulent than the R3B2 strain, producing wilt symptoms on most cultivars of zonal, regal and ivy types. Variation in susceptibility of geranium cultivars to the two R1B1 strains was observed. The R3B2 strain UW551 had a much more restricted host range and was not able to infect most regal geranium cultivars when applied as a soil drench. Many of the scented cultivars were found to be resistant to all three strains of R. solanacearum, when tested using the drench inoculation method. The greatest variation in type of resistance was observed between the scented geranium cultivars and specific strains of R. solanacearum.