BACTERIAL WILT HOST RELATIONSHIPS
Floral and Nursery Plants Research Unit
2009 Annual Report
1a.Objectives (from AD-416)
To determine the susceptibility of commercial geranium (Pelargonium) cultivars to bacterial wilt caused by Ralsonia solanacearum, and whether certain plants may act as asymptomatic hosts; to determine whether susceptibility is correlated with genetic relatedness of the host cultivar; to determine the susceptibility of other greenhouse-grown ornamental crops to Ralstonia solanacearum; to compare isolates of the bacterium from different outbreaks to correlate with geographic origin; to determine freeze survival of the bacterium in soil; to investigate chemical control measures; and to identify genes associated with the survival and pathogenicity at different temperatures, evaluate pathogen populations in relation to their ability to cause pathogenicity to agricultural crops at various temperatures and determine potential environmental fate and movement in the United States.
1b.Approach (from AD-416)
An empirical approach will be used to examine the genetic and physiological capability of exotic strains of bacterial wilt to access their ability to become established and spread within U.S. agriculture. Once introduced Ralstonia solanacearum is know historically to be spread via river systems. The project will further address the survival of distinct genetic populations in various water types and assess the ability to infect and survive under different temperature regimes.
Ralstonia solanacearum race 3 biovar 2 (R3B2) strains are distributed in the coldest areas of the world where R. solanacearum is found and are therefore thought to be cold tolerant. Previously we had determined that there are putative cold shock genes that aid in the survival of R3B2 and that some race 1 strains in the US also have these genes. We also compared the pathogenicity of R3B2 strains with other races of Ralstonia in environmental chambers at 18C and at 30C. Both UW551 and R1B1 strains isolated from ornamentals were found to be pathogenic on tomato and potato at both 18C and at 30C, although variation in virulence was observed among isolates tested. We concluded that there are other genes that are not unique to R3B2 that aid in pathogenicity under cool weather conditions. In order to determine what genes were being expressed during pathogenicity inducing conditions, protein profiles were compared under both warm and cool weather conditions for multiple strains of bacterial wilt. We identified a set of proteins differentially produced under cool weather in strains with different pathogenic behavior at cool temperatures. Expression of some of these proteins seems correlated with the pathogenic behavior of specific strains and is potentially linked to pathogenicity at different temperatures.
Agricultural globalization has accentuated the movement of plant pathogens into new environments. Many of these plant pathogens are not unique to tropical, subtropical, or temperate regions of the world. Therefore their introduction poses no additional risk to agriculture or the environment. However, there are exceptions. One of these exceptions is “Bacterial Wilt” caused by Ralstonia solanacearum. Certain Races of this pathogen have been designated as a “Select Agent” under the Agricultural Bioterrorism Protection Act of 2002. Ralstonia solanacearum Race 3, Biovar 2 strains (R3B2) have been given this designation because of historical evidence of their ability to survive and kill solanaceous crops such as potato under cool climate conditions. Strict regulations have been implemented by USDA/APHIS in order to prohibit establishment of R3B2 in the United States. It is important to determine the potential environmental fate and movement of different Ralstonia solanacearum populations within the United States. This research will provide information necessary for prudent regulatory procedures.
Research activities under this agreement were monitored by e-mails, reports, and in-person discussion when attending a professional meeting.