USFWS
Genetic Monitoring for Managers
Alaska

 

Type of GEM

Category 1b GeM Project Example: Identifying pathogens and parasites

Monitoring changes in the diversity and distribution of plant pathogens: an example using Ralstonia solanacearum, a bacterial wilt.

Perez et al. 2008, Norman et al. 2009

There is an increasing need to monitor changes in genetic diversity of pathogens because this can affect their ability to utilize new host species and increase their rate of spread. Perez et al. (2008) were interested in genetic diversity of Ralstonia solanacearum, a bacterial wilt, in order to provide information for creating a breeding program for wilt-resistant tomatoes and ornamental plants. However, the genetic techniques they used could be used for monitoring changes in the genetic diversity and spread of pathogens. For example, their approach could have applicability to monitoring changes in genetic diversity of the oomycete plant pathogen Phytophthora ramorum that is responsible for Sudden Oak Death disease in North America, and how this diversity increases the spread to other host species beyond oaks.

 

The two examples shown here are focused on the soilborne bacterium R. solanacearum, which is considered the most destructive bacterial plant disease across the globe (Perez et al. 2008). It is widespread in the tropics and subtropics where it causes substantial economic impacts to important crops including potato, tomato, banana and tobacco. R. solanacearum entered North America on ornamental crop material, and has caused damage on anthurium, pothos, ornamental ginger, gerbera, zinnia, salvia, verbena, heliconia, sunflower, and geranium (Norman et al. 2009).

Both studies in this example were interested in the number of different strains of the bacterium and their place of origin; Perez et al. (2008) investigated different strains found on economic crops in Guatemala, whereas Norman et al. (2009) focused primarily on ornamental plants cultivated in the U.S. Both studies used a gene in the bacterium called endoglucanase, to look for variation among different strains. This was done by gene sequencing, which finds subtle differences in the order of nucleotides within the gene that could indicate different strains. Both studies also used a process called repetitive polymerase chain reaction (rep-PCR) to identify clusters of similar strains of the bacterium that could indicate different points of origin.

In Guatemala, bacterium collected at 59 sites indicated that there were 3 strains of the bacterium that matched strains previously identified from Asia and America (Perez et al. 2008). The study in North America collected 107 new strains of R. solanacearum and compared them with 32 previously identified strains, and found that most of the new strains were genetically distinct from the strains that were already infecting plants on the continent (Norman et al. 2009).

The methods used in these studies have potential applicability to natural ecosystems, where exotic pathogens are increasingly more prevalent. Managers could employ these methods to determine whether a given pathogen originated from one source or many, as well as monitor changes in genetic diversity in relationship to the number of host species.