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
Perez et al.
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.