April 2024 - 18

Potatoes infected with soft rot.
ideal growing conditions for bacterial
soft rot pathogens to grow. "
Mid-Atlantic states saw more
bacterial soft rot symptoms, Leiby said,
with large losses in New Jersey.
" Several New Jersey potato fields
were not harvested because of tubers
breaking down just before harvest,
so these fields were abandoned and
disked, " he said. " We tried to track it
down and work backwards to figure out
where those seed potatoes came from
and how the infections took place. "
Carolee Bull, professor of bacterial
systematics and plant pathology in PSU's
Department of Plant Pathology and
Environmental Microbiology, led the
PSU team that identified the pathogens.
She said in a news release that the
findings could help better understand
disease epidemiology.
" For example, the pathogens may
have different optimum temperatures
for growing or for producing these
symptoms in the potatoes, " she
said. " So, the severity of the disease
may change depending on different
climate conditions. "
A FAMILIAR THREAT
While some of the species found
were novel, Bull told Spudman that soft
rot and blackleg are well-established
diseases in Pennsylvania.
18
Spudman * April 2024
A healthy potato plant does not show the wilting of those infected with blackleg.
" We are now armed with information regarding
who the enemy is. Now we need to come up with
management strategies. "
- Carolee Bull, Penn State University
" They may have been a problem on
and off, for as long as farmers have
been growing potatoes - depending on
environmental conditions and which
cultivars of potatoes were being used, "
she said.
The outbreak in 2014-2016, however,
drew increased attention.
" This disease was severe all over the
East Coast states and some other places,
so researchers around the country
began to try to tease apart exactly what
happened and identify the pathogens
present in those samples, " Bull said.
" We reported some of this research
previously, in a larger study around the
entire country, then did a more detailed
study just for Pennsylvania. "
Certain lots of certified seed potatoes
seemed to be more affected than others,
leading growers to wonder if the source
of the seed was part of the problem,
Leiby said. In addition, some varieties
seemed more susceptible than others.
The topic was much discussed among
North American plant pathologists
and potato seed producers in 2015.
Researchers at Colorado State
University, North Dakota State and the
University of Maine joined the hunt for
answers, Leiby said.
Bull did more detailed studies and
isolated pathogens from symptomatic
tissue samples.
" The organisms we reported
included a number that were new for
Pennsylvania and a couple that were
new to the U.S. " she said. " We don't
know if they are actually new; they had
not yet been isolated or distinguished
from other pathogens. "
In the past, similar pathogens had
been reported as Erwinia carotovora,
Erwinia chrysanthemi or Erwinia
atroseptica, Bull said. Erwinia carotovora
was isolated in the early 1900s.
" In recent years, more taxonomic
work has divided them into two
April 2024

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