June 2019 - 10

Pathogens in asparagus crowns spotlighted
By Stephen Kloosterman
Associate Editor
Cleaner crowns are a way to avoid rot
in asparagus crowns, stems and roots, and
identifying the fungi on the plants may help
manage those pathogens.
A new study by Michigan State
University (MSU) is examining the role
pathogens play in limiting asparagus
yields. Sara Getson, a master's degree
student studying under Mary Hausbeck,
chair of MSU's Department of Plant, Soil
and Microbial Sciences, spoke about her
research at Oceana Asparagus Day, held in
March in New Era, Michigan.
Michigan is the country's secondhighest
asparagus-producing state,
behind Washington, and Oceana and
Mason counties, in the northwest corner
of the state's lower peninsula, together
are Michigan's largest asparagusgrowing
region.
" The take-home message from our
research thus far is to employ strong
management strategies at the nursery
level, " she said. " Since fusarium is
a seed-borne pathogen in asparagus,
control tactics are most effective and
feasible before transplanting into the
production fields. "
She conducted a survey experiment
to find out what species of fusarium are
associated with one-year-old transplants,
and then which of those are capable of
causing disease in asparagus. A similar
Getson said. " Some are known to just
hang out. "
Previous studies have found the
presence of pathogenic species including
proliferatum, oxysporum and moniliforme.
" It will be interesting to see if
they've shifted at all, " Getson said.
In the meantime, she said, the most
Asparagus roots, left, and crown, right, exhibiting symptoms of fusarium infection.
Photo: Michigan State University/Sara Getson
survey hasn't been conducted in nearly
30 years in Michigan asparagus, and a
better picture of the pathogens would help
inform management recommendations
seeking to target those specific diseasecausing
fusaria species, she said.
One-year-old crowns of asparagus
were pulled from three growers, two from
Oceana County and one in southwest
Michigan's Berrien County - another
production area in the state.
Preliminary results showed that fungi
from the fusarium genus were present in
crowns from all three areas and between
the different cultivars that were sampled -
Jersey Supreme, Guelph Millennium and
Guelph Eclipse. It was also present in both
fields that had been fumigated before and
those that had not. Infection rates ranged
from 25% to 47%.
The concern for asparagus growers
is that certain fusarium species - not
all - can weaken the plant if it is stressed
by high heat and drought, causing stem,
crown and root rot.
Growers can diagnose the presence
of fungi from the fusarium genome to
an extent. Chlorosis (yellowing) and
dying back of the ferns is one symptom.
Digging up asparagus crowns, especially
of mature plants, can be a prohibitively
difficult, but on asparagus crowns and
roots - the fusarium lesions appear as
red-brown sections on the roots and in a
cross-cut section of the crown.
Getson is cultivating tissue samples
from the crowns in the survey study.
The next step is sequencing the DNA
from the samples to see which fungi are
present. She will later grow asparagus
seedlings and inoculate them with
different fusarium species collected to
see if they can cause disease.
" Some are known to be pathogenic, "
effective practice continues to be
soaking crowns in fungicide prior to
their being transplanted. According
to a separate study Hausbeck's group
conducted, biological fungicide products
didn't seem to have much effect.
" Industry standard treatment of
Cannonball WP was the only treatment
that resulted in statistically healthier
crowns compared to the untreated
control, " according to the study
proceedings published for Oceana
Asparagus Day. " Cannonball-treated
crowns produced seedlings with
significantly increased fern weight "
compared to other products.
Fusarium fungi species can linger in
the ground years after they are spread
by a new planting, Getson said.
" A major reason that we are targeting
the nursery crowns and the seedbeds for
management is primarily because once
you get the asparagus crowns into the
production field, they can be susceptible
to whatever that's out there, " she said.
" And once the crown is established, it's
really difficult to get materials down to
the crown, the root system. " VGN
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June 2019

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