Download Managing Goss’s Wilt in Manitoba

Managing Goss’s Wilt in Manitoba
Wilt Billing & Bryce Rampton - DuPont Pioneer
Background
Symptoms
Hybrid Screening
In 2009, Goss’s Wilt Bacterial Blight (Clavibacter michiganensis subsp.
nebraskensis) was confirmed in Manitoba corn fields. The disease was first
discovered in corn fields in two Nebraska counties in 1969. For several
decades it remained confined to this region in the western corn belt.
However in the mid to late 2000’s it spread beyond this area. Presently, it
was confirmed in several US states previously thought not to contain the
disease (Figure 1). In 2013 it was also confirmed in 5 corn fields in Alberta.
Symptoms of Goss’s wilt often appear following the tassel stage on the upper
canopy. Early leaf symptoms are elongated lesions of water-soaked, grayishgreen tissue that progress to long dead streaks with wavy, irregular margins
(Figure 3a). These streaks extend along the leaf veins, which suggests a
bacterial infection. One of the most characteristic symptoms of Goss’s wilt is
leaf “freckles” that develop within the streaks. In addition, a sticky exudate
forms in the lesion, which dries to form a glistening residue, or varnish, along
the edge of the lesion. As lesions enlarge, they form large areas of necrotic
tissue on the leaves (Figure 3b), and eventually, leaves wilt and dry up (Figure
3c). Wet weather and high relative humidity encourage development of Goss’s
wilt. The disease tends to be more severe in or adjacent to fields with high
levels of corn residue
Plants may also be infected systemically by Goss’s wilt, especially in the
seedling stage. These plants have discolored vascular tissue (Figure 3d), with a
slimy bacterial exudate in the stalk. Plants are commonly stunted and wilt or die
as if drought stressed.
In order to provide products with high levels of resistance DuPont Pioneer has
actively screens its inbred and hybrid germplasm. Screening activities
historically done in La Salle, CO have since expanded across the corn
growing regions following the spread of the disease. Local screening
activities performed out of DuPont Pioneer’s Carman, MB and Moorhead, MN
research centers have been facilitating the development of resistant hybrids in
the <85CRM maturity for western Canada.
.
3a
3b
Researchers artificially wound plants and apply inoculum produced from local
bacterial strains into the opening in the leaf tissue creating a consistent entry
point for the organism. This consistent pressure in a controlled environment
is essential to understand exact levels of resistance and to provide accurate
ratings for growers on commercial products.
Figure 5: DuPont Pioneer
Hybrid Disease
Classification Scale
1
3
Susceptible
5
Moderately
Resistant
7
9
Resistant
Pioneer also utilizes molecular breeding techniques in conjunction with its
field screening to identify alleles responsible for resistance in it’s germplasm.
Once hybrids are commercialized, further categorization takes place in
DuPont Pioneer’s Proving GroundTM field scale strip trials planted throughout
areas of known Goss’s infection. Differences in Goss’s resistance are rated to
verify disease characterizations. This step provides confidence in Goss’s wilt
resistance hybrid ratings and allows hybrids showing improved resistance to
Goss’s wilt to be positioned in areas of know infection. Currently, several
hybrids are identified and commercially available with moderately resistant or
resistant ratings for Goss’s wilt.
3d
3c
Figure 1: Current Distribution of Goss’s Wilt across North America (Map courtesy of
DuPont Pioneer, Johnston Iowa).
In recent years the disease has spread across the main corn growing region
of Manitoba’s Red River Valley. Goss’s wilt can be a minor problem, or it
may cause devastating damage with corn yield losses of 50 percent. With
the spread of the disease across the corn belt and into Western Canada,
managing Goss’s Wilt is becoming a priority for producers in new corn
growing regions. Surveys conducted by DuPont Pioneer from 2010-2013
identified Goss’s Wilt throughout the Red River Valley. This poster helps to
identify Goss’s Wilt, and outline methods used to manage it
Disease Lifecycle
Local screening for disease resistance, along with other key agronomic traits,
offer a complete corn hybrid package for growers in affected regions, aiding
corn producers in Western Canada to combat Goss’s Wilt.
Management
Figure 3: Various Stages of Goss’s Wilt infection (Photo’s provided by Scott Heuchelin,
DuPont Pioneer Research Scientist - Field Pathology)
Observations
Goss’s wilt limits yield by reducing green leaf area and causing premature
death in corn plants. Timing of the infection plays a critical role in the disease’s
influence on grain yield. Early infections lead to the greatest yield reductions,
whereas late infections may have little yield impact. Yield reductions in excess
of 50% have been documented in Manitoba when susceptible hybrids were
infected early in the growing season (pre-tassel). Other agronomic issues such
as stalk lodging may result from fields that have prematurely died from Goss’s
wilt. This can result in further yield reductions (harvest losses) and quality.
Infected Plants
Uninfected Plants
Since Goss’s Wilt is a bacterial disease, no rescue measures are available for
it’s control. Fungicides have no activity on bacterial infections. Preventing or
avoiding infection are crucial. Where the disease is already present in a field,
growers can minimize damage by using these management practices:
Prevention/Sanitation
Goss’s wilt may be transmitted from field to field by equipment and weather
that move infected residue. Harvest and tillage equipment, balers, and wind
can all transfer infected residue and soil to previously uninfected fields. To
help avoid spreading the pathogen, harvest and till infected fields last and
clean equipment of crop residue and soil before moving to other fields.
Reducing Corn Residue & Grassy Weeds
Crop rotation, tillage and good weed control, can reduce the amount of
residue remaining on the soil surface to infect the new crop. Crop rotation to a
non-host crop such as soybeans, dry beans or alfalfa allows for an additional
year of corn residue decomposition between corn crops. Deep tillage is
especially effective at incorporating and burying infected residue. However,
these practices only reduce, but do not prevent disease occurrence. Goss’s
wilt can still occur on fields that are first-year corn and in fields that are
plowed. Goss’s wilt also survives on barnyard grass and green foxtail.
Resistant Hybrids
With identification of levels of resistance to Goss’s wilt in early maturing
parent lines and hybrids, hybrid resistance is the primary method for disease
management of Goss’s wilt. Continued local screening of genetic material,
identification of sources of resistance, and recombination into new, improved
hybrids, are instrumental to combating this disease.
Figure 2: Lifecycle of Goss’s Wilt (Courtesy of DuPont Pioneer, Johnston, Iowa)
Figure 4: Ear size reduction caused by Goss’s Wilt (Photo provided by Wilt Billing, DuPont
Pioneer September 2011)
References
Field Facts - Goss’s Wilt of Corn, DuPont Pioneer 2005
www.Pioneer.com