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Maize ear rots under
different cropping systems
T
he fungi that cause maize ear rots commonly known as
Gibberella (
Fusarium graminearum
), Fusarium (
Fusarium
verticillioides
) and Diplodia (
Stenocarpella maydis
) can also
produce mycotoxins in maize grain.
In maize, the most important stage of ear rot infection and mycotoxin
contamination is during pre-harvest production, where disease in-
cidence and mycotoxin contamination are influenced by numerous
factors ranging from climatic conditions, soil fertility, insect damage,
susceptibility of plant variety and agricultural practices.
Tillage influences both the physical and chemical properties of the
soil and increase inoculum pressure of these fungi, therefore a re-
duction in tillage practices may significantly influence maize ear rot
fungi, but this is entirely dependent on the individual fungi’s life cycle
and survival mechanisms. Crop rotations have also been identified
as a viable method for disease control in no-till systems.
These cropping systems have not been sufficiently evaluated in
South Africa and therefore the effect of cropping systems and the
role of crop rotations on maize ear rots and mycotoxins were investi-
gated in Buffelsvallei (North West Province) and Erfdeel (Free State)
over a six-year (2009/2010 - 2014/2015) and four-year (2011/2012
- 2014/2015) period, respectively.
Cropping systems evaluated (
Table 1
) were:
Monoculture maize conventional tillage
Monoculture maize no-till
Two- and three-year rotation systems consisting of maize
cowpea and maize
cowpea
babala (all no-till), respectively.
In Buffelsvallei, two additional crop rotations, maize
sunflow-
er and maize
sunflower
babala (all no-till) were included.
Naturally infected trials were visually evaluated for disease sever-
ity or incidence while fungal and mycotoxin contamination of maize
grain were quantified.
Buffelsvallei
Fungal contamination
According to statistical analyses, the cropping system had a signifi-
cant effect (P = 0,01) on Gibberella ear rot infection (
Table 2
) and
Diplodia ear rot incidence (P = 0,01,
Table 3
) in the 2010/2011 season.
Gibberella ear rot was significantly higher in the three-year maize
cowpea
babala rotation and Diplodia ear rot incidence was signifi-
cantly higher in the three-year maize
cowpea
babala and maize
cowpea
sunflower rotation.
It is important to note that the fungal amount of Gibberella (rang-
ing from 2,62 ng/μL - 59,07 ng/μL) quantified from maize grain could
have had reduced grain quality and yield in the 2010/2011 season
and on the other hand, the Diplodia ear rot incidence (ranging from
0,29% - 2,11%) was relatively low and would not have led to yield loss
and a reduction in grain quality in the 2013/2014 season.
Mycotoxin production
The cropping system had a significant effect on the accumulation of
fumonisins in the 2011/2012 season (P = 0,05,
Table 4
) and on deox-
ynivalenol in the 2011/2012 season (P = 0,03,
Table 5
).
Fumonisin accumulation was higher in the two-year sunflower ro-
tation and deoxynivalenol accumulation was higher in maize grain
from monoculture conventionally tilled maize. Although the data
were statistically significant, only the maize/sunflower rotation had
ON FARM LEVEL
Crop systems / Maize ear rots
Integrated pest control
DR BELINDA JANSE VAN RENSBURG
and
PROF BRADLEY FLETT,
ARC-Grain Crops, Potchefstroom
CROP SYSTEM
CULTIVATION
SEASON
1
2
3
Maize monoculture
CT*
Maize
Maize
Maize
Maize monoculture
NT#
Maize
Maize
Maize
Maize
cowpea
NT#
Maize
Cowpea
Maize
Maize
sunflower
NT#
Sunflower
Maize
Sunflower
Maize
babala
cowpea
NT#
Maize
Babala
Cowpea
Maize
babala
sunflower
NT#
Sunflower
Maize
Babala
TABLE 1: CROP SYSTEMS AND ROTATIONS AT BUFFELSVALLEI AND ERFDEEL.
BUFFELSVALLEI
CROP SYSTEM
CULTIVATION
SEASON
1
2
3
Maize monoculture
CT*
Maize
Maize
Maize
Maize monoculture
NT#
Maize
Maize
Maize
Maize
cowpea
NT#
Maize
Cowpea
Maize
Maize
babala
cowpea
NT#
Maize
Babala
Cowpea
ERFDEEL
* CT – Conventional till
# NT – No-till