THERMOTHERAPY TO CONTROL SEED-BORNE DISEASES IN DRY BEANS.
Friesen, A.P.*, McCreary, C.M., Barton, W.R, Robinson, D., Conner, R.L., and Gillard, C.L.
The objective of this experiment is to determine if microwave radiation can be effective in managing
seed-borne diseases such as anthracnose, common bacterial blight (CBB) and halo blight and whether it
will provide practical disease control in the field. To determine the efficacy of the treatments, lab studies
were conducted for seed germination and disease control. The results from the lab study were then used
to determine the optimal exposure time for field studies.
Lab Study:
Various microwave radiation treatments were applied to navy and pinto (kidney for halo blight) seed
using a home microwave oven (General Electric JES 1142 WPC microwave, with a rotating glass plate
and 1100W, 2450 MHZ output). Microwave exposures at 10 s intervals (0-90 s) were tested and were
then evaluated for seed germination using the Canadian Germination Commission (CGC) warm germ
test and disease control using potato dextrose agar amended with 50% lactic acid. In the germination
experiment, a significant drop in germination was seen after 50 s for all the seed lots.
In analysing the disease plates, there was less disease control of the bacterial blights, compared to
anthracnose. Microwave radiation from 10-40 s showed no significant improvement in the control of the
pathogens for both market classes compared to the untreated control. However, seed exposed to
microwave radiation for greater than 50 s showed a significant improvement in disease control, except
for CBB.
From these results, an optimal exposure time of 40-50s was determined for each seed lot, based on
increased control of anthracnose and a minor (<10%) decrease in germination. Using the results of this
lab study, a maximum rate (1X) and 1/2X rate for microwave radiation exposure was determined for the
2012 field trials Ontario and Manitoba.
Field Study:
Using the optimal exposure times determined in
the lab study a randomized complete block design
(RCBD) was used to compare the effect of
microwave radiation alone and in combination
with two chemical seed treatments, a BASF
experimental and an industry standard which was
Cruiser Maxx Beans + Dynasty for anthracnose
and Kocide 2000, for the blights. Ratings for %
disease severity (leaf, stem, and pod) were
conducted throughout the season. In addition,
ratings for plant emergence, vigour, yield, pick and
economic threshold (data not shown) were carried
out.
Trt #
1
2
3
4
5
6
7
8
9
10
Treatment
Uninfected (‘Disease Free’) Control (UC)
Infected Control (IC)
BASF EXP
Industry Standard
1
/2X Microwave (25 seconds)
1X Microwave (50 seconds)
1
/2X Microwave + BASF EXP
1X Microwave + BASF EXP
1
/2X Microwave + Industry Standard
1X Microwave + Industry Standard
For emergence, all studies showed a decrease in emergence when the microwave treatment was applied.
However, this was expected based on the maximum exposure rate set which accounted for the up to a
10% loss seen in some trials. The chemical seed treatment increased emergence compared to the
infected control treatment in some trials, but the results were not consistent. The CruiserMaxx Beans +
Dynasty decreased vigour in the anthracnose trials, but this effect was short term and showed no long
term effect throughout the season. A similar response was not observed for Kocide 2000 in the blight
trials.
The blight trials were evaluated for disease incidence using a 1-9 scale (Standard System for Evaluation
of Bean Germplasm, CIAT) and pod infection was evaluated based on the percentage pod area infected.
For the CBB trials, differences in disease incidence were seen in three of six trials, where the microwave
treatment, the chemical treatment and the combination of the two had less disease compared to the
infected control. The use of chemical seed treatments tended to control common bacterial blight better
than microwave when applied alone and no additional control was seen when microwave treatment was
added to the chemical treatments. The pod infection and yield results were inconsistent across the trials
and few differences were seen between treatments. In the halo blight trials, differences for disease
incidence were only seen between the controls and the chemical seed treatments. For pod infection no
significant differences were seen for any of the treatments and this was reflected in the yield data as
well.
Anthracnose disease infection was measured on the leaf veins, stems, and pods, based on a percent plant
area infected. In general, the pinto trials had few differences between treatments. Therefore, discussion
will focus on the results from the navy bean trials in Exeter and Ridgetown, ON. Treatments responded
similarly at both sites for leaf vein infection and at Exeter only for pod infection. Precipitation was low
early in the season at Exeter, resulting in lower leaf vein disease severity compared to Ridgetown. The
uninfected control (UC) exhibited the lowest % disease severity of all treatments. The Cruiser Maxx
Beans+Dynasty treatments (4, 9, & 10) were significantly better than the infected control (IC), as well as
all other treatments except the UC. The BASF EXP treatments (3, 7, & 8) were significantly better than
the IC; however, disease control was lower than Cruiser Maxx Beans+Dynasty treatments. The 1/2X and
1X microwave treatments (5 & 6, respectively) provided no significant improvement in the control of
anthracnose compared to the IC. Both seed treatments applied alone or in combination with microwave
radiation were significantly better than the 1/2X and 1X microwave treatments, except for BAS EXP (trts
3, 7, & 8) at Ridgetown. There was no additive effect seen when chemical and microwave treatments
were combined, except for 1X Microwave Radiation + Cruiser Maxx Beans+Dynasty (trt 10) at
Ridgetown.
In conclusion, the lab studies showed that microwave radiation improved disease control after 40-60 s of
exposure with little effect on seed germination. However in the 2012 field trials, the use of microwave
radiation alone did not result in a sufficient increase in the control of any of the diseases. It was also
observed that the use of chemical treatment alone was more effective than microwave radiation and the
combination of chemical treatment and microwave radiation showed little additive effect for control.
Further field testing will occur in 2013 to confirm these results.