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AGRICULTURAL RESEARCH & EDUCATION CENTER
IFAS, University of Florida
Bradenton AREC Research Report GC1981- 2 March 1981
POTATO CULTIVAR RESPONSE TO ACUTE SULFUR DIOXIDE LEVELS
T. K. Howe and S. S. Woltz1
Burning high sulfur content fossil fuels to meet future energy needs
increases the potential of SO air pollution problems in Florida. Local power
plants have already begun planning conversions to facilitate the use of coal or
coal-oil mixtures in the place of long-favored oil. SO air pollution is not
a serious problem currently, but the threat is very reaf for the future. At
AREC-Bradenton, efforts are directed toward identifying the tolerances of
various agricultural plant species to airborne SO. This work will relate to
quantifying the SO2 levels agriculture can tolerate and how it can adjust to
'Sebago' and 'Atlantic' potato cultivars were fumigated in greenhouse
chambers with varying rates of SO2 and then rated with respect to their relative
susceptibility to sulfur dioxide. Experiments were conducted in February and
April of 1980. Seed pieces were planted in 15 cm plastic pots containing
Florida peat: Virgin Myakka fine sandy soil: Vermiculite (1:1:1 by volume)
amended with 1.5 lb superphosphate containing 4% FTE 503, 15 lb dolomite, and
fumigated with 2 lb methyl bromide-chloropicrin (MC-33), per 64 cu ft of
media. Plants were grown in a greenhouse until fumigation. Nutrition was
supplemented with Osmocote 14:14:14 (14N: 6.1P: 11.6K, ca. 5 g/pot) as needed.
Pots of each cultivar were placed alternately on 2 benches in each of several
specially designed greenhouse chambers. Individual houses received a single
level of SO2.
The exposures for 6 1/2 week-old plants in February were equivalent to 4
ppm and 8 ppm SO2 per hour and were applied as follows: 0.5 ppm SO2 for 8
hours, 1 ppm SO for 4 hrs, 2 ppm SO for 2 hrs and 2 ppm SO for 4 hrs. This
regime was applied on 2 consecutive days. On the first day temperatures in the
chambers were 17-32 (62-89 F) during the 8 hr exposure with relative humidities
of 50-20%. On the second day, temperatures were 15-34 oC (59-93 OF) with
relative humidities of 98-42%. Fumigation began at about 9AM. Light levels
varied throughout the 8 hr intervals.
In April, 6 week-old plants were exposed to the equivalent of 3 ppm SO
per hour and were applied as follows: 1 ppm SO for 3 hrs, 2 ppm SO2 for 1.5
hrs, 3 ppm SO2 for 1 hr. Plants were only exposed to SO on one day. Temperatures
were 36-38 *C (96-100 F) and relative humidity was 45-2 % over the 3 hr exposure.
Light levels were not measured in February or April, but the days selected
approached full sunlight. The chambers used received about 30% full sunlight.
: Plants were visually rated for percent leaf area necrosis 3 days after final
exposure to SO Foliage was then harvested from the entire length of all
plants and analyzed for total sulfur content in February and April (1, 2).
T. K. Howe is Assistant in Plant Physiology at AREC-Bradenton, 5007-60th
Street East, Bradenton, Fl. 33508. S. S. Woltz is Plant Physiologist at
Silicone rubber impressions were made of the lower leaf surface (4) to determine
the number of stomates, or breathing pores, for each cultivar on upper and
middle leaves. Stomatal function was ascertained by monitoring leaf vapor
diffusive resistance of abaxial leaf surfaces with an autoporometer (LI-COR LI-
65 with LI-20S diffusive resistance sensor) at zero and 2 ppm SO2. Statistical
analysis was carried out with the main assumption that no inherent differences
existed between chambers.
Foliar scorch injury appeared initially as interveinal water-soaked areas
and was followed by development of tan necrosis. The damage is very similar in
aspect to a number of other toxic agents such as pesticides and other air
pollutants. Usually SO, damage was restricted to the upper half of the potato
plant. In February (Table 1), there was very little to no injury as a result
of the first day of fumigation. This led to the repetition of exposure to SO2
on the second day, in order to obtain higher levels of damage. Following the
second exposure, there was an increase in scorch injury with SO levels, but
there was no difference in scorch injury between the cultivars of given SO,
levels following the successive exposures. Sulfur content increased for fumigated
as compared to nonfumigated plants, and this accumulation occurred over a 2 day
period. There were no differences between the two cultivars in sulfur content
at any specific SO2 level.
In April, the results showed that 'Atlantic' was significantly more susceptible
to SO -induced injury than 'Sebago' at the higher levels of SO (Table 2).
Total sulfur contents among SO2 levels and between cultivars ware not significantly
different. Sulfur analysis of potato foliage apparently was not adequate to
assess the small amounts of sulfur taken up by the plants during acute SO2
exposure (high level-short duration).
Stomatal frequency (Table 3) was not significantly different between the
cultivars for upper (less mature) or middle (fully mature) leaves. The number
of pathways for gas exchange apparently does not determine the differences in
susceptibility to SO2.
Stomate response was monitored during exposure to 2 ppm SO. No differences
existed in the stomatal resistance of the stomates for either clItivar as
compared to controls or between the cultivars. On the first day of fumigation
in February, resistance values stayed at about 5 sec/cm. On the second date in
February, resistance values remained at about 1.5 sec/cm. Increased stomatal
conductance (gas exchange) on the second day may reflect a response to the
increased relative humidity as compared to the previous day. Research has
shown that stomatal conductance increases at high relative humidities and
decreases at low relative humidities (3). Decreased gas exchange in response
to low relative humidity may explain the lack of injury to potato on the first
day. Lower gas exchange provides some protection from injury since any SO
which enters is metabolized and will not accumulate as sulfite which is toxic.
Conversely, greater gas exchange may overload the metabolic capabilities of the
plant and SO, will accumulate as sulfite. In April, as in February, there was
no stomatal response to 2 ppm SO2 by either cultivar. The stomatal resistance
ranged from 5-6 sec/cm.
Potato cultivar susceptibility was not consistent in these 2 experiments
and may be related to any of several factors. First, the lack of difference
between the two cultivars after the second exposure in February may have been
influenced by previous exposure history. The response on the second day may
have been influenced by exposure on the first day. Our unpublished observations
on zinnia indicated previous exposure to SO may enhance SO uptake; this may
or may not have affected the relative differences in cultivar injury response
of potato in February. Second, the plants in February received more SO than
the plants in April. This may account for the apparent differences in experiments
since some masking of differences between cultivars may have occurred. Third,
'Atlantic' was more susceptible than 'Sebago' in April, possibly a reflection
of higher temperatures during exposure than in February.
Although cultivar differences in susceptibility are ambiguous, these results
do indicate that both cultivars are realtively tolerant to high levels of SO2.
Exposure duration at these levels is critical. Marked differences in injury
occur between 2 and 4 hours at 2 ppm SO (Table 1). Lower concentrations are
less toxic than the higher concentrations when total exposures are the same,
since smaller amounts can be metabolized more effectively.
Potato is an important crop throughout Florida. It is one of many that
may be affected by increased use of coal for power generation in the future.
There is a wide range of susceptibility-tolerance categories for the response
of plants to SO2 based on the assessment of injuries. Information on how
species respond to SO exposure can be used in land-use-planning for locating
fossil fuel burning facilities, new agricultural production sites and the
selection plant material use within the vicintiy of SO2 emissions.
1. Butters, B. and E. M. Chenery. 1959. A rapid method for the determination
of total sulfur in soils and plants. Analyst 84:239-245.
2. Massoumi, A. and A. H. Cornfield. 1963. A rapid method for determining
sulfate in water extracts of soils. Analyst 88:321-322.
3. Rist, D. L. and D. D. Davis. 1979. The influence of exposure temperature
and relative humidity on the response of pinto bean foliage to sulfur
dioxide. Phytopathology 69:231-235.
4. Zelitch, I. 1961. Biochemical control of stomatal opening in leaves.
Proc. Nat. Acad. Sci., U.S. 47:1423-1433.
Table 1. Leaf damage sustained and accumulation of sulfur in
response to SO exposures in 'Atlantic' and 'Sebago'
potato cultivars for February 1980.
% Leaf % Total
Scorch Injuryz Foliar Sulfury
Atlantic' 'Sebago' 'Atlantic' 'Sebago'
Control 0.0 0.0 0.88 0.85
0.5 ppm 8 hrs 0.0 1.0 1.15 1.05
1 ppm 4 hrs 0.9 0.5 1.04 1.14
2 ppm 2 hrs 4.3 3.2 1 16 0.99
2 ppm 4 hrs 19.3 22.8 1.28 1.35
LSD (5%) 6.1 0.25
ZVisual estimation, 3 days after exposure, 8 replicates per mean.
tOry weight basis, tissue harvested 3 days after exposure, 8
replicates per mean.
XTwo successive days of exposures at these levels of SO2.
Table 2. Leaf damage sustained and accumulation of sulfur in response
to SO2 exposures in 'Atlantic' and 'Sebago' potato cultivars for
% Leaf Scorch Injuryz % Total Foliar Sulfury
'Atlantic' 'Sebago' 'Atlantic' 'Sebago'
Control 0.0 0.0 0.93 0.91
1 ppm-3 hrs 0.8 0.0 0.87 0.98
2 ppm-1.5 hrs 5.0 0.0 0.91 0.90
3 ppm-1 hr 7.0 0.6 1.10 1.10
LSD (5%) 1.7 N.S.
ZVisual estimation, 3 days after exposure, 12 replicates per mean.
YDry weight basis, harvested 3 days after exposure, 3 replicates, per
mean, each replicat consisting of 4 pots.
XSingle day of exposure at these levels of SO2.
Table 3. Potato Cultivar Stomatal Frequency,
Number of Stomates
Cultivar Leaves Leaves
'Atlantic' 16.2 11.1
'Sebago' 18.7 10.1
ZExpanding leaves near top, 11 replicates
per mean for 'Sebago', 12 replicates per mean
Y6th node from top or bottom, abaxial count,
11 replicates per mean.