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Evidence of ozone injury to a crop plant in India
~hnarphcrie Printed
.x,,vi,o-t
in Great
Vol. 20, No. 7, pp. 150-1503.
00044981186
1986.
Pergamon
Britain.
13.00 + O.C@ Journals
Ltd.
EVIDENCE OF OZONE INJURY TO A CROP PLANT IN INDIA 0.
M.
BAMBAWALE
Central Potato Research Station, P.B. No. 1, Jalandhar-144003, India Abstract-Evidence is presented to show that a serious leafspotdisease of potato which appeared each year in the Punjab since 1978 is primarily due to ozone: (i) The symptoms of the leafspot were similar to the ozone stipple of potato reported in the U.S.A. (ii) Activated charcoal and ethylenediurea effectively controlled the spots. (iii) Elevated ozone in the atmosphere was detected with the bioindicators Nicotiana t&cum var. BelW3 and potato variety Cherokee. This is the first report of ozone injury to a crop plant in India. Key word index: Air pollution, ozone, potato, tobacco.
were EDU spray (500 ppm EDU in 0.36 % glycerol and 0.1 y0 triton in water) or control spray (0.36 % glycerol and 0.1% triton in water). In 1982 six randomly selected plants in each replicated plot were sprayed on 5 November, 14 November, 4 December and 20 December. In 1983 all the plants in a plot were sprayed at 12 day intervals starting from 5 November. Paired ‘t’ test (Goulden, 1959) was employed to compare the significance of the treatments.
INTRODUCTION In 1978, a leaf spot of potato, distinct from the common fungal and bacterial leaf spots, was observed in Jalandhar and many other areas of the Punjab. Eleven wide spectrum fungicides and antibiotics did not control the development of the leaf spot (unpublished). Large scale isolations in the autumnof 1979,1980,1981 and spring of 1980,198l and 1982 and microscopic examinations did not indicate fungi or bacteria as the causal agent of the leafspot. The symptoms of the disease were similar to those caused by ozone (0,) in the U.S.A. (Heggestad, 1973). Experiments were conducted to verify ozone as a possible cause. MATERIALS AND METHODS Field experiments
Activated charcoal and ethylenediurea (N-(2-(2-0x0-1imidoz.olidinyl)ethyl)N’-phenylurea) were evaluated for control of the disease. A susceptible variety Kufri Jyoti (Solonurn tuberosum L.) was grown. The crop was raised in plots of 4.2 m x 2.8 m with 6Ocm row spacing and 20cm plant spacing. The trials were planted on 4 October 1982 and 5 October 1983. All the recommended cultural practices were followed. A paired treatment experiment with four replications was conducted in 1982 to evaluate activated charcoal. The treatments were: (i) dusting with activated charcoal each at ca 200 g plot- ‘; (ii) no dusting (control). Dustings were made on 12 November and 2 December using cotton dabs to achieve a fine cover of the dust on both leaf surfaces. Excess dust was removed by gently shaking the plants. Activated charcoal was also used for developing a relatively oxidant free atmosphere around the plants. Jute cloth, double walled, open top fixtures (1.75 m length x 1.2 m width x 1.75 m height) were constructed around the plants in the centre row of the plots on 11 November 1982. Fixtures were supported with bamboo sticks and each fixture accommodated eight plants. The plots were furrow irrigated. The jute cloth had approximately 11 threads per 2.54 & and the threads varied in thickness from 1 to 1.5 mm. The outer side of the jute cloth of two fixtures was painted with a 10 ‘Awater suspension of activated charcoal on 11 November, 23 November and 4 December 1982. Two fixtures were left untreated. To evaluate ethylenediurea (EDU) against the leaf spot, a paired treatment experiment with three replications in 1982 and six replications in 1983 was conducted. The treatments
Pot experiments
EDU and activated charcoal were also evaluated on plants raised in pots in 1982and 1983.The recommended doses ofN, P, K and Farm Yard Manure (FYM) were first thoroughly mixed with soil before filling the pots. Seed tubers of Kufri Jyoti were planted on 14 October in 1982 and on 11 October in 1983. The experiment was conducted in completely randomized design with 10 and 25 plants in 1982 and 1983, respectively. In 1982 the application of activated charcoal (dusting with cotton dabs) and EDU (spraying of 500 ppm water solution in 0.36 y0 glycerol and 0.1 ‘Atriton) were made on 25 October and 10 December 1982 and 1 January 1983. In 1983 the chemicals were applied on 14 November, 5 December and 26 December. Instead of dusting as in 1982 activated charcoal was sprayed (0.5% water suspension of activated charcoal in 0.36 % glycerol and 0.1 y0 triton) in 1983 to achieve more uniform coverage of the plants. EDU was used at similar concentration as in 1982.The control plants in 1982 and 1983 were sprayed with 0.36% glycerol and 0.1 y/; triton in water. In each experiment the leaf spot intensity was recorded on 10 plants per plot or on each plant in a treatment where a limited number of plants were used. A severity scale with ten grade ratings (0.0, 0.1, 1.0, 5.0, 10.0, 25.0, 50.0, 75.0, 95.0 and 100% leafareacovered with spots) was used for recording the disease on a compound leaf each from the top, middle and bottom one-third portions of a plant. The ‘4 disease intensity was derived as below. 7; disease intensity =
The % disease intensity data from each replication of a treatment was subjected to angular transformation and then analyzed statistically. Detection of ozone in the atmosphere Nicotiana taJnuen variety EM-W3 was used for detecting elevated O3 in the ambient air during spring 1983. One-
1501 AE 20:7-M
Z (grade rating x grade frequency) total number of observations made
Short Communications
1502
month old seedlings were transplanted in earthen pots filled with sandy loam soil premixed with recommended doses of N, P, K and FYM. The appearance of O3 injury in the form of leaf spots was recorded from January to April. Potato varieties Cherokee and Teton with known susceptible and resistant reaction to ozone (Heggestad, 1973)were planted in 6 m single rows on 15 October 1983 under normal cultivation practices. The typical Oa injury was recorded on 10 January 1984 on 25 plants of each variety. RESULTS AND
DlSCUSlON
Description of symptoms of the leaf spot on potato
The spots first appear on the lowest leaves of 4&50 day old potato plants and advance acropetally, covering the whole plant by maturity. The symptoms appear as numerous, tiny, light greyish, superficial, irregularly shaped specks on the under surface of the leaves. In about 2 days these enlarge in size to l-2 mm and become bifacial lesions in about 3-4 days. Necrotic spotting of both the surfaces is also common. On the lower surface of the leaves the spots appear slightly depressed and glossy (Fig. 1) whereas on the upper surface they are dull brown. The spots are mainly interveinal. At this stage leaves may show chlorosis. In advanced stages the spots coalesce and cover almost the entire leaf surface. The a&ted leaves eventually abscise. These symptoms agree closely with 03 injury on potato reported in the U.S.A. (Heggestad, 1973). Control of the leaf spot
In the field experiments, activated charcoal as a dust application provided almost complete protection from the leaf spot (Table 1). Activated charcoal has been shown to be effective against O3 stipple on tobacco as a direct dust application (Jones, 1963). The activated charcoal painted fixtures gave remarkable protection to the plants (Table 1). Activated charcoal is widely used for filtering air to remove oxidants, although mostly by a forced filteration (Heagle et al., 1973). The cloth passive type of filtration system has previously been shown (Taylor and Rich, 1962) to provide protection from oxidant injury. The effectiveness of activated charcoal as a dust application and in the filtration system suggests that oxidants are most likely responsible for causing the leaf spot. EDU provided effective protection to the plants from the leaf spot both during 1982 and 1983 field trials (Table 1).
Fig. 1. Irregularly shaped specks on potato variety Kufri Jyoti. The spots on the lower leaf surface are slightly depressed and glossy.
Clarke et al. (1983) also obtained effective protection of potato plants from O3 injury by application of EDU. Cathey and Heggested (1982) have shown that for the two major air pollutants, SO1 and OS, EDU gave protection to plants only from 03. Effectiveness of EDU in the present study thus suggests that the pollutant was 03.
Table 1. Efficacy of activated charcoal and ethylenediurea in the control of the potato leaf spot S. No.
Treatments (a)
Experimental conditions
1.
Field
2.
Field
3.
Field
4.
Pot
(i) Activated charcoal dusting (ii) Control (i) Activated charcoal filtered air (ii) Unfiltered air (i) (ii) (i) (ii)
Ethylenediurea spray Control Ethylenediurea spray Activated charcoal dusting/spray (iii) Control CD. (0.05)
% leaf spot 1983 1982 1.0 (5.6). 38.1(38.1) 3.9 (ll.o)*
._
37.3 (37.6)
9.9(17.7) 0.1 (2.1)
4.7 (12.3). 38.5 (38.4) 4.0(11.7) 2.6 (7.7)
28.7 (32.2) (4.2)
25.9 (29.4) (4.5)
7.2 (14.7). 33.2 (35.0)
(a) See text for details. (b) Figures in parentheses are angular transformations. *Denotes paired ‘t’ test significance at P = 0.05.
Short Communications
1503
Teton it was 0.2%. The symptoms were typical of those caused by Oj. Bel-W3 has been successfully employed in a countrywide survey of 0, levels (Ashmore et al., 1978). Instrumentation needed for direct measurement of 0s was not available. The symptoms on potato and tobacco leaves in India were similar to those attributed to O1 in the U.S.A. (personal communication, Dr H. E. Heggestad). All the above results leave little doubt that 0s is primarily responsible for causing the leaf spot in the Punjab. OJ at the earth’s surface is formed by action of sunlight on products of fuel combustion such as constituents in motor iehicle exhausts. The increased vehicular traffic (Anonymous, 1982)and mechanization of agriculture in the Puniab (March 1976’motor vehicles in the Punjab = 1,75,038 and ‘March 1980 = 3,14,6@4) may have made available the precursors to elevate OJ sufficiently to injure sensitive vegetation. Acknowledgement-I
am thankful to Dr H. E. Heggestad, Beltsville Aericultural Research Centre. Beltsville. Marvland. U.S.A. and- Dr M. R. Ashmore, Imperial Cdllege-Field Station, Silwood Park, Berks, U.K. for valuable suggestions. The antioxidant EDU was very kindly supplied by E. I. du Pont de Nemours and Co., U.S.A. I am also thankful to my colleagues Mr A. K. Somani and Mr P. M. Govindakrishnan for help and useful discussions.
REFERENCES
Fig. 2. Fleck symptoms on Nicotiana tabacum variety BelW3 due to ozone. Oldest lesions are almost white and new lesions at leaf base are dark.
In the pot studies also, activated charcoal and EDU provided effective control of the leaf spot (Table 1), thus verifying the results of the field trials. Detection oi ozone in the atmosphere
The damage due to O3 in the form of characteristic upper surface leaf stipple was noticed on Nicotiana tabacum variety Bel-W3. The symptoms (Fig. 2) resembled those described in the literature (Heggestad, 1966) as caused by ozone. The stipple was noticed throughout spring 1983 (February-April) when the potato had appreciable (30.1”‘) leaf spot. In autumn 1983 the potato varieties Cherokee and Teton under field conditions gave the same susceptible and resistant reaction to ambient O3 as has been reported in the literature (Heggestad, 1973).On Cherokee the leaf spot intensity was 35.6 % and on
Anonymous (1982) India, a reference manual 1982, p. 583. Publications Division, Ministry of Information and Broadcasting, Govt. of India, New Delhi. Ashmore M. R.. Bell J. N. B. and Rielv C. L. (1978) A survev of ozone levels’ in the British Isles* using ‘indidator plaits. Nature 276, 813-815. Cathey H. M. and Heggestad H. E. (1982) Ozone and sulfur dioxide sensitivity of petunia: modification by ethylenediurea. J. Am. Sdc. Ho&c. Sci. 107, 1028-1035. _ Clarke B. B., Henninger M. R. and Brennan E. (1983) An assessment of potato losses caused by oxidant air pollution in New Jersey. Phytopathology 73, iO4108. _ Goulden C. H. (1959) Method of Statistical Analvsis. . IZD. 467. Asia Publish&g H&se, Bombay. Heagle A. S., Body D. E. and Heck W. W. (1973) An open-top field chamber to assess the impact of air pollution on plants. J. Envir. Quality 2, 365-368. Heggestad H. E. (1966) Ozone as a tobacco toxicant. J. Air Pollut. Control Ass. 16, 691494. Heggestad H. E. (1973) Photochemical air pollution injury to potato in the Atlantic Coastal States. Am. Potato J. 50, 315-328.
Jones J. L. (1963) Ozone damage: protection for plants. Science 140, 1317-1318. Taylor G. S. and Rich S. (1962) Anti-Ozonant treated cloth protects tobacco from fleck. Science 135, 928.
.x,,vi,o-t
in Great
Vol. 20, No. 7, pp. 150-1503.
00044981186
1986.
Pergamon
Britain.
13.00 + O.C@ Journals
Ltd.
EVIDENCE OF OZONE INJURY TO A CROP PLANT IN INDIA 0.
M.
BAMBAWALE
Central Potato Research Station, P.B. No. 1, Jalandhar-144003, India Abstract-Evidence is presented to show that a serious leafspotdisease of potato which appeared each year in the Punjab since 1978 is primarily due to ozone: (i) The symptoms of the leafspot were similar to the ozone stipple of potato reported in the U.S.A. (ii) Activated charcoal and ethylenediurea effectively controlled the spots. (iii) Elevated ozone in the atmosphere was detected with the bioindicators Nicotiana t&cum var. BelW3 and potato variety Cherokee. This is the first report of ozone injury to a crop plant in India. Key word index: Air pollution, ozone, potato, tobacco.
were EDU spray (500 ppm EDU in 0.36 % glycerol and 0.1 y0 triton in water) or control spray (0.36 % glycerol and 0.1% triton in water). In 1982 six randomly selected plants in each replicated plot were sprayed on 5 November, 14 November, 4 December and 20 December. In 1983 all the plants in a plot were sprayed at 12 day intervals starting from 5 November. Paired ‘t’ test (Goulden, 1959) was employed to compare the significance of the treatments.
INTRODUCTION In 1978, a leaf spot of potato, distinct from the common fungal and bacterial leaf spots, was observed in Jalandhar and many other areas of the Punjab. Eleven wide spectrum fungicides and antibiotics did not control the development of the leaf spot (unpublished). Large scale isolations in the autumnof 1979,1980,1981 and spring of 1980,198l and 1982 and microscopic examinations did not indicate fungi or bacteria as the causal agent of the leafspot. The symptoms of the disease were similar to those caused by ozone (0,) in the U.S.A. (Heggestad, 1973). Experiments were conducted to verify ozone as a possible cause. MATERIALS AND METHODS Field experiments
Activated charcoal and ethylenediurea (N-(2-(2-0x0-1imidoz.olidinyl)ethyl)N’-phenylurea) were evaluated for control of the disease. A susceptible variety Kufri Jyoti (Solonurn tuberosum L.) was grown. The crop was raised in plots of 4.2 m x 2.8 m with 6Ocm row spacing and 20cm plant spacing. The trials were planted on 4 October 1982 and 5 October 1983. All the recommended cultural practices were followed. A paired treatment experiment with four replications was conducted in 1982 to evaluate activated charcoal. The treatments were: (i) dusting with activated charcoal each at ca 200 g plot- ‘; (ii) no dusting (control). Dustings were made on 12 November and 2 December using cotton dabs to achieve a fine cover of the dust on both leaf surfaces. Excess dust was removed by gently shaking the plants. Activated charcoal was also used for developing a relatively oxidant free atmosphere around the plants. Jute cloth, double walled, open top fixtures (1.75 m length x 1.2 m width x 1.75 m height) were constructed around the plants in the centre row of the plots on 11 November 1982. Fixtures were supported with bamboo sticks and each fixture accommodated eight plants. The plots were furrow irrigated. The jute cloth had approximately 11 threads per 2.54 & and the threads varied in thickness from 1 to 1.5 mm. The outer side of the jute cloth of two fixtures was painted with a 10 ‘Awater suspension of activated charcoal on 11 November, 23 November and 4 December 1982. Two fixtures were left untreated. To evaluate ethylenediurea (EDU) against the leaf spot, a paired treatment experiment with three replications in 1982 and six replications in 1983 was conducted. The treatments
Pot experiments
EDU and activated charcoal were also evaluated on plants raised in pots in 1982and 1983.The recommended doses ofN, P, K and Farm Yard Manure (FYM) were first thoroughly mixed with soil before filling the pots. Seed tubers of Kufri Jyoti were planted on 14 October in 1982 and on 11 October in 1983. The experiment was conducted in completely randomized design with 10 and 25 plants in 1982 and 1983, respectively. In 1982 the application of activated charcoal (dusting with cotton dabs) and EDU (spraying of 500 ppm water solution in 0.36 y0 glycerol and 0.1 ‘Atriton) were made on 25 October and 10 December 1982 and 1 January 1983. In 1983 the chemicals were applied on 14 November, 5 December and 26 December. Instead of dusting as in 1982 activated charcoal was sprayed (0.5% water suspension of activated charcoal in 0.36 % glycerol and 0.1 y0 triton) in 1983 to achieve more uniform coverage of the plants. EDU was used at similar concentration as in 1982.The control plants in 1982 and 1983 were sprayed with 0.36% glycerol and 0.1 y/; triton in water. In each experiment the leaf spot intensity was recorded on 10 plants per plot or on each plant in a treatment where a limited number of plants were used. A severity scale with ten grade ratings (0.0, 0.1, 1.0, 5.0, 10.0, 25.0, 50.0, 75.0, 95.0 and 100% leafareacovered with spots) was used for recording the disease on a compound leaf each from the top, middle and bottom one-third portions of a plant. The ‘4 disease intensity was derived as below. 7; disease intensity =
The % disease intensity data from each replication of a treatment was subjected to angular transformation and then analyzed statistically. Detection of ozone in the atmosphere Nicotiana taJnuen variety EM-W3 was used for detecting elevated O3 in the ambient air during spring 1983. One-
1501 AE 20:7-M
Z (grade rating x grade frequency) total number of observations made
Short Communications
1502
month old seedlings were transplanted in earthen pots filled with sandy loam soil premixed with recommended doses of N, P, K and FYM. The appearance of O3 injury in the form of leaf spots was recorded from January to April. Potato varieties Cherokee and Teton with known susceptible and resistant reaction to ozone (Heggestad, 1973)were planted in 6 m single rows on 15 October 1983 under normal cultivation practices. The typical Oa injury was recorded on 10 January 1984 on 25 plants of each variety. RESULTS AND
DlSCUSlON
Description of symptoms of the leaf spot on potato
The spots first appear on the lowest leaves of 4&50 day old potato plants and advance acropetally, covering the whole plant by maturity. The symptoms appear as numerous, tiny, light greyish, superficial, irregularly shaped specks on the under surface of the leaves. In about 2 days these enlarge in size to l-2 mm and become bifacial lesions in about 3-4 days. Necrotic spotting of both the surfaces is also common. On the lower surface of the leaves the spots appear slightly depressed and glossy (Fig. 1) whereas on the upper surface they are dull brown. The spots are mainly interveinal. At this stage leaves may show chlorosis. In advanced stages the spots coalesce and cover almost the entire leaf surface. The a&ted leaves eventually abscise. These symptoms agree closely with 03 injury on potato reported in the U.S.A. (Heggestad, 1973). Control of the leaf spot
In the field experiments, activated charcoal as a dust application provided almost complete protection from the leaf spot (Table 1). Activated charcoal has been shown to be effective against O3 stipple on tobacco as a direct dust application (Jones, 1963). The activated charcoal painted fixtures gave remarkable protection to the plants (Table 1). Activated charcoal is widely used for filtering air to remove oxidants, although mostly by a forced filteration (Heagle et al., 1973). The cloth passive type of filtration system has previously been shown (Taylor and Rich, 1962) to provide protection from oxidant injury. The effectiveness of activated charcoal as a dust application and in the filtration system suggests that oxidants are most likely responsible for causing the leaf spot. EDU provided effective protection to the plants from the leaf spot both during 1982 and 1983 field trials (Table 1).
Fig. 1. Irregularly shaped specks on potato variety Kufri Jyoti. The spots on the lower leaf surface are slightly depressed and glossy.
Clarke et al. (1983) also obtained effective protection of potato plants from O3 injury by application of EDU. Cathey and Heggested (1982) have shown that for the two major air pollutants, SO1 and OS, EDU gave protection to plants only from 03. Effectiveness of EDU in the present study thus suggests that the pollutant was 03.
Table 1. Efficacy of activated charcoal and ethylenediurea in the control of the potato leaf spot S. No.
Treatments (a)
Experimental conditions
1.
Field
2.
Field
3.
Field
4.
Pot
(i) Activated charcoal dusting (ii) Control (i) Activated charcoal filtered air (ii) Unfiltered air (i) (ii) (i) (ii)
Ethylenediurea spray Control Ethylenediurea spray Activated charcoal dusting/spray (iii) Control CD. (0.05)
% leaf spot 1983 1982 1.0 (5.6). 38.1(38.1) 3.9 (ll.o)*
._
37.3 (37.6)
9.9(17.7) 0.1 (2.1)
4.7 (12.3). 38.5 (38.4) 4.0(11.7) 2.6 (7.7)
28.7 (32.2) (4.2)
25.9 (29.4) (4.5)
7.2 (14.7). 33.2 (35.0)
(a) See text for details. (b) Figures in parentheses are angular transformations. *Denotes paired ‘t’ test significance at P = 0.05.
Short Communications
1503
Teton it was 0.2%. The symptoms were typical of those caused by Oj. Bel-W3 has been successfully employed in a countrywide survey of 0, levels (Ashmore et al., 1978). Instrumentation needed for direct measurement of 0s was not available. The symptoms on potato and tobacco leaves in India were similar to those attributed to O1 in the U.S.A. (personal communication, Dr H. E. Heggestad). All the above results leave little doubt that 0s is primarily responsible for causing the leaf spot in the Punjab. OJ at the earth’s surface is formed by action of sunlight on products of fuel combustion such as constituents in motor iehicle exhausts. The increased vehicular traffic (Anonymous, 1982)and mechanization of agriculture in the Puniab (March 1976’motor vehicles in the Punjab = 1,75,038 and ‘March 1980 = 3,14,6@4) may have made available the precursors to elevate OJ sufficiently to injure sensitive vegetation. Acknowledgement-I
am thankful to Dr H. E. Heggestad, Beltsville Aericultural Research Centre. Beltsville. Marvland. U.S.A. and- Dr M. R. Ashmore, Imperial Cdllege-Field Station, Silwood Park, Berks, U.K. for valuable suggestions. The antioxidant EDU was very kindly supplied by E. I. du Pont de Nemours and Co., U.S.A. I am also thankful to my colleagues Mr A. K. Somani and Mr P. M. Govindakrishnan for help and useful discussions.
REFERENCES
Fig. 2. Fleck symptoms on Nicotiana tabacum variety BelW3 due to ozone. Oldest lesions are almost white and new lesions at leaf base are dark.
In the pot studies also, activated charcoal and EDU provided effective control of the leaf spot (Table 1), thus verifying the results of the field trials. Detection oi ozone in the atmosphere
The damage due to O3 in the form of characteristic upper surface leaf stipple was noticed on Nicotiana tabacum variety Bel-W3. The symptoms (Fig. 2) resembled those described in the literature (Heggestad, 1966) as caused by ozone. The stipple was noticed throughout spring 1983 (February-April) when the potato had appreciable (30.1”‘) leaf spot. In autumn 1983 the potato varieties Cherokee and Teton under field conditions gave the same susceptible and resistant reaction to ambient O3 as has been reported in the literature (Heggestad, 1973).On Cherokee the leaf spot intensity was 35.6 % and on
Anonymous (1982) India, a reference manual 1982, p. 583. Publications Division, Ministry of Information and Broadcasting, Govt. of India, New Delhi. Ashmore M. R.. Bell J. N. B. and Rielv C. L. (1978) A survev of ozone levels’ in the British Isles* using ‘indidator plaits. Nature 276, 813-815. Cathey H. M. and Heggestad H. E. (1982) Ozone and sulfur dioxide sensitivity of petunia: modification by ethylenediurea. J. Am. Sdc. Ho&c. Sci. 107, 1028-1035. _ Clarke B. B., Henninger M. R. and Brennan E. (1983) An assessment of potato losses caused by oxidant air pollution in New Jersey. Phytopathology 73, iO4108. _ Goulden C. H. (1959) Method of Statistical Analvsis. . IZD. 467. Asia Publish&g H&se, Bombay. Heagle A. S., Body D. E. and Heck W. W. (1973) An open-top field chamber to assess the impact of air pollution on plants. J. Envir. Quality 2, 365-368. Heggestad H. E. (1966) Ozone as a tobacco toxicant. J. Air Pollut. Control Ass. 16, 691494. Heggestad H. E. (1973) Photochemical air pollution injury to potato in the Atlantic Coastal States. Am. Potato J. 50, 315-328.
Jones J. L. (1963) Ozone damage: protection for plants. Science 140, 1317-1318. Taylor G. S. and Rich S. (1962) Anti-Ozonant treated cloth protects tobacco from fleck. Science 135, 928.