Cucurbit Genetics Cooperative Report 8:57-61 (Article 22) 1985
Eason, Gwen and R. A. Reinert
North Carolina State University, Raleigh, NC 27650
Ozone (O3) is the most common cause of air pollutant-induced crop injury (3). Sulfur dioxide (SO2) can enhance or reduce the effects of O3 on crop plants, and at higher concentrations over time, injure crop plants without the presence of other pollutants (4).
For the peat few summers, air pollution has been suggested as a probable cause for some of the different foliar in juries observed on watermelon (1). Controlled experiments were conducted to study the effects of exposures to O3, alone and in combination with SO2, on watermelon plants and to determine whether or not foliar injuries noted on field plants could be duplicated with these exposures.
Seeds of each of ten watermelon cultivars were planted in ten cm. plastic pots of Metro Mix 220 (a peat, vermiculite, perlite mixture) on July 11, 1984. Sixteen seedlings of each cultivar were transplanted into fifteen cm. pots and maintained in a charcoal-filtered greenhouse until transported to the field on August 8. Four plants of each cultivar were placed in each of four open-top chambers in which the concentration of O3 could be monitored and regulated (2). Each chamber was used for one of the following treatments: carbon-filtered air, 0.02, 0.04, and 0.06 ppm O3, each added to nonfiltered air. Exposures were conducted seven days a week, seven hours a day (1000 hours-1700 hours), for four weeks. Data were recorded every other week as percent of total leaf surface injured on each plant, and injury symptons were described. Table 1 gives final injury estimates.
| Carbon- | PPM O3 | Added to Nonfiltered Air | ||
| Cultivar | Filtered Air |
0.02 | 0.04 | 0.06 |
| Baby Fun | 0 | 35 | 53 | 50 |
| Black Diamond | 0 | 37 | 32 | 57 |
| Calhoun Grey | 0 | 25 | 22 | 57 |
| Charleston Grey | 0 | 10 | 13 | 43 |
| Crimson Sween | 0 | 10 | 40 | 43 |
| Dixie Queen | 0 | 10 | 35 | 50 |
| Jubilee | 0 | 23 | 20 | 43 |
| Petite Sweet | 0 | 32 | 58 | 70 |
| Sugar Baby | 0 | 43 | 70 | 82 |
| Sugar Bush | 0 | 40 | 43 | 63 |
zfollowing 31 days of O3 treatment.
Watermelon cultivars varied in their sensitivity to O3, although almost all cultivars showed increased injury at the 0.06 level.’Charleston Grey’ appeared to be less O3 sensitive than the other cultivars. ‘Petite Sweet,’ ‘Sugar Baby,’ and ‘Sugar Bush’ appeared to be more sensitive to O3 than the other cultivars tested. Injuries were very similar to those seen in the field–interveinal chlorosis, followed by necrosis and whitening of the leaves.
‘Charleston Grey,’ ‘Sugar Baby,’ and ‘Petite Sweet’ were then chosen for studying the effects of O3 in combination with SO2. Seed were planted in Metro Mix 220 on September 7, 1984. Plants were transplanted into twenty liter containers and taken to the field site on October 1, 1984. Exposures started the following day and continued until frost, forty days later. Four levels of O3 (carbon filtered air, nonfiltered air, and 0.04 ppm or 0.06 ppm O3 added to nonfiltered air) and three levels of SO2 (0.0 ppm, 0.075 ppm, or 0.15 ppm SO2 added to O3 treatment) were used in the experiment. Plants were exposed to SO2 for four hours (1000-1400 hours) and to O3 for seven hours (1000-1700 hours) daily. Twenty-four open-top chambers were used in this experiment, and all treatments were replicated twice.
In order to obtain more objective injury data, plants were checked every other day, and leaves were tagged as soon as any pollutant injury developed. Table 2 shows the number of injured leaves per cultivar at harvest.
| O3 | SOx | Petite Sweet |
Sugar Baby |
Charleston Grey |
| Carbon – | 0.0 | 0.0 | 0.0 | 0.0 |
| Filtered | 0.075 | 0.0 | 0.0 | 0.0 |
| Air | 0.15 | 0.0 | 0.0 | 0.0 |
| Nonfiltered | 0.0 | 0.0 | 0.0 | 0.0 |
| Air | 0.075 | 0.0 | 0.0 | 0.0 |
| 0.15 | 0.0 | 0.0 | 0.0 | |
| 0.04y | 0.0 | 4.5 | 4.0 | 3.3 |
| 0.075 | 7.8 | 6.5 | 5.0 | |
| 0.15 | 9.0 | 6.5 | 1.8 | |
| 0.06y | 0.0 | 10.3 | 8.3 | 7.0 |
| 0.075 | 10.8 | 8.3 | 5.3 | |
| 0.15 | 11.3 | 9.5 | 6.3 |
zfollowing 40 days of exposures.
yppm O3 added to nonfiltered air.
xppm SO2 added to carbon-filtered or nonfiltered air.
No injury occurred on any of the plants in chambers where O3 was not added, even at the highest concentration of SO2. The number of injured leaves for all cultivars tended to increase as the O3 concentration increased. The cultivar response to a combination of SO2 and O3 was not similar. ‘Charleston Grey’ may be less sensitive to O3 when SO2 is present. In all cases, damage symptoms resembled O3 injury.
These results reflect preliminary work. Cultivar differences apparently exist, but more replication and larger plant samples are needed to reduce error in injury estimates. We were able to reduce interference from most cultural factors with the container-grown plants, but other factors–like differing plant maturity rates among the cultivars–need to be examined in relation to pollutant sensitivity. Also, experiments need to be conducted in order to determine the effects of pollutant-induced injury on yields.
Literature Cited
- Decoteau, Dennis R., James E. Simon, and Gerry E. Wilcox. 1985. Air
Pollution Hits Midwest Melons, American Vegetable Grower 33 (1):17. - Heagle, A. S., D. E. Body, and W. W. Heck. 1973. An open-top field chamber
to assess the impact of air pollution on plants. J. Environ. Qual.
2:365-368. - Hill, A. Clyde, Howard E. Heggestad, and Samuel N. Linzon. 1970. Ozone.
In: A Pictorial Atlas, eds. Jay S. Jacobson and A. Clyde Hill,
pp. B1-B22, Pittsburgh,PA: Air Pollution Assoc. 102 pp. - Reinert, R. A. 1984. Plant response to air pollutant mixtures.
Ann. Rev. Phytopathol. 22: 421-442.