Effects of Air Quality on Growth, Yield, and Quality of Watermelon

Watermelon, Citrullus lanatus (Thunb.) Matsum & Nakai cv. Sugar Baby, were grown in the field as a fall crop in open-top chambers (OTC) in southwestern Indiana with either charcoal-filtered (CF) or nonfiltered (NF) air. Ozone and sulfur dioxide were continuously monitored in OTC and ambient air. There was a significant decrease in marketable yield by weight (19.9%, P = 0.05), percentage of marketable fruit by number (20.8%, P = 0.10), and total yield by weight (21.5%, P = 0.05) from plants grown in the NF air treatment compared with those grown in CF air. Ozoneinduced foliar injury was significantly greater on plants grown under NF conditions. Ambient concentrations of 03 in southwestern Indiana caused foliar injury ( P = 0.10) and significant yield loss to a fall crop of watermelons. Ambient concentrations of O3 have caused substantial foliar injury to watermelon in southern Indiana, which has resulted in a breakdown of the canopy during fruit maturation (Decoteau et al., 1986). Ozone injury to watermelons grown under field conditions, previously known only as “yellow crown dieback”, appears initially as premature chlorosis and chlorotic mottle; advanced stages exhibit bleaching and stippling of leaves, followed by tissue breakdown and loss of canopy biomass. The smaller-fruited cultivars, such as ‘Petite Sweet’, ‘Blue Belle’, and ‘Sugar Baby’, appear to be more senReceived for publication 6 Sept. 1989. Journal Paper no. 11,671, Purdue Univ. Agr. Expt. Sta., West Lafayette, IN 47907. This research was supported in part by the U.S. Dept. of Agriculture (Cooperative Agreement Res. Grant no. 58-51144-6001), the Purdue Agr. Expt. Sta. (Grant no. 425-1165-0035-65078), and the Indiana Dept. of Env. Management. We express appreciation to Robert Philbeck and Jeff Barton for the design and installation of the air quality ‘monitoring system; David Tingey, EPA-Corvallis for permitting us to use their open-top chambers; Dexter and Billie Bloebaum who permitted some of the studies on their farm; Meb Lang, Tom Mouzin, Angie Ruppel, and Angie Thompson for assistance in maintaining field plots; and Walter Heck for his valuable suggestions. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Present address: Mississippi State Univ., P.O. Box 231, Crystal Springs, MS 39059. 2Person to whom reprint requests should be addressed. 3Air Quality Research Program, U.S. Dept. of Agriculture/Agricultural Research Service, North Carolina State Univ., Raleigh, NC 27650. “Present address: Dept. of Plant Pathology, The Pennsylvania State Univ., University Park, PA 16802. HORTSCIENCE, VOL. 26(8), AUGUST 1991 sitive than mediumto large-fruited cultivars such as ‘Crimson Sweet’, ‘Jubilee’, or ‘Charleston Grey’ (Decoteau et al., 1986; Simini et al., 1987). Although O3 injury has led to substantial deterioration of the foliar canopy, the degree to which O3 stress could affect watermelon growth and yield was unknown. In a study to determine the growth and yield effects of O 3 on muskmelon, plants of ‘Superstar’ muskmelon (Cucumis melo L. var. reticulatus) grown in nonfiltered (NF) open-top chambers (OTC) showed significant increases in the severity of visible foliar injury, 21% less marketable fruit weight, and 21% fewer marketable fruit than those from carbon-filtered (CF) OTCs (Snyder et al., 1988). Because watermelon foliage appears to be more sensitive to O3 injury than that of muskmelon (Simini et al., 1987, 1989), and the yield of muskmelon was significantly depressed by O3, we hypothesized that ambient concentrations of O3 in southwestern Indiana would also depress the yield of watermelons. Because watermelon are an important horticultural crop in southwestern Indiana, grown commercially on ≈ 1100 ha in a five-county area (Daviess, Gibson, Knox, Sullivan, and Table 1. Percentage of hourly ambient O3 concent during watermelon growing season, 1986. This study was carried out on a commercial farm in Decker, Ind., during Summer and Fall 1986. The site was selected because severe O3-induced foliar injury on watermelons was previously observed at this location (Decoteau et al., 1986; Simon et al., 1986). Treatments consisted of two levels of ambient O3. This was accomplished with the use of OTCs (Heagle et al., 1979; Snyder et al., 1988) into which either CF or NF air was introduced continuously through the watermelon canopy of all chambers. This experiment was conducted in the latter part of the growing season and followed a similar experiment with muskmelon (Snyder et al., 1988). Although watermelons are not often grown so late into the fall, our previous monitoring studies (unpublished data) indicated that while O3 concentrations are higher in the spring, O3 is present in sufficient concentrations during the fall to induce injury on sensitive crops. The experimental design was a randomized complete block, with six plants per treatment chamber and six replications of each of the two treatments. The study was tested by analysis of variance using SAS (SAS, 1985). The concentration of O3 within each OTC was monitored continuously, throughout the growing season, with a chemiluminescent O3 analyzer (Bendix Corp., Model 8002, Ronceverte, W.Va.) as described by Heagle et al. (1979). Hourly means of O3 concentrations were calculated for both treatments over the period of time from transplanting to final harvest. In addition, ambient O3 and SO2 were monitored at the farm site, in cooperation with the Indiana Dept. of Environmental Management (DEM) as part of their statewide network of air pollution monitoring (Simon et al., 1986). Ozone concentrations were monitored continuously with a UV photometer (Dasibi, Model 1003AH). Ambient O3 concentrations were calculated for 10 categories over the range of 0.000 to 0.100 ppm (Table 1). Ambient SO2 was measured Vigo counties), and 1300 ha statewide in Indiana (Bureau of the Census, 1984), the objectives of this study were to quantify effects of air quality on growth, yield, and quality of watermelon. rations (ppm) in each of 10 ranges at Decker, Ind.,