Air pollutants influence the growth, yield and quality of many horticultural crops. It is difficult to determine and evaluate the impact of air pollution on the horticulture industry for the following reasons: The variable environments in which horticultural crops are grown markedly influence the amount of foliar injury caused by air pollutants. The large number of cultivars within horticultural crop species contribute to the magnitude of understanding necessary to evaluate pollutant effects. Genetic, morphological and physiological differences among species and cultivars within species also influence foliar injury and plant sensitivity. The amount of economic loss in horticultural crops due to air pollutants varies from year to year. This variation is probably most directly related to daily and seasonal variations in ambient concentrations of air pollutants. Horticultural crops may be subjected to high pollutant concentrations at different stages of plant maturity. These different stages of growth and development may be differentially affected by pollutant concentration and thus influence yield. Past estimates of crop yield losses have been based primarily on assessment of visual injury. Presently, there is a lack of suitable methodology to assess air pollution impacts under field conditions. Open-top chambers (40, 60) are an improvement but better techniques are needed. Finally, air pollution research is published in a variety of scientific journals and some of these references may not come to the attention of horticultural scientists.
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. Ozone-induced 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.