The productivity, product quality and competitive ability of important agricultural and horticultural plants in many regions of the world may be adversely affected by current and anticipated concentrations of groundlevel ozone (O 3 ). Exposure to elevated O 3 typically results in suppressed photosynthesis, accelerated senescence, decreased growth and lower yields. Various approaches used to evaluate O 3 effects generally concur that current yield losses range from 5% to 15% among sensitive plants. There is, however, considerable genetic variability in plant responses to O 3 . To illustrate this, we show that ambient O 3 concentrations in the eastern United States cause substantially different levels of damage to otherwise similar snap bean cultivars. Largely undesirable effects of O 3 can also occur in seed and fruit chemistry as well as in forage nutritive value, with consequences for animal production. Ozone may alter herbicide efficacy and foster establishment of some invasive species. We conclude that current and projected levels of O 3 in many regions worldwide are toxic to sensitive plants of agricultural and horticultural significance. Plant breeding that incorporates O 3 sensitivity into selection strategies will be increasingly necessary to achieve sustainable production with changing atmospheric composition, while reductions in O 3 precursor emissions will likely benefit world food production and reduce atmospheric concentrations of an important greenhouse gas.

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The influence of N and K rates in Hoagland's nutrient solution on Jalapeño pepper (Capsicum annuum L.) plant growth and pod production was determined on greenhouse-grown plants in sand culture. Varying the rates of N (1 to 30 mm) and K (1 to 12 mm) in Hoagland's solution identified optimum concentrations for Jalapeño plant growth and pod production. Two experiments were conducted to determine Jalapeño pepper sensitivity to differential fertilization. In the experiment seeded in April, nutrient treatments began at transplanting, and in the one seeded in May, treatments began after all plants had flower buds and half had flowered. Biomass and pod production per plant responded curvilinearly to N rate in both experiments. Optimum N rate for pod yield was 15 mm. Nitrogen rate affected pungency of pods only in the first experiment, with 1 mm N reducing capsaicin levels in fruit compared to other N rates. Biomass, fruit count, and fruit weight per plant increased linearly with increasing K rate in the first experiment and curvilinearly with K rate in the second experiment. The optimum K rate for pod yield was 6 mm. Potassium rates did not affect pod pungency. Jalapeño peppers grown in sand culture required 15 mm N and at least 3 mm K for optimum pod production.

Mulch surface color affected the growth of bell pepper (Capsicum annuum L.) plants, the amount and quality of upwardly reflected light, and the soil temperatures under the mulch. Of the surface colors evaluated (black, red, yellow, and white), plants grown over red mulch were the tallest. The darker (black and red) mulches reflected less total light and more far-red (FR) relative-to-red (R) light, and soil temperatures recorded in the afternoon and evening were warmer than under the yellow and white mulches. Plant growth responses to mulch surface color were also observed when soil temperature differences among the mulch color treatments were minimized by placing insulation boards between the mulch surface and the soil. Sensitivity of young pepper plants to a high or low FR: R light ratio was demonstrated by exposing plants to 15 minutes of FR or 15 minutes of R light at the end of the photosynthetic period each day for 14 consecutive days in a controlled environment. Plants that received the FR (high FR: R ratio) were 51% taller than plants exposed to R (low FR: R ratio) light treatments. The similar responses of pepper plants to differences in FR: R ratios associated with mulch color and end-of-day light treatments provide evidence that pepper plant growth is affected by relatively small changes in light environment induced by the surface color of the mulch.

The effect of planting population density (as a function of in-row plant spacing and number of rows per bed) on the growth, yield, and pod distribution of cayenne pepper (Capsicum annuum var. annuum L. cv. Carolina Cayenne) was investigated in a 2-year study. In 1988, 15 -, 30-, 45-, and 60-cm in-row spacings in a single row were evaluated, and in 198915 -,30-, and 60-cm in-row spacings in single and double rows were evaluated. Plant population densities at these respective spacings ranged from≈ 11,100 to 44,400 and 11,100 to 88,900 plants/ha. In 1988, pepper plants grown at the highest density (15-cm in-row spacing, 44,400 plant/ha) produced less fruit per plant but more fruit per hectare than those grown in lower densities. In 1989, yields with either a 15-cm in-row spacing in a single row or a 30-cm in-row spacing in double rows (both with 44,400 plants/ha) were higher than in the others. In general, less fruit were located in the lower part of the plant canopy when planted in higher plant population densities.