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  • Author or Editor: Albert H. Markhart x
  • Journal of the American Society for Horticultural Science x
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High temperature reduces fruit set in bell pepper [Capsicum annuum L. var. annuum (Grossum Group)], and reduction of pepper productivity, resulting from high temperature, may be a direct effect of temperature or an indirect effect of water stress induced by increased vapor pressure deficits (VPDs) at high temperature. We evaluated responses of plant growth, reproduction, net photosynthesis (PN), chlorophyll fluorescence, predawn respiration, leaf water potential, and stomatal conductance of `Ace' and `Bell Boy' bell pepper to elevated temperature (33 °C) with increased VPD (2.1 kPa) or elevated temperature with no increase in VPD (1.1 kPa). VPD had no effect on flower number or fruit set and did not adversely influence the physiological processes measured. Therefore, deleterious effects of high temperature on pepper fruit set does not appear to be temperature induced water stress, but is more likely a direct temperature response. Elevated temperature decreased fruit set but not flower production. Gas exchange measurements suggest failure to set fruit was not due to reduced leaf photosynthesis.

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Abstract

The relationship of foliar injury in Pinus sylvestris (Scots pine) to low temperature and irradiance levels was studied in growth chambers at –l°C(warm) and –7°(cold) under 3 light treatments: 1) nonshaded (1000 watt, Metalarc), 2) 47% shade cloth, and 3) 4-mil white polyethylene. During the 9-week treatment period, plants were tested for hardiness, electrolyte leakage, chlorophyll content, and relative water content. Foliar injury was observed in plants under the cold treatment but the degree of injury was not related to irradiance level. After 6 weeks, electrolyte leakage levels were greater than 50% for all cold-treated plants. No foliar injury occurred on warm-treated plants regardless of light treatment. Minimizing desiccation and rapid temperature fluctuations did not prevent injury. Needle water content of plants from both temperature regimes decreased about 6% over the duration of the experiment. Maximum foliar temperature fluctuations were 5.5° (l.l°/minute) and 4° (0.8°/minute) in the cold and warm chambers, respectively. Although warm-treated plants showed no injury during the treatment period, they deteriorated after several weeks in the greenhouse. Severe root injury to the warm-treated plants may have caused this deterioration.

Open Access