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This study was carried out to investigate the defoliation of 3 different cultivars of Hibiscus syriacus as affected by varying temperature (field and greenhouse temperature), shading (25, 50%), fertilization (8, 16 mM nitrate) and irrigation (watering twice a day, once every two or five days) treatments. Greenhouse environment (25±5℃) significantly delayed defoliation, and the total chlorophyll content under highest temperature was higher than any other treatments. Defoliation was delayed by increasing shading levels. Nitrate fertilization delayed defoliation at relatively high concentration (16 mM). Water stress accelerated defoliation. Changes in peroxidase (POD) and polyphenol oxidase (PPO) activities appeared extremely low and superoxide dismutase (SOD) activity was high under greenhouse environment. A close correlation between chlorophyll content and either POD, PPO, or SOD was noted, and it was also related significantly to the delay of defoliation.
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