Response of rice (Oryza sativa l.) tillering to sub-ambient levels of ultraviolet-B radiation
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The negative impact of enhanced ultraviolet-B (UV-B) radiation has been demonstrated for rice, but few studies have examined the effects of low UV-B radiation on rice growth and physiology. The objective of this study was to determine the effects of low UV-B radiation on rice physiology with special emphasis on tiller initiation and development in two popular US rice cultivars, 'Cocodrie' and 'Clearfield 161 (CL161)'. Plants received no natural UV-B radiation because of the UV-absorption characteristics of the greenhouse glass, hence UV-B was artificially supplied by supplemental UV-B lighting. Plants were grown in soil collected from research plots, and were exposed to UV-B radiation of 0, 4 (sub-ambient) or 8 kJ m-2 day-1 (ambient) for 29 days in one experiment and 87 days in a second experiment. 'Cocodrie' had no differential response among 0, 4 and 8 kJ m-2 day-1 UV-B treatments for all the parameters measured except for plant height, which showed 5% decrease at ambient UV-B conditions. For 'CL161' sub-ambient UV-B radiation exposure decreased vegetative tiller production (25%) and total panicle dry weight (15%). The decrease in tiller production was not due to a decrease in carbohydrate content or increase in auxin content under the low UV-B radiation. 2007 The Authors.