Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 2/24/2002
Publication Date: 2/24/2002
Citation: Stiers, E.N., Burgos, N.R., Gealy, D.R., Counce, P.A. 2002. PHOTOSYNTHETIC RESPONSE OF RICE AND RED RICE (ORYZA SATIVA) TO SHADING. Rice Technical Working Group Meeting Proceedings. P. 162-163. Interpretive Summary:
Technical Abstract: Rice and red rice are categorized under the same genus and species. They are similar in their morphological and molecular structures, yet red rice is more competitive than today's cultivated rice varieties. We hypothesize that the higher competitive nature of red rice can be attributed partly to higher photosynthetic efficiency. A field study was conducted at the Rice Research and Extension Center in Stuttgart, Arkansas in 2000 and 2001 to compare the photosynthetic response of rice and red rice to shading and nitrogen under noncompetitive conditions. The study utilized a split-split plot design. Two rice varieties, 'Wells' and 'Bengal,' and two red rice ecotypes, Stuttgart strawhull and Katy red rice (a putative cross between red rice and rice), were transplanted on June 15 and May 14 in 2000 and 2001, respectively. Plots were 1m2 and contained two plants of the same variety. Nitrogen in the form of urea was applied one week after transplanting at 0, 100, and 200 kg/ha. Rice and red rice were subjected to 50% light reduction for one week 10 days after anthesis. Photosynthesis rates were measured using a LiCor CO2 gas analyzer 2 days after initiation of the shade treatment. At harvest, the number of tillers, panicles, biomass, and grain count per plant were recorded. In 2001, prior to shade removal, leaf samples were taken to extract chlorophyll content using an acetone extraction method determined for rice (Krishnan, 1996). Chlorophyll was quantified using calculations prescribed by Lictenthaler and Wellburn (1983). The photosynthesis rate of each variety was determined. Due to technical problems in 2000, photosynthesis readings were not useful for Stuttgart strawhull. In 2000, photosynthesis rates for Katy red rice and the rice cultivars were comparable when unshaded; however, Katy red rice photosynthesized at a higher rate than the rice cultivars in 50% shade. In 2001 under reduced light, Katy red rice photosynthesized at a higher rate than 'Bengal' but not 'Wells' as was seen in the previous year. Under shade, Stuttgart strawhull was less efficient than Katy red rice, but still photosynthesized at a higher rate than 'Bengal'. The only yield related parameter affected by shade was panicle number. In 2000 and 2001, the number of panicles produced by Stuttgart strawhull was higher than Katy red rice and the rice cultivars and was not affected by shade. In 2000, Katy red rice produced more panicles than 'Bengal' under shade and high nitrogen. This was not the case in 2001 when 'Bengal' produced more panicles than Katy red rice at all nitrogen levels when subjected to 50% shade. When unshaded, 'Bengal' produced more panicles than Katy red rice at the 0 and 200 kg N ha-1. Total chlorophyll content in the rice varieties was higher than in red rice. Shade did not affect the chlorophyll a/b ratio in the rice varieties, but increased this ratio in Katy red rice, and decreased it in Stuttgart strawhull. Increase in chlorophyll b is a shade- adaptation mechanism and could explain Stuttgart strawhull's increased photosynthetic ability when shade stressed.