AOBPreview originally published online on October 21, 2008
Annals of Botany 2009 103(2):171-180; doi:10.1093/aob/mcn201
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Contrasting physiological responses by cultivars of Oryza sativa and O. glaberrima to prolonged submergence
1 Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan
2 University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
* For correspondence. E-mail sakajun{at}affrc.go.jp
Received: 2 August 2008 Returned for revision: 11 August 2008 Accepted: 28 August 2008 Published electronically: 21 October 2008
Background and Aims Oryza glaberrima: is widely grown in flood-prone areas of African river basins and is subject to prolonged periods of annual submergence. The effects of submergence on shoot elongation, shoot biomass, leaf area and CO2 uptake were studied and compared with those of O. sativa.
Methods: A wide selection of lines of O. sativa and O. glaberrima, including some classified as submergence tolerant, were compared in field and pot experiments. Plants were submerged completely for 31 d in a field experiment, and partially or completely for 37 d in a pot experiment in a growth chamber.
Key Results: Leaf elongation and growth in shoot biomass during complete submergence in the field were significantly greater in O. glaberrima than in O. sativa. So-called submergence-tolerant cultivars of O. sativa were unable to survive prolonged complete submergence for 31–37 d. This indicates that the mechanism of suppressed leaf elongation that confers increased survival of short-term submergence is inadequate for surviving long periods underwater. The O. sativa deepwater cultivar ‘Nylon’ and the ‘Yélé1A’ cultivar of O. glaberrima succeeded in emerging above the floodwater. This resulted in greatly increased shoot length, shoot biomass and leaf area, in association with an increased net assimilation rate compared with the lowland-adapted O. sativa ‘Banjoulou’.
Conclusions: The superior tolerance of deepwater O. sativa and O. glaberrima genotypes to prolonged complete submergence appears to be due to their greater photosynthetic capacity developed by leaves newly emerged above the floodwater. Vigorous upward leaf elongation during prolonged submergence is therefore critical for ensuring shoot emergence from water, leaf area extension above the water surface and a subsequent strong increase in shoot biomass.
Key words: Flooding, leaf area, net assimilation rate, Oryza glaberrima, O. sativa, photosynthesis, rice, stress adaptation, submergence escape
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