Morphological and physiological traits of roots and their relationships with shoot growth in super rice

Success in super rice breeding has been considered a great progress in rice production in China. This Study aimed to test the hypothesis that an improved root system may contribute to better shoot growth and consequently to higher grain yield in super rice. Two super rice varieties Liangyoupeijiu (an indica hybrid) and Huaidao 9 (a japonica inbred) and two elite check varieties Yangdao 6 (an indica inbred) and Yangfujiang 8 (a japonica inbred) were field-grown at Yangzhou, China in 2006 and 2007. Root and shoot dry weight (DW) was significantly greater in super rice varieties than in check ones throughout the growth season in both years, so was the root length density. Root oxidation activity (ROA) and root zeatin (Z) zeatin riboside (ZR) content, in per plant basis, were significantly greater in super rice than check varieties before and at heading time. However, both ROA and root Z + ZR content, oil her in per plant basis or per unit root DW basis, were significantly lower in 'super' rice than in check varieties at the mid- and late grain filling stages. Grain yield of the two 'super' rice varieties, on average, was 10.2 t ha(-1) in 2006 and 11.4 t ha(-1) in 2007, and was 13% and 21% higher than that of check varieties, respectively. The high grain yield was mainly due to a larger sink size (total number of spikelets) as a result of a larger particle. The percentage of filled grains of the two Super rice varieties, on average, was 72.9% in 2006 and 79.0% in 2007, and was 19.4% and 12.9%, respectively, lower than that of the check varieties. The mean ROA and root Z + ZR content during the grain filling period significantly cot-related with the percentage of filled grains. Collectively, the data Suggest that an improved root and shoot growth, as showing a larger root and shoot biomass and greater root length density during the whole growing season and higher ROA and root Z + ZR content per plant at early and mid-growth stages, contributes to the large sink size and high grain yield in the super rice varieties. The data also Suggest the yield Of Super rice varieties can be further increased by an increase in filled grains through enhancing root activity during grain filling. (C) 2009 Elsevier B.V. All rights reserved.