Morphology And Physiology Of Roots And Their Relationships With Yield Formation In Super Rice

China has made great progress in super rice breeding and which is well known in the world. So far a number of super rice varieties have been released and adopted in rice production. These varieties would have great importance in both improving the overall production capacity of rice in China and ensuring food safety supplies. Roots are an integral part of plant organs and involved in acquisition of nutrients and water, synthesis of plant hormones, organic acids and amino acids, and anchorage of plants. Root morphology and physiology play an important role in the growth and development of aboveground plants. However, little is known about morphological and physiological characteristics of roots and their relations with grain yield in super rice. Using typical super rice cultivars as materials, this study investigated changes in morphological and physiological traits of roots and their relationships with grain yield in super rice at different growth stages and at different nutrient treatments. The main results are as follows:1. Two super rice cultivars, Liangyoupeijiu (indica-inclined two-line hybrid) and Yangjing4038(japonica), and two high-yielding rice cultivars, Yangdao6(indica) and Yangfujing8(japonica), were grown in nutrient solution. Changes in morphological and physiological traits of roots and their relationships with growth and development at different growth stages were investigated. The results showed that both super rice varieties had a greater yield potential and a higher grain yield than the two elite check varieties. The higher grain yield of the super rice varieties was mainly due to a larger sink size as a result of a larger panicle. Root and shoot dry weight was significantly greater in super rice varieties than in check ones throughout the growth season. Root oxidation activity (ROA), root total absorbing surface area and active absorbing surface area, the number of cells in ultrastructure in root-tip and root zeatin (Z) zeatin riboside (ZR) content, in per plant basis, were significantly greater in super rice than check varieties at the early stage. The large root biomass was mainly attributed to more number of roots, while the large shoot biomass was mainly due to a larger LAI throughout the growth season. The low percentage of filled grains was closely associated with a quick decreased root activity during grain filling. These results suggest the yield of super rice varieties could be further increased by an increase in filled grains through enhancing root activity during grain filling.2. Two super rice cultivars, Liangyoupeijiu (indica-inclined two-line hybrid) and Yangjing 4038(japonica), and two high-yielding rice cultivars, Yangdao6(indica) and Yangfujing8(japonica), were grown in nutrient solution. Four levels of phosphorous (P) and potassium (K) treatments, High P (P was30%higher than standard nutrient solution), Low P (P was30%lower than standard nutrient solution), High K (K was30%higher than standard nutrient solution), Low K (K was30%lower than standard nutrient solution), and control (CK, the standard nutrient solution), were imposed from heading to maturity. Changes in morphological and physiological traits of roots and their relationships with grain yield at different P and K levels during grain filling were observed. The results showed that the grain yield, root oxidation activity, Z+ZR content, shoot and root dry weight, and the ratio of root to shoot during the grain filling period were all increased with the increase in P and K application for all the tested cultivars, and the reduction in P and K application showed the opposite effects. The results indicate that, through proper P and K management, root senescence during grain filling could be effectively alleviated, and the growth of aboveground and underground parts, and seed setting rate be improved, leading to realization of great yield potential in super rice.3. Two super rice cultivars, Liangyoupeijiu (indica-inclined two-line hybrid) and Huaidao9(japonica), two high-yielding check cultivars, Shanyou63(indica hybrid) and Zhendao88(japonica), were field-grown. Three nitrogen (N) treatments, no N application (TO), mid amount of N at210kg hm-2for indica and240kg hm-2for japonica cultivars (T1), and high amount of N at300kg hm-2for indica and360kg hm-2for japonica cultivars (T2), were conducted. Changes in morphological and physiological traits of roots and their relationships with grain yield in super rice at different N levels were studied. The results showed that the grain yield of the two super rice cultivars was increased with the increase in N application. Root oxidation activity and Z+ZR content, shoot and root dry weight and the ratio of root to shoot during the grain filling period were increased with the increase in N application. At the condition of N rate from TO to T1, grain yield of the two check cultivars was increased with the increase in N application, root oxidation activity, Z+ZR content, shoot and root dry weight, and the ratio of root to shoot during grain filling were also increased. When the N rate was at T2level, the grain yield, root oxidation activity, Z+ZR content, shoot dry weight, root dry weight and the ratio of root to shoot of the two check cultivars were decreased significantly. The results suggest that root and shoot growth and grain yield of super rice could be improved through proper N management.