Changes in Morphological and Physiological Traits of Roots and Their Relationships with Grain Yield during the Evolution of Mid-season Indica Rice Cultivars in Jiangsu Province

Roots are involved in acquisition of nutrients and water,synthesis of plant hormones,and anchorage of plants.However,little is known what changes in root physiology and morphology during the evolution of rice cultivars.In this study,13 typical mid-season indica rice cultivars (including hybrid combinations) applied in the production in Jiangsu Province during the last 60 years were used,which were classified into four types of early tall cultivars,dwarf cultivars,semi-dwarf cultivars,and super rice cultivars according to their application times,plant types and genotypes.All the tested cultivars were grown in the field and changes in morphological and physiological traits of roots and their relationships with grain yield during the evolution of cultivars were investigated.Results showed that the root dry weight,root weight density,root length,root length density and root diameter were increased with the evolution of the cultivars at main growth stages.From the heading stage,the shoot dry weight was increased with the evolution of the cultivars.Compared with other cultivars,the root-shoot ratio of super rice cultivars was increased at the mid-tillering and panicle initiation stages,but showed no significant differences among the four types of cultivars at latter growth stages.Specific root length was decreased with the evolution of the cultivars at the mid-tillering stage,and showed no significant differences among the four types of cultivars at other growth stages.The root oxidation activity,leaf photosynthetic rate,total absorbing surface area and active absorbing surface area of root,and the content of cytokinins (zeatin + zeatin riboside) in root bleeding and grain yield were increased with the evolution of the cultivars.Increase in grain yield was attributed mainly to the increase in total number of spikelets,which resulted mainly from a large panicle.Regression analysis showed that the root dry weight,root length,root diameter,root oxidation activity,total absorbing surface area and active absorbing surface area of root very significantly correlated with grain yield.The results suggest that the improved root and shoot growth increases grain yield of the modern cultivars,especially super rice cultivars.