Effect of Shading on Root System Morphology and Grain Yield of Rice Plants (Oryza sativa L.) : II. An analysis on primary roots

Using the same materials reported in the previous paper, the effect of shading (78% of full solar radiation) from panicle formation stage to heading, on the number, form, type and growth direction of primary roots of rice plants were investigated. Shading decreased the number of 'elongated roots' and 'stunted roots' per hill and per culm respectively, but it had no effects on the composition and the number of productive culms. The total number of primary roots of shaded plot was about 90% of that of control plof A remarkable decrease in primary root number by shading was observed in the 11th and 12th shoot units where emergence and elongation of primary roots took place just during the shading treatment. The number of 'stunted roots' in the 11th shoot unit, and further the number of 'elongated roots' as well in the 12th shoot unit were decreased. Shading affected the type of 'elongated roots' in the 11th and 12th shoot units, the type A (less tapering) roots tended to decrease, on the other hand, the type C (highly tapering) roots tended to increase. Shading had no effect on the growth direction of primary roots, however, their number at each direction tended to decrease proportionately. From the above investigations, it was assumed that both the mass and the morphology of primary roots developed during panicle formation till heading have close relationships with grain yield of rice plants.