Effect of Foliar Application of Triacontanol on Growth and Yield of Rice Plants : III. Its relevance to the development of roots

The purpose of this study was to clarify the effects of triacontanol (TRIA) on the roots growth and the appearance stage of the effects, and to clarify the relationship between root development and hulled rice weight. The cultivar used was Koshihikari. This experiment was conducted to investigate the development of roots in the main. Root dry weight increased in TRIA-treated plots 2 weeks after application, and the effects continued until the maturing stage. In TRIA-treated plots at the late growth stage, root dry weight increased, and the ratios of root weight to top weight and to leaf area (R/T ratio and RW/LA ratio) were higher than in non-treated plot. Root respiration and total sugar content in root increased by TRIA-application. In particular, the rate of increase of hulled rice weight was enhanced by application at heading time and by application in three stages (tillering stage, young panicle formation stage and heading time). The weight of hulled rice was correlated positively with the R/T and RW/LA ratios at heading time and at the maturing stage, respectively. From these results it was inferred that TRIA application enhanced the growth of roots and enlarged the stomatal aperture owing to higher water absorption ability in roots, which increased to the hulled rice weight by maintaining a high photosynthetic rate to the maturing stage.