Takeo Sakaigaichi

Diurnal and Phenological Changes in the Rate of Nitrogen Transportation Monitored by Bleeding in Field-Grown Rice Plants (Oryza sativa L.)

Abstract Nitrogen uptake is essential for rice growth and yield. Thus, the development of a simple and rapid method for monitoring nitrogen absorption is strongly required. We examined the fundamental properties of nitrogen transportation monitored by bleeding, including diurnal and phenological changes, to discuss whether the analysis of bleeding sap could be used for monitoring nitrogen uptake by rice. The rate of nitrogen transportation monitored by bleeding was estimated from a combination of the nitrogen concentration in bleeding sap and bleeding rate. We found a clear diurnal change in the rate of nitrogen transportation monitored by bleeding; it was higher in the daytime than at night. In this study, the diurnal change innitrogen uptake was not influenced by soil temperature but by the light condition. The rate of nitrogen transportation monitored by bleeding showed a phenological change with a peak around the panicle formation stage, while the bleeding rate peaked at around heading and was correlated with root length. The nitrogen concentration in bleeding sap continued to decrease gradually from the early growth stage. The cumulative amount of nitrogen uptake estimated by the bleeding sap analysis was less than half of that estimated by the plant analysis before the maximum tiller number stage, but the difference between these values decreased with plant growth. There was a significant positive correlation between the cumulative amount of nitrogen uptake estimated by these analyses throughout the growing period.

Effect of Stubble Shaving after High-Level Cutting on the Growth and Yield of Forage Sugarcane, KRFo93-1, under Multiple Ratooning Cultivation

Abstract In the production of sugarcane, stubble shaving that cuts the residual stubble of the previous crop is carried out to promote ratoon crop growth. On the other hand, in the production of feed crops, it is generally considered that high-level cutting increases the yield of the regrowth crop. In this study, the growth and yield of the forage sugarcane subjected to high-level cutting without stubble shaving (HC) were compared with those of the plants subjected to stubble shaving (Control) to clarify the necessity of stubble shaving in the cultivation of a forage sugarcane variety, KRFo93-1. The influence of high-level cutting on the growth and yield of ratoon crop was evaluated from the first ratoon crop (RC1) to sixth ratoon crop (RC6). Tiller number in the Control plot was not different from that in the HC plots in all ratoon crops from RC1 to RC6. Stem length was significantly larger in HC than in the Control plot in all ratoon crops at the initial stage of regrowth, and in RC1, RC3, RC5 and RC6 around the harvest time. Dry matter yield was significantly higher in HC than in the Control plot in RC1, RC3, RC5, RC6 and in the sum of the ratoon crops. Although no significant difference was observed in RC2 or RC4, the dry matter yield of HC exceeded that of Control plot. The increase in the dry matter yield of HC was due to an enhancement of stem growth, since the single stem dry weight were larger in HC than in Control plot. Thus, cultivation management without stubble shaving is recommended in KRFo93-1.

Evaluation of the juice brix of wild sugarcanes (Saccharum spontaneum) indigenous to Japan

Abstract Modern sugarcane cultivars are derived from the interspecific crossing between Saccharum officinarum and wild sugarcane, Saccharum spontaneum. The introgression of valuable characteristics from wild sugarcane is recognized as extremely important, but this process typically requires long-term effort over multiple generations of backcrosses owing to the low sugar content of the initial interspecific hybrids. In this study, we aimed to identify Japanese wild sugarcanes with high juice brix in order to promote effective interspecific crossing of sugarcane. Sixty-four accessions from the Nansei Islands and 70 accessions from the Honshu were evaluated for juice brix. Wild sugarcanes with high juice brix were demonstrated to exist among wild sugarcanes indigenous to the Honshu. A significant difference was observed between the median juice brix values of wild sugarcanes of the Nansei Islands and those of the Honshu. The relationship between juice brix and stem traits was then examined in 20 wild sugarcanes, 10 each from the Nansei Islands and the Honshu. The reproducibility of juice brix value in both experiments was confirmed. In contrast to juice brix, stem traits, such as length, diameter, and volume, were typically smaller in wild sugarcanes from the Honshu. Moreover, a negative correlation was observed between the index of stem volume and juice brix. In this study, we identified outstanding wild sugarcanes with high juice brix. Using germplasms from the identified wild sugarcanes in interspecific crossing could contribute to the increases in both yield and sugar content.