Takayoshi Terauchi

Genotypic Variation of the Ability of Root to Penetrate Hard Soil Layers among Japanese Wheat Cultivars

Abstract The hard soil in the field is a major constraint for the cereal production because it mechanically restricts the root expansion and water absorption. The ability of root to penetrate into the hard soil is an important factor affecting yield stability of wheat (Triticum aestivum L.) under hard soil and drought conditions. We investigated the variation in the penetrating ability of roots (PA) among Japanese wheat cultivars and its relationship with other shoot and root characters to acquire basic information to develop the cultivars with a higher PA. The evaluation was conducted by the two experiments using the two groups of cultivars: 1) 43 Hokkaido cultivars in the first experiment, 2) 38 Honsyu, including Shikoku and Kyusyu, cultivars in the second experiment. In each experiment, one seedling of each cultivar was grown in a pot with a disc made of paraffin and Vaseline mixture (PV) as a substitute for the hard soil layer. The number of roots penetrating through the PV disc per plant (NRP), the number of seminal and crown roots reached the PV disc per plant (NRR) and the penetration index (PI = NRP/NRR) of each cultivar were evaluated as the traits related to PA. NRP significantly varied with the cultivar from 4.0 to 29.7 and 3.0 to 22.0 in the first and second experiments, respectively. NRP were significantly correlated with NRR (r=0.644** in the first and r=0.477** in the second experiment) and PI (r=0.863** in the first and r=0.811** in the second experiment), but the relationships between NRR and PI were not significant (r=0.260 in the first and r=0.190 in the second experiment). NRR was significantly correlated with the degree of winter growth habit (requirement of vernalization), root dry weight (DW) above the PV disc, the number of stems and leaf DW in each population. Correlations between PI and other characters were low or not significant. These results indicate that a large genotypic variation exists among Japanese wheat cultivars in NRP, and that PI is a suitable indicator of PA. Cultivars with a high PA detected in this study will be useful genetic resources of wheat to improve the yield stability under drought and hard soil conditions.

Effects of drought and shading on non-structural carbohydrate stored in the stem of potato (Solanum tuberosum L.).

Abstract Most studies on non-structural carbohydrate (NSC) are concentrated on the leaf and tuber, and little is known about NSC in the stem and its function. To test the hypothesis that NSC stored in stem contributes to stable tuber bulking under stress conditions, we grew plants in pots in a greenhouse under drought and shading conditions for 17 d during tuber bulking. Compared with the control, drought and shading significantly reduced leaf and stem dry weights (DW) and total NSC concentration in the main stem base. However, tuber DW increased by 77% in drought and by 46% in shading conditions relative to the control. The contributions of NSC loss in the stem to tuber DW increase in drought and shading conditions were 37% and 54%, respectively. This study suggests that NSC stored in the stem base is supplied to tuber under stress conditions to support tuber bulking.

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.

Comparison of ratoon yield under high-level cutting in two varieties of forage sugarcane, KRFo93-1, and Shimanoushie

Abstract High-level cutting without stubble shaving has been recommended in the cultivation of forage sugarcane, KRFo93-1. However, it is unclear whether this management practice is appropriate for the more recently developed variety Shimanoushie. Therefore, the aim of this study was to compare the dry matter yield of both varieties to high-level cutting. The study included five ratoon crops (RC1–RC5). In KRFo93-1, dry matter yield was higher in HC plots (high-level cutting without stubble shaving plots) than in Control plots (stubble shaving after high-level cutting plots), and the differences were significant for the first three ratoon crops. A similar trend was observed in Shimanoushie; however, the dry matter yield of HC plots was slightly lower than Control plots in RC4 and RC5 owing to a lower stem number. Although the sum of dry matter yield of five ratoon crops was significantly higher in HC plots of both varieties, the influence of high-level cutting was more effective in KRFo93-1 than in Shimanoushie.

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.