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Sugarcane smut, caused by Sporisorium scitamineum, is one of the most important sugarcane diseases in Japan. Wild sugarcane, Saccharum spontaneum, is known to be a key breeding material to obtain high-yielding clones. In this study, we sought to identify Japanese wild sugarcane accessions with high resistance to smut. Thirty wild sugarcanes and three sugarcane cultivars were tested by the pinprick method. The results of the inoculation tests aided in identifying wild sugarcanes with high resistance to smut disease, namely JW90, Iriomote8, and Iriomote15. After screening the germplasm, progeny distribution of smut resistance from the inoculation test and dry matter productivity in the smut disease-free field were compared. The highly resistant wild sugarcane accession had a much better impact on progeny distribution of smut resistance compared with the susceptible accession. No relationship was found between smut resistance and dry matter productivity in both populations.

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.

Sugarcane production in Japan dropped to a record low of 1,186,000 tons in 2004. Severe drought and tropical storms (typhoons) often reduce sugarcane yields. In order to avoid these environmental stresses, an early harvest system and early maturing cultivars are required. The maturing characteristics of one early maturing clone (“KY96T-547”) were thus investigated in breeding experiments to clarify effective methods of identifying early maturing clones. The results of spring planting crops in a regular breeding program and autumn planting crops intended for early harvest were also analyzed. Among the spring planting crops, the early maturing clone exhibited earlier increases in brix value at the top position of the stem, with higher orders of brix for this clone also being observed at the top. The coefficient of variance for the top brix among approximately 50 clones was higher than that for other stem positions. The coefficient of variance was higher at the beginning of October, when the brix values of early maturing clones increased. This is the best time for screening at the research site . Among the autumn planting crops, the early maturing clone matured October or November at the same level as in the regular harvest season.

Sugarcane is an important crop and also a potential feed resource in the Southwestern Islands of Japan. We investigated chemical composition and in situ degradability of two Japanese sugarcane varieties, a common variety, NiF 8 and a new variety developed for cattle feed, KRFo 93-1. We also evaluated these sugarcanes as alternatives to sugarcane top and imported oaten hay, i.e. commonly used roughages in the Southwestern Islands. The crude protein (CP) contents of both sugarcane varieties were usually lower than those of sugarcane top and oaten hay, showing a decrease with advancing maturity after ratooning. On the other hand, the non-fiber carbohydrate contents of both varieties and the effective degradability of dry matter in NiF 8 increased with advancing maturity, possibly due to sucrose accumulation. The effective degradability of neutral detergent fiber for KRFo 93-1 decreased with advancing maturity, being lower than that for sugarcane top and close to that of oaten hay. Overall, highest nutritional benefits would be obtained at a later stage harvest for NiF 8 and at an earlier stage harvest for KRFo 93-1. CP and/or energy supplements are needed when either of the sugarcane varieties is used as an alternative to sugarcane top or imported oaten hay.

In Japan a high dependency on imported food, particularly livestock feed, has resulted in the accumulation of large amounts of nutrients, especially nitrogen, in the form of livestock manure. Cultivating feed crops that can take up a large amount of N would not only mitigate the water pollution caused by the nitrate leached from the livestock sector, but would also improve food self sufficiency. Sugarcane (Saccharum spp.) is considered to be a promising candidate in this respect. Two field experiments were conducted in 2006 and 2007 in Kagawa to evaluate the dry matter (DM) yield, N content and nitrate-N concentration of sugarcane under high N input. The first experiment was designed as a factorial experiment with two factors, varieties/lines/clones and N rates set at two levels, 30 g m−2 year−1 and 60 g m−1 year−1, with three replicates. In the second experiment, 30 varieties/lines/clones of sugarcane and related genera as well as control crops were planted (n = 2) and a single N rate of 45 g m−...

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 in nitrogen 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.

ポットおよび水田で栽培した水稲品種コシヒカリを用いて, 追肥窒素が水稲に吸収される様相を把握するため, 追肥後における茎基部からの出液速度と出液の窒素濃度から出液中の窒素量を推定し, その経時的な推移について検討した. ポット, 圃場試験ともに, 出液の窒素濃度は硫安追肥後6時間目以降に上昇が認められ, 24時間目に最大となった後は漸減した. 出液の窒素濃度の上昇までに6時間以上が経過しているが, これは追肥が土壌中で拡散して根に吸収されて木部導管に入るまでに要する時間と考えられた. 圃場試験の追肥後168時間目では, 追肥区の出液の窒素濃度が追肥を施用しない対照区と同じレベルまで低下しており, 追肥の吸収は終了したと考えられた. なお, 出液の窒素分析の結果から, 圃場試験の追肥後168時間目での追肥硫安の利用率を推定すると約55％であった. 一方, 出液速度は, ポット, 圃場試験ともに, 出液の窒素濃度の上昇から12時間以上が経過した後に, 追肥区で対照区よりも高くなった. この時間的なズレが生じた原因は, 導管液中の窒素化合物の増加が直接的に根の吸水を促進したというよりは, 追肥による根の生理機能の向上により, 間接的に根の能動的吸水が促進されたためと考えられた. 葉色の反応はさらに遅れて, 追肥後48時間目に初めて追肥区が対照区よりも高くなった. 以上のように, 出液の窒素分析から, 追肥が吸収される様相を詳細かつ迅速に把握できることが明らかとなり, さらに追肥窒素の利用率や土壌中での挙動についても把握できる可能性が示された.