Abstract The flotation method of ultra-fine bubbles (UFB) aims to address pollution and has been used for combating the undesirable water conditions of contaminated soils. Hence, water containing UFB is gaining increasing attention for potential agricultural applications. Although certain hypotheses have been proposed, such as the collection of ions in water through the electrical characteristic of UFB, no clear experimental data have been provided. We found that improvement in turbidity may cause the adsorption of fine soil particles in the water by the UFB, thereby improving the quality of the water. The data from the paddy field showed that a decrease in turbidity (below 2 nephelometric turbidity units) occurred over a short period of time (3 days). UFB concentration is directly related to turbidity with a coefficient of determination of 0.93. This phenomenon was also observed through the distribution of bubbles and soil particles, where the average particle size increased because of the aggregation of soil particles and the decrease in turbidity in the paddy field, indicating that UFB collect soil particles and thereby improve water quality. Therefore, UFB are highly effective in cleaning rice field water and will be a preferred method for purifying the environment in the future.

Abstract The extensive and intensive use of herbicides has resulted in the spread of herbicide-resistant weeds in many crop production systems; therefore, it is imperative to devise new organic weed control methods. Recently, the application of spent coffee grounds (SCG) in agricultural fields has been found to inhibit plant growth and germination and is thus considered a potentially effective weed control measure. This study aimed to evaluate the effects of different amounts and methods of SCG application on weed growth through field experiments. The field experiments were conducted in an upland field converted from a paddy in western Japan. The results show that the plow-in application of over 10 kg m⁻² of SCG and mulching application of 20 kg m⁻² decreased the weed dry weight compared with the control. In addition, the growth of weed species of families other than Gramineae, such as wingleaf primrose-willow and horseweed, was not significantly affected by SCG application. Weed species of families other than Gramineae are dominant in some upland fields. Hence, the inhibitory effect of SCG on weeds may be lower in original upland fields than in the upland field converted from paddy field that was investigated in the present study. Overall, this study demonstrated that the plow-in application of 10 kg m⁻² of SCG every 4 mo was effective for weed control in an upland field converted from a paddy field. Because SCG worked against grass weeds under the specific conditions in this study, it would be valuable to explore other potential applications of this novel means of weed control.

The production of pearl millet (Pennisetum glaucum (L.) R.Br.) is important in Namibia, in sub-Saharan Africa, owing to the prevailing low precipitation conditions. Most fields supporting crop production in northern Namibia are located in a network of seasonal wetlands. The aim of the present study was to evaluate the effects of ridging and fertilizer application on the yield and the growth of pearl millet in the seasonal wetlands under different rainfall conditions. The study was conducted for two years (2017–2018) in the experimental fields in northern Namibia, and yield, yield components, and growth parameters were evaluated in relation to the application of different fertilizers (manure and mineral) with and without ridge-furrows. Manure fertilizer application presented the highest yield in 2018, whereas mineral fertilizer application showed the highest yield in 2017. The proportion of rainfall was the highest during the mid-growth period in 2017, and the reproductive stage in 2018. Thus, pearl millet plants under manure fertilization overcame damage resulting from waterlogging stress during the seed setting stage by improving the soil and plant nutrient conditions. In contrast, the plants under mineral fertilization were more tolerant to large amounts of rain during the mid-growth period. In this study, yield was mainly determined by total dry weight, and it was closely related to panicle density in both years. Therefore, we concluded that fertilizer application, including additional fertilizer based on the growth diagnostic, could be important for improving crop production in seasonal wetlands.

In the cultivation of Citrus fruit, pruning in late winter after harvest is important to obtain excellent flower buds in the next spring and a rich harvest of superior fruit in the following winter; a large number of pruned leaves are usually discarded. The purpose of this study was to determine the utility value of pruned leaves of Citrus unshiu. A methanol extract of pruned C. unshiu leaves showed a porcine pancreatic lipase inhibitory activity. Fractionation of C. unshiu leaf extract (CUL-ext) followed by bibliographic and chromatographic analyses revealed that a part of the pancreatic lipase inhibitory activity of CUL-ext was attributable to nobiletin (1), rutin (2), and hesperidin (3). Thus, pruned C. unshiu leaves may be a reasonable natural resource for the preparation of ingredients with lipase inhibitory activity.

Flooding has globally become common, and thus cultivation techniques to adapt to the stress are required. We have developed a technique called “close mixed-planting” using flood-adapted rice (Oryza sativa L.) and upland crops with tangled root systems, showing that this technique can mitigate the damage caused to upland crops by flooding. However, the plant response during the reproductive stage has not yet been examined. In this study, we estimated the alleviative effects of close mixed-planting on the growth inhibition and physiological damage to pearl millet (Pennisetum glaucum) caused by flooding at the reproductive stage in northern Namibia. Pearl millet and NERICA4 (Oryza spp., interspecies of O. sativa and O. glaberrima) were used. Four-week-old single- and mixed-crop pearl millets were transplanted and grown for 22 days, and then flooding treatment was administered for 28 days. The growth and physiological parameters of single pearl millet were significantly decreased by flooding stress, and the parameters did not recover during a 14-day recovery period compared with those of unflooded single and mix-cropped pearl millet. On the other hand, the damage to mix-cropped pearl millet by flooding was suppressed. Thus, the mixed-cropping mitigated the anoxic stress of pearl millet caused by flooding at the reproductive stage and contributed to the improved growth after the recovery period. This result suggested that the close mixed-planting with rice can contribute to the mitigation of flooding damage not only at the vegetative stage but also at the reproductive stage of pearl millet in the semi-arid African country, Namibia.

In the Cuvelai Seasonal Wetland System (CSWS) of North-central Namibia, there are widespread manifestations of seasonally flooded river and seasonally closed wetland ecosystems (ponds). These wetlands are called oshana (seasonally flooded river wetland) and ondombe (seasonally closed wetland) according to the local language. This study was initiated to find out the soil fertility status of ondombes and whether they could be utilized for agricultural purposes unlike the present situation. Soil salinity and sodicity were determined to find out impact of such adverse conditions on possibility of food production. A total of 70 representative ondombes were identified from three selected villages. A total of 210 soil samples were collected from upper, middle and lower positions adjacent to ondombes, and 15 soil samples from each 5 upland fields in the three villages and 102 soil samples from different spots of the flood plain in the three oshanas for comparison. The results indicated that the mean soil pH (H2O) in ondombe was 6.3, the means of organic C and total N were 6.28 and 0.41 g kg-1; respectively, the mean of available P was 4.81 mg P kg-1. The means of exchangeable Ca, Mg, K, and Na in ondombe were 2.31, 1.44, 0.21, and 0.61 cmolc kg-1, respectively. Most soil nutrients were higher in lower ondombe positions than on upper and middle positions. Organic C, exchangeable Mg, and clay at the ondombe soils were significantly higher than those at the croplands. The means of electrical conductivity of saturation extract (ECe) and sodium adsorption ratio (SAR) in ondombe soils were 0.62 ds m-1 and 7.32, respectively; even though most of the ondombe soils did not exhibit salinity and sodicity problems. Hence, one can conclude that an ondombe soil has an appropriate condition for agriculture, and may only be prone to sodicity whenever the sodium content is high, as sometimes observed.

The purpose of this study was to examine an inhibitory effect of mango leaf extracts on advanced glycation end products (AGEs) formation and to identify these active ingredients, and also to investigate a relationship between leaves maturation and the inhibitory activity. A methanolic extract of old dark green mango leaf extract (OML-ext) exhibited an inhibitory activity of AGEs formation in nonenzymatic glycation of albumin. The inhibitory activity of OML-ext was attributable to 3-C-β-D-glucosyl-2,4,4’,6-tetrahydroxybenzophenone (1), mangiferin (2) and chlorophyll. Inhibitory effect of young dark reddish brown mango leaf extract (YDL-ext) on AGEs formation was similar to that of OML-ext. The inhibitory activity of YDL-ext was attributable to 1 and 2, in addition, a part of the the activity of YDL-ext due to anthocyanins whose content is highest in young dark reddish brown mango leaves. Considering the amounts of leaves obtained from pruning, old dark green leaves may be a reasonable natural resource for the preparation of ingredients with inhibitory activity of AGEs formation.

The purpose of this study was to search edible ripe Citrus fruits which are applicable for functional food materials as juice, tea and/or jam with sweet taste and rich aroma. A fifty percent ethanolic extract (CMR-ext) obtained from the edible ripe fruit of Citrus madurensis exhibited an inhibitory activity of antigen-induced degranulation in anti-dinitrophenyl (DNP) IgE antibody sensitized rat basophilic leukemia (RBL) -2H3 cells. The inhibitory effect of the CMR-ext on degranulation in RBL-2H3 cells was attributable to 3’,5’-di-C-β-glucopyranosylphloretin (1) which is a constituent of C. madurensis. The effect of 1 on Akt and mitogen-activated protein kinases (MAPK) phosphorylation was examined in RBL-2H3 cells. Western blot analysis revealed that 1 (50 μM) inhibited the degranulation by suppression of Akt and p38 phosphorylation.

This study aims to develop a geographical method to understand
subjective activities of local farmers to be focused on the diversity of
cropping system in rural area of northern Namibia. In this study, households’
data were collected using three different types of methodologies; aerial photos
taken by Unmanned Aerial Vehicle (UAV), semi-structured interview, and a mental
map drawn by farmers. As a result, obvious differences were observed among data
collected by three different methodologies. This result showed a possibility of
application of multiple survey methodologies to enhance researchers’
understanding toward farmers’ creative and subjective activities.

Deep penetration of an axile root is one of the important factors that allow crops to form deep root systems. In this study, the nodes from which the deepest penetrated roots had emerged were examined at the heading stage in upland rice and maize grown in large root boxes and in the field. Both experiments were designed to measure the direction, length, and rooting nodes of each root. In maize, the growth angles of axile roots increased with vertical elongation as rooting nodes acropetally advanced. The roots that emerged from the lower nodes, namely from coleoptilar to the second node, exhibited conspicuously horizontal elongation in the field, reaching 2.3 m in width at the maximum. The roots that emerged from higher than the fifth node were too short to penetrate deeply. Thus, these roots became the deepest root in less or no probability under field conditions. On the other hand, the fourth nodal root, which had an intermediate growth angle and length, had the highest probability. In upland rice, the deepest roots emerged from the nodes lower than the forth node on the main stem in the root boxes. In the field, however, the deepest roots emerged at later stages, that is, the roots from the middle nodes on the main stem and from the low nodes on the primary and secondary tillers were the deepest roots. Five out of nine of the deepest roots were from the prophyll nodes in three field-grown upland rice. The deepest roots from the same plant were estimated to have emerged and grown at approximately the same stage.

A device to measure soil penetration resistance in a root box (24cm×2cm×40cm) was developed, and its validity was examined for the revised root box method. The device was constructed with the metal probe (2.3 mm diameter and 50 cm length piano wire), strain gauge, linear displacement transducer, reversible motor and X-Y recorder. The main characteristic of this device is to push the needle type probe into the soil continuously about 40 cm downward at a constant rate to measure the penetration resistance easily and quickly as a function of soil depth.
Edge effect was examined using probes with different diameters ranging from 0.95 to 2.3 mm. Edge effect was found to be negligible for any measured soil resistance value. Comparing spot resistance and continuous resistance, the skin friction was almost statistically constant (meaning it did not accumulate) under around 10 cm soil layer. The trend of the variation of both resistances as a function of soil depth was similar especially in the pattern of their peaks. Thus, the measured values were considered to be valid and therefore practical to use in determining penetration resistance as a function of soil depth, as a relative value.
Age hardening process of the soil in the root box as a function of soil depth was examined under submerged condition. Penetration resistance tended to get bigger as soil depth increased.

The root boxes (24cm×2cm×40cm) filled with soil at two different soil bulk densities of 1.33 g/cm³ (control) and 1.50 g/cm³ (compact), were prepared for studying mutual relationship between the variation of penetration resistance as a function of soil depth and radial expansion growth of root axis. Upland rice was grown under both soil conditions for two weeks, and the root systems were sampled by pinboard method. Penetration resistance determined by a developed penetrometer showed several peaks of resistance throughout the entire depth of the root boxes caused by the presence of soil boundary layers resulting from the procedure of soil filling up. There were also found variations of root diameter of seminal axis and lst order lateral roots emerged from the seminal axis as a function of soil depth. In the compact plot, patterns of the penetration resistance corresponded well with those of root diameter. However, in the control, the correspondence of both patterns was not as clear as in the compact. These results indicated that patterns of soil mechanical impedance along the entire depth of the root box could be recorded in root axes as the history of radial expansion growth when root tips were exposed to higher mechanical impedance. The result obtained in this experiment suggested the necessity of considering the patterns of soil mechanical impedance in the growth media for the study of root-soil interaction.

https://doi.org/10.1007/978-981-10-7308-3

（全ページ）p.406 （共著者）日本作物学会編 安藤・---・飯嶋・---（102名との共同執筆のため以下省略） （分 担） pp.136-137. （概 要）日本作物学会の用語委員会がとりまとめた基本用語の解説書。形態部門の「根系」を解説した．

（全ページ）p.208 （共著者）坂上潤一編、朝川・--・飯嶋・（39名との共同執筆のため以下省略） （分 担） pp.242-244 （概 要）第6章 5．湿地帯でのイネ栽培と塩害 湿地における洪水被害と作物栽培技術の活用の事例として、ナミビア国北中部地域に形成される季節性湿地帯への稲作導入課程と塩害を紹介した．

（全ページ）p.208 （共著者）森田茂紀編、阿部・飯嶋・（以下28名との共同執筆のため省略） （分 担） pp.156-161（概 要）植物の根系が積極的に環境を改変する事例として、インドネシアの傾斜地コ－ヒ－園での事例を紹介した。

At present, simultaneous occurrence of floods and droughts in the same place has become common globally. Under such weather conditions, crop cultivation techniques that might accommodate both extremes of water abundance are required to stabilize crop production. During the process of development of a mixed cropping system of flood-tolerant rice and drought-tolerant grain crops, we found a new possibility in mixed cropping—enhancement of the flood tolerance of upland crops. The “close mixed-planting” is the technique growing the two plant species in a same portion where their root systems tightly tangled each other. This technique improved the growth and yield of upland crops subjected to flush flood stresses. Oxygen transfer was confirmed between the two species mix-cultured in water, implying its contribution to the phenomenon that improved the flood tolerance of upland crops in fields. This technique also enhanced the drought tolerance of rice by the hydraulic phenomenon. Water absorbed by the roots of upland crops from deep soil is released into the shallow soil during night. Close mixed-planting enabled rice to capture the released water resulting the improvement of drought resistance of rice. Mixed cropping of wet and dryland crops is a new concept that will help farmers overcome both flood- and drought stresses under variable environmental conditions due to climate change.

温暖化の進行により、水田転換畑の一時的な湛水が常態化することが予見できる。本研究では、イネ／ダイズ接触混植群落に亀裂処理を施すことにより、ダイズの一時的な湛水ストレスを緩和しうる新規な栽培技術を提案することを目指す。加えて、超微細気泡水の灌漑がダイズの湛水ストレスを緩和しうるかについても検討する。ダイズは、普通ダイズに加えて付加価値の高い極大粒黒ダイズを研究対象とする。イネは、陸稲と水稲を対象とする。イネは、① 転換畑に設置済みの農業用水を利用し、節水栽培による子実生産を目指すか、② 中耕時～出穂期に薬剤・機械除草する。直播による接触混植と、混植苗の移植とを比較し、混植における機械化も検討する。圃場試験として、近畿大学、神戸大学付属農場、龍谷大学、滋賀県立大学、兵庫県立農林水産技術総合センター（以下、兵庫農技）の、近畿地方の３県、5地点において異なる圃場試験を実施する。近畿大では小規模コンクリート製のモデル水田において、接触混植したイネを手刈りすることによりダイズが受ける競合作用を低減することができるかどうかを検討する。神戸大では、亀裂処理用深耕アタッチメントを試作するとともに、イネとダイズの直播、中耕時亀裂処理－培土、収穫のための機械化などを検討する。龍谷大ではエダマメを用いた亀裂処理試験を実施するとともに、ダイズの生理機能を評価する。滋賀県大では、湛水処理区と対照区を設けて、亀裂処理と接触混植による湛水ストレス緩和試験を実施するとともに超微細気泡水の投与試験を実施する。超微細気泡水の諸効果を検証するため、水田での灌漑試験も実施する。兵庫農技ではLiCとLの土性の異なる圃場で亀裂処理と接触混植実験をそれぞれ実施し、湛水処理区も設ける。さらに播種時期や機械化の検討も行う。以上から、気候変動に伴う水環境の著しい変動に対処しうるダイズとイネ栽培を検討する。

本研究では、申請代表らがこれまでに公表した「萌芽的な技術提案」である、「根粒着生制御」と「接触混植」の複合が、ダイズの湿害ストレス緩和に有効であるかどうかを明らかにすることを目的とする。前年度までの研究進展により、奈良県、滋賀県、兵庫県の近畿地区3県にまたがるフィ-ルド試験を実施し、イネとダイズの接触混植と亀裂処理という萌芽的な栽培技術の融合を目指した基礎研究を展開し、研究目的を達成する。まず、奈良県では近畿大学に隣接する農家圃場と、近畿大学実験圃場内の小型のコンクリ-ト制実験圃場において、接触混植試験を実施した。農家圃場では、イネが先行するリレ-播種によってイネ／ダイズの接触混植試験を実施した。現場での作業体系を考えると接触混植苗をセルトレイで栽培する手法は社会実装には程遠いため、接触混植の直播技術としての成立を目指す。小型の実験圃場では、競合と補完関係を検討するため、イネとダイズの栽培距離を数段階替えて実験を実施した。滋賀県立大学においては、7アール規模の実験水田で前年度と同様な接触混植―亀裂処理実験を実施した。亀裂処理は別研究で開発した亀裂処理機を使用して実施した。亀裂処理の実施後に、長期間の干ばつ被害が発生し易いため、転換畑に備えられた灌漑水を用いてフラッシュ灌漑を実施した。兵庫県立農林水産技術総合センターでは、黒ダイズの丹波黒を供試して亀裂処理試験を実施した。黒ダイズにおける生育初期の土壌湛水ストレス耐性は不明であるため、本年度は初めてのフィールド試験となった。これまでの成果をまとめた学会発表を行うとともに投稿した原著論文が採択されオンライン公表された。

新型コロナウイルス（Covid-19）禍により渡航が制限されたため、オンラインによりナミビア、ボツワナ、日本の3ヵ国での試験や研究成果を詳細に打ち合わせ、以下の研究と、研究成果の共同執筆・国際会議での報告などを実施した。① 接触混植試験：ナミビア北部では、ソルガムとトウジンビエの接触混植が農家の自助努力などにより徐々に広がりを見せている。そこで、ナミビア大学オゴンゴ校内の附属農場施設内で、トウジンビエとソルガムの接触混植試験を実施した。農家圃場においても栽培を希望する農家に種子を提供し、農家圃場における栽培試験を実施した。② 亀裂施肥試験：本試験のためにナミビア国で作成した新型の亀裂施肥機をベースにして日本ではコストを考慮し、亀裂処理に特化した新型アタッチメントを作成した。その走行試験を神戸大学等で実施し、今後の普及を検討中である。 ③ ボツワナ大学では、ナミビアから導入したイネ品種群の栽培試験を2019/2020作付け期に開始し、2021/2022まで3か年に渡る栽培トライアルを継続中である。2021/2022からは小規模フィ―ルドでの作付けを開始し、種子の更新と栽培試験を拡大した。 ④ ナミビアとボツワナの研究サイト周辺の農家圃場では季節湿地が形成されるためメタン発生の増大が懸念される。そこで地球温暖化の進行を阻止するためウルトラファインバブル水灌漑によるメタン削減の可能性を議論し、現地への導入を目指したフィールド試験を日本で開始した。 ⑤ 研究成果5報の原著論文がアクセプトされた。 ⑥ 国際学会（アジア作物学会議）で４報の口頭発表と、国内学会（日本作物学会）で２報の口頭発表を実施した。

ウルトラファインバブル水の作物成長促進効果を明らかにすることを目指す。

アフリカの半乾燥地には、洪水や干ばつによって食糧不足になるリスクが高い地域が依然として多く残されている。砂漠国ナミビアでも季節湿地の不安定な水環境が問題となっており、食糧安全保障の観点から現地農業を再構築する必要がある。そこで本研究では、頻発する洪水や干ばつ年でも常に一定以上の穀物生産が維持されるような新しい栽培システムを考案する。新規導入作物のイネと現地主食のトウジンビエを混作し、水収支と経済性を評価する。社会・自然環境インパクトから、現地の自給自足農民の生活向上に資する農法の導入と半乾燥地の水環境保全とを永続的に両立させ、南部アフリカに広がる季節湿地を最大限に活用したモデル農法を提案する。（参照（参照 https://www.jst.go.jp/global/kadai/h2306_namibia.html および https://www.jica.go.jp/oda/project/1100521/index.html））

The purpose of the present study is to clarify the effectiveness of crack fertilization that is the new technique to enhance soybean yield by the application of nodule bacteria to soybean just before flowering. In addition, we conducted at two different region of Hokkaido and main island of Japan (Shiga and Nara prefecture) to evaluate that the technique is useful in all region of Japan. In cold region of Hokkaido, soybean yield did not increase by the technique compared with the control. In the main island, however, soybean yield in an upland field and an upland field converted from a paddy increased by the application of the technique. The application of charcoal into the crack between rows just before flowering was effective to increase soybean yield in an upland, and the application with nodule bacteria below rows before sowing significantly increased soybean yield in an upland converted from a paddy.

Seasonal wetland formed by the flood water from the upper catchments of Angola is the characteristics of densely populated north central Namibia, the desert southwest African country. This study aimed to introduce rice cropping in the seasonal wetland region where the water resources have not been used for crop production before. Then, harmonization between the water resource development and conservation of water environment of semiarid region was tested. The results indicated that rice cropping can be possibly integrated with the existence pearl millet based traditional cropping, and that water environment would not be modified by the subsistent rice cultivation with low yield level.

Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. In this study, we proposed a new cultivation technique termed"crack fertilization". It is the technique to utilize the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduce root nodule bacteria, fertilizers, and soil amendments to the deep subsoil layer. Nitrogen fixation activities at three to six weeks after the crack fertilization were significantly enhanced, and nodule number was also significantly increased at the lower portion of the root system. These results indicated that the soybean nodulation control, i.e. timing and position of nodulation, as well as the enhancement of nitrogen fixation activities were possible by the newly developed crack fertilization technique.

今年度の研究では,飛行時間型2次イオン質量分析計(Tof-SIMS)を活用し,安定同位体でラベルした重水の吸収過程を視覚化し,養水分の吸収と移動経路を明らかにするための方法論を確立することを目的とした.まず,これまでに実施したTof-SIMSを用いた作物の水吸収に関わる実験系についての問題点を確認した.すなわち「よく晴れた日の蒸散が盛んな条件下では,根から吸収した水は木部ではなく師部を介して茎部の皮層細胞などの柔組織に分配される」という本研究で得られた新たな知見に対して,投稿した国際雑誌の審査委員から,蒸散がはたして盛んに行われているかどうかの判断基準を強く問われた.そこで,日射と,蒸散量,蒸発量との関係を調査したところ,植物体のサイズにより,蒸散速度と培地からの蒸発量との関係が異なることが判明した.今後,実験条件をそろえるための工夫が必要であることがわかり,予備的な検討を始めたところである.上記の論文投稿は,最終的に不採択となったため,指摘された諸点を訂正した後,別の国際誌に現在投稿中である.他の成果として,根粒への水の流入経路は,木部や師部からではなくアポプラスト経由の水の流れが主体をなす,という結論について関連データを補足実験により確認したうえで,学会発表を行った.他研究者と議論したうえで,本成果についても執筆を開始した.さらに,培地からの水吸収と水放出現象についての研究成果についても,その整理を開始したところである.本研究の最終年度であるため,本研究で得られたすべての成果から,今後の研究の方向性についてさまざまな視点から議論した.

Namibia, situated in south west Africa, is an arid county with two famous desert of Namib and Kalahari. The aim of this research is to introduce extensive rice cultivation which will harmonize with the water environment in the flooding ecosystem, oshanas, in northern Namibia. This rice cultivation should be beneficial for the local subsistence fanners, and harmonize with the existing pearl millet farming, stable food for Namibian people. We, first discussed the direction of four years research, and focused on pearl millet water use research and rice cultivar selection study, and stress environment study in Namibian flooding fields. At flowering time, the SD value of intercropped cowpea was similar to that of wetland water, while that in pearl millet was much lower than those of both the wetland water and groundwater. This indicated that intercropped pearl millet did not have full access to the wetland water when there was competition with cowpea for water derived from various water sources. Paddy yield was 19% higher in the wetland, oshana than in the floodplain. In the second season of evaluation, there was a slight increase in overall yield in the oshana, but the yield in the floodplain reduced by 20%, possibly, because of stress by excessive water as result of the flood that occurred during plant growth. The results indicated that both locations can be used for rice production ; but oshanas are more suitable than floodplains because of the prevailing sunny and dry environment. In the wet season experiment under a saline-affected oshana, a salt tolerant genotype Pokkali produced the highest absolute and relative paddy yield. Generally, the results of these experiments indicated that Pokkali may be cultivated under saline-affected oshanas during the wet season, although its growth duration is relatively long. We have also introduced Japanese traditional rice post harvesting machines, and agreed to continue the rice research project for future Namibia.

作物の根は分泌層で覆われており、この層を介して根圏土壌中の物質が吸収される。本研究は、根-土壌界面に存在する分泌層内での物質の動きを明らかにする方法論を検討し、安定同位体でラベルした水や窒素が根圏から分泌層を介して根面へ取り込まれる過程を明らかにすることを目的として、以下の研究を実施した。今年度は、昨年検討したシリコン板法とともに、寒天培地法も含めて検討を継続するとともに、飛行時間型2次イオン質量分析計(Tof-SIMS)による安定同位体の取り込みに関する実験も実施した。まずシリコン板法では直接、粘液を観察することが困難であった。そこで様々な濃度の寒天培地を試験したが、同様に寒天への封入では、真空中での脱水により寒天がくずれてしまいうまく観察ができなかった。そこで、やはりクライオシステムで観察する必要があることを認識し、まずは植物サンプルでの飛行時間型2次イオン質量分析計での観察手法の確立を先決課題として実施した。イネでは真空中での組織の保持がうまくできなかったため、茎や'根の直径の大きなダイズを用いて、真空中での観察を実施した。クライオミクロトームで切断した根と茎切片を観察したところ、すべてのイオンの総和であるトータルイオン観察によって木部導管や師部組織を観察することが可能となった。次に安定同位体として簡易な暴露が可能な重水を用いて、一定時間吸収させた後の重水の分布を観察したところ、木部導管部位では重水の組織への吸収を認めず、この手法での同位体の吸収を観察することが可能であることを確かめた。次にクライオシステムで同様の観察を行ったところ、より鮮明な観察が可能となった。今後はこれまで試したシリコン板法や寒天培地法をクライオシステムで観察する実験系を確立する必要がある。

In rhizosphere soil, mucilage and root border cells form a functional entity, the mucilage-border cells complex (MB complex). Firstly, the longevity of the released border cells into real soil was analyzed. Many of the border cells present in the rhizosphere soil for relatively longer duration at least more than 10 days. The longevity would depend on the origin of border cells; i.e., root cap layers when the cells are sloughed off. The cells from the inner layer would stay longer in soil due to its younger stage of the cell maturity. The MB complex is utilized by rhizosphere bacteria, which in turn are under strong grazing pressure of the soil food web, in particular protozoa. Next, we investigated the role of MB complex on the protozoan positive effects for plant growth. Weight of fully hydrated MB complex of 27 rice cultivars was firstly quantified. Secondly, 16 cultivars with different levels of MB complex production were selected for root border cells (RBC) enumeration. The weight of MB complex varied among the cultivars and some of the higher MB complex producing cultivars also produced higher number of RBC. Generally speaking, presence of protozoa enhanced lateral root growth and carbon ＆ nitrogen uptake. Further, upland cultivars responded well to amoebal effects as compared with the lowland cultivars. Positive correlation between MB complex production and increased lateral root growth by amoeba revealed that MB complex have a functional role of facilitating a symbiotic relationship with amoeba, which is the first evidence of the new role of MB complex.

This research was conducted in collaboration with Philippine Root Crop Research and Training Center, Leyte State University to evaluate genotypic variation in cassava and sweetpotato in drought tolerance and to identify the traits that are closely related to the tolerance. In addition to the collection of the Center, we further collected a number of genotypes from several drought-prone areas m the Philippines. Sevearl surveys among the rootcrop growing Canners indicated that the question on decision-making strategies by farmers on sustained adoption of a variety is different from the question of preference to grow a certain variety. The former involves more than just traits preference ; and includes other considerations, such as resources, availability of planting materials, use and market, perceived or actual physical or environmental constraints, etc., which is a subject for futher study. Under water stress, dry matter is a product of water use (WU) and water use efficiency (WUE). Based. on this concept, the growth responses of 28 cassava genotypes and 18 sweelpotato genotypes to water stress were examined in a series of pot experiments In cassava, drought significantly reduced dry matter production. Results of a correlation analysis indicate that the genotypic variation in dry matter response to drought was better explained by that in WUE than in WU. In sweetpotato, dry matter production was also significantly reduced in droughted plants. The drought treatment significantly reduced WU, while it scarcely affected WUE. These facts clearly show that the reduction of WU but not WUE caused dry matter reduction, which is opposite to the case of cassava. The results of a series of field experiments generally support those obtained by the pot experiments, which are necessary to validated by the evaluation of Genotype x Environment Interaction in further study.

植物根の表層部は粘液等の分泌物に覆われていることが知られている。この粘液層は水や無機塩の植物体への取り入れを介在する働きをもつだけでなく、土壌のさまざまな物理・化学的ストレスから根を保護することが示唆されている。粘液層は以上のような重要な働きを担うにもかかわらず、この層がどのような土壌条件においてどの程度根の表面を覆っているのかは全く明らかにされてはいない。本研究では、植物根の根圏土壌中での粘液分泌動態を視覚的に明らかにするとともに、根圏土壌内の安定同位体炭素および水素の濃度勾配から、分泌物の土壌中への拡散範囲を定量的に把握することを目的とした。 3ヵ年の研究で、植物根による根圏土壌中への粘液分泌動態をCCDカメラにより視覚的に捉え、分泌が日周変動することを明らかにした。さらに、トウモロコシを^<13>CO_2とD_2Oで暴露し、根圏土壌中に放出される安定同位体の存在量を分析し、土壌の乾燥条件下では炭素の放出量は増加するが、水の放出量は減少することを明らかにした。しかしながら根圏土壌内の安定同位体の濃度勾配については、根に付着した土壌鞘の外側への同位体の放出が確認できなかった。現行の方法論では、根の周辺部における根圏土壌と非根圏土壌を選別すること、言い換えれば根毛の発達により形成される土壌鞘と非土壌鞘の選別にはある程度時間がかかる。そのため、解剖顕微鏡下での土壌の選別作業中に土壌水が蒸発し、その結果同位体分別が起こっていることが推定される。そこで、飛行時間型2時イオン質量分析計により土壌表面における同位体水素の検出を試みることを新たな目標として設定した。そのための予備的な試みとして、トウモロコシをD_2Oで暴露し、根軸内での安定同位体の分布を調査しているところである。現状では、同位体が根全体に均一に分布する像しか得られていない。この理由は現状では不明であり、今後、異なる条件下で測定を繰り返すことにより、技術的な問題点を解明していきたい。

ナミビア大学農学部の教員陣の能力強化のためナミビア大学講師を受け入れ、論文博士取得に向けた共同研究を実施した。

Plant roots grown in compacted soils have to overcome the mechanical impedance of the soil to root elongation. The friction between soil and the growing root may be decreased by the layer of root border cells. We tried to evaluate the role of the root border cells to decreasing the soil mechanical impedance. In the series of experiment, we found the following: 1. For the first time, we quantified the rate of sloughing of root border cells in an abrasive growth medium. The number of maize root border cells increased as a result of compaction, from 1930 to 3220 d^<-1> per primary root. The whole of the cap surface area was covered with detached cells in compacted sand, compared with about 7% of the surface area in loose sand. 2. We developed an image analysis procedure to quantify cell locations in the median longitudinal section of root caps. Only 7% of cells in the outermost layer of the root were associated with the columella region of the cap. 3. Mechanical impedance slightly enhanced meristematic activities in the lateral region of the root cap. Cell production rates were 2,010 cells d^<-1> in compact and 1,570 cells d^<-1> in loose. 4. The presence of a root cap alleviates much of the mechanical impedance to root penetration, and enables roots to grow faster in compacted soils. 5. The contribution of root border cells to the reduction in soil resistance by the presence of root cap was 58%. 6. A technique was developed to separate root border cells from soil particles. The number of root border cells in wet soil was significantly greater than that in the dry soil. In conclusion, the lubricating layer of root border cells decreases frictional resistance to soil penetration.

No-tillage systems have several advantages reducing soil erosion and production cost comparing with conventional tilled ones, and also they would be suitable for current demand for environmental sound technologies such as saving energy inputs and carbon dioxide exhausted. However, it is pointed out that reduced tillage may cause increased soil compaction which is detrimental to crop growth, especially for inhibited nutrient acquisitions due to restricted root system development. Most species of crop plants enable to form symbiotic associations with arbuscular mycorrhizal fungi, nutrient uptake particularly immobile elements of phosphorus are enhanced with the associations. This study showed that restricted root functions could be restored by utilizing the mycorrhizal symbiosis. The mycorrhizal fungi colonize with host plant roots, establishing the hyphal network structure in soils. This structure functions not only in nutrients transport to the plants from soils but also in exploring other hosts. The hyphal structure is disturbed in conventional tilled systems, but remained in no-tillage ones hence mycorrhizal benefits to help root functions are greatly displayed. As such, we found that the mycorrhizal association under notilled soil conditions counteracts compacted soil stress for pigeon pea. It was also observed that decreases in the fungal infective potential due to the soil disturbance are different among fungal species and also with the presence of other species. Moreover, we demonstrated that the plant can not acquire phosphate sufficiently only with root exudates to solubilize sparingly soluble sources, a mycorrhizal network function as the interaction is significant. Probably, the root and rhizosphere microbes would compete for phosphate released from the sources, the mycorrhizal fungi could increase the competitive ability of the plants due to their larger surface area.

植物の根冠からは粘液が分泌され、根冠周辺部において粘液層が形成される。粘液層は植物根の生長や機能に対して様々な役割を担っていることが指摘されている。しかし、土壌中での粘液分泌の実態が不明であるため、とくに土壌と根の相互作用に関連した役割については、推測の域を出ないものが多い。そこで、本研究では土壌中を伸長している根から分泌される根冠粘液を直接観察する方法を検討し、それが土壌中における粘液の分泌動態を把握する方法論となりうるかどうかを判定することを目的とした。実体顕微鏡を取り付けたモノクロチルドCCDカメラで土壌中を伸長しているトウモロコシ種子根の根端を、透明なアクリル板越しに撮影した。この方法によって、種子根の根端部とアクリル板との間に粘液状の物質が観察された。この物質が根冠粘液であるかどうかを、パネル上の粘液の残存性とその染色性、さらに、移植固体の根端部と針金の先端部の観察の比較等によって総合的に評価した。その結果、この物質が根冠粘液であると結論した。本法によって、粘液の分泌動態を把握しうるかどうかを確かめるため、画像として取り込んだ粘液の分布範囲を面積として定量化することによって、分泌の日周変動を調査した。その結果、粘液面積は、夜間の22時から4時にかけて大きく、昼間の10時から12時に最低値を示した。また、最大値を記録した24時の面積は、最低値であった10時よりも約40%大きな値を示した。以上の結果から、土壌中で分泌された根冠粘液の増減には日周変動があることを明らかにし、本法によって土壌中における根冠粘液の分泌動態が把握しうると結論した。さらに、根冠粘液の分泌と根の伸長生長との関係についての基礎的知見を得るために、分泌量と根の伸長速度との関係についても検討した結果、粘液の分泌量は種子根の伸長生長と関連性があることを定量的に認めた。

A crop root system consists of roots differing in developmental and anatomical features. This study aimed to examine functional difference among those roots. First, we showed that in rice root system, in addition to the conventional developmental analysis the fractal analysis that quantifies the complexity of root system structure and the topological analysis that quantifies the branching pattern are quite effective for characterizing root system structure. Then, among the roots, rspecially lateral roots were shown to sharply respond to the changes in moisture conditions in soil and culture conditions in vitro. Carbon and nitrogen dynamics, and changes in succinic dehydrogenase and peroxidase activity with aging indicated that seminal root axis and its lateral roots differ in aging pattern. The differences were also found in the dynamics of endogenous abscisic acid and zeatin riboside. An examination of root system structure for several food legume species revealed that genetic variation exists mainly due to lateral root development, and their taproot elongation growth exhibits plasticity when grown under different conditions. In a peanut root system, arbuscular mycorrhiza was formed mostly on lateral roots, but scarcely on taproot axis. On those lateral roots, the mycorrhizal colony occurrence increased acropetally especially in relatively aged roots that initiated on the proximal portion of the taproot axis. Further, the formation of mycorrhiza altered root system morphology through lateral root development, where the responses differed between 1st and 2nd order lateral roots. As such, through characterizing root members in a root system with a special attention to their ages, this study showed that the functional differences exist among the roots such as developmental response to various environmental factors, metabolic and physiological activity, and affinity with mycorrhizal fungus, and they contribute to the overall function of an entire root system by playing their specific roles.

土壌の物理性が不良な耕地条件下では、作物根の伸長生長は抑制されることが知られている。この伸長生長の低下率は、ある一定期間における根の伸長速度として表示されるが、これまでの研究では1日単位の伸長量よりもさらに微細な伸長速度にふれた報告はほとんど見あたらない。そこで、本研究では土壌のストレスに対する根の伸長抑制を評価する上で、これまでの研究で欠けていた、時・分単位の伸長生長の変動を明らかにすることを目的とした。具体的には、根の伸長生長における日周性リズムが存在するか否か、さらにリズムが存在する場合にはそれが内因性のリズムであるか否か、を明らかにすることを本研究の到達点として設定した。この目的を達成するため、根圏の水・養分・温度・光などの環境因子が一定の条件下で根の伸長生長を観測しうるシステムを作成した。低照度域においても感度良好なCCDビデオカメラで撮影した根端部の位置をタイムラプスビデオに記録し、コンピュータ上で画像処理した。観察対象とする根は、イネ、白花ル-ピン、モロコシの種子根とし、播種後約3週間程度に渡って種子根の伸長リズムを調査・解析した。数種の作物根の時・分単位の伸長速度には明らかな変動が認められた。数日間の調査期間中における1時間当たりの伸長速度の最大値は、最小値の1.4から6.7倍であった。昼夜温度が変化する場合には伸長速度は昼夜間で明らかに異なっており、伸長速度は温度に依存する傾向が認められたが、恒温条件下では昼夜間の伸長速度には明確な差異は認められなかった。このことは、伸長速度の変動は日周の温度変動に依存する変動パターンを示しうることを暗示した。今後、明暗が交代する通常の条件と、連続明条件の二つの条件で観察を行ない、その結果の違いによって、伸長パターンが外因性か内因性かを判定する必要を認めた。

作物根の根冠ムシゲルは、土壌中で伸長するより根端と土壌粒子との間の摩擦抵抗を緩和する潤滑油のような働きをしていることが従来より推測されてきたが、土壌の特定部位における粘性の高いムシゲルの動態を捉えることは困難であるため、その実態の直接的な証明は現在までなされていない。本研究では実際に土壌中で生育している作物根の根端部位を解剖顕微鏡レベルでタイムラピスビデオシステムを利用して数日間連続的に観察することを主体として、この仮説の真偽を直接的に証明することを目的とした。透明なアクリル板製の根箱を作成し鉛直下方に対し15度傾斜した状態で固定し、上下方向に根箱が移動できるようにした。ズ-ム式実体顕微鏡に接続したCCDビデオカメラを根箱に垂直になるように固定し、アクリル板上に展開したトウモロコシ種子根根端部とその周辺部の土壌を数十倍の倍率でビデオカメラに撮影した。入力信号は、タイムラプスビデオレコーダーに記録させた。播種方向、播種後の種子根の齢、土壌の充填状態、含水比などの検討を行ない、最も観察に適した条件下において、約2日間のビデオ観察を繰り返した。その結果、種子根根軸とアクリル板の間にムシゲル様物質の存在を確認した。このムシゲル様物質の量は増減しているように観察できたが、今後、根軸とアクリル板との接触状態が一定になるようにして検討を行なう必要がある。現段階では、土壌粒子と根冠との間にあるムシゲルは完全には撮影が行なえていない。ある時間帯において部分的に根冠ムシゲルが観察される場合もあるが、観察結果はまだ安定はしていない。ムシゲルが土壌粒子間に拡散してしまい観察が容易ではないと考えられるので、今後とくに観察視野のコントラストと解像度を高めることと、土壌の物理的条件のさらなる改良を平行して観察を進める予定である。

This study aimed to examine the root system development and plasticity in sweetpotato and cassava in relation to their drought tolerance. Among the huge genetic stock developed or collected so far, several genotypes for each species were selected for this study. Specifically, we have conducted a series of pot and root box experiments to evaluate the root system development in both species under high root-zone temperature stress and drouht stress imposed at different growth stages, for various periods and degrees. Major findings were : 1) high root-zone temperature promoted the shoot growth, while it inhibited the whole root system development in general, but development in the lateral roots of high branching orders (2nd and 3rd) was promoted ; 2) both species were very sensitive to drought stress which generally reduced shoot and root growth. However, rewatering after drought promoted especially the development of lateral roots of high branching orders ; 3) genotypic differences were also noted in the responses to drought. There was a genotype in each species that maintained or increased root growth under drought (cv. VSP-2 for sweetpotato and cv. PSR-74 for cassava). Besides, four farmers' fields in Leyte, Philippines, planted with different sweetpotato varieties were visited, in which we surveyed the root system development and soil physical and chemical conditions so that the results of the pot experiments be verified. In addition, field experiments are now being attempted to evaluate the drought tolerance including water relations and the root system development in the field. For the purpose, a rain shelter is being constructed at the moment. As such, in this study, we showed the development and responses of the root system to the soil stresses which are the least-studied part of the root crops. Efforts still continue to complete the experiments and survey, and organize the data for publication.