[in Japanese]

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The effects of furrow saline water irrigation (EC=8dSm^-1) on the emergence and growth of maize were investigated under two different bed shapes (flattop and sloping beds) and three different soil types (SL, CL, and LiC) in a greenhouse. The results : (1) Emergence rates in the flattop beds were lower than those in the sloping beds, especially in the SL (70%). (2) Although plant heights in the flattop beds were shorter than in the sloping beds, heights in the LiC greatly increased after 21 days. (3) Dry weight showed the same tendency as that of the plant height. (4) Soil water contents at the seeding place showed the lowest (5%-15%) in the SL of both bed shapes. (5) EC_e in the flattop beds after seeding was greater (10-15 dSm^-1) than in the others, especially in the SL. (6) Salt distribution in the beds showed the highest salinity at the peak or around the peak in the sloping beds and in the surface at the shoulder in the flattop bed. (7) The early seedling growth of maize closely related with the salt distribution in the beds. These results provided useful information to elucidate the relation between salt accumulation and early seedling growth.

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Effect of the form and composition of nitrogen in a culture solution on the growth of rice seedlings raised on a cotton mat spread on a hydroponic apparatus for vegetables was investigated. The nitrogen composition, NH₄-N:NO₃-N, in the Kimura B solution was modified as follows:28%:72% (plot 1), 44%:56% (plot 2), 72%:28% (plot 3), 100%:0% (plot 4). Plant length, root length and root dry weight were greatest in plot 1 followed by plot 2, 3 and 4. In plots 1 and 2, the plant length was same level as that in seedlings raised in a box. However, the seedlings in plots 1 and 2 had longer roots than those raised in a box, and were suspected to be injured by transplanting. Thus, nutrient application was modified to change the plant form as follows:the culture solution was not applied during the first seedling-raising period, NO₃-N-rich culture solution (NH₄-N:NO₃-N=28%:72%) was applied during the second period, and culture solution containing only NH₄-N as the nitrogen source was applied during the last period. The seedlings raised by this method had nearly the same plant length and root length as those raised in boxes. Moreover, there was no distinctive difference in growth characteristics after transplanting between the seedlings raised by this method including different nitrogen compositions and raised in box.

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Source and sink organs are closely related with each other in the process of soybean yield determination. We examined the effects of source and/or sink restriction on the flowering habit, pod set and dry-matter production by removing the leaves (L), flowers (F) and/or both (L&F) from each main stem or branches at the full-flowering stage. The number of nodes increased with the removal of L or F, especially on the raceme with compound leaves. Removal of either L or F decreased the number of pods, and this extent was larger when the L or F were removed from the branches than from the main stems and when F was removed than when both L & F were removed. Removal of L or F accelerated the flowering on the non-treated main stem or branches. Removal of both L & F increased the number of flowers than removal of L or F alone. Thus, either the source or sink restriction was compensated by the increase in flower bud number. Either source or sink removal increased the pod set on the non-treated main stem or branches. Crop growth rate was decreased by removal of L or F, and this extent was larger when L or L & F were removed from the branches, but the net assimilation rate increased by the removal of L owing to the decrease in leaf area index. Pod growth rate on the branches with L removed was higher than that on the main stem with L removed, which revealed that the growth of branches was largely dependent on the assimilate from their main stem. Higher net assimilation rate in the L and L & F removed plots indicates that the surplus supply of assimilate from leaves to adjacent axil asselerates the development of flower buds considerably and promotes the pod set.

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This study was undertaken to estimate the optimum time to harvest the grains of winter wheat with high amylogram viscosity. In 1996 and 1997, three characteristics;kernel weight, grain moisture content and falling number of two cultivars, Chihoku-komugi and Hokushin, were determined during the ripening stage. The samples were taken from five different field locations in Hokkaido. In both years, the time of maximum grain weight (T_max), which indicates physiological maturity, varied with the weather conditions during the ripening stage. Grain moisture content decreased gradually to 40% at a similar rate in all cases, but the rate of decrease below 40%, decrement in moisture content varied with the field location and year (weather conditions). In 1996, grain viscosity started to increase late and slowly, the maximum falling number being less than 300 sec in many locations. In 1997, the viscosity started to increase earlier 32 to 34 days after heading. Hokushin had a higher falling number and kept the viscosity value of over 300 sec for a longer period than Chihoku-komugi. It was concluded that in order to avoid low amylogram viscosity, we have to harvest the grains when the falling number is over 300 sec. This is because at this stage, Tmax had already been reached.

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Research was conducted to define the characteristics of common buckwheat in the Kyushu area by using local and breeding varieties containing various origins and ecotypes. In 1995, summer cultivation was researched, and the results showed the need to develop a new variety that has a short growing period and resistance to pre harvest germination for summer cultivation in the Kyushu area. As a result of autumn cultivation, by the use of 3 years data from 1995 to 1997, the differences in years and variety were indicated to be statistically significant for all agronomic characters. It seemed that the characters of productivity, however, such as total weight and grain yield, were influenced easily by environmental effects. On the other hand, there were high year-to-year correlations of morphological characters, such as plant heights, number of nodes, and 1, 000-grain weights, showing that these characters were indicators of varietal characteristics. It was indicated that big growing characters are advantageous for obtaining high grain yield. These genetic resources showed varietal differences, depending on their origins. Especially, the native varieties of the Kyushu area had a long growing period and high grain yield, showing that they were suitable ecotypes for growing in that area.

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Recently, the heading of rice grown in early season in the paddy fields near streets, roads, and stores with artificial light in Miyazaki was occasionally delayed because of illuminations at night, which became a serious problem in rice production. The objective of this study was to determine how illuminations at night affected heading and the yield and its components in rice (Koshihikari, Kirarimitazaki) cultivated in the early season. From transplanting to heading, the critical light intensities affecting the heading time of rice were 4 and 30 Lx in Koshihikari and Kirarimiyazaki, respectively, indicating that the delaying effect on the heading time of Koshihikari rice was more obvious than that of Kirarimiyazaki. When Koshihikari rice was treated from the 3rd to 18th day before panicle formation, the effect of treatment in this study was most significant and followed during the 2nd day before panicle formation to the 12th day after panicle formation. in From tillering to heading, with Koshihikari rice the critical light intensities were 6 Lx, the heading time was delayed by about 25 days, and plant culm height became longer in comparison with control when treated with the intensity of 117 Lx. When the time of illuminations was near the heading time of rice, the percentages of the ripened grains and yield tended to decrease. Furthermore, when the rice was treated from the 2nd day before panicle formation to heading, the yield of Koshihikari rice was lowest. As a result, Kirarimiyazaki coul reduce the damages of yield in the early season in paddy fields near streets or roads with illumination at night because there existed a difference of the effect of illumination on growth of rice between Koshihikari and Kirarimiyazaki.

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This study was conducted to clarify seedling establishment of direct seeded rice without coating of oxygen-generator, water temperture and dissolved oxygen conditions on the soil surface in flooded paddy fields [FPF] at northern Kyushu for development of low cost and labor saving production. The mean water temperature a day during 14 days after seeding ranged from 21.8 to 29.0°C. On the other hand, the mean diurnal dissolved oxygen content in flooded water ranged from 4.7 to 11.6 mgL^-1 which were high enough for germination and rooting of rice seeds. Eemergence percentage in FPF varied from 0% to 89% among 72 varieties. There were 11 varieties with more than 80% of emergence percentage. Eight varieties of them had a ancestor 'Asahi'. The floating seedling rate + turned down seedling rate in FPF varied from 4% to 64% among 65 varieties of which had emergence percentage was 10% over. There was no significant correlation between emergence percentage and floating seedling rate + turned down seedling rate among the 11 rice varieties with high emergence percentage rate. Therefore, tere were rice cultivars that were superior in emergence of 80% over and floating seedling rate + turned down seedling rate of 10% less (i.e., Shinriki, Haenuki and Domannaka). High emergence percentage varieties had heavy grains, high bulk density of 1.1 over. Low floating seedling rate + turned down seedling rate varieties had high bulk density of 1.1 over and grown seminal root slowly. These results were helpful to select and breed varieties with good emergence and establishment in direct seeded rice without coating of oxygen-generator on the soil surface in flooded paddy field.

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Deep-rooted and shallow-rooted doubled-haploid lines of wheat were selected based on the root growth angle of seedlings. First, 129 normal growth doubled haploid lines were primary selected from the 535 genetically fixed doubled haploid lines. Secondly, the root growth angle of 7-day-old seedlings was measured by the basket method. Nine lines showing a large angle of root growth from the horizontal and 9 lines showing a small angle were selected and named the D group and S group, respectively. These wheat lines were grown in fields and the root length density in 0-30 cm depth and 0-15 cm distance from the plant base was measured at the late growth stage by an improved monolith method. The root depth index of D group was significantly larger than that in the S group. Moreover specific root length was also larger in the D group. The two groups were not different in tiller number, leaf color, top dry weight and grain yield. The differences found were only in plant height and 1000-grain weight. Therefore, these two groups of wheat lines can be used in further experiments on the growth of wheat with different root depths.

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A new method of root-system analysis was designed based on root diameter. Using this method the formation of the root system in the rice cultivar, Hinohikari, was examined and the root system of 40 cultivars at the full heading stage compared. The morphology of the root system was visualized and analyzed based on the pipe model theory. Next, a distribution chart of the root volume was drawn for each the root-diameter classes based on the ideal pipe theory, and the "mean root-diameter index" which is the root diameter at the distribution peak of the root volume was calculated. In the distribution chart of root volume, the groups of thick and fine roots were distinguishable with a boundary at about 0.4 mm. Then, the "fine root ratio", which is the ratio of the volume of fine roots to that of all roots, the "thick root index", which is the root diameter at the peak of root-volume distribution in the thick root group, and the "fine root index" which is the root diameter at the root-volume distribution peak of the fine root group, were calculated. The results clearly showed a pattern of increase with the increase in root volume of rice and clarified the atructure of the root system based on root thickness and root volume. The root system was classified into two groups, the thick root group mainly consisting of crown roots and the fine root group mainly consisting of lateral roots. Each group had a peculiar distribution peak of root volume, and the two groups were distinguished from each other more clearly after the panicle formation stage. The "mean root-diameter index", "thick root index", "fine root index" and "fine root ratio" were suggested to be good indicators of growth of the root system and of varietal difference in morphology of the root system.

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Tall and dwarf isogenic lines of sorghum (Plainsman tall type and Plainsman short type), soybean (Hyuga and Hyuga dwarf line), and rice (Ginbozu and Tangin) were grown by using 15 L containers to compare the relationships between consumptive use (CU) and dry matter increase (ΔW) and the yield between them. The linear relationships were found between CU and ΔW. CU at ΔW=0 was nearly equal to evaporation (E_s), except for two soybean strains. Transpiration efficiency (ΔW/[CU-E_s]) did not differ significantly between tall and dwarfisogenic lines. Hyuga consumed the largest amount of water because it had large ΔW and low transpiration efficiency (TE) and larger CU at ΔW=0. Two sorghum strains did not differ in CU from Ginbozu and Tangin because of their larger ΔW, respectively, though they had the highest TE. Dwarf lines were always smaller in CU than tall lines were in all the examined crops. Furthermore, they were inferior to tall lines in the absolute yield, but they tended to be less in CU to achieve the same yield. These characteristics of dwarf lined will be useful in both viewpoints of the avoidance of drougt injury and the efficient use of water.

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The diurnal change and change with the daily change of Leaf-rolling rate (LRR), and the effect of LRR on leaf water potential (LWP) under a high-temperature/low-humidity condition were examined. At noon, LRR of cv.C-115 and cv.Koshihikari was 45 and 5%, respectively, but LWP was nearly the same in both cultivars. This suggests that the difference in LRR between the two cultivars is not attributed to the difference in LWP. The daily mean LRR in the generally cultivated cultivar was near zero at the young seedling stage, and increased with plant growth. The strains that have a well-known rolled leaf gene, however, exhibited a high LRR at all developmental stages, and showed a diurnal change with the maximum value at noon. The daily change was related to the temperature and humidity, which are related to evaporation. A high LRR has been reported to suppress transpiration. In Koshihikari showing low LRR, neither LRR nor LWP was influenced by exposure to high-temperature / low-humidity condition, but in C-115 showing a high LRR, both LRR and LWP were increased by exposure to such conditions. These results suggest that LWP is affected by leaf-rolling. If we assume that a high LRR reflects the increase of boundary-layer resistance, the cultivars with a high LRR are considered to have a higher boundary-layer resistance and thus keep high LWP under high evaporative demand.

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To pursue the possibility of controlling apple snail damage on rice seedlings, the preferences and feeding behavior of the apple snail, under the use of fruits and vegetables as attractants in rice fields, were investigated. The apple snails showed higher preferences for specific fruits and vegetables, such as melons, watermelons, lettuce, eggplants, and tomatoes than for rice seedlings. Many more apple snails were observed adhering to and feeding on those fruits and vegetables than on rice seedlings when the seedlings, fruits and vegetables were simultaneously placed in one container. Most apple snails found their preferred food directly, or they moved to it after leaving unpreferred food within six hours. Moreover, the apple snails stayed on melons and eggplants for clearly a longer time period than on rice seedlings. Therefore it is suggested that vegetables in rice fields would attract the apple snails and may contribute to reduce apple snail damage on rice seedlings.

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The fluorine included in factory effluents may pollute river water, irrigation water and paddy field soil. The effect of soil fluorine at the concentrations 100, 279, 458, 816, 1173, 1352, and 1531 ppm on growth of Oryza sativa L.cv.Koshihikari under soil culture was investigated in 1991, and that at 100, 279, and 458 ppm in 1992. The leaf-emergence rate and the number of stems per hill were not influenced by 279 ppm soil fluorine, but decreased by 458 ppm soil fluorine, and obviously decreased by further increase in the soil fluorine concentration. The number of ears per hill and of the grains per hill were not depressed by 279 ppm soil fluorine, but decreased by 458 ppm soil fluorine and further decreased with increasing concentrations of the soil fluorine. The percentage of ripened grains and the 1000- kernel weight of the brown rice were not affected by soil fluorine at a concentration of 458 ppm. The dry weight of each organ of rice plant was not decreased by 279 ppm soil fluorine, but the dry weights of unhulled rice, leaves, sheaths (including culms) and roots were markedly decreased by 458 ppm soil fluorine. It was found that the dry weights of all organs of rice plant were obviously decreased by soil fluorine at high concentrations.

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The effect of fluorine (HF) added to the culture solution on the growth of Oryza sativa L.cv.Koshihikari was investigated. HF was added to the culture solution at 50 ppm for 10 days at the active-tillering and panicle formation stages. The number of stems per hill was decreased by fluorine added, either at the tillering or panicle formation stages, especially by the fluorine treatments at the panicle formation stage. The dry weights of unhulled rice, leaves, leaf sheath (culm included), and roots were markedly decreased by the fluorine treatment. The number of ears per hill and the grains per hill were also decreased by fluorine. Thus, the dry weight of all organs, the number of ears per hill, and the number of grains per hill were decreased by the fluorine treatment at the panicle formation stage more severely than that at the active-tillering stage. A significant correlation was recognized between the number of ears per hill, the number of grains per hill and weight of unhulled rice. It was found that the effect of fluorine on the growth and yield of rice plants when given at the vegetative stage were different from that given at the reproductive stage.

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Although rice yield in 1999 was no less than the normal value, high air temperature during the 1999 summer season damaged the apparent quality of rice kernels in a large area of Japan. The percentage of rice kernels qualified as the first grade by inspection grade, was significantly decreased by the occurrence of milky-white kernels, white core and white-backed kernels in the Tohoku and Hokuriku area where the air temperature during the early ripening stage in 1999 was 3-5°C higher than the normal air temperature. In the Kyusyu area, low solar radiation with a high air temperature continued for a long term, and it affected not only the rice yield but also the apparent quality and palatability of rice kernels. On the other hand, the release and extension of new high temperature tolerant variety, as well as proper management for rice growth under a high air temperature condition, contributed to the reduction of the damage in Chiba prefecture. In this study, we analyzed the effects of weather conditions in 1999 on the ripening and quality of rice, and the factors such as variety and cultivation method relating to the damage by high air temperature. Research subjects in crop science will be also discussed.

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