Shuichi Asanuma

Rhizoplane microorganisms of rice seedlings as examined by scanning electron microscopy

Abstract Rhizoplane microorganisms of water cultured rice seedlings inoculated with soil microorganisms were examined by scanning electron microscopy and optical microscopy. Composition of the bacterial flora on the rhizoplane were also studied. Microorganisms on rhizoplane were limited only in bacteria consisting mostly of rods. They were distributed in every region except the root tip zone. Bacterial aggregations were common at ruptured sites of epidermal cells and cell junctions. They were also dispersed and adhered on mucigel, bare epidermal surface, and root hairs. The area covered with bacteria in the whole root surface was, however, relatively small (1–9%, average 4.6%). Some rhizoplane bacteria were seen to invade into the roots through ruptured sites on epidermis and mucigel. The composition of bacterial flora on rhizoplane was much simpler than that in the paddy soil from which soil inocula were prepared. Pseudomonas and Bacillus occupied about 60 and 40 per cent of the total found in rhizoplane...

Variation in acid-Al tolerance of Bradyrhizobium japonicum strains from African soils.

Abstract Seventy-six strains of Bradyrhizohium japonicum (54 African and 22 exotic) were examined for their tolerance to acidity (pH 4.5), low P (5 μM) and high Al (50 and 100 μM) levels by using an agar plate method. Forty-four strains were tolerant to acidity regardless of P levels (1,000 or 5 μM) of the medium and 22 were sensitive. The remaining 10 strains differed in their tolerance to acidity depending on the level of P of the medium; nine required a low P (5 μM) level for being tolerant but one required a high P level (1,000 μM). All of the 21 strains which could grow under the most severe stress conditions used, consisting of low P and high Al (100 μM) levels at pH 4.5, showed tolerance to acidity at both levels of P. Isolates from a highly acidic soil (Ultisol, pH(H2O) 4.3) of Onne, south-eastern Nigeria, showed different levels of acid-Al tolerance but tended to be more tolerant than those from a slightly acidic soil (Alfisol, pH (H2O) 6.4) of Ibadan, south-western Nigeria. However, 20% of the O...

Effects of soil microorganisms on the growth and on the nitrogen and phosphorus absorption by rice seedlings

Abstract The growth and the nitrogen and phosphorus absorption by rice seedlings were examined under sterile and non-sterile conditions. Sterile seedlings were cultured aseptically for 2 weeks in a sterilized nutrient solutions, a half of which were inoculated with 10-4 diluted paddy soil suspension. In addition a short-term 32p absorption experiment was carried out using rice seedlings precultured in the same way as above in a phosphate-free nutrient solution. Microorganisms retarded the growth of the seedlings, especially root elongation. However, in the presence of microorganisms the roots became thicker and they formed laterals and root hairs close to their tips. More nitrogen was absorbed by the sterile plants at 25 and 50 ppm of nitrogen, whereas more by the inoculated plants at 100 and 200 ppm. As regard to phosphorus absorption, the sterile plants absorbed more phosphorus at phosphorus levels ranging from 5 to 50 ppm. A short-term experiment with 32p revealed that the sterile plants absorbed more ...

Drought-induced root plasticity of two upland NERICA varieties under conditions with contrasting soil depth characteristics

Abstract To identify differences in root plasticity patterns of two upland New Rice for Africa (NERICA) varieties, NERICA 1 and 4, in response to drought under conditions with contrasting soil profile characteristics, soil moisture gradients were imposed using a sloping bed system with depths ranging 30–65 cm and a line-source sprinkler system with a uniformly shallow soil layer of 20 cm depth. Varietal differences in shoot and root growths were identified only under moderate drought conditions, 11–18% v/v soil moisture content. Further, under moderate drought soil conditions where roots could penetrate into the deep soil layer, deep root development was greater in NERICA 4 than in NERICA 1, which contributed to maintaining dry matter production. However, under soil conditions with underground impediment to deep root development, higher shoot dry weight was noted for NERICA 1 than for NERICA 4 at 11–18% v/v soil moisture content, which was attributed to increased lateral root development in the shallow soil layer in NERICA 1. Enhanced lateral root development in the 0–20-cm soil layer was identified in NERICA 1 even under soil conditions without an impediment to deep root development; however, this did not contribute to maintaining dry matter production in upland rice. Thus, we show different root developmental traits associated with drought avoidance in the two NERICA varieties, and that desirable root traits for upland rice cultivation vary depending on the target soil environment, such as the distribution of soil moisture and root penetration resistance.

Pseudomonas cepacia—A Characteristic Rhizoplane microorganisms in rice plant

Abstract Rice rhizoplane microorganisms consist mostly of Bacillus sp. and Pseudomonas sp. Isolated Pseudomonas strains from rice rhizoplane specifically accumulated nitrite in a medium containing rice root extract and nitrate. On the other hand, all strains of isolated Bacillus were found to be almost inactive in accumulating nitrite. Therefore, Pseudomonas was estimated to be specifically responsible for the microbial effect on root growth, because the effect of nitrite on root growth was found in a previous investigation to be nearly the same as that obtained with the combined rhizoplane microorganisms. Isolated Pseudomonas strains were further studied taxonomically and all of them were identified as Pseudomonas cepacia.

Pedological perspective of gully erosion sites within Kendu escarpment-Sondu Miriu Region, West Kenya

Gully erosion is a common feature in western Kenya, rendering large expanses of otherwise arable land uncultivable and uninhabitable. Gully erosion in the area was classified into two types: the Awach-type and the Sondu-type. The current study aimed at providing insight into physical and chemical properties of soil that promote soil erosion and determine the gully formation type. Field studies were conducted at 4 sites (3 eroded and 1 non- eroded). Physical (particle size distribution, structure stability, infiltration rate, dispersibility, and soil hardness), and chemical (pH, exchangeable cations, total-C, and total-N) properties of soil samples collected from the sites were analyzed in the laboratory. The results showed alkaline pH; high exchangeable sodium (Na) percentage (ESP); fragile soil structure; high dispersibility; and low infiltration rate are major factors contributing to the formation of Awach-type of gully. In contrast, impermeable top layer of hard crust and coarse-textured soil layers beneath it in addition to high ESP facilitated the formation of Sondu-type of gully. Soils of the eroded sites and the non-eroded sites differed mainly in the ESP, which influenced the soil structure stability, water infiltration rate, and soil dispersibility. Susceptibility of soil layers to erosion depended on the magnitude of ESP and sand content. Keywords : Exchangeable sodium percentage, gully erosion, infiltration rate, Kenya, soil dispersion, soil structure.

Vertical changes in denitrification activity and denitrifying bacterial populations in Kuroboku upland soil with slurry application

Abstract The vertical changes in the denitrification activity and de nitrifying bacterial populations were investigated in a Kuroboku upland soil with slurry application, where the nitrogen balance had been determined (Niimi and Nishida 1999: Estimation of denitrification by using δ15N values in upland field applied with a large amount of slurry barnyard manure. In 10th Nitrogen Workshop Program and Abstracts, IV, p. 41). Averaged cell density of the denitrifying bacterial populations significantly increased in relation to the level of slurry application, 0, 60, 150, and 300 fresh-wt. Mg ha−1. The denitrifying bacterial populations showed a higher correlation with the potential denitrification activity than with the fresh denitrification activity. Averaged contribution of the potential denitrification activity in three soil layers (approximately 5–20, 20–45, and 45–80 cm) to the total activity was 90, 9.5, and 0.4%, respectively. Annual nitrogen loss associated with the denitrification activity in the 0, 60, 150, and 300 Mg ha−1 plots was found to amount to 15.6, 20.0, 41.5, and 94.7 kg-N ha−1 y−1 based on the data from the fresh denitrification activity and to 38.6, 39.1, 163.8, and 611.8 kg-N ha−1 y−1 based on the data from the potential denitrification activity. The above results indicate that by only conducting a surface soil survey, it was possible to obtain a rough estimation of the nitrogen loss associated with the potential denitrification activity in a Kuroboku upland soil with slurry application.

EFFECT OF SOIL MICROORGANISMS ON THE GROWTH OF ROOTS IN RICE SEEDLINGS : II. Nitrite Formation by Rhizoplane Microorganisms and the Effect of Nitrite on the Root Development under Aseptic Condition

Abstract Nitrite formation by rhizoplane microorganisms of rice seedlings was examined in comparison with that by nonrhizosphere paddy soil microorganisms. Effect of nitrite on root growth of rice seedlings was also investigated under aseptic water culture condition. Rhizoplane microorganisms accumulated much nitrite than the other microorganisms in a root extract medium. The accumulated nitrite maintained a stationary level for more than 2 days. In glucose enriched media, both group of microorganisms accumulated nitrite only temporarily. Formation of lateral roots and root hairs was stimulated in the solution containing 1.12-11.2 ppm NO2 --N but elongation of primary roots was depressed under 5.6-11.2 ppm NO2 --N concentrations. Growth of rice seedlings was inhibited at concentrations higher than 5.6 ppm. Comparative studies indicated that effect of soil microorganisms on root morphology would have been caused by nitrite produced by rhizoplane microorganisms.

SATREPS Program Challenging Global Issues on Crop Production: Overview

Food is essential to human life, but there remain not a few people who cannot be accessible to adequate amount and quality of food, especially in some developing countries. Since a major portion of human diet comes from crop products, a continuous increase in crop production is required to feed the burgeoning population. Crop growth is strongly regulated by environmental factors such as temperature, precipitation, and soil property. An excess and/or deficit in water availability, supra- or suboptimal temperature, and poor soil fertility are major prevalent environmental factors likely to restrict crop productivity in developing regions. Risks of outburst of diseases and insects, which could be accentuated by projected global warming, are also threatening future crop production worldwide. Advanced technologies are expected to be applied, through international collaboration, to address global issues threatening developing countries. Based on this idea, the program named “Science and Technology Research Partnership for Sustainable Development (SATREPS)” was initiated in 2008. The verification of the effectiveness should provide useful information for the future opportunities to apply these technologies to address the issues limiting crop productivity in the developing regions.

Lessons Learned from SATREPS Projects and Perspectives

Cutting-edge science and technology such as genome analysis is a useful technology in genomic characterization of living organisms, biological diversity analysis, breeding, and any other genome-related science. In this chapter, we tried to find how the cutting-edge science and technology was utilized in solving the global-scale problems in developing countries, particularly in research for development fields using bioresources. For this purpose, we examined the effectiveness of cutting-edge technologies in addressing the issues challenged by the nine projects reported in Chaps. 2, 3, 4, 5, 6, 7, 8, 9, and 10 of this book. In any case, the state-of-the-art technologies were found to be effective only when conventional technologies were applied complementarily. For example, the genome analysis using next-generation sequencer was found to be a very useful technology in identifying the traits of genetic materials in the research of plant breeding. However, to solve the problems and apply the results for development, breeding materials needed to be tested in the process of selection of promising materials toward new varieties-candidates under the field conditions whether they adapt to the real conditions through G (genetic traits) × E (environmental conditions) × M (management such as fertilization and water control) experiments. Many projects reported herewith showed that conventional technologies were also used and useful in those experiments. Therefore, we conclude that both cutting-edge and conventional technologies are required in a harmonious manner in solving the problems and applying the results for development in developing countries. At the same time, capacity building of researchers is essential to obtain new knowledge for understanding the problems and new technologies to solve the problems.