Rice Fields In Japan Research Articles

Range Expansion and Invasive Capacity of the Wing Di- and Polymorphic Insects: A Short Review

In this review article the invasive potential of wing dimorphic and polymorphic insects is discussed by presenting two case studies and overviewing the general knowledge of the dispersal abilities of these insects. Flying morphs of the wing dimorphic rice planthoppers Nilaparvata lugens and Sogatella furcifera continuously re-invade the rice fields in Japan and Northern China, where subsequent generations of dimorphic populations build up, causing several economic damages. The rapid range expansion of the wing dimorphic bush cricket Metrioptera roeselii in Central and Northern Europe in the 2000s was documented and extensively studied. These case studies are analysed, and the general relation of wing dimorphism and polymorphism and invasive potential is briefly discussed using the extensive knowledge on the wing dimorphism and polymorphism present in different insect orders.

Historical mapping of rice fields in Japan using phenology and temporally aggregated Landsat images in Google Earth Engine

Mapping the expansion or reduction of rice fields is fundamental for food and water security, greenhouse gas emission accounting, and environmental management. The historical mapping of rice fields with satellite images is challenging because of the limited availability of remote sensing and training data from past decades. The use of phenology-based algorithms has been proposed for mapping rice fields because they can take advantage of rice fields’ characteristic spectral signature during the transplanting phase and do not need training data. However, in order to employ phenology-based algorithms effectively for the historical rice mapping of large areas, we need to incorporate automatized methods able to deal with non-usable data (e.g., cloud cover) and with spatial inconsistencies in the number of available images for each pixel. Here we propose the combination of a pixel-based, phenological algorithm with the temporal aggregation of all available Landsat images to produce national level historical maps of rice fields in Japan from the 1980s onwards. We used temporally aggregated metrics (median, percentiles, etc.), derived from spectral indices of a large number of images within the Google Earth Engine, to minimize the issue of inconsistent image availability and reduce the effects of outliers in phenology-based algorithms. We produced seven rice field maps, for the periods 1985–89, 1990–94, 1995–99, 2000–04, 2005–09, 2010–14, and 2015–19. The overall map accuracies ranged from 83% to 95% when validated with visually interpreted aerial photography. We detected a 23% decrease in the area of rice fields at a country level, although the changes varied greatly among prefectures. Here we present the first freely available historical rice field maps of Japan from the 1980s onwards, together with the source code, and a web application that enables the exploration of the maps and data relating to the derived rice field area changes. The application of temporal aggregation is promising for dealing with the gap-filling of large amounts of satellite data, reducing the issue of data outliers and providing an effective use of the historical Landsat archive for phenology-based crop detection algorithms. Our maps could greatly help researchers, conservationists and policymakers studying the drivers and consequences of rice field changes, and our methods could be extrapolated to map rice fields at large scales in other regions of the world.

Sensors for UAVs dedicated to agriculture: current scenarios and challenges

Sensors for UAVs dedicated to agriculture: current scenarios and challenges

Evaluating Farm Management Performance by the Choice of Pest-Control Sprayers in Rice Farming in Japan

With rapidly advancing technologies such as IoT, AI, robotics, and others, smart agriculture in Japan has been introduced and tested throughout the country. The validity of the implementation of smart agriculture could be measured by using cost analysis, working capacity assessment, and management efficiency analysis. In this study, we focused on pest-control management, wherein unmanned aerial vehicles (UAVs) for crop spraying have been recently introduced. In order to clarify the validity of UAVs for rice fields in Japan regarding costs and performance, we conducted a comparative study of pest-control sprayers, specifically: (1) tractor- mounted boom sprayers, (2) remote-control spraying helicopters (RC helicopters), and (3) UAVs. We estimated pest-control costs and the working capacity of each method. We also evaluated the management efficiency of 21 case scenarios of different pest-control sprayers and field areas ranging from 0.5 to 30 ha using data envelopment analysis (DEA) based on an input-oriented model. We used the input of pest-control cost and the output of gross farm income and surplus working capacity. Pest-control costs per unit area of boom sprayers, RC helicopters, and UAVs were approximately 925,597 yen/ha (US $8819/ha), 6,924,455 yen/ha (US $65,975/ha), and 791,724 yen/ha (US $7543/ha), respectively. The working capacity during pest-control scheduled days was 120, 195, and 135 ha, respectively. DEA results suggested that UAVs would be more efficient than boom sprayers and RC helicopters for the analyzed cases. UAVs for crop spraying showed relatively low cost and high management efficiency compared to the boom sprayers and RC helicopters; hence UAVs could be a suitable replacement to save cost and time.

Taxonomic assessments of some Cyprinotinae Bronstein, 1947 species(Crustacea: Ostracoda) from Japanese and Korean rice fields, including(re-) descriptions of six species and a review of the type species of the subfamily.

Rice is the staple food crop for approximately half the world's population, but some common and abundant taxa inhabiting rice fields, such as ostracods, are poorly studied. For many ostracod species only brief, initial descriptions are available, hindering reliable identifications, and so their ecological roles in rice fields remain obscure. This study partially addresses this problem by assessing the taxonomic validity of six species of Cyprinotinae ostracods reported from rice fields in Japan and South Korea: Cyprinotus uenoi Brehm, 1936, Hemicypris megalops Sars, 1903, Hemicypris ovata Sars, 1903, Hemicypris vulgaris Okubo, 1990, Heterocypris rotundata (Bronstein, 1928), and Hemicypris kawagaensis Okubo, 2004 nomen nudum. Type material of C. uenoi was not designated and Brehm's ostracod collection is missing, but Japanese and Korean records of C. uenoi differ significantly from Brehm's original description. The Japanese and Korean species is described and named herein as Cyprinotus cassidula sp. nov. Japanese specimens reported to be Hemicypris megalops are probably misidentified, but details of the carapace of Hemicypris megalops are obscure due to poor preservation of type material. Examination of topotype material of Hemicypris posterotruncata Bate, 1970, a sub-fossil from near Lake Turkana in Kenya, demonstrates that this species is extant in Asian rice fields. Investigation of type material of Hemicypris kliei (Lindroth, 1953) has revealed that it is not a senior synonym of Hemicypris posterotruncata, contrary to previous studies. Size and morphological data indicates that Hemicypris vulgaris is a large form of Hemicypris posterotruncata and the two species are treated as synonyms herein. Examination of paralectotypes of Hemicypris ovata indicates that it is very similar to Hemicypris posterotruncata, especially the larger morphotypes, but as these two species can be distinguished by morphological features they are both retained as separate species. However, Japanese records of Hemicypris ovata are considered misidentifications of the larger forms of Hemicypris posterotruncata. Hemicypris kawagaensis, which has only been reported once from East Asia, is herein regarded as a junior synonym of Hemicypris barbadensis Broodbakker, 1983, and is likely an alien species in Asia. Asian specimens previously identified as Heterocypris rotundata show sufficient differences to European specimens to determine that they are not conspecific. This species is described as Heterocypris savatenalintonae sp. nov. Taxonomic descriptions of Hemicypris ovata, Hemicypris posterotruncata, Hemicypris megalops, Hemicypris kliei, Heterocypris savatenalintonae sp. nov., and Cyprinotus cassidula sp. nov. are presented. Finally, it is noted that past redescriptions of Cyprinotus cingalensis Brady, 1886, the type species of the genus and the subfamily Cyprinotinae Bronstein 1947, are based partly on other species.

Interspecific competition between two self-fertile and one related sexual species of tadpole shrimp Triops (Branchiopoda, Notostraca) with reproductive interference, Allee effect and environmental fluctuation

Invasive alien species of tadpole shrimp Triops, originated from America, were first introduced into rice fields of Japan in the 1910s and have spread around Japan. In the 1950s, a European species of Triops also seems to have entered Japan. Originally, Japanese paddy fields had Asian Triops species as a prehistoric naturalised animal. A new invasive Triops from Western Australia has been reported in the south part of Japan, occasionally forming mixed populations. The expansion of Triops has resulted in negative ecological and potential economic impact. Longhursts revision did not contain any specimens of the richest collection in the world, i.e., Daday Collection in the Hungarian Natural History Museum. And therefore, Naganawa surveyed at least 20 times as many samples as those by Longhurst, and number the named Triops granarius s.l. species group from Africa-India to Siberia-Asia at eight species, organised in the same genus. As for the establishment or extinction patterns, based on Tilmans competition model, we built a simple mathematical competition model between two self-fertile and one related sexual species of Japan, incorporating reproductive interference. To make the mathematical model more natural, we also assumed environmental fluctuation and Allee effect, which reduces the population growth rate of sexual species with low density. Intense reproductive interference drove the competition to sexual exclusion of self-fertile species. However, even under intense reproductive interference, Allee effect allowed self-fertile species to survive when the competition started with the lower densities; contrary to the survival of sexual species when the competition started with the higher densities.

Rice grain quality degradation and economic loss due to global warming in Japan

Global warming is predicted to have significant impacts not only on crop productivity but also on crop quality, leading to economic loss. In the present study, focusing on grain quality of rice in Japan, we assessed the impact of global warming on the occurrence of low quality rice grain called ‘chalky rice grain’, and the incurred economic loss. Using 10 future climate scenarios and a simulation model to estimate the occurrence of chalky rice grain, we showed that global warming will double the occurrence of chalky rice grain by the 2040 s under RCP8.5. This corresponds to one third of paddy rice fields in Japan showing a decrease in grain grade. This would produce an annual economic loss of 401.4 million US$/yr under RCP8.5 in the 2040 s. These results suggest that the development and implementation of national and local adaptation strategies are urgently needed for rice production in Japan.

Weedy rice represents an emerging threat to transplanted rice production systems in Japan

Weedy rice is a conspecific weed of cultivated rice (Oryza sativa L.) and is a primary weed of direct‐seeded rice production systems worldwide. The shift in the method of establishing rice, that is, from transplanting to direct seeding, is considered the main reason for the emergence of weedy rice in Asia and, more recently, Japan. Japan has increasingly adopted directly seeded rice, even though this practice remains limited. In this study, I confirmed the relationship between weedy red rice emergence and the adoption of direct‐seeded rice in Japan. Twenty‐seven areas from eight prefectures infested with weedy rice were selected to confirm the relationship between the rice planting method and the emergence of weedy rice. Fields that were severely infested with weedy rice were selected as survey fields for this study. I found no relationship between the method of planting rice and weedy rice emergence. Changes to herbicide application, duration of rice production and hand weeding also contribute to the emergence of weedy rice in transplanted rice fields in Japan. The results of this study indicate that weedy rice could become a serious problem in Japan, even in transplanted rice fields.

A Nondestructive Method to Estimate Plant Height, Stem Diameter and Biomass of Rice under Field Conditions Using Digital Image Analysis

Plant phenotyping intends measuring complex plant traits, and is important in agricultural research for enhancing yield improvement. Manual plant phenotyping is laborious and destructive, and hence a less-laborious and non-destructive method is required. Here, we proposed a nondestructive method to estimate continuous data of plant traits such as height, stem diameter and biomass using a low cost time-lapse camera. The camera was installed at a rice field in Japan, and captured images for four target plants every three hour. The plant height and stem diameter were determined from the images by referencing scale bars that were placed next to the target plants and above the ground surface. Both the height and the diameter were compared to directly measured ones, and the relationships between those were in good agreement. Plant volumes were estimated from the height and stem diameter assuming a shape of rice plant is cylindrical. Above ground biomass without panicles was determined by rice plants sampled from the field. The determined biomass increased in proportion to the plant volume, and its relationship used to produce continuous data of the rice biomass. The results suggest that the proposed method can be considered as a useful tool of the plant phenotyping.J. Environ. Sci. & Natural Resources, 10(1): 1-7 2017

Detection of Magnaporthe oryzae chrysovirus 1 in Japan and establishment of a rapid, sensitive and direct diagnostic method based on reverse transcription loop-mediated isothermal amplification.

Magnaporthe oryzae chrysovirus 1 (MoCV1) is a mycovirus with a dsRNA genome that infects the rice blast fungus Magnaporthe oryzae and impairs its growth. To date, MoCV1 has only been found in Vietnamese isolates of M. oryzae, and the distribution of this virus in M. oryzae isolates from other parts of the world remains unknown. In this study, using a one-step reverse transcription PCR (RT-PCR) assay, we detected a MoCV1-related virus in M. oryzae in Japan (named MoCV1-AK) whose sequence shares considerable similarity with that of the MoCV1 Vietnamese isolate. To establish a system for a comprehensive survey of MoCV1 infection in the field, we developed a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for direct detection of the virus. The sensitivity of the RT-LAMP assay was at least as high as that of the one-step RT-PCR assay. In addition, we detected MoCV1-AK in M. oryzae-infected oatmeal agar plates and lesions on rice leaves using the RT-LAMP assay without dsRNA extraction, by simple sampling with a toothpick. Preliminary screening of MoCV1 in Japanese M. oryzae isolates indicated that MoCV1 is currently distributed in rice fields in Japan. Our results provide a first example of the application of RT-LAMP for the detection of mycoviruses, which will accelerate surveys for mycovirus infection.

Characterization of sulfonylurea-resistant Schoenoplectus juncoides having a target-site Asp376Glu mutation in the acetolactate synthase

Schoenoplectus juncoides, a noxious weed for paddy rice, is known to become resistant to sulfonylurea (SU) herbicides by a target-site mutation in either of the two acetolactate synthase (ALS) genes (ALS1 and ALS2). SU-resistant S. juncoides plants having an Asp376Glu mutation in ALS2 were found from a paddy rice field in Japan, but their resistance profile has not been quantitatively investigated. In this study, dose–response of the SU-resistant accession was compared with that of a SU-susceptible accession at in vivo whole-plant level as well as at in vitro enzymatic level.In whole-plant tests, resistance factors (RFs) based on 50% growth reduction (GR50) for imazosulfuron (ISF), bensulfuron-methyl (BSM), metsulfuron-methyl (MSM), bispyribac-sodium (BPS), and imazaquin (IMQ) were 176, 40, 14, 5.2 and 1.5, respectively. Thus, the accession having an Asp376Glu mutation in ALS2 was highly resistant to the three SU herbicides and moderately resistant to BPS, but was not substantially resistant to IMQ. This is slightly different from the earlier results reported from other weeds with an Asp376Glu mutation, in which the mutation confers resistance to broadly all the chemical classes of ALS-inhibiting herbicides.In enzymatic tests, ALS2 of S. juncoides was expressed in E. coli; the resultant ALS2 was subjected to an in vitro assay. RFs of the mutated ALS2 based on 50% enzymatic inhibition (I50) for ISF, BSM, MSM, BPS, and IMQ were 3699, 2438, 322, 80, and 4.8, respectively. The RFs of ALS2 were highly correlated with those of the whole-plant; this suggests that the Asp376Glu mutation in ALS2 is a molecular basis for the whole-plant resistance. The presence of two ALS genes in S. juncoides can at least partially explain why the whole-plant RFs were less than those of the expressed ALS2 enzymes.

Aminivibrio pyruvatiphilus gen. nov., sp. nov., an anaerobic, amino-acid-degrading bacterium from soil of a Japanese rice field

A novel anaerobic bacterium that could ferment amino acids and organic acids was isolated from an anaerobic, propionate-oxidizing enrichment culture originating from soil of a rice field in Japan. Cells of the isolate, designated strain 4F6E(T), were Gram-staining-negative, oxidase- and catalase-negative, non-spore-forming, vibrio-shaped, motile rods (0.8×2.0-2.5 µm) with two or three lateral flagella. Growth occurred at 20-42 °C (optimum at 37-40 °C), at pH 6.4-8.4 (optimum at pH 7.3) and at 0-1.5 % (w/v) NaCl (optimum at 0-0.5 %). Good growth occurred on glycine, serine, cysteine, pyruvate and citrate, whereas poor growth was observed on threonine, glutamine, L-malate, α-ketoglutarate, peptone and Casamino acids. In co-culture with the hydrogen-utilizing methanogen Methanobacterium formicicum JCM 10132(T), strain 4F6E(T) oxidized alanine, valine, leucine, isoleucine, methionine, aspartate, glutamate, histidine, asparagine and fumarate. Yeast extract was required for growth. The G+C content of genomic DNA was 61.9 mol%. A phylogenetic analysis based on comparison of the 16S rRNA gene sequence showed that the type strains of Fretibacterium fastidiosum, Aminobacterium colombiense and Aminobacterium mobile, members of the family Synergistaceae, were the closest relatives of strain 4F6E(T), with low sequence similarities (89.3, 89.5 and 86.2 %, respectively). Strain 4F6E(T) contained iso-C13 : 0 (24.43 %), iso-C15 : 0 (16.47 %) and C19 : 1ω11c/C19 : 1ω9c (16.32 %) as the major fatty acids, which differed from those of F. fastidiosum, Aminobacterium colombiense and Aminobacterium mobile. On the basis of phenotypic, chemotaxonomic and phylogenetic differences between strain 4F6E(T) and the type strains of F. fastidiosum and Aminobacterium species, we propose that strain 4F6E(T) represents a novel genus and species, Aminivibrio pyruvatiphilus gen. nov., sp. nov. The type strain of Aminivibrio pyruvatiphilus is strain 4F6E(T) ( = JCM 18417(T) = DSM 25964(T)).

First Report of the Cyst Nematode (Heterodera elachista) on Rice in Hunan Province, China.

During a survey for the cyst nematodes (Heterodera elachista) from May to June of 2011, cyst nematodes were detected in hilly rice fields in five counties (Changsha, Pingjiang, Hengdong, Shaoyang, and Xiangxiang) of Hunan Province, China. Cyst nematodes obtained from soil samples and harvested rice root samples at these five locations had uniform morphological and molecular characteristics. Cysts (n = 20) had the following characteristics: spherical to lemon shaped, vulval cone ambifenestrate, vulval bridge narrow, medium sized underbridge, with a few dark brown bullae, body length (not including the neck) ranging from 354 to 586 μm (mean = 438.9 μm, st. dev. = 63.7); body width ranged from 283 to 495 μm (354.5, 60.1); fenestrate length of 30 to 50 μm (37.4, 5.0) and width of 25 to 47.5 μm (35.1, 7.1); underbridge length from 70 to 95 μm (83.4, 8.2); and vulval slit length from 30.3 to 55.5 μm (40.3, 9.1). J2 (n = 20) had the following characteristics: body length ranging from 404 to 525 μm (mean of 461.6 μm, st. dev. = 34.5); stylet length from 20 to 25 μm (22.5, 1.1) with rounded knob; tail length of 60 to 87.5 μm (67.3, 6.9); and hyaline terminal tail ranged from 30 to 50 μm (37.5, 6.4); lateral field with three lines. The mean and range of J2 were longer than those reported for H. elachista by Nobbs et al. (1) and Tanha et al. (4), but other morphological character values were within the range of those reported (4). DNA from a single cyst was extracted, the rDNA-internal transcribed spacer (ITS) and D2/D3 fragments of the 28S RNA were amplified with universal primers TW81 and AB28, D2A and D3B, respectively. Five ITS sequences (JN202913, JN202914, JN202915, JN202916, and JN202917) and five D2/D3 sequences (JN202918, JN202919, JN202920, JN202921, and JN202922) from nematode samples collected in Changsha, Hengdong, Shaoyang, Pingjiang, and Xiangxiang, respectively, were submitted to GenBank. These ITS sequences were remarkably similar to each other and exhibited 98.6 to 99.3% similarity with that of H. elachista isolate from Iran (AF498391), and 98.8 to 99.4% similarity with that of H. elachista isolates from Ningxia Province, China (HM560778 and HM560779). The D2/D3 sequences exhibited 99.7 to 100% similarity with that of H. elachista isolates from Ningxia Province, China (HM560842 and HM560843). These characteristics indicated that the five populations were H. elachista belonging to the 'cyperi' group (1,2). In glasshouse evaluations of the pathogenicity of these isolates, 500 second-stage juveniles were inoculated onto five 20-day-old seedlings of rice (Weiyou No.227) in 4.5-cm diameter 30-cm high tubes with six replicates. After 8 weeks, stunting and reduction of leaf length were observed and cysts were extracted from dried soil of each tube using sieves. Brown cysts (92 to 204) and white females (14 to 40) were obtained from inoculated rice from each tube. H. elachista can decrease yield by 7 to 19% and has the most severe impact during the later stages of plant growth (3). H. elachista has been previously identified from rice fields in Japan and Iran (3). To our knowledge, this is the first report of H. elachista on rice in Hunan Province, China.

Differences in susceptibility of five cladoceran species to two systemic insecticides, imidacloprid and fipronil

Differences in susceptibility of five cladocerans to the neonicotinoid imidacloprid and the phenyl-pyrazole fipronil, which have been dominantly used in rice fields of Japan in recent years, were examined based on short-term (48-h), semi-static acute immobilization exposure tests. Additionally, we compared the species sensitivity distribution (SSD) patterns of both insecticides between two sets of species: the five tested cladocerans and all other aquatic organisms tested so far, using data from the ECOTOX database of U.S. Environmental Protection Agency (USEPA). The sensitivity of the test species to either imidacloprid or fipronil was consistent, spanning similar orders of magnitude (100 times). At the genus level, sensitivities to both insecticides were in the following descending order: Ceriodaphnia > Moina > Daphnia. A positive relationship was found between body lengths of each species and the acute toxicity (EC(50)) of the insecticides, in particular fipronil. Differences in SSD patterns of imidacloprid were found between the species groups compared, indicating that test cladocerans are much less susceptible than other aquatic species including amphibians, crustaceans, fish, insects, mollusks and worms. However, the SSD patterns for fipronil indicate no difference in sensitivity between cladocerans tested and other aquatic organisms despite the greater exposure, which overestimates the results, of our semi-static tests. From these results, Ceriodaphnia sp. should be considered as more sensitive bioindicators (instead of the standard Daphnia magna) for ecotoxicological assessments of aquatic ecosystems. In addition, we propose that ecotoxicity data associated with differences in susceptibility among species should be investigated whenever pesticides have different physicochemical properties and mode of action.

Assessment of the methane mitigation potentials of alternative water regimes in rice fields using a process‐based biogeochemistry model

AbstractRice production is a substantial source of atmospheric CH4, which is second only to CO2 as a contributor to global warming. Since CH4 is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH4 emissions. In this study, we used a process‐based biogeochemistry model (DNDC‐Rice) to assess the CH4 mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC‐Rice using site‐scale data from three rice fields in Japan with different water regimes. The observed CH4 emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC‐Rice gave acceptable predictions of variation in daily CH4 fluxes and seasonal CH4 emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC‐Rice to simulate CH4 emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH4 emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO2 and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO2 Eq. ha−1 yr−1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO2 Eq. yr−1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national‐scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan.

Rhizomicrobium palustre gen. nov., sp. nov., a facultatively anaerobic, fermentative stalked bacterium in the class Alphaproteobacteria isolated from rice plant roots

Facultatively anaerobic bacterial strains (A48(T), RR25 and RR54) were isolated from roots of living rice plants in an irrigated rice-field in Japan. The three strains had identical 16S rRNA gene sequences and showed almost the same phenotypic properties examined. Cells of the strains were Gram-negative, non-spore-forming rods. Reproduction of cells was by binary fission as well as by budding. Cells occurred singly or in pairs arranged angularly. Some cells, including dividing cells, were motile with a single polar flagellum. Cells developed a polar prostheca (stalk) with a holdfast-like structure and the cell with the stalk budded a daughter cell. The strains were chemoorganotrophs and utilized various sugars as growth substrates. The strains fermentatively produced acetate and lactate as well as small amounts of ethanol and H(2) from the substrates. Growth temperature and pH ranges for growth were 15-40 degrees C and pH 5.5-7.3 with optimum growth at 30-35 degrees C and pH 6.8. NaCl concentration range for growth was 0-1.0% (wt/vol) with an optimum at 0% (wt/vol). Catalase and oxidase activities were not detected. The strains reduced Fe(III) to Fe(II) in the presence of glucose, while they did not reduce nitrate, fumarate, malate or sulfate. The major cellular fatty acids of the strains were C18:1omega7, anteiso-C15:0, iso-C15:0, C16:0 and C18:0. Ubiquinone Q-10 was the major respiratory quinone and the genomic DNA G + C contents were 53.4-55.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences placed the strains in the class Alphaproteobacteria and the strains formed a novel deep branch in the phylogenetic trees constructed. Based on the differences in 16S rRNA gene sequences and phenotypic properties of the novel strains from those of their relatives, we proposed that the strains be assigned in the novel genus and species as Rhizomicrobium palustre gen. nov., sp. nov. The type strain of the novel species is strain A48(T) (= JCM 14971(T) = DSM 19867(T)).

MOVEMENT DECISIONS BY INTERMEDIATE EGRETS

An Intermediate Egret (Egretta intermedia) catching a tadpole in a flooded rice field in Japan. Animal movements in heterogeneous environments play a crucial role in a variety of ecological processes. But few studies have revealed what causes animals to show multispatial scale movements within the framework of optimal theories. Using detailed information on movement paths and prey captures by Intermediate Egrets in rice fields, we explored the effects of individual experience at multitemporal scales on subsequent movement parameters. A mobile GIS system (left), which consists of a portable GPS receiver, a laser rangefinder, and an electronic compass, allowed information about a target location to be recorded from a distant observation point (right). Simultaneously, we recorded the timing, duration, and type of behavior of the focal egret. This study showed that the framework of optimal foraging theories is useful for explaining comprehensively the different movement modes in animals. We also concluded that considering both area-avoided and restricted searches at multitemporal scales is important for understanding movement decisions, particularly in organisms searching for hierarchically distributed resources. The results of the study suggested that egrets make different adaptive decisions at different spatial scales. Prey attacks in the previous 1 minute caused egrets to walk away (area-avoided search, left) at a small spatial scale, whereas those in the preceding 8 minutes caused egrets to stay around (area-restricted search, right) at a large spatial scale. Also, the timing of patch departure by flying seemed to follow predictions by the marginal value theorem. These photographs illustrate the article “Hierarchical movement decisions in predators: the influence of foraging experience at more than one spatial and temporal scale” by Tatsuya Amano and Naoki Katayama, tentatively scheduled to appear in Ecology in 2009.

Changes in major capsid genes (g23) of T4-type bacteriophages with soil depth in two Japanese rice fields

Although microbial communities in soil are well known to change with soil depth, the changes in viral communities with soil depth have not been documented. This study examined the soil depth profiles of T4-type phage communities in two Japanese rice fields from g23 clones in soil DNA extracts to a depth of 1 m. T4-type phage communities changed with soil depth, and the communities were grouped into two groups: the communities of the surface soil layers, where rice roots developed densely, and those of the subsoil layers. Although coarse- and fine-textured soils were stratified in the subsoil layers in both profiles, denaturing gradient gel electrophoresis band patterns and phylogenetic affiliation of g23 were highly similar to each other among the subsoil layers in both fields, indicating that soil texture did not affect T4-type phage communities in these fields. In addition, some clones had g23 sequences identical to those retrieved from rice fields in Northeast China, indicating that closely related viruses and their hosts distribute across the sea between rice fields in Japan and Northeast China.

Diet composition of the endangered giant water bug Lethocerus deyrolli (Hemiptera: Belostomatidae) in the rice fields of Japan: Which is the most important prey item among frogs, fish, and aquatic insects?

AbstractThe food habits of the endangered giant water bug, Lethocerus deyrolli, were studied in the rice fields of Nose, in the north of Osaka Prefecture, Japan. Field observations revealed that frogs were the most important prey item. Frogs represented 86.4% and 78.6% in the diet of L. deyrolli in spring and summer, respectively. Among seven species of three families (Hylidae, Rhacophoridae, and Ranidae) exploited by L. deyrolli, the most important food item was adult Hyla japonica in spring and juvenile Rana nigromaculta in summer. Fish and aquatic arthropods were not considered important foods for L. deyrolli. The frog‐dependent food habits indicate that the recovery and conservation of frogs should be prioritized to protect L. deyrolli from extinction.

Nucleotide substitutions in the acetolactate synthase genes of sulfonylurea-resistant biotypes of Monochoria vaginalis (Pontederiaceae)

Some point mutations in acetolactate synthase (ALS) confer resistance to ALS-inhibiting herbicides in weeds. To clarify the evolution of the herbicide resistance of Monochoria vaginalis, a weed in rice fields in Japan, the nucleotide sequences of four genes encoding ALS were surveyed in five sulfonylurea-resistant (SU-R) and five sulfonylurea-susceptible (SU-S) biotypes. In the ALS1 gene, two SU-R biotypes showed nucleotide substitutions changing Pro197 to Ser and Leu, respectively. In a different gene, ALS3, three other SU-R biotypes showed either of the two nonsynonymous nucleotide substitutions seen in ALS1. Only two biotypes geographically located distantly from each other shared the same mutation conferring SU resistance in the same gene. These patterns of nucleotide substitutions indicate that the SU-R phenotype was acquired independently by different biotypes. Nucleotide diversity values of the genes showing SU-R mutations were higher than those of ALS2 lacking any SU-R mutation and of a putative pseudogene, ALS4. This result suggests that the maintenance of nucleotide variability within target genes provides an opportunity for the evolution of SU-R phenotypes by herbicide-driven selection for mutations conferring resistance.