Young Rice Plants Research Articles

Discovery of anisiflupurin, an inhibitor of cytokinin dehydrogenase that mitigates heat-induced yield reduction in rice.

In a screening of anilinopurine, anisiflupurin was identified as potent inhibitor of cytokinin dehydrogenase/oxidase (CKX). Inhibitors of CKX have been supposed to be potent plant growth regulators to alleviate the detrimental effects of abiotic stress on crop production. The aim of the study was to profile anisiflupurin in a set of physiological assays and to evaluate its potential for heat stress mitigation in rice field trials. Anisiflupurin delayed dark-induced senescence and increased transpiration in detached maize leaves in a dose-dependent manner. Similarly, the transpiration of young rice plants under heat stress was increased for several days after application with anisiflupurin. Application of anisiflupurin during early phases of generative growth not only restored heat-induced pollen alterations it increased grain yield in field grown rice under heat conditions as demonstrated in a large field program conducted in southeast Asia. Thereby, efficacy of anisiflupurin was rate-dependent and most effective when applied during early generative growth phases prior heat stress. Application of anisiflupurin secures seed setting by protecting pollen development and enhances grain weight under heat stress conditions in rice. The results of this research opens up a promising avenue for mitigating the adverse effects of heat stress in rice cultivation. © 2024 Society of Chemical Industry.

Marker-Assisted Introgression of the Salinity Tolerance Locus Saltol in Temperate Japonica Rice

BackgroundRice is one of the most salt sensitive crops at seedling, early vegetative and reproductive stages. Varieties with salinity tolerance at seedling stage promote an efficient growth at early stages in salt affected soils, leading to healthy vegetative growth that protects crop yield. Saltol major QTL confers capacity to young rice plants growing under salt condition by maintaining a low Na+/K+ molar ratio in the shoots.ResultsMarker-assisted backcross (MABC) procedure was adopted to transfer Saltol locus conferring salt tolerance at seedling stage from donor indica IR64-Saltol to two temperate japonica varieties, Vialone Nano and Onice. Forward and background selections were accomplished using polymorphic KASP markers and a final evaluation of genetic background recovery of the selected lines was conducted using 15,580 SNP markers obtained from Genotyping by Sequencing. Three MABC generations followed by two selfing, allowed the identification of introgression lines achieving a recovery of the recurrent parent (RP) genome up to 100% (based on KASP markers) or 98.97% (based on GBS). Lines with highest RP genome recovery (RPGR) were evaluated for agronomical-phenological traits in field under non-salinized conditions. VN1, VN4, O1 lines were selected considering the agronomic evaluations and the RPGR% results as the most interesting for commercial exploitation. A physiological characterization was conducted by evaluating salt tolerance under hydroponic conditions. The selected lines showed lower standard evaluation system (SES) scores: 62% of VN4, and 57% of O1 plants reaching SES 3 or SES 5 respectively, while only 40% of Vialone Nano and 25% of Onice plants recorded scores from 3 to 5, respectively. VN1, VN4 and O1 showed a reduced electrolyte leakage values, and limited negative effects on relative water content and shoot/root fresh weight ratio.ConclusionThe Saltol locus was successfully transferred to two elite varieties by MABC in a time frame of three years. The application of background selection until BC3F3 allowed the selection of lines with a RPGR up to 98.97%. Physiological evaluations for the selected lines indicate an improved salinity tolerance at seedling stage. The results supported the effectiveness of the Saltol locus in temperate japonica and of the MABC procedure for recovering of the RP favorable traits.

Can the reductive dissolution of ferric iron in paddy soils compensate phosphorus limitation of rice plants and microorganisms?

Biogeochemical cycles of phosphorus (P) and iron (Fe) are tightly interlinked, especially in highly weathered acidic subtropical and tropical soils rich in iron (oxyhydr)oxides (Fe(III)). The quantitative contribution of the reductive dissolution of Fe(III)-bound inorganic P (Pi) (Fe–P) in low-redox paddy soils may cover the demands of rice plants (Oryza sativa L.) and microorganisms. We hypothesized that microbially-driven Fe(III) reduction and dissolution can cover the P demand of microorganisms but not of the young rice plants when the plants’ P demand is high but their root systems are not sufficiently developed. We grew pre-germinated rice plants for 33 days in flooded rhizoboxes filled with a paddy soil of low P availability. 32P-labeled ferrihydrite (30.8 mg kg−1) was supplied either (1) in polyamide mesh bags (30 μm mesh size) to prevent roots from directly mobilizing Fe–P (pellets-in-mesh bag treatment), or (2) in the same pellet form but without a mesh bag to enable roots accessing the Fe–P (pellets-no-mesh bag treatment).Without mesh bags, Pi was more available leading to increases in microbial biomass carbon (MBC) by 18–55% and nitrogen (MBN) by 4–108% in rooted soil as compared to Pi pellets not directly available to roots. The maximum enzyme activities (Vmax) of phosphomonoesterase and β-glucosidase followed this pattern. During rice root growth, day 10 to day 33, MBC and microbial biomass phosphorus (MBP) contents in both rooted and bottom bulk (15–18 cm) soil gradually decreased by 28–56% and 47–49%, respectively. In contrast to our hypothesis, the contribution of Fe–P to MBP remarkably decreased from 4.5% to almost zero from 10 to 33 days after rice transplantation, while Fe–P compensated up to 16% of the plant P uptake at 33 days after rice transplantation, thus outcompeting microorganisms. Although both plants and microorganisms obtained Pi released by Fe(III) reductive dissolution, this mechanism was not sufficient for the demand of either organism groups.

Predation by the carrion crow Corvus corone (Passeriformes: Corvidae) on the apple snail Pomacea canaliculata (Architaenioglossa: Ampullariidae) in different locations in Japan

Alien species are exposed to novel species interactions in invaded ecosystems, and predators are important components of biotic resistance against aliens. The apple snail Pomacea canaliculata (Lamarck) (Architaenioglossa: Ampullariidae) was introduced to many countries, and causes severe problems including damage to young rice plants. Biotic resistance against the apple snail is generally weak in modernized rice fields, but carrion crows Corvus corone Linnaeus (Passeriformes: Corvidae) are observed to prey on apple snails. Thus, we investigated predation on the apple snails by the crows in three locations in Japan, and compared predation pressure, prey size, and predation methods among locations and different months/years in Ehime Prefecture. Carrion crows preyed on relatively small snails among subadults and adults in paddy fields. Predation rate within 1.2 m from the levee was as high as 87.1% in Ehime, 14.1% in Fukuoka (both in 2 days), and 1.1% in Nara (in 4 days). Thus, predation by crows is considered to be effective in reducing the density of snails in paddy fields in Ehime and possibly in Fukuoka. However, the period of predation and the intensity of predation varied from year to year in Ehime over a 3-year study period.

Comparative study of salicylic acid contents in young wheat and rice plants and their anticancer activities in HepG2 and Caco-2 cells

Some recent results reported that aspirin (acetylsalicylic acid) had a positive effect on the treatment of certain types of cancer. However, the results cannot be generalized and it is not always clear whether it is a direct anticancer effect or a general health effect. Since plants produce different amounts of salicylic acid, we have sought a relationship between the salicylic acid content of some plant extracts and their anticancer activity. Growing of wheat and rice plants were carried out under controlled conditions. The salicylic acid content was determined by high-performance liquid chromatography. The viability and cell cycle assays were performed on HepG2 and Caco-2 cell lines. Despite the high content of salicylic acid, the extracts from rice plants did not show significant anticancer activity. In spite of the low salicylic acid content, the positive effect of wheat germ was confirmed in both tests. There is no direct relationship between the salicylic acid content of the plant extracts and their anticancer activity. However, it has been proven that young wheat germ is more effective than mature leaf.

ESTIMATION OF THE COLLECTION RICE ACCORDING TO RESISTANCE TO CEREAL APHID

Ordinary cereal aphid causes great damage to rice plants in the Rostov region and the Krasnodar Territory. Its harmful effects can be limited with the help of plant genetic resistance. The study of resistance of collection rice material to aphids has only recently begun. Therefore, there is a need to analyze the hereditary polymorphism of rice samples according to resistance to ordinary cereal aphid. 494 collection samples of the laboratory for rice breeding and seed production at the FSBSI Agricultural Research Center “Donskoy” were the material for the research. In laboratory VIR conditions, young rice plants were infected by the Krasnodar ordinary aphid, after which there was performed a phenotypic damage assessment using a scale from 0 (no damage) to 10 (plant death). Due to the study it was found that most of the samples were unstable or weakly stable. There were identified 15.1% of relatively stable forms, their damage was 1–4 points. Most samples showed a wide range of variation in plant damage from 1 to 10 points. Only 41 samples out of the 494 studied ones were homogeneous, all plants of which received the same point (1, 2, 3, 4, 8, or 10); the rest samples were heterogeneous. 167 samples received two variants of points, 226 samples received three, 60 samples received four. The rice samples ‘Kandidat’, ‘Komandor’, ‘PF-4186’, ‘Norin 31’, ‘Priozerny 61’, ‘Don 7243’, ‘Don 4237’ can be recommended as sources of resistance to ordinary cereal aphid to develop new rice varieties.

Deep RNAseq indicates protective mechanisms of cold-tolerant indica rice plants during early vegetative stage.

Cold-tolerance in rice may be related to increased cellulose deposition in the cell wall, membrane fatty acids unsaturation and differential expression of several newly identified genes. Low temperature exposure during early vegetative stages limits rice plant's growth and development. Most genes previously related to cold tolerance in rice are from the japonica subspecies. To help clarify the mechanisms that regulate cold tolerance in young indica rice plants, comparative transcriptome analysis of 6h cold-treated (10°C) leaves from two genotypes, cold-tolerant (CT) and cold-sensitive (CS), was performed. Differentially expressed genes were identified: 831 and 357 sequences more expressed in the tolerant and in the sensitive genotype, respectively. The genes with higher expression in the CT genotype were used in systems biology analyses to identify protein-protein interaction (PPI) networks and nodes (proteins) that are hubs and bottlenecks in the PPI. From the genes more expressed in the tolerant plants, 60% were reported as affected by cold in previous transcriptome experiments and 27% are located within QTLs related to cold tolerance during the vegetative stage. Novel cold-responsive genes were identified. Quantitative RT-PCR confirmed the high-quality of RNAseq libraries. Several genes related to cell wall assembly or reinforcement are cold-induced or constitutively highly expressed in the tolerant genotype. Cold-tolerant plants have increased cellulose deposition under cold. Genes related to lipid metabolism are more expressed in the tolerant genotype, which has higher membrane fatty acids unsaturation, with increasing levels of linoleic acid under cold. The CT genotype seems to have higher photosynthetic efficiency and antioxidant capacity, as well as more effective ethylene, Ca2+ and hormone signaling than the CS. These genes could be useful in future biotechnological approaches aiming to increase cold tolerance in rice.

Is there hope for sustainable management of golden apple snails, a major invasive pest in irrigated rice?

The golden apple snail or GAS (Pomacea canaliculata) is an important invasive pest in irrigated rice that feeds on young rice plants. In many countries in SE-Asia, governments have recently decreased their support of training courses for snail management, because farmers are now considered to know how to effectively manage this pest. Although a great number of sustainable control methods is recommended which do not involve the use of pesticides, it is uncertain whether these are taken up by farmers. Probably, the easiest way to control GAS, is the application of synthetic ‘instant kill’ molluscicides, which can have detrimental effects on the environment, non-target species, and health. The aim of this study was to develop ideas for solutions on how to achieve a sustainable management of GAS without or at least a decreased use of molluscicides. In a large-scale approach, we conducted interviews with rice farmers in seven regions across Vietnam and the Philippines, assessing the participation in training courses, knowledge on snail ecology, the methods of controlling and the utilization of the snail, and the farmers’ suggestions on how to improve pest snail control. Only 23% of the farmers had previously received training in GAS management. We found that training neither had positive nor negative effects on the number of sustainable methods applied, molluscicide avoidance, concern about using molluscicides, or on the farmers’ knowledge about GAS. As much as 74% of the respondents applied molluscicides. Contrary to recommendations, farmers applied only few sustainable control methods. All farmers had clear knowledge gaps about GAS, especially in species identification, which can even further the ongoing decline of native mollusks in rice landscapes. We conclude that the decision to phase out information campaigns has been taken to rash, and that trainings in our study regions carried through previously had limited success, and thus need revision. To decrease molluscicide use, and to promote sustainable management on the large scale, we synthesized our results, and we suggest that information for farmers might be provided through media often accessed, such as TV, radio or the internet (e.g. by entertainment − education). We further discuss the potential of community cooperation to achieve sustainability. As there are distinct limitations to these approaches, we have developed the concept of local GAS management and utilization companies (GASMUC) which could take over sustainable control and utilization of GAS, and native mollusk conservation for an entire community.

English

Environmentally friendly technologies, such as the use of bacteria (e.g. Bacillus spp.) to control fungal diseases of rice (Oryza sativa L.), represent a promising alternative for the sustainability of agricultural ecosystems. The present work aimed to isolate, identify, and evaluate (in vitro) various Bacillus spp. from the rice phylloplane for their potential to control the rice fungus Magnaporthe oryzae. Samples were taken from the phylloplane of healthy young rice plants growing in commercial fields in ten municipalities of Maranhao (Brazil), and Bacillus spp. were subsequently isolated and molecularly identified. Both experiments utilized a randomized design, and data were submitted to analysis of variance as well as means comparison by the Tukey test. Twelve bacterial isolates were obtained and identified. Using a control isolate (B25), four in vitro M. oryzae-inhibition methods were compared, with the ‘circle’ method ultimately providing the highest mycelium growth inhibition. The most promising experimental isolates for biological control were then identified as B. methylotrophicus isolates B41, B31, and B22, which achieved 90.41, 69.47, and 67.55% inhibition, respectively. This study demonstrates the potential of Maranhao Bacillus spp. isolates for use as biological fungal-control agents. Key words: biological control, pathogen, rice.

The red swamp crayfish Procambarus clarkii in Europe: Impacts on aquatic ecosystems and human well-being

Procambarus clarkii is currently recorded from 16 European territories. On top of being a vector of crayfish plague, which is responsible for large-scale disappearance of native crayfish species, it causes severe impacts on diverse aquatic ecosystems, due to its rapid life cycle, dispersal capacities, burrowing activities and high population densities. The species has even been recently discovered in caves. This invasive crayfish is a polytrophic keystone species that can exert multiple pressures on ecosystems. Most studies deal with the decline of macrophytes and predation on several species (amphibians, molluscs, and macroinvertebrates), highlighting how this biodiversity loss leads to unbalanced food chains. At a management level, the species is considered as (a) a devastating digger of the water drainage systems in southern and central Europe, (b) an agricultural pest in Mediterranean territories, consuming, for example, young rice plants, and (c) a threat to the restoration of water bodies in north-western Europe. Indeed, among the high-risk species, P. clarkii consistently attained the highest risk rating. Its negative impacts on ecosystem services were evaluated. These may include the loss of provisioning services such as reductions in valued edible native species of regulatory and supporting services, inducing wide changes in ecological communities and increased costs to agriculture and water management. Finally, cultural services may be lost. The species fulfils the criteria of the Article 4(3) of Regulation (EU) No 1143/2014 of the European Parliament (species widely spread in Europe and impossible to eradicate in a cost-effective manner) and has been included in the “Union List”. Particularly, awareness of the ornamental trade through the internet must be reinforced within the European Community and import and trade regulations should be imposed to reduce the availability of this high-risk species.

Preliminary Study on the Radar Vegetation Index (RVI) Application to Actual Paddy Fields by ALOS/PALSAR Full-polarimetry SAR Data

Abstract. Kim and van Zyl (2001) proposed a kind of radar vegetation index (RVI). RVI = 4*min(λ1, λ2, λ3) / (λ1 + λ2 + λ3) They modified the equation as follows. (2009) RVI = 8 * σ0hv / (σ0hh + σ0vv +σ0hv ) by L-band full-polarimetric SAR data. They applied it into rice crop and soybean. (Y.Kim, T.Jackson et al., 2012) They compared RVI for L-, C- and X-bands to crop growth data, LAI and NDVI. They found L-band RVI was well correlated with Vegetation Water Content, LAI and NDVI. But the field data were collected by the multifrequency polarimetric scatterometer. The platform height was 4.16 meters from the ground. The author tried to apply the method to actual paddy fields near Tsukuba science city in Japan using ALOS/PALSAR, full-polarimetry L-band SAR data. The staple crop in Eastern Asia is rice and paddy fields are dominant land use. A rice-planting machine comes into wide use in this areas. The young rice plants were bedded regularly ridged line in the paddy fields by the machine. The space between two ridges of rice plants is about 30 cm and the wave length of PALSAR sensor is about 23 cm. Hence the Bragg scattering will appear depending upon the direction of the ridges of paddy fields. Once the Bragg scattering occurs, the backscattering values from the pixels should be very high comparing the surrounding region. Therefore the radar vegetation index (RVI) would be saturated. The RVI did not follow the increasing of vegetation anymore. Japan has launched ALOS-2 satellite and it has PALSAR-2, L-band SAR. Therefore RVI application product by PALSAR-2 will be watched with deep interest.

O2 dynamics in the rhizosphere of young rice plants (Oryza sativa L.) as studied by planar optodes.

Background and aimsRadial O2 loss (ROL) strongly affect the O2 availability in the rhizosphere of rice. The ROL create an oxic zone around the roots, protecting the plant from toxic reduced chemical species and regulates the redox chemistry in the soil. This study investigates the spatio-temporal variability in O2 dynamics in the rice rhizosphere.MethodApplying high-resolution planar optode imaging, we investigated the O2 dynamics of plants grown in water saturated soil, as a function of ambient O2 level, irradiance and plant development, for submerged and emerged plants.ResultsO2 leakage was heterogeneously distributed with zones of intense leakage around roots tips and young developing roots. While the majority of roots exhibited high ROL others remained surrounded by anoxic soil. ROL was affected by ambient O2 levels around the plant, as well as irradiance, indicating a direct influence of photosynthetic activity on ROL. At onset of darkness, oxia in the rhizosphere was drastically reduced, but subsequently oxia gradually increased, presumably as root and/or soil respiration declined.ConclusionThe study demonstrates a high spatio-temporal heterogeneity in rhizosphere O2 dynamics and difference in ROL between different parts of the rhizosphere. The work documents that spatio-temporal measurements are important to fully understand and account for the highly variable O2 dynamics and associated biogeochemical processes and pathways in the rice rhizosphere.

Southern Cutgrass,Leersia hexandraSwartz1, Allows Rice Water Weevils2to Avoid Summer Diapause

Abstract. The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is an important insect pest of rice, Oryza sativa L., in the United States and Asian countries. Previous reports indicated that most first-generation adults (summer weevils) entered reproductive diapause with only a few of the population reproducing to form a second generation. However, the environmental factors responsible for diapause induction have not been thoroughly studied. Southern cutgrass, Leersia hexandra Swartz, is a widely distributed perennial grass in the rice ecosystem of regions where rice water weevil occurs. After feeding on cutgrass for 30 days, summer weevils initiated oviposition rapidly after being transferred to young rice plants, and the percentage of ovipositing weevils was 80–100% after 2 weeks. Summer weevils feeding on southern cutgrass did not enter diapause but developed into a reproductive state, suggesting the grass might allow rice water weevils to avoid summer diapause. Such “d...

Oviposition and larval development of a stem borer, Eoreuma loftini, on rice and non‐crop grass hosts

AbstractA greenhouse study compared oviposition preference and larval development duration of a stem borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), on rice, Oryza sativa L. cv Cocodrie (Poaceae), and four primary non‐crop hosts of Texas Gulf Coast rice agroecosystems. Rice and two perennials, johnsongrass, Sorghum halepense (L.) Pers., and vaseygrass, Paspalum urvillei Steud. (both Poaceae), were assessed at three phenological stages. Two spring annuals, brome, Bromus spec., and ryegrass, Lolium spec. (both Poaceae), were assessed at two phenological stages. Phenological stages represented the diversity of plant development stages E. loftini may encounter. Plant fresh biomass, dry biomass, and sum of tiller heights were used as measures of plant availability. Accounting for plant availability, rice was preferred over non‐crop hosts, and intermediate and older plants were preferred over young plants. Johnsongrass and vaseygrass were 32–60% as preferred as rice when considering the most preferred phenological stages of each host. Brome and ryegrass received few or no eggs, respectively. Eoreuma loftini larval development (in degree days above developmental threshold temperatures) was fastest on rice and slowest on johnsongrass and vaseygrass. Development duration was only retarded by plant stage on young rice plants. Foliar and stem free amino acid concentrations were determined to help provide insights on the mechanisms of E. loftini oviposition preference and developmental performance.

Bioinformatic Analysis of Epigenetic and MicroRNA Mediated Regulation of Drought Responsive Genes in Rice

Drought stress response is a complex trait regulated at multiple levels. Changes in the epigenetic and miRNA regulatory landscape can dramatically alter the outcome of a stress response. However, little is known about the scope and extent of these regulatory factors on drought related cellular processes and functions. To this end, we selected a list of 5468 drought responsive genes (DRGs) of rice identified in multiple microarray studies and mapped the DNA methylation regions found in a genome wide methylcytosine immunoprecipitation and sequencing (mCIP-Seq) study to their genic and promoter regions, identified the chromatin remodeling genes and the genes that are targets of miRNAs. We found statistically significant enrichment of DNA methylation reads and miRNA target sequences in DRGs compared to a random set of genes. About 75% of the DRGs annotated to be involved in chromatin remodeling were downregulated. We found one-third of the DRGs are targeted by two-thirds of all known/predicted miRNAs in rice which include many transcription factors targeted by more than five miRNAs. Clustering analysis of the DRGs with epigenetic and miRNA features revealed, upregulated cluster was enriched in drought tolerance mechanisms while the downregulated cluster was enriched in drought resistance mechanisms evident by their unique gene ontologies (GOs), protein-protein interactions (PPIs), specific transcription factors, protein domains and metabolic pathways. Further, we analyzed the proteome of two weeks old young rice plants treated with a global demethylating agent, 5-azacytidine (5-azaC), subjected to drought stress and identified 56 protein spots that are differentially expressed. Out of the 56 spots, 35 were differently expressed in the sample with both demethylation and drought stress treatments and 28 (50%) were part of DRGs considered in the bioinformatic analysis.

Efficacy of essential oils from bark and leaf of Cinnamomum zeylanicum on root knot nematode, Meloidogyne graminicola in rice seedlings and young rice plants

The present study was conducted to evaluate the efficacy of essential oils from leaf and bark of cinnamon, Cinnamomum zeylanicum in controlling Meloidogyne graminicola and their effects on rice seedlings and young rice plants. This study was done; to determine the LC50 of essential oils of the extracts of cinnamon leaf and bark to kill 50% of second stage juveniles (J2) of Meloidogyne graminicola in rice root galls; to determine the efficacy of essential oils of cinnamon; in controlling J2 in rice seedlings and young rice plants; and on the growth of rice plants.Cinnamon bark oil sample used in the current study contained about 72% cinnamaldehyde and the leaf sample contained about 86% eugenol. LC50 for cinnamon leaf oil and cinnamon bark oil for killing 50% of juveniles of M. graminicola in rice root galls after three days of the treatment was 0.326 ppm and 0.454 ppm respectively. Number of galls in the root system of nematode infested rice seedlings was significantly reduced when they were treated with 0.9 ppm of cinnamon leaf oil and bark oil compared to untreated controls. However, the nematicidal activity between the cinnamon leaf oil and bark oil was not significantly different. The root gall index of infested young rice plants was significantly lowered when they were treated with either cinnamon leaf oil or bark oil compared to untreated controls. It was revealed that the mean plant height and the mean number of roots of essential oil treated plants were positively correlated with the number of root galls whereas, the number of dead plants and the mean percentage chlorosis were negatively correlated. Nevertheless, the mean root length did not show any significant correlation with number of root galls. This study concludes that essential oils of cinnamon leaf which contained 86% eugenol and bark which contained 72% cinnamaldehyde are similarly effective in suppression of M. graminicola in rice seedlings and young rice plants. According to the rates of application of essential oils of cinnamon leaf and bark, none of them have significant negative effect on the plant growth. Hence, they can be used as an alternative nematicide against the rice root knot nematode, M. graminicola in early stage of rice plants.Keywords: Cinnamomum zeylanicum; essential oils; Meloidogyne graminicola;Oryza sativaDOI: http://dx.doi.org/10.4038/josuk.v6i0.4220J Sci.Univ.Kelaniya 6 (2011) : 45-54

Effects of rice hispa damage on grain yield

Rice hispa [Dicladispa armigera (Olivier) (Chrysomelidae: Coleoptera)] is a major rice pest in Bangladesh. Adults feed on the green tissue of the leaf blade externally and grubs are leaf miners. Rice hispa (RH) prefers young rice plants, but, in their absence, it also attacks maturing plants. Some reports estimate time- and space-specific damage ranging from 14% to 62% yield losses from RH (Alam 1977, Karim 1987, Islam 1989, Chatterjee and Bera 1990, Nath and Dutta 1997). However, the relationship between damage level and grain loss is not clear. Therefore, we carried out several experiments at BRRI under irrigated conditions in the 1999 aus (summer rice) and transplant aman (monsoon rice) seasons.

Study on approaches to integrated control of <i>Meloidogyne graminicola</i> in rice

This study presents the results obtained from the studies carried out to find out the response of Meloidogyne graminicola to different rice varieties and to different soil amendments when applied with and without NPK fertilizer in young rice plants. The use of soil amendments such as poultry manure and cow dung significantly reduced the nematode population, the total percentage of yellow leaves and dead leaves and significantly increased the plant growth. Two varieties namely, Bg 300 and Bg 352 were found to be immune for M. graminicola not allowing the nematodes to penetrate the roots. The varieties Bg 350, Bg 356, Bg 357 and Bg 360 were categorized as resistant. These varieties allowed the nematodes to penetrate the roots, but the development and the reproduction of the nematodes were not permitted. The varieties Bg 11, Bg 351, and Bg 358 were found to be susceptible for the nematode, M. graminicola of which Bg 351 is highly susceptible host with high rate of reproduction while Bg 358 and Bg 11 are less susceptible with low rate of reproduction of the nematode. This study also revealed that the young plants of susceptible varieties were unable to compensate the nematode damage under unfertilized conditions. Keywords: root-knot nematode; Meloidogyne graminicola; Oryza sativa; management DOI: 10.4038/josuk.v3i0.2736J. Sci. Univ. Kelaniya 3 (2007) : 29-46

Effects of Arsenic Compound Amendment on Arsenic Speciation in Rice Grain

Rice consumption is a major source of arsenic for Asian populations. Arsenic is present in rice grain both as inorganic arsenic and as dimethylarsinic acid (DMA). It is unclear whether DMA in rice is taken up from the soil or synthesized in planta. We investigated the effect of DMA, methylarsonic acid (MMA) and arsenite amendment on arsenic speciation in rice grain grown in soil and in solution culture. We also investigated the methylation of arsenic in solution culture under suppression of bacterial activity. When rice was grown under flooded conditions after the heading stage, DMA amendment to the soil resulted in higher DMA concentration in brown rice and rice straw. In the solution culture, not only DMA amendment but also MMA or arsenite amendment increased the DMA concentration in brown rice and rice straw. DMA was detected in the solution amended by MMA or arsenite with young rice plants. When the solution included the antibacterial agent chloramphenicol, DMA concentration in the solution decreased dramatically. When only the soil was incubated with MMA or arsenite, only a slight amount of DMA was detected in the soil. These results suggest that rice rhizosphere associated bacteria would be involved in the formation of DMA in brown rice.

Possible chemical forms of cadmium and varietal differences in cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.)

In rice (Oryza sativa L.), cadmium (Cd), a toxic heavy metal, is found in phloem sap and eventually accumulates in the grains. To further characterize phloem-transported Cd, the chemical forms of Cd and other metals and varietal differences in phloem sap Cd concentrations were investigated in young rice plants. The size-exclusion chromatography elution times for Cd-bound compounds indicated that phloem Cd in cv. Nipponbare exists mainly as an approximately 13 kDa complex. Protease digestion of rice phloem sap reduced the bound Cd content from 92 to 19%. The remaining Cd may bind to low-molecule SH compounds. An experiment examining in vitro addition of Cd2+ to phloem sap from non-Cd-treated plants revealed that rice phloem sap constitutively contains Cd chelators. The major Cd peak is distinguishable from those of Fe, Zn, Cu, Mn, Ni and Co, which probably bind to nicotianamine, 2′-deoxymugineic acid, citrate and histidine. The Cd concentrations of the phloem saps in three varieties (Milyang 23, LAC 23 and Koshihikari) grown under the same soil conditions were correlated with their grain Cd concentrations, which had been reported previously, whereas the concentrations of the xylem saps were not. In conclusion, rice phloem sap Cd differs from other metals as it may bind to a novel approximately 13 kDa protein and SH compounds, and the concentration of Cd in rice phloem sap may be a key determinant of its grain content.