Rice Agroecosystems Research Articles

Enchytraeid Community (Annelida, Clitellata, Enchytraeidae) and Its Dependence on Edaphic Conditions in Rice Agroecosystems in Russia

Communities of soil animals (meso- and macrofauna) in rice paddies tend to be fragmented, and have extremely low abundance. Nevertheless, some groups, such as enchytraeids, may become dominant in flooded conditions, as shown in tropical rice agroecosystems. However, the fauna and functional composition of enchytraeids (Annelida, Clitellata, Enchytraeidae) under such conditions have not yet been studied at temperate latitudes. We have investigated enchytraeid communities and the ratio of their functional groups in the main rice-growing regions of Russia: Krasnodar krai, Primorsky krai, and the Republic of Kalmykia. Samples were taken in summer–early autumn of 2016 in four habitat types: flooded rice paddies, drained paddies occupied by upland crops, adjacent bunds, and undisturbed grasslands (control). Generalized linear model analysis showed that the factor habitat type and its interaction with the factor region had a significant effect on the total enchytraeid abundance, with the factor region alone having no such effect. Their abundance was the highest in the control habitats and bunds (mean and standard error for all the regions: 3278 ± 1131 and 3255 ± 762 ind./m2, respectively), being insignificantly lower in the paddies under upland crops (1282 ± 850 ind./m2) and decreasing to a minimum of 415 ± 323 ind./m2 in the flooded paddies. A comparison between the last two habitat types shows that enchytraeids can relatively quickly restore their abundance in the rice paddies after draining. Principal component analysis revealed a positive correlation between the density of enchytraeids belonging to basophilous ecological group and bioavailable phosphorus content. The correlation between the abundance of acidophilous enchytraeids and this parameter was negative. Thus, the abundance ratio of enchytraeid ecological groups could be used as an informative indicator of the concentrations of nutrient elements and depends on physical and chemical characteristics of paddy soils. Despite the low abundance of enchytraeids in these soils, they can be an important component of the detrital food webs during periods of paddy-drainage in intensive rice agroecosystems at temperate latitudes.

Soil nematode communities in temperate rice-growing systems

We compared soil nematode abundance, genus richness and feeding groups composition between four different biotope types (flooded rice paddies, upland crops planted one year after flooded rice, rice paddy bunds, and seminatural control grasslands) in temperate rice-growing systems in Russia. Our survey covered three major rice producing regions: Krasnodarsky Krai, Republic of Kalmykia in European Russia and Primorsky Krai in the Russian Far East, which have not been studied with this respect so far. Genus richness, C–P, maturiry (MI), Enrichment (EI) and Structure (SI) indices, and the total abundance of nematodes were strongly region-specific. The most of the highest values (18 genera, C–P = 2.6 ± 0.1, abundance 208.6 ± 10.1 ind. g−1 soil dwt) were found in Primorsky Krai and the lowest (6 genera, C–P = 2.1 ± 0.1, EI = 22.0 ± 1.3; SI = 55.4 ± 1.2; abundance 64.5 ± 3.3 ind. g−1 soil dwt) in Kalmykia. The highest values of enrichment and structure indices were discovered in Krasnodar Krai (EI = 53.1 ± 6.0 and SI = 82.9 ± 1.4 respectively). The abundance of the nematode feeding groups was in opposite rather driven by biotope type than the region. In the flooded rice paddies, the abundance of predatory nematodes was significantly lower than in control grasslands (2.1 ± 1.0 and 9.5 ± 3.0 ind. g−1 soil dwt, respectively). Alternatively, the abundance of fungivores increased in flooded rice paddies. We conclude that rice growing considerably alters the relative abundance of nematode feeding groups and consequently their role in detrital food webs due to alteration of the overall structure of a micro food web and specifically negative effects of flooding on predatory nematodes. Bunds act as important reservoirs of soil nematode diversity in the rice agroecosystems.

Conservation reliance of a threatened snake on rice agriculture

Conservation-reliant species require perpetual management by humans to persist. But do species that persist largely in human-dominated landscapes actually require conditions maintained by humans? Because most extant populations of giant gartersnakes (Thamnophis gigas) inhabit the highly modified rice agricultural regions of the Sacramento Valley, we sought to evaluate whether giant gartersnakes are indeed a conservation-reliant species dependent on maintenance of rice agriculture and its infrastructure for their continued existence. Specifically, we examined the extent to which giant gartersnakes use rice fields themselves, and whether survival of adult giant gartersnakes was influenced by the amount of rice grown near their home ranges and daily movements. We found that although giant gartersnakes only use rice fields minimally and then only between mid-June and early September, their survival was lower when less rice agriculture was available near the areas they inhabited. Survival was particularly low in early spring, when giant gartersnakes emerge from brumation but rice fields are not yet flooded. The incongruity between the phenology of rice growing and giant gartersnake foraging requirements suggests that although giant gartersnakes are reliant on the rice agroecosystem, rice agriculture is likely suboptimal habitat for giant gartersnakes. Giant gartersnakes’ reliance on the rice agroecosystem challenges the notion of preservation-based conservation, but provides opportunities for win-win scenarios benefitting both rice farmers and giant gartersnakes. Our study highlights that in addition to land use, the timing of land management might be crucial for conservation-reliant species.

Развитие Apus concniformis Sh. в рисовых посевах Ташкентской области

The results of studies on the study of Apus concniformis Sh. in rice crops of the Tashkent region. This is the main pest that lives in rice agroecosystem. Apus concniformis Sh. inflicts great harm by destroying young seedlings of rice. In the variant with a crustacean density per 1 m2 — 10, 15 and 20 specimens accordingly, death of sprouts was observed — 10.3, 18.4, 23.8 and 30.8. In areas where the density of the crustacean per 1 m2 was from 5–15 specimens. The crop yield decreased by 10.3–30.8% or 7.1–21.2 centner per hectare.

A Pathovar of Xanthomonas oryzae Infecting Wild Grasses Provides Insight Into the Evolution of Pathogenicity in Rice Agroecosystems.

Xanthomonas oryzae (Xo) are globally important rice pathogens. Virulent lineages from Africa and Asia and less virulent strains from the United States have been well characterized. Xanthomonas campestris pv. leersiae (Xcl), first described in 1957, causes bacterial streak on the perennial grass, Leersia hexandra, and is a close relative of Xo. L. hexandra, a member of the Poaceae, is highly similar to rice phylogenetically, is globally ubiquitous around rice paddies, and is a reservoir of pathogenic Xo. We used long read, single molecule real time (SMRT) genome sequences of five strains of Xcl from Burkina Faso, China, Mali, and Uganda to determine the genetic relatedness of this organism with Xo. Novel transcription activator-like effectors (TALEs) were discovered in all five strains of Xcl. Predicted TALE target sequences were identified in the Leersia perrieri genome and compared to rice susceptibility gene homologs. Pathogenicity screening on L. hexandra and diverse rice cultivars confirmed that Xcl are able to colonize rice and produce weak but not progressive symptoms. Overall, based on average nucleotide identity (ANI), type III (T3) effector repertoires, and disease phenotype, we propose to rename Xcl to X. oryzae pv. leersiae (Xol) and use this parallel system to improve understanding of the evolution of bacterial pathogenicity in rice agroecosystems.

An Integrated Approach to Assessing the Soil Quality and Nutritional Status of Large and Long-Term Cultivated Rice Agro-Ecosystems

The aim of this study is to develop an integrated approach to soil quality and fertility assessment in high-yielding rice agro-ecosystems threatened due to overexploitation of soil resources by intensive agriculture. The proposed approach is implemented considering representative pilot fields allocated throughout a study area based on the assumption that soils of similar general properties present a similar nutritional status due to common long-term management practices. The analysis includes (a) object-based image analysis for land zonation, (b) hot-spot analysis for sampling scheme evaluation, (c) setting of critical thresholds in soil parameters for detecting nutrient deficiencies and soil quality problems, and (d) Redundancy Analysis, TITAN analysis, and multiple regression for identifying individual or combined effects of general soil properties (e.g., organic matter, soil texture, pH, salinity) or non-soil parameters (e.g., topographic parameters) on soil nutrients. The approach was applied using as a case study the large rice agro-ecosystem of Thessaloniki plain in Greece considering some site specificities (e.g., high rice yields, calcareous soils) when setting the critical thresholds in soil parameters. The results showed that (a) 62.5% of the pilot fields’ coverage has a simultaneous deficiency in Zn, Mn, and B, (b) organic matter (OM) was the most significant descriptor of nutrients’ variance, and its cold spots (clustered regions of low OM values) showed important overlapping with the cold spots of K, Mg, Zn, Mn, Cu, and B, (c) a higher rate of availability increase in P, K, Mg, Mn, Zn, Fe, Cu, and B was observed when the OM ranged between 2 and 3%, and (d) the multiple regression models that assess K and P concentrations based on general soil properties showed an adequate performance, allowing their use for general assessment of their soil concentrations in the fields of the whole agro-ecosystem.

Ecosystem hero and villain: Native frog consumes rice pests, while the invasive cane toad feasts on beneficial arthropods

Lowland irrigated rice fields serve the dual purpose of providing an essential food crop to the world’s most populous regions and functioning as man-made wetlands that harbor a diversity of organisms. Amphibians occupy rice fields throughout Asia and South America, but little is known about their functional role in the rice ecosystem. We conducted field surveys in Los Baños, Philippines over two separate rainy seasons (2015 and 2017) to determine whether native Luzon wart frogs and invasive cane toads consume rice pests, and if so, which species was more effective in doing so. We also examined diet composition to test whether the two species compete for food resources in rice fields. We found that despite smaller body sizes, the Luzon wart frog consumed the same total mass of prey as the cane toad (although it consumed fewer total prey items), and that pests made up the largest proportion (54.1%) of its total diet. In contrast, the majority (89.4%) of the cane toad’s diet consisted of beneficial arthropod predators. Taxonomic analyses of diet composition and breadth revealed that the diet of Luzon wart frog was distinct from that of the cane toad, although there was overlap, and that both species consumed diverse array of prey. Taken together, these data suggest adult Luzon wart frogs may provide effective pest control services, and that they may not be in direct competition over food resources with adult cane toads in rice fields. We also present the first evidence suggesting that cane toads may indirectly damage rice crops by consuming beneficial predators integral to the function of lowland rice ecosystems. We suggest that rice agro-ecosystems should be managed to promote species such as the native Luzon wart frog, and to reduce populations of the introduced cane toad in order to safeguard native biodiversity while simultaneously improving yields and reducing insecticide input.

Assessment of crop growth, soil properties and crop yield in an upland acidic soil with inorganic fertilizer blended with organic amendments in summer rice cropping seasons

PurposeIntensification of rice cultivation to meet the growing demand has imbalanced the nitrogen level in soil. Amendments of inorganic fertilizers increase yield, but at the same time affects the environment. Hence, different amendments are to be investigated which acting sustainably on soil and the environment upholds yield gains.MethodsA study was carried out on acidic sandy loam soil in the irrigated summer seasons of the years of 2015–2016 and 2016–2017 to examine the effects of various amendments on rice growth, soil health and yield. The applied amendments were inorganic fertilizer blended with crop residues, farm yard manure and compost made of daily household green wastes.ResultsThe highest yield of 53.33 ± 2.09 Q/ha was recorded with application of inorganic fertilizer blended with compost and the lowest yield of 32.71 ± 3.09 Q/ha without amendment. Strong positive correlations were found between soil moisture and volumetric water content (0.982 at p < 0.001), manganese and copper (0.900 at p < 0.001), whereas available phosphorus and manganese showed a strong negative correlation (− 0.901 at p < 0.001). Performing stepwise regression analysis, yield was found affected mostly by soil moisture and total carbon out of evaluated 17 soil traits.ConclusionThe inorganic fertilization blended with the compost increased rice yield by 13.61% over inorganic fertilizer but a higher yield associated with compost demoted total nitrogen contents in soil, leading to lower soil nitrogen fertility and providing a negative feedback to sustainable agriculture. More research is required on compost development and application in different rice agroecosystems.

Life cycle assessment of rice production systems in different paddy field size levels in north of Iran

Life cycle assessment (LCA) had proven to be an appropriate assessment tool for analysis of agro-ecosystems by identifying, quantifying, and evaluating the resources consumed and released into the environment. In order to assess the relevant environmental impacts of rice agro-ecosystems due to a specific process, using LCA method, two factors concerned with resource utilization and contaminant emissions were calculated in north of Iran during 2016 and 2017. All the management practices/inputs were monitored and recorded with the help of local experts without interference in farmer's practices. After preliminary evaluation, 100 paddy fields were selected in three planting systems (low input, conventional, and high input) which were predicted in two planting methods (semi-mechanized and traditional) in small, medium, and large farm size levels. Functional unit was considered as one ton paddy yield. The finding revealed that in both regions, all the impact categories and environmental pollutant were almost same and farmer's management practices are close to each other. Also, climate change (CC) in Amol and Rasht regions was 277.21 and 275.79kgCO2eq., respectively. The most CC, global warming potential (GWP 100a), and cumulative energy demand (CED) in both regions were observed in high-input system for semi-mechanized method. Furthermore, the result for the impact categories of terrestrial acidification (TA), freshwater eutrophication (FE), marine eutrophication (ME), agricultural land occupation (ALO), water depletion (WD), metal depletion (MD), and fossil depletion (FD) was similar to the CC, GWP, and CED where the highest amounts in both regions statistically went to high-input system, traditional planting method, and small farms. Moreover, in both regions, high-input and conventional systems emitted higher heavy metals than low-input system. Furthermore, the most heavy metal emission in the air was achieved in small farm, and medium farm got the next rank. Additionally, the high consumption of chemical inputs, such as fossil fuels and fertilizers, in the high-input and conventional systems led to an increase of environmental pollutant in comparison with low-input systems. Therefore, to increase the sustainability of agro-ecosystems, as well as to reduce the environmental impacts of pollutant, reforming the pattern of chemical input consumption and reducing the use of non-renewable energy sources are essential.

Environmental fate of bensulfuron-methyl and MCPA in aerobic and anaerobic rice-cropping systems

Bensulfuron-methyl (BM) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are herbicides widely used in rice agroecosystems, and are commonly found in their environments, especially in water resources. The objective of this study was to evaluate the sorption-desorption, leaching, and dissipation of BM and MCPA under aerobic and anaerobic rice cropping conditions. For this purpose, a three-year field experiment was conducted in SW Spain using four management systems: aerobic with sprinkler irrigation and tillage (ST), sprinkler irrigation and no-tillage (SNT), long-term sprinkler irrigation and no-tillage (SNTLT), and anaerobic with flooding and tillage (FT). At the end of the experiment, the partition coefficients (Kd-values) in ST were (2.7, 3.1, and 3.9) and (1.2, 1.5, and 1.9) times significantly lower than the values in {SNT, SNTLT, and FT} for BM and MCPA, respectively. Greater sorption was related to lower values of soil pH for both herbicides and to higher contents in humic acids for BM and fulvic acids for MCPA. The persistence was much longer for BM (t1/2 = 26.9–52.1 days) than for MCPA (t1/2 = 1.54–21.1 days) in all management systems, and both herbicides' dissipation rates were generally greater under aerobic than under anaerobic conditions. The mobility of MCPA was much greater than that of BM. Compared with SNT and SNTLT, leaching losses of the applied BM were greater by 51% for ST, and of the applied MCPA by 55% and 99% for ST and FT, respectively. Therefore, only aerobic rice production with no-tillage in the short- or long-terms could be considered as alternative management strategies with which to reduce water contamination by BM and MCPA in rice-growing environments.

Odonata in rice agroecosystems: Testing good practices for their conservation

Paddy systems have recently lost their original value as surrogate habitat for several wetland species due to rice farming intensification. Changes in water regimes largely compromised the survival of many aquatic organisms formerly abundant in rice fields, such as Odonata, inducing the introduction of new agricultural practices supposed to mitigate the negative impacts of intensive rice cultivation on biodiversity. For instance, the construction of a water retention structure (ditch) within paddies has been incentivized in Italy, in order to reduce the detrimental effects of drying periods on aquatic organisms. In this research, we investigate the effects of ditch occurrence and dimensions on Odonata diversity in rice fields, and furthermore we evaluate the response of these insects to vegetation height on paddy and canal banks, as an approximation of grass management intensity. Field surveys revealed that ditch occurrence may not be sufficient to improve the suitability of rice fields as breeding habitat for Odonata, especially for sensitive species. Paddies with ditches of larger dimensions supported more abundant adult populations than other field types, but no clear differences have been observed concerning larval stages. Conversely, the occurrence of a well-developed bank vegetation produced clear benefits for these insects in rice fields, while a not significant effect have been observed along irrigation canals. In order to achieve Odonata conservation in rice agroecosystems, together with the excavation of large ditches within paddies, the creation of a network of semi-natural wetlands should be encouraged, as well as the implementation of extensive grass management strategies on rice field and canal banks.

Including grain legume in rice–wheat cropping system improves soil organic carbon pools over time

Deterioration of soil physical quality and depletion of soil organic carbon (SOC) are widespread challenges in tropical rice–wheat growing regions. Consequently, soil productive capacity, production sustainability, and resource use efficiency have declined in this agro-ecosystem. Ecological engineering approach such as legume inclusion in cropping system offers several ecosystem services, and thus, may serve an important role in the restoration of soil health. Given that, a long-term (2003–2015) field experiment was conducted to assess the impact of four rice-based crop rotation treatments [rice–wheat, rice–chickpea, rice–wheat–mungbean, rice–wheat–rice–chickpea] each with three levels of nutrient management treatments [control, integrated nutrient management, chemical fertilizers] on soil aggregation, soil carbon pools, and carbon stabilization. Legume inclusive rotations increased water stable macro-aggregates (WSMA) over rice–wheat rotation in both surface (0–0.2 m) and subsurface (0.2–0.4 m) soil depths. In surface soil, WSMA was the highest in rice–wheat–mungbean rotation (65%) followed by rice–chickpea rotation (57%) and was the least in rice–wheat rotation (50%). Subsequently, grain legume inclusive rotations had the higher aggregate ratio and mean weight diameter over rice–wheat rotation, being the highest in rice–wheat–mungbean rotation. Rice–wheat–mungbean and rice–chickpea rotations had higher carbon concentration in coarse macro-aggregates, meso-aggregates, and coarse micro-aggregates as compared with rice–wheat rotation. Grain legume inclusive rotations increased active carbon pool (9–18%), SOC (6–17%), and carbon management index (5–7%) over rice–wheat rotation, and the order was rice–wheat–mungbean > rice–chickpea ≥ rice–wheat–rice–chickpea > rice–wheat. Integrated nutrient management treatment resulted in higher macro-aggregate (7%), mean weight diameter (6%), active carbon pool (22%), passive carbon pool (16%), SOC (20%), and carbon management index (22%) over the chemical fertilizer treatment. Thus, it is concluded that inclusion of grain legume in lowland rice-based rotation and integrated nutrient management could improve soil aggregation, carbon concentration in aggregates, and soil carbon pools in the tropical soils. The study highlights the prospects of strategic designing of legume inclusive rotation/s for rice agro-ecosystem health and its sustainability.

Climate change impacts on rice productivity in the Mekong River Delta

Rice is consumed by more people than any other grain. Globally, Vietnam is one of the largest exporters of rice, with the majority of production occurring in the tropical, low-lying Mekong River Delta. Agriculture in the Mekong River Delta is susceptible to yield losses from rising temperatures, sea level rise, and land use change as urban expansion replaces productive farmland. Most studies that assess climate change impacts to rice paddy yields are conducted at global- or continental-scales, and use general information on management practices to simulate production. Here, we use management information from farmers and published information on soils collected in Can Tho, a centrally-located province in the Mekong Delta. These data, along with projected mid-century (2040–2069) climate data for the RCP4.5 and RCP8.5 greenhouse gas emissions scenarios, are used to drive the Decision Support System for Agrotechnology Transfer (DSSAT) platform to project future rice paddy yields using the CERES-Rice model. The results indicate that yields decline for all three rice-growing seasons in Can Tho city for both emissions scenarios when CO2 fertilization is not considered (5.5–8.5% annually on average depending on the emissions scenario). Increasing irrigation and fertilizer did not offset these losses, but simulated CO2 fertilization did compensate for yield declines caused by increasing temperatures (yields were modeled to be up 23% higher when CO2 fertilization is considered). However, we caution that estimated yield gains from CO2 fertilization are optimistic, and these modeled values do not consider rises in ozone, which can diminish yields. Continued and future dam construction could negatively affect agriculture in the region, and current government policies prohibit rice paddy farmers from diversifying their livelihoods to adapt to these changes. Monitoring rice agroecosystems at a fine-scale, as this study does, is necessary to best capture the impact that varying management practices can have on local yields. When these differences are captured, future impacts of climate change can be modeled more effectively so that local policymakers can make informed decisions about how to offset yield losses and use farmland more efficiently.

Occurrence, abundance and distribution of plant-parasitic nematodes associated with rice (&lt;i&gt;Oryza&lt;/i&gt; spp.) in different rice agroecosystems in Togo

Rice is the second most important cereal in Togo. Among constraints that affect rice production, plant parasitic nematodes are of great importance. The objective of this study was to determine the distribution, abundance and frequency of plant nematodes in different agroecological zones of Togo. A total of 50 composite soil and root samples (25 each) were taken from 25 fields (5 per zone) randomly selected from the five agroecological zones. Nematodes were extracted from 100 ml soil and 1g fresh root samples using the Hermann techniques. Nematodes were then fixed and mounted on slide and identified to genus level using identification keys. The survey documented twelve plant-parasitic nematode genera among which ten, (Hirschmanniella spp., Meloidogyne spp., Xiphinema spp., Scutellonema spp., Helicotylenchus spp., Heterodera spp., Criconema spp., Pratylenchus spp., Trichodorus spp. and Tylenchid spp.), were recorded from lowland, two (Helicotylenchus and Scutellonema) from upland and five (Dolichodorus spp., Helicotylenchus spp., Tylenchorhynchus spp., Scutellonema spp. and Xiphinema spp.), from flooded ecosystem. Hirschmanniella spp., Meloidogyne spp and Helicotylenchus spp. were the most frequent and abundant plant-parasitic nematode genera recorded from more than 71% of the samples. Helicotylenchus spp., Hirschmanniella spp., Meloidogyne spp. and Scutellonema spp., were recorded in both soil and root samples while Pratylenchus spp., Heterodera spp. and Tylenchorhynchus spp., were found to be associated to root and Trichodorus spp., Tylenchid spp., Xiphinema spp., Criconema spp. and Dolichodorus spp., were recorded from soil samples only. The high diversity of nematode genera recorded in the survey is attributed to the rice ecosystem, which is mostly characterized by lowland ecosystem with intensive cropping. This study established the evidence that nematodes could be important constraints for rice production, suggesting further research focusing on their damage potential and development of effective rice nematode management strategy for sustainable rice production in Togo.Keywords: plant parasitic nematode, abundance, occurrence, rice ecosystem, distribution.

Larvicidal potential of Skermanella sp. against rice leaf folder (Cnaphalocrosis medinalis Guenee) and pink stem borer (Sesamia inferens Walker).

Insect pests in the rice agroecosystem, particularly the leaf folder, Cnaphalocrosis medinalis (Guenee) and stem borer, Sesamia inferens (Walker), cause significant yield losses. These pests are generally managed by farmers by application of insecticides and a few biocontrol agents. As a component of integrated pest management, biocontrol agents play a dynamic role in pest control. Although diverse microbial communities are available in the rice ecosystem, bacterial genera such as Bacillus and Pseudomonas spp. are broadly used as biocontrol agents. Therefore, an attempt was made to identify other effective entomopathogenic bacteria to manage the above mentioned pests. In this study, the two entomopathogenic bacteria isolated from diseased pink stem borer (S. inferens Walker) larvae collected from rice fields were identified as Skermanella sp. (KX611462) and Serratia sp. (KX761232). The larvicidal activity of these two bacteria was evaluated against third instar larvae of C. medinalis and S. inferens in in vitro assays and on potted rice plants (Oryza sativa var. TN1). The results of this study demonstrated 50% (LC50) larval mortality of C. medinalis at 2.95 × 103 and 5.88 × 103 colony forming units (CFU) ml-1 for Skermanella sp. and Serratia sp., respectively, under in vitro conditions, 2.57 × 104 and 3.38 × 104 CFU ml-1, respectively, in whole plant assays. Similarly, the LC50 value for Skermanella sp. was 3.80 × 104 CFU ml-1 and Serratia sp. was 2.29 × 105 CFU ml-1 for S. inferens larvae. Our study reports the larvicidal activity of Skermanella sp. against C. medinalis and S. inferens.

Eroding Traditional Knowledge Systems Plea Scientific Validation: Ecological Characterization of Traditionally Managed Semi-Deep Water Rice Field Agroecosystem in Barak Valley, Assam, Northeast India

Traditional ecological knowledge (TEK) systems illustrate various ways and means of natural resource utilization and management, which has come into being through keen observations as well as the age-old trial and error methods. However, such knowledge systems are gradually eroding due to various reasons. Proper documentation, characterization, scientific validation, and popularization of such knowledge systems would help in preserving them for posterity. The present study characterizes the ecological attributes of a traditional rice farming system called Asra in Karimganj district of Barak Valley, Assam. The objective was to investigate the water properties and community composition of plankton and rice stem epiphyton of the water logged Asra rice field agro-ecosystem. The substantial contribution of Asra rice field ecosystems in maintaining the overall biodiversity of the system has been highlighted in the present study. The study revealed the presence of 77 genera of phytoplankton and 55 genera of rice stem phyto-epiphyton, which belonged to six major classes viz., Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae, Xanthophyceae and Zygnemophyceae. Besides, 29 genera of zooplankton and 14 genera of rice stem zoo-epiphyton belonging to five major groups viz., Protozoa, Cladocera, Copepoda, Ostracoda and Rotifera were also recorded. The study shows that the Asra rice fields are rich repository of plankton and rice stem epiphyton, the natural live food resources for fish. The study emphasizes on conservation of traditional farming system like Asra, and stresses on the need for sustainable utilization of the existing bioresources in such system by introducing the concurrent practice of rice-fish culture in the study area.

Genetic structure of Magnaporthe oryzae populations in three island groups in the Philippines

Genetic structure of the rice blast pathogen, Magnaporthe oryzae was characterized using 453 monoconidial isolates collected from different rice agroecosystems from Luzon, Visayas and Mindanao, the three island groups in the Philippines in experimental plots and in farmer fields. Using 12 microsatellite markers, a total of 93 new multi-locus genotypes (MLGs) were determined when compared to the reference isolates representing the genotypes previously published. Analysis revealed a weak geographic structuring of pathogen genotypes, with some of those collected from Luzon clustering with those from Visayas or Mindanao. Nevertheless, none of the strains from Mindanao clustered with those from the Visayas and none from Visayas clustered with those from Mindanao. This structure likely results from limited natural migration and from some events of long distance migration, probably through the transport of infected seeds. Significant genetic differences were noted on isolates collected from distinct rice agroecosystems. A subset of 30 isolates, representative of MLGs, were tested for fertility status. Of these, eight induced the production of perithecia, of which six were male-fertile and two were also female-fertile. In addition, MAT1.1 isolates represented 36% of our sample whereas it represented only 5% in the collection of reference strains. Pathogenicity test of a subset of 24 isolates inoculated to 16 differential rice varieties demonstrated that most isolates were avirulent to varieties which carry the resistance genes Pi1, Pi33 Pi9, Pikm, and the combination of Piz and Pish.

Landscape composition, configuration, and trophic interactions shape arthropod communities in rice agroecosystems

Abstract Increasing landscape heterogeneity of agroecosystems can enhance natural enemy populations and promote biological control. However, little is known about the multiscale effects of landscape heterogeneity on arthropod communities in rice agroecosystems, especially in combination with trophic interactions. We examined for the first time how landscape heterogeneity, measured by four independent metrics of landscape composition and configuration at three spatial scales, affected species abundance and species richness of rice arthropods within four functional groups and the abundance of the most common species at 28 sites in the Philippines. We additionally examined the influence of trophic interactions among these functional groups. We found that both the compositional and configurational landscape heterogeneity in combination with trophic interactions determined the structure of rice‐arthropod communities. Herbivore abundance decreased with increasing landscape diversity. The abundance of parasitoids and species richness of both parasitoids and predators increased with the structural connectivity of rice bunds. Fragmentation of the rice landscape had a clear negative effect on most arthropod groups, except for highly mobile predatory arthropods. Abundance of common predators and detritivore species decreased with increasing complexity in the shape of rice patches. Trophic interactions, measured as the abundance of prey, outweighed the importance of landscape heterogeneity for predators. In contrast, parasitoids responded positively to configurational landscape heterogeneity but were unaffected by prey abundance. Synthesis and applications. Our research shows how landscape heterogeneity and trophic interactions have different effects on different functional groups. While predator abundance was solely driven by the availability of prey, all other functional groups in the rice‐arthropod community were significantly affected by the composition and configuration of surrounding landscape features. Landscape management aiming to improve biodiversity and biological control in rice agroecosystems should promote a diversity of land uses and habitat types within 100–300 m radii to reduce the presence of pests. Management practices should also focus on maintaining smaller rice patches and the structural connectivity of rice bunds to enhance populations of the natural enemies of rice pests. Future research should focus on the temporal and spatial manipulation of rice fields to maximize the effects of biological control.

Cadmium-mediated morphological, biochemical and physiological tuning in three different Anabaena species

Cyanobacteria are a natural inhabitant of paddy field and enhance the crop productivity in an eco-friendly manner. Cadmium (Cd) is a perilous trace metal element which not only limits the crop productivity but also inhibits the growth and nitrogen-fixing ability of these diazotrophs as well as the biodiversity of rice field semiaquatic agroecosystems. However, the impact of Cd toxicity in diazotrophic cyanobacteria is yet not adequately addressed. Therefore, in the present study, three diazotrophic cyanobacterial species, i.e., Anabaena sp. PCC7120, Anabaena L31, and Anabaena doliolum were subjected to their LC50 doses of Cd, and their physiological (PSII, Psi, respiration, energy status and nitrogen fixation rate), biochemical variables (such as antioxidant contents and antioxidant enzymes) together with morphological parameters were evaluated. The results of physiological variables suggested that the Cd exposure adversely affects the photosynthesis, respiration, and biological nitrogen fixation ability across three Anabaena species. The results of biochemical variables in terms of accumulation of antioxidants (glutathione, thiol, phytochelatin and proline) content as well as antioxidant enzymes such as glutathione S-transferase (GST), glutathione reductase (GR), catalase-peroxidase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) revealed that their inter-species stress tolerance behavior may be attributed to the differential accumulation of antioxidants as well as differential antioxidant enzyme activity in three species. Furthermore, the enhanced antioxidant enzymes activity such as GST, GR, CAT, and SOD in Anabaena L31 advocated significantly higher as compared to Anabaena PCC7120 and Anabaena doliolum. In conclusion, Cd-toxicity assessment regarding physiological, biochemical and morphological aspects across three species identified Anabaena L31 as Cd-resistant species than the other two tested species, i.e., Anabaena PCC7120 and Anabaena doliolum.

Effect of Refugia on Spatial and Temporal Distribution of Arthropods on Rice Agroecosystem (Oryza sativa Linn.)

Effect of Refugia on Spatial and Temporal Distribution of Arthropods on Rice Agroecosystem (Oryza sativa Linn.)