Increasing the yield of drip-irrigated rice by improving photosynthetic performance and enhancing nitrogen metabolism through optimizing water and nitrogen management.

Drip irrigation under plastic film mulching is an important technique to achieve water-conserving and high-efficiency rice (Oryza sativa L.) production in arid areas, but the grain yield of drip-irrigated rice is much lower than the expected yield (10.9-12.05 t·hm-2) in practical production applications. Therefore, we hope to further understand the photosynthetic physiological mechanism of drip-irrigated rice yield formation by optimizing water and nitrogen management during the growth period and provide a scientific reference for improving yield and nitrogen use efficiency (NUE) of drip-irrigated rice in arid areas. In 2020 and 2021, T-43 (a drought-resistant; V1) and Liangxiang-3 (a drought-sensitive cultivar; V2) were cultivated under two water treatments (W1: limited drip irrigation, 10200 m3·hm-2; W2: deficit drip irrigation, 8670 m3·hm-2) and three nitrogen fertilization modes with different ratios of seedling fertilizer:tillering fertilizer:panicle fertilizer:grain fertilizer (N1, 30%:50%:13%:7%; N2, 20%:40%:30%:10%; and N3, 10%:30%:40%:20%). The photosynthetic characteristics, nitrogen metabolism, yield, and NUE were analysed. The results showed that compared with other treatments, the W1N2 resulted in 153.4-930.3% higher glutamate dehydrogenase (GDH) contents and 19.2-49.7% higher net photosynthetic rates (P n) in the leaves of the two cultivars at 20 days after heading, as well as higher yields and NUE. The two cultivars showed no significant difference in the physiological changes at the panicle initiation stage, but the P n, abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid (GA3), and zeatin riboside (ZR) levels of V1 were higher than those of V2 by 53.1, 25.1, 21.1, 46.3 and 36.8%, respectively, at 20 days after heading. Hence, V1 had a higher yield and NUE than V2. Principal component analysis revealed that P n and GDH were the most important physiological factors affecting rice yield performance. In summary, the W1N2 treatment simultaneously improved the yield and NUE of the drought-resistant rice cultivar (T-43) by enhancing the photosynthetic characteristics and nitrogen transport capacity and coordinating the balance of endogenous hormones (ABA, IAA, GA3, and ZR) in the leaves.

Enhancing genetic gain through the application of genomic selection in developing irrigated rice for the favorable ecosystem in Bangladesh.

Increasing selection differential and decreasing cycle time, the rate of genetic improvement can be accelerated. Creating and capturing higher genetic with higher accuracy within the shortest possible time is the prerequisite for enhancing genetic gain for any trait. Comprehensive yield testing at multi-locations at early generations together with the shortest line fixation time can expedite the rapid recycling of parents in the breeding program through recurrent selection. Genomic selection is efficient in capturing high breeding value individuals taking additive genetic effects of all genes into account with and without extensive field testing, thus reducing breeding cycle time enhances genetic gain. In the Bangladesh Rice Research Institute, GS technology together with the trait-specific marker-assisted selection at the early generation of RGA-derived breeding lines showed a prediction accuracy of 0.454-0.701 with 0.989-2.623 relative efficiency over the four consecutive years of exercise. This study reports that the application of GS together with trait-specific MAS has expedited the yield improvement by 117 kg ha-1·year-1, which is around seven-fold larger than the baseline annual genetic gain and shortened the breeding cycle by around 1.5 years from the existing 4.5 years.

The impact of the rice production system (irrigated vs lowland) on root-associated microbiome from farmer's fields in western Burkina Faso.

Due to their potential applications for food safety, there is a growing interest in rice root-associated microbial communities, but some systems remain understudied. Here, we compare the assemblage of root-associated microbiota in rice sampled in 19 small farmer's fields from irrigated and rainfed lowlands in Burkina Faso, using an amplicon metabarcoding approach of the 16S rRNA gene (prokaryotes, three plant samples per field) and ITS (fungi, one sample per field). In addition to the expected structure by root compartments (root vs rhizosphere) and geographical zones, we showed that the rice production system is a major driver of microbiome structure. In irrigated systems, we found a higher diversity of prokaryotic communities from the rhizosphere and more complex co-occurrence networks, compared to rainfed lowlands, while fungal communities exhibited an opposite pattern (higher richness in rainfed lowlands). Core taxa were different between the two systems, and indicator species were identified: mostly within Bacillaceae in rainfed lowlands, and within Burkholderiaceae and Moraxellaceae in irrigated areas. Finally, a higher abundance in rainfed lowlands was found for mycorrhizal fungi (both compartments) and rhizobia (rhizosphere only). Our results highlight deep microbiome differences induced by contrasted rice production systems that should consequently be considered for microbial engineering applications.

Life Cycle Thinking for the environmental and financial assessment of rice management systems in the Senegal River Valley.

Rice is a staple food in Senegal, which however imports more than 70% of the rice consumed annually to meet its domestic demand. Despite governmental efforts to increase rice self-sufficiency, both rice supply and yields remain low. Senegalese farmers face challenges related to irrigation infrastructure and fertiliser access, besides those derived from climate change. This study applies Life Cycle Assessment (LCA) combined with financial Life Cycle Costing (LCC) to evaluate alternative scenarios for rice management in the Senegal River Valley and identify sustainability hotspots and potential improvements. Specifically, rice cultivation in Ross Béthio (Saint Louis, Senegal) is assessed based on the observed agricultural practices during the dry seasons of 2016 and 2017. Two scenarios capturing conventional (CONV) and intensive (INT) practices are compared to two reference scenarios (SAED scenarios) according to the recommendations of the official agricultural advisory service. The INT scenario generates the lowest impacts per kg of paddy rice in seven out of thirteen impact categories, including climate change, freshwater and marine eutrophication, ozone depletion and water scarcity. This is due to the higher yields (7.4 t ha-1) relative to CONV (4.8 t ha-1) and the two reference SAED scenarios (6.0 t ha-1). The two latter scenarios show the lowest values in the remaining categories, although they also generate slightly lower profits than INT (138 € t-1 vs. 149 € t-1) due to increased labour costs for additional fertilisation treatments. The results from both LCA and LCC underline the importance of increasing yields to decrease environmental impacts and production costs of rice when estimated per kg of product. Well-designed fertiliser application doses and timing and increased mechanisation can deliver further environmental benefits. Additional improvements (e.g. in irrigation, crop rotations, straw management) could be considered to promote the long-term sustainability and profitability of rice production in Senegal. LCA in combination with financial LCC is identified as a decision-support tool for evaluating the sustainability of alternative crop management practices. Life Cycle Thinking can still benefit from experiential learning based on information exchange between farmers, researchers and extension agents to contribute to a sustainable agriculture and ultimately to food security in Africa.

Environmental adaptation of the root microbiome in two rice ecotypes.

The root microbiome plays a key role that can influence host plant growth and abiotic stress. While there has been extensive characterization of community structure, spatial compartmentalization, and the impact of drought stresses on the root microbiome in rice and other plants, there is relatively little known about the differences in root microbiome among rice ecotypes in natural upland and lowland fields. Herein, we used two rice ecotypes, upland and irrigated ecotype rice (two Indica and two Japonica genotypes), as a model to explore the responses of the root microbiome under different environmental conditions. We aimed to identify environment-induced adaptation in the root bacterial and fungal composition of rice ecotypes by high-throughput sequencing. Rice from lowland field or upland had significantly altered overall bacterial and fungal community compositions of the two ecotypes, with diversity of both ecotypes greatly decreased from lowland field to upland. The overall response of the root microbiome to upland conditions was taxonomically driven by the enrichment of family Enterobacteriaceae and genera Serratia, and phylum Ascomycota. Interestingly, rice ecotypes specifically enriched root microbes when they were transferred from their original environment, such as the enrichment of class Thermoleophilia and phylum Actinobacteria when the irrigated ecotype rice was moved from lowland to upland field. These results revealed that different environmental conditions and rice ecotypes resulted in a restructuring of root microbiome communities, and suggested the possibility that components responsible for the beneficial attributes in the altered root microbiome might contribute to the adaptation of different ecotypes in natural fields.

Rice-duck co-culture for reducing negative impacts of biogas slurry application in rice production systems.

Nitrogen (N) and phosphorus (P) losses are a potential limitation for the direct application of biogas slurry as a substitute for chemical fertilizer in irrigated rice production systems. The hypothesis was tested that a rice-duck co-culture promotes the rice N and P use efficiencies, reducing the losses of these nutrient elements through run-offs and enabling the use of biogas slurry as a substitute for chemical fertilizers. A field split-plot experiment was carried out to test the hypothesis. Our results showed that the direct application of biogas slurry was harmful for rice production. Compared with rice monoculture under chemical fertilization, biogas slurry application reduced N and P accumulation in grains, P use efficiency, and grain yield by 3.6%, 7.8%, 12.7%, and 14.8%, respectively, but increased the total N and P concentrations in the surface water 1.4- and 2.7-fold, respectively, on average on the eleventh day after fertilization. However, rice-duck co-culture compensated for the negative effects of biogas slurry on rice production. Under the biogas slurry application and in line with our hypothesis, the rice-duck co-culture significantly increased N and P accumulation and use efficiencies, as well as grain yield to levels similar to those acquired with chemical fertilization treatments. Meanwhile, total N and P concentrations were significantly lower for rice-duck co-culture than those of rice monoculture under biogas slurry application. Our results suggest that rice-duck co-culture can maintain rice yield and reduce the risks of N and P loss to local environments when utilizing biogas slurry as a substitute for chemical fertilizers.

Cytogenotoxicity of rice crop water after application of the tricyclazole fungicide

ABSTRACT Tricyclazole is currently one of the fungicides recommended for the treatment of diseases in irrigated rice. However, there is relatively little information on its cytotoxic and genotoxic potential. The objective of this study was to evaluate the cytotoxicity and genotoxicity of rice crop water after apllication of the tricyclazole fungicide through the Allium cepa L. test. The rice crop water samplings were collected before and 1, 15 and 30 days after application of the fungicide in rice plant shoots. The Allium cepa roots were placed in contact with the rice crop water to check for possible chromosomal abnormalities and mitotic index of the bioindicators meristematic cells. The data obtained by the Allium cepa test indicates that the application of the tricyclazole fungicide leads to an increase in the genotoxic activity in the rice crop water, through the appearance of chromosomal abnormalities, without, however, causing significant effects on the mitotic index. The major chromosomal alterations observed were anaphasic and telophasic bridges and laggard chromosomes.

Identification of QTLs for yield and agronomic traits in rice under stagnant flooding conditions.

BACKGROUND: Stagnant flooding, where water of 25-50 cm remains until harvest time, is a major problem in rainfed lowland areas. Most of the Sub1 varieties, which can withstand around 2 weeks of complete submergence, perform poorly in these conditions. Hence, varieties tolerant of stagnant flooding are essential. RESULTS: This paper presents the first study to map QTLs associated with tolerance to stagnant flooding, along with a parallel study under normal irrigation, using an F7 mapping population consisting of 148 RILs derived from a cross of Ciherang-Sub1 and the stagnant-flooding tolerant line IR10F365. Phenotypic data was collected for 15 key traits under both environments. Additionally, survival rate was measured under stress conditions. Genotyping was performed using the Illumina Infinium genotyping platform with a 6 K SNP chip, resulting in 469 polymorphic SNPs. Under stress and irrigated conditions, 38 and 46 QTLs were identified, respectively. Clusters of QTLs were detected in both stress and normal conditions, especially on chromosomes 3 and 5. CONCLUSIONS: Unique and common QTLs were identified and their physiological consequences are discussed. These beneficial QTLs can be used as targets for molecular breeding and can be further investigated to understand the underlying molecular mechanisms involved in stagnant flooding tolerance in rice.

Influence of the wind on water application uniformity of a mechanical lateral move irrigation equipment using rotating plate sprinklers / Influência do vento na uniformidade de aplicação de água de um equipamento de irrigação mecanizada tipo lateral móvel usando emissores de placa oscilante

ABSTRACT: Investigations demonstrate that the wind is the factor that causes the biggest negative influence on water application of sprinkler irrigation systems. Therefore, this paper aims to evaluate, in in-field conditions, the influence of wind on the water distribution uniformity of a mechanical lateral move sprinkler system used for irrigation in rice crop in the South of Rio Grande do Sul State, Brazil. The equipment is located at the Campo Experimental de Terras Baixas (ETB) of EMBRAPA/CPACT and operates with water emitters model I-Wob installed in drop tubes in a distance of 2.8m above the soil surface, having a uniform space of 2.3m between each other and pressure regulators of 68.9kPa. Sixteen in-field evaluations were done and they permitted to infer that the higher is the wind speed, the lower are the values of Christiansen Uniformity (CU) and of Distribution Uniformity (DU) coefficients. Besides, it can be affirmed that even in unfavorable wind conditions, the mechanical lateral move irrigation equipment presented desirable indexes of water application uniformity.

RESUMO: Estudos demonstram que o vento é o fator que causa maior influência negativa na aplicação de água de sistemas de irrigação por aspersão. Sendo assim, este estudo tem por objetivo avaliar, em condições de campo, a influência do vento sobre a uniformidade de distribuição de água de um sistema mecanizado do tipo lateral móvel, utilizado na irrigação de arroz no sul do Rio Grande do Sul. O equipamento, localizado no Campo Experimental de Terras Baixas (ETB) da EMBRAPA/CPACT, opera com emissores de água modelo I-Wob instalados em tubos pendurais a uma distância de 2,8m da superfície do solo, espaçados uniformemente entre si em 2,3m, com reguladores de pressão de 68,9kPa. As 16 avaliações de campo realizadas permitiram inferir que quanto maior a velocidade do vento menor os valores dos coeficientes de uniformidade de Christiansen (CU) e de distribuição (UD). Além disso, pode-se afirmar que, mesmo em condições adversas de vento, o equipamento de irrigação mecanizada do tipo lateral móvel apresentou índices desejáveis de uniformidade de aplicação de água.

Abundance and potential impact of granivorous birds on irrigated rice cultivation, Itajaí, Santa Catarina, Brazil / Abundância e potencial impacto das aves granívoras no cultivo de arroz em Itajaí, Santa Catarina, Brasil

The assemblage of granivorous birds in the irrigated paddy-fields was evaluated over an annual cultivation cycle by means of 12 monthly samplings undertaken in each of 3 areas (of a total of 90 ha) in Itajaí, Santa Catarina, between August 2010 and July 2011. Of a total of 10 species, distributed among 5 families and 2 orders, Sturnella superciliaris (43.88%) and Sicalis flaveola (36.88%) were the most abundant. The regular species contributed with 45.17%, followed by the occasional (30.37%) and the seasonal (24.43%). Only the abundance of S. flaveola presented significant differences between the months of sampling (F11-33 = 7.1290, p < 0.01) as a result of the lower values recorded in December and January. The diversity and evenness indices showed similar fluctuation, with mean values ranging between 0.47 ± 1.37 and 0.29 ± 0.83, respectively. The average losses per hectare, due to the action of S. superciliaris and S. flaveola , were 8.35 ± 1.66 and 6.10 ± 1.48 kg of rice, equivalent to R$ 49.07 in the 3 areas monitored, giving a total average annual loss of 82.9 kg for the 90 ha of rice monitored.(AU)

A assembleia de aves granívoras no cultivo de arroz irrigado foi avaliada ao longo de um ciclo anual da cultura, por meio de 12 amostragens realizadas em 3 áreas (90 ha) no município de Itajaí, Santa Catarina, entre agosto de 2010 e julho de 2011. Foram registradas 10 espécies, distribuídas em 5 famílias e 2 ordens, sendo a Sturnella superciliaris (43,88%) e a Sicalis flaveola (36,88%) as que participaram com as maiores abundâncias. As espécies regulares contribuíram com 45,17%, seguidas das ocasionais (30,37%) e sazonais (24,43%). Apenas a abundância de S. flaveola foi significativamente diferente entre os meses de amostragens (F11-33 = 7,1290; p < 0,01), influenciada pelos menores valores entre dezembro e janeiro, enquanto os índices de diversidade e equitabilidade apresentaram a mesma tendência de flutuação, com valores médios oscilando entre 0,47 ± 1,37 e 0,29 ± 0,83 respectivamente. O prejuízo médio por hectare, estimado pela ação de S. superciliaris e S. flaveola , foi de 8,35 ± 1,66 e 6,10 ± 1,48 kg de arroz, equivalente a R$ 49,07 nas 3 áreas monitoradas, obtendo-se uma média anual de perda de 82,9 kg em 90 ha de cultivo de arroz estudados.(AU)

Requisitos de clientes para o desenvolvimento de um implemento a fim de fechar taipas abertas para drenagem / Customer requirements for development of an implement for closing levees opened for drainage

O arroz irrigado é cultivado na maior parte do RS com aplainamento da superfície do solo em desnível e sistema de cultivo mínimo. Com a semeadura em solo seco, há necessidade de conformar drenos, que cortam transversalmente as taipas, na área de cultivo. Para o estabelecimento da lâmina de água definitiva, essas taipas abertas para drenagem devem ser fechadas e, para essa finalidade, não existe um equipamento específico que execute tal atividade com devida agilidade e qualidade, sendo necessário o desenvolvimento de um implemento com este fim. Ainda, para o processo de desenvolvimento de máquinas agrícolas, faz-se necessário o levantamento de uma série de informações. Na fase de projetação, essas informações são necessárias para o estabelecimento das necessidades dos clientes/usuários e dos requisitos dos clientes, para posteriormente serem transformadas em requisitos de projeto e estabelecidas as especificações de projeto. Desse modo, este trabalho objetivou determinar os requisitos dos clientes, a partir das suas necessidades, para o projeto de um implemento com a função de fechamento de taipas abertas para drenagem no arroz irrigado. As informações foram levantadas a partir de pesquisas bibliográficas e aplicação de questionários a futuros clientes/usuários. Como resultados, foram identificadas as necessidades dos clientes, assim como 25 requisitos de clientes.

The irrigated rice is grown on most part of RS with planning surface on sunken soil and minimum tillage system. With the dry soil sowing there is a need to conform drains, which cut across the levees in the growing area. For the establishment of a definitive water slide, these open for drainage levees must be closed and for this goal there is no specific equipment that execute such activity with agility and quality, being necessary the development of an implement. Still, for the agricultural machinery development process, the raising of a lot of information is required. At the design specification phase, this information is required for the constitution of the customer/users needs and requirements, in order to be transformed in design requirements and later establish the design specifications. Thereby, this study had the objective of determining the customer requirements, starting from customer needs, to design an implement for closure of open levees for drainage of irrigated rice. All the information was obtained from bibliographic research and questionnaire application to future customers/users. The customer needs, as well as, 25 customer requisites were identified as results.

Toxic and micronutrient elements in organic, brown and polished rice in Brazil.

Concentration levels of As, Cd, Hg, Pb, Tl, Sn, Sb Co, Cu, Mn, Se, Zn, Cr, Ni and Mo in different types of rice cultivated in irrigated fields in Brazil were evaluated. Arsenic, Cd, Pb, Zn, Mn and Cu were found in higher concentrations in brown rice samples, suggesting the prevalence of these elements in the bran. Meanwhile, lower concentrations of Pb, Mo, Cr, Se and Co were found in parboiled rice. Organic rice did not differ of cultivated conventionally rice. Thallium, Hg and Sb were not detected in any rice sample whose limits of detection were 0.7 µg kg(-1), 2.5 µg kg(-1) and 8 µg kg(-1), respectively. The concentrations of the investigated elements were compared with those reported for polished rice and brown rice from other countries, unveiling concentrations in general at the same level for rice produced at non-contaminated sites.

Seletividade de agrotóxicos utilizados na cultura do arroz irrigado ao fungo Metarhizium anisopliae, agente de controle microbiano de Tibraca limbativentris / Selectivity of chemical pesticides used in rice irrigated crop at fungus Metarhizium anisopliae, microbial control agent of Tibraca limbativentris

Para subsidiar a utilização de táticas de manejo integrado para o inseto-praga Tibraca limbativentris, avaliou-se a compatibilidade in vitro entre o isolado CG 891 de Metarhizium anisopliae e os agrotóxicos utilizados na cultura do arroz irrigado. Os parâmetros avaliados foram crescimento vegetativo, esporulação e germinação em pré e pós-contato do fungo, com duas doses de fipronil, tiametoxam, fenitrotiona, carbofurano, pirazossulfurom-etílico, bentazona, clomazona, glifosato e quincloraque; e uma dose de triciclazol e azoxistrobina. Reduções significativas no crescimento vegetativo e esporulação de M. anisopliae foram observadas para fenitrotiona, carbofurano e azoxistrobina. Observou-se redução na germinação em pré-contato para o agrotóxico azoxistrobina. O valor percentual da germinação alterou a classificação dos agrotóxicos com relação a sua seletividade sobre o entomopatógeno. No entanto, os resultados mostram que in vitro os agrotóxicos fenitrotiona, carbofurano, glifosato e azoxistrobina são prejudiciais ao isolado CG 891 de M. anisopliae.

Searching for integrated control strategies for the insect-pest Tibraca limbativentris, the in vitro compatibility between isolated CG 891 of Metarhizium anisopliae and several pesticides used in the culture of irrigated rice was evaluated. The followings parameters were studied: vegetative growth, sporulation and the germination viability in pre- and post-contact of the fungus for two concentrations of fipronil, thiametoxan, fenitrothion, carbofuran, pyrazosulfuron-ethyl, bentazon, clomazone, glyfosate and quinclorac and one concentration of tricyclazole and azoxystrobin. Significant reductions in the vegetative growth and sporulation of M. anisopliae were observed for fenitrothion, carbofuran and azoxystrobin. The germination in pre-contact was affected by azoxystrobin. The percentage of germination changed the classification of pesticides in relation to its selectivity on the fungus. However, the results show that in vitro, the pesticides fenitrothion, carbofuran, glyfosate and azoxystrobin are harmful to isolated CG 891 of M. anisopliae.

Teor e qualidade de substâncias húmicas de planossolo sob diferentes sistemas de cultivo / Content and quality of humic substances of a Albaqualf under different management systems

Este trabalho teve por objetivo avaliar e comparar os teores e as características químicas das substâncias húmicas (SHs) de um Planossolo háplico submetido a diferentes sistemas de cultivos de arroz. Amostras de solo foram coletadas em um experimento de longa duração (19 anos) nas profundidades de 0-0,025, 0,025-0,05, 0,05-0,20m e no topo do horizonte B. Os tratamentos avaliados foram: APC-Sistema de cultivo contínuo de arroz (preparo convencional) e controle de invasoras com herbicida, APD-Sucessão de azevém x arroz sob plantio direto e SN-Solo mantido em condições naturais (pastagem nativa). As SHs e a fração não-húmica (NH) foram obtidas por meio de fracionamento químico. O teor de carbono do solo e na forma de SHs e NH foram determinados, respectivamente, pelos métodos Walkley-Black e espectrofotométrico. As características químicas e moleculares das SHs foram avaliadas por espectroscopias de infravermelho e UV/Vis e por análise elementar. Em comparação ao solo natural, o sistema APD preservou os teores de carbono orgânico total e de todas as frações húmicas, enquanto que o sistema APC provocou perdas de carbono orgânico total e de todas as frações húmicas nas camadas superficiais (<0,05m). A proporção de ácidos fúlvicos em relação ao carbono total aumentou em profundidade, sugerindo mobilização desta fração no perfil. O sistema de manejo afetou a composição da matéria orgânica principalmente na camada de 0 a 0,025m, ocorrendo SHs de menor grau de decomposição, mais polares e contendo menor proporção de estruturas alifáticas que no sistema APD.

The objective of this study was to evaluate and compare the content and chemical characteristics of humic substances (SHs) of an Albaqualf under different soil management systems. Soil samples were collected in a long-term field experiment (19 years) from the 0-0.025; 0.025-0.05 and 0.05-0.20m layers and from the top of the B horizon. The following treatments were evaluated: APC-continuous rice crop system under conventional tillage and weed control with herbicides; APD-no-tillage system with rye-grass in the winter and rice in the summer, and SN-soil under natural condition with native grassland. The SHs and the non-humic fraction (NH) were obtained by chemical fractioning. The content of total soil carbon and those occurring as SHs and NH were determined by the Walkley-Black and spectrophotometric methods, respectively. To determine the chemical and molecular characteristics of the SHs, UV-visible and infrared spectroscopy techniques and elementar analyses were employed. In comparison to the soil under natural condition (SN), the no-tillage system (APD) maintained total soil organic carbon concentrations as well as the content of SHs. The conventional tillage reduced soil total organic carbon and the content of SH in the upper layers (<0.05m). The proportion of fulvic acid in relation to the total soil organic carbon increased with soil depth, suggesting the mobilization of this fraction along the profile. The soil management system affected the composition of the organic matter mainly in the 0 to 0.025m layer, where the SH showed a lower decomposition and higher polaricity degree and contained smaller proportion of aliphatic structures than SH in the APD system.

Diversidade genética de Tibraca limbativentris Stål (Hemiptera: Pentatomidae) de Santa Catarina e do Rio Grande do Sul, usando marcadores RAPD / Genetic diversity of Tibraca limbativentris Stål (Hemiptera: Pentatomidae) of Santa Catarina and Rio Grande do Sul, Brazil, using RAPD

O trabalho objetivou testar protocolos de extração de DNA e caracterizar populações de Tibraca limbativentris, Stål, importante inseto-praga do arroz. Os insetos foram coletados em Joinville, Rio do Oeste e Turvo, em Santa Catarina, e Agudo, Uruguaiana, Pelotas e Palmares do Sul, no Rio Grande do Sul. Testaram-se seis protocolos de extração de DNA citados na literatura, e um novo protocolo adequado à espécie em questão. DNA de dez indivíduos de cada população foi extraído usando o melhor protocolo e reações de RAPD foram realizadas com dez iniciadores. O novo protocolo mostrou os melhores resultados e foi utilizado nas reações de PCR, que geraram 151 bandas polimórficas, permitindo acessar diferenças genéticas entre todas as populações; não ocorreram indivíduos de uma população agrupados com os de outra. A maior similaridade intrapopulacional foi encontrada em Uruguaiana (22 por cento), e a menor em Palmares do Sul (50 por cento), também a população mais divergente das demais. O valor Gst foi 0,5215, e de Nm 0,4588; esses valores refletem a pouca similaridade entre as populações. O menor Nm foi apresentado quando Palmares do Sul e Pelotas foram incluídos nas comparações, em consonância com a maior divergência apresentada por essas populações em relação às outras. Não se observou relação entre a distância geográfica e a similaridade genética das populações, o que refletirá o modelo de dispersão de T. limbativentris, ainda desconhecido. Estudos explorando as estratégias de dispersão da espécie poderiam ajudar no entendimento da distribuição do inseto, evidenciando qual a principal fonte de variabilidade genética.

The work was carried out to test DNA extraction protocols and to characterize populations of Tibraca limbativentris Stål, an important rice insect-pest. Insects were collected in Joinville, Rio do Oeste and Turvo, in Santa Catarina State, and Agudo, Uruguaiana, Pelotas and Palmares do Sul, in Rio Grande do Sul State, and six literature-referenced protocols, besides a new one, were tested. DNA from ten individuals of each population was extracted using the best protocol and RAPD reactions were carried out with ten initiators. The new protocol showed the best results and was used in the PCR reactions, that generated 151 polymorphic bands, allowing to access genetic differences among all the populations; no individuals from one population were clustered with individuals from another. The largest intrapopulacional similarity was found in Uruguaiana (22 percent), and the smallest in Palmares do Sul (50 percent), which was also the most divergent population in relation to the others. The Gst was 0.5215, and the Nm was 0.4588; these values reflect the low similarity between the populations. The smallest genic flow was obtained when Palmares do Sul and Pelotas were included in the comparisons, in accordance with the largest divergence of these two populations in relation to the others. There was no significant relation between geographic distance and genetic similarity, which can reflect unknown model of dispersion of T. limbativentris. New studies exploring the species dispersion strategies may help to understand the insect distribution and to unveil the main factors linked to the genetic variability within and between populations.