Investigación Agraria

Management and control of the citrus huanglongbing (HLB)

O huanglonbing (HLB), ou greening, é a pior doença dos citros e está associado às bactérias “Candidatus Liberibacter spp.”. Nas Américas, a mais comum bactéria é “Ca. L. asiaticus”, que é transmitida pelo psilídeo asiático dos citros Diaphorina citri Kuwayama (Hemiptera: Liviidae). O manejo da doença envolve: i) plantio de mudas sadias, produzidas em viveiros protegidos e certificados; ii) eliminação do inóculo, que deve ser realizado após minuciosas e eficientes inspeções de plantas sintomáticas, e: iii) controle do vetor D. citri, realizado também após levantamentos populacionais. Se essas medidas não forem adotadas, a doença pode causar grandes prejuízos e inviabilizar o plantio de citros na região e/ou no país.

The huanglonbing (HLB), or greening, is the worst disease of citrus and is associated with the bacteria "Candidatus Liberibacter spp.". In the Americas, the most common bacterium is "Ca. L. asiaticus", which is transmitted by the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae). Management of the disease involves: i) planting of healthy plants grown under protected and certified nurseries; ii) elimination of inoculum, which should be done after thorough and efficient inspections of symptomatic plants, and: iii) D. citri vector control, also performed after population surveys. If these measures are not adopted, the disease can cause great damage and derail the citrus crop in the region and/or country.

**Control biológico del complejo de hongos causantes de la mancha foliar en maíz dulce (Zea mays var. saccharata) con bacterias benéficas**

Con el objetivo de evaluar la eficiencia de Bacillus sp., Pseudomonas fluorescens y Streptomyces sp. en el control de hongos causantes de la mancha foliar en maíz dulce y determinar su mecanismo de acción, se realizaron experimentos en el Laboratorio de Fitopatología y en el campo experimental de la Facultad de Ciencias Agrarias, San Lorenzo. El Experimento 1 consistió en determinar la inhibición in vitro del crecimiento y desarrollo del complejo de patógenos asociados a esta etiología a través de la producción de compuestos anti microbianos hidrosolubles y de gases volátiles inespecíficos producidos por las bacterias. Se registró el porcentaje de reducción de crecimiento micelial y el porcentaje de inhibición de la germinación de conidios. El experimento 2 consistió en determinar a campo la reducción de la intensidad de la enfermedad en plantas de maíz dulce. Los tratamientos fueron la suspensión de cada bacteria, un testigo absoluto y un testigo químico (Azoxystrobin 20% + Tebuconazole 20%). In vitro se redujo significativamente el crecimiento micelial de Bipolaris sp., Curvularia sp. y Exserohilum turcicum y se inhibió la germinación de E. turcicum por las tres bacterias. A campo se constató la eficiencia significativa de control de las tres bacterias estudiadas. Bacillus sp. redujo la intensidad en 43%, Pseudomonas fluorescens en 36% y Streptomyces sp. en 19%. Las tres bacterias benéficas son agentes de control biológico por su efecto antagónico y por disminuir la severidad de la mancha foliar en maíz dulce.

In order to evaluate the efficiency of Bacillus sp., Pseudomonas fluorescens, and Streptomyces sp. in the control of leaf spot of sweet corn and determine the mechanism of action exerted by them, experiments were carried out at the Phytopathology Laboratory and in the experimental field of the Facultad de Ciencias Agrarias, San Lorenzo. Experiment 1 consisted in determining in vitro the inhibition of the growth and development of the complex of pathogens associated with this etiology through the production of anti microbial water soluble compounds and non-specific volatile gases produced by bacteria. It was registered the percentage reduction of mycelial growth and percentage inhibition of the germination of conidia. The experiment 2 consisted in determining under field conditions the reduction of the intensity of the disease in sweet corn plants. The treatments were each bacteria suspension, an absolute control and a chemical control (Azoxystrobin 20% + Tebuconazole 20%). In vitro, the mycelial growth of Bipolaris sp., Curvularia sp. and Exserohilum turcicum reduced significantly and the germination of E. turcicum was inhibited by the three bacteria. In the field experiment, it was confirmed the significant control efficiency of the three studied bacteria. Bacillus sp. reduced the intensity by 43%, Pseudomonas fluorescens by 36% and Streptomyces sp. by 19%. The three beneficial bacteria are agents of biological control for producing antagonistic effect and reducing the severity of leaf spot in sweet corn.

**Identificación de enfermedades virósicas transmitidas por semillas de poroto (Vigna unguiculata (L.) Walp.)**

Los experimentos se realizaron en la Facultad de Ciencias Agrarias de la Universidad Nacional de Asunción, San Lorenzo, Paraguay. El periodo de ejecución estuvo comprendido entre los meses de enero a abril de 2013, este trabajo se realizó con el objetivo de detectar enfermedades virales transmitidas por semillas de poroto (Vigna unguiculata (L.) Walp.), mediante pruebas biológicas y serológicas. Se recolectaron muestras de seis variedades de semillas y plantas de poroto de parcelas infectadas, ubicadas en el Campo experimental del Instituto Paraguayo de Tecnología Agraria (IPTA), Choré, Departamento de San Pedro. Se realizó la siembra de las semillas colectadas, de las variedades San Francisco, Crema Ñu, Chore S·BR1 Poty, Negro, Crema Japonés y Moteado. Las plantas resultantes que presentaron síntomas fueron sometidas al test de ELISA utilizando anticuerpos específicos a los virus Cowpea severe mosaic virus (CpSMV) y Cowpea aphid-borne mosaic virus (CABMV) respectivamente, de manera a detectar la transmisión del virus por semillas. Posteriormente, a partir del material foliar macerado, de las muestras que dieron reacciones positivas en el test, se realizaron inoculaciones mecánicas a plantas sanas de tres especies indicadoras: Chenopodium amaranticolor, Vigna unguiculata y Sesamun indicum. Todas las variedades de poroto dieron positivo al CABMV y al CpSMV solo las variedades negro y moteado. Se detectó la transmisión del CABMV a través de semillas de poroto de la variedad San Francisco, presentando un porcentaje de transmisión del 6%.

The experiments were conducted at the Facultad de Ciencias Agrarias of the Universidad Nacional de Asunción, San Lorenzo, Paraguay. The implementation period was from January to April 2013, with the aim of detecting seed-borne viral disease of bean (Vigna unguiculata (L.) Walp.), by biological and serological tests. For this purpose samples were collected from six (6) varieties of seeds and plants of V. unguiculata infected plots located in the experimental field of the Instituto Paraguayo de Tecnología Agraria (IPTA), Chore, Department of San Pedro. It was performed the sowing of the seeds collected, San Francisco, Crema Ñu, Chore S-BR1 Poty, Negro, Crema Japonés, Moteado. The resulting plants with symptoms were subjected to ELISA test using specific antibodies to the virus Cowpea severe mosaic virus (CPSMV) and Cowpea aphid-borne mosaic virus (CABMV), respectively, so as to detect the transmission of the virus by seeds. Subsequently, from macerated leaf material samples that gave positive reactions in the test, mechanical inoculations were performed to three healthy plants indicator species: Chenopodium amaranticolor, Vigna unguiculata and Sesamum indicum. All varieties tested were positive to CABMV but only the Negro and Moteado varieties were positive to CpSMV. Transmission of CABMV through bean seeds of the variety San Francisco was detected, having a transmission rate of 6%.

Pyriproxyfen and Diflubenzuron effects on the reproduction of Nezara viridula (L.) [Hemiptera: Pentatomidae]

O percevejo Nezara viridula é uma praga importante em varias culturas e regiões do mundo. Neste estudo, avaliou-se o efeito do inseticida do piriproxifem sobre a fecundidade e fertilidade de N. viridula e o efeito do diflubenzurom na formação do aparelho reprodutor. Foram realizados dois bioensaios em laboratório. No primeiro bioensaio, experimentou-se uma baixa concentração do piriproxifem sobre casais adultos de N. viridula. Posterior à cópula, avaliou-se o número de ovos/fêmea (fecundidade) e o número de ninfas eclosionadas (fertilidade). No segundo bioensaio, avaliou-se o efeito do diflubenzurom na morfologia do aparelho reprodutor feminino e masculino de N. viridula. Os resultados indicam uma redução de 23,61% no número de ovos por fêmea provocada pelo piriproxifem, na concentração testada, que não foi significativa em relação à testemunha. Entretanto, 52,39% da fertilidade de ovos diminuiu, impedindo a eclosão de ninfas, provavelmente por afetar a formação do embrião. Entretanto, o diflubenzuron afetou o desenvolvimento dos órgãos femininos e masculinos. Tanto o piriproxifem e o diflubenzurom tem potencial de diminuir a progênie de N. viridula, e podem ser incluídos em programas de manejo integrado pragas, uma vez que sejam realizados estudos de eficácia dos produtos a campo.

The green stink bug Nezara viridula is an important pest in many crops and regions of the world. In this study the effect of pyriproxyfen on fecundity and fertility of N. viridula and the effect of diflubenzuron in the reproductive system was evaluated. Two bioassays were conducted in laboratory. In the first, low concentration of pyriproxyfen was tested on adult pairs of N. viridula. After copulation, we assessed the number of eggs/female (fecundity) and the number of hatched nymphs (fertility). In the second bioassay, we evaluated the effect of diflubenzuron in the morphology of female and male reproductive system of N. viridula. The results show that pyriproxyfen, at the tested concentration did not reduce significantly the number of eggs/female (23.61%). A decrease of 52.39% in eggs fertility, was observed preventing nymphs hatching probably due to embryo malformation. Diflubenzuron affected female and male development and reproductive organs. Thus, both pyriproxyfen and diflubenzuron have potential to decrease N. viridula progeny and can be included in integrated pest management. However, field studies are needed.

**Efecto del riego sobre la abundancia de Raoiella indica en plantas de Cocos nucifera L.**

El ácaro rojo de las palmeras, Raoiella indica Hirst es una plaga en plantaciones de coco en el Caribe. Hasta el presente no existe información disponible sobre el efecto de las prácticas culturales sobre las poblaciones de este ácaro. En este estudio se evaluó el efecto del riego sobre la abundancia de R. indica en plantas de Cocos nucifera en condiciones de umbráculo en el Decanato de Agronomía de la Universidad Centroccidental Lisandro Alvarado, Venezuela. Plantas de coco var. Enano Amarillo Malayo de 1-2 años de edad fueron infestadas artificialmente con 20 hembras adultas. Posteriormente, las plantas fueron divididas en tres grupos (T0= 100%, T1= 50% y T2= 25% del requerimiento de agua de riego). Cada siete días se contó el número de huevos y formas móviles por folíolo en cada uno de los tratamientos. Durante todo el ensayo, el número de huevos y formas móviles fue significativamente mayor en plantas regadas con el 100% de su requerimiento hídrico. Los resultados obtenidos sirven de base para futuros estudios por lo que se sugiere evaluar los posibles cambios bioquímicos en la hoja por efecto de la supresión del riego de modo a entender mejor cuales cambios bioquímicos ocurren y su posible relación con la dinámica poblacional de R. indica.

The red palm mite, Raoiella indica Hirst is a pest on coconut plantations in the Caribbean. To date there is no available information on the effect of cultural strategies on this mite population. In this study the effect of irrigation on R. indica abundance on Cocos nucifera plants was evaluated under greenhouse conditions at the Faculty of Agronomy, Universidad Centroccidental Lisandro Alvarado, Venezuela. Coconut plants var. Malayan Yellow Dwarf of 1-2 years-old were artificially infested with 20 adult females. Subsequently, the plants were divided into three groups (T0= 100%, T1= 50% and T2= 25% of water requirement). Every seven days the number of eggs and motile forms per leaflet was counted in each treatment. Throughout the test, the number of eggs and motile forms was significantly higher on plants irrigated with 100% of its water requirement. The results provide the basis for future studies, thus it is suggested to evaluate the possible biochemical changes in leaves due to the suppression of irrigation, to better understand biochemical changes and their possible relation with R. indica population dynamics.

Water erosion and loss of sediment, water and chemical elements during rainfall events in two rural watersheds

As atividades agrícolas geram impactos sobre o ambiente e necessitam de constante estudo e monitoramento para melhorar o entendimento das formas e grau de contaminação. O trabalho teve como objetivo quantificar e comparar as perdas de água, sedimento em suspensão e alguns elementos químicos durante dois eventos pluviais sequentes, em duas bacias hidrográficas (BH) rurais situadas no assentamento Alvorada, em Júlio de Castilhos, Rio Grande do Sul, Brasil. As BH’s estudadas possuem 144,5 ha (BH140) e 79,5 ha (BH80), com diferentes proporções de uso do solo. Os eventos pluviométricos ocorreram nos dias 18 (45,9 mm) e 19 (39,7 mm) de setembro de 2012. A perda de água por escoamento superficial na BH140 foi de 5,5% e na BH80 de 15,2%. Na BH140, a máxima concentração de sedimento em suspenção medida foi de 1,4 g l-1 contra 0,9 g l-1 na BH80. O fósforo solúvel nas amostras de água + sedimento na BH80 oscilaram entre 0,01 e 0,02 mg L-1; e na BH140 alcançaram 0,06 mg L-1. O fósforo total das amostras de água + sedimento da BH140 foi superior ao da BH80, alcançando os valores máximos de 2,10 e 0,47 mg L-1 na BH140 no primeiro e segundo evento, respectivamente. As BH’s apresentaram baixa perda de fósforo, perda moderada de bases (Ca, Mg, K e Na) e outros elementos químicos que constituem a estrutura do solo como Fe, Al, Mn e transferência insignificante de elementos traços metálico aos cursos de água

Agricultural activities generate impacts on the environment and require constant study and monitoring to improve understanding of the forms and degree of contamination. The present study aimed to quantify the losses of water, sediment and chemical elements during two rainfall events in two rural watersheds (RW) from an agricultural settlement in Júlio de Castilhos, State of Rio Grande do Sul, Brazil. The studied RWs have an area of 144.5 ha (RW140) and 79.5 ha (RW80), with different land use distribution. The monitored rainfall events occurred in 18 (45.9 mm) and 19 (39.7 mm) September 2012. Water loss by runoff in the RW140 was 5.5%, and in RW80 was 15.2%. In the RW140 the highest concentration of suspended sediment was 1.4 g L-1 compared to 0.9 g L-1 in RW80. The levels of soluble phosphorus in the water samples + sediment in the RW80 ranged between 0.01 and 0.02 mg L-1 and en the RW140 reached 0.06 mg L-1. Total phosphorus in samples of water samples + sediment in the RW140 was higher than the RW80, reaching maximum values of 2.10 and 0.47 mg L-1 in the RW140 in the first and second event, respectively. Both RWs in this study showed low phosphorus losses, moderate losses of bases (Ca, Mg, K e Na) and elements that are constituents of the soil structure as Fe, Al, Mn, and insignificant losses of metallic trace elements.

Reporte de la Micobiota Uredinal y Ustilaginal en poáceas forrajeras en Paraguay

Las royas y los carbones son hongos fitoparásitos muy importantes en diversos cultivos. Varias especies reportadas a nivel mundial son de importancia económica al afectar especies forrajeras que son utilizadas para alimentación de animales. Como la producción ganadera paraguaya está basada en pasturas es de suma importancia conocer los patógenos que puedan afectar la calidad de la biomasa y de semillas de los pastos. Esta investigación presenta las principales especies de la micobiota Uredinal y Ustilaginal que se presentan en las poáceas forrajeras en el territorio paraguayo. Se realizaron colectas durante las cuatro estaciones del año 2013, de diferentes especies de poáceas en potreros de los Departamentos de Alto Paraná, Caaguazú, San Pedro y Central (Región Oriental), así como de Villa Hayes y Boquerón (Región Occidental). Se realizó una descripción sintomatológica en las plantas, ubicación y características de uredios y telios, como así también la morfología y tipos de esporas encontradas en las diferentes especies de pastos. Los hongos uredinales hallados fueron Puccinia levis en Urochloa brizantha, Puccinia oahuensis en Digitaria eriantha, Uromyces setariae-italicae en Urochloa humidicola y el hongo ustilaginal Tilletia ayresii en Panicum maximum cv. Colonial y P. maximum cv. Gatton panic.

Rusts and smuts are very important plant parasitic fungi in various crops. Several species that affect economically important forage species and are used for animal feed are reported globally. As Paraguay's livestock production is based on pastures, it is extremely important to know the pathogens that may affect the quality of grasses biomass and seed. This research presents major species of the micobiota Ustilaginal and Uredinal observed on forage grasses in the Paraguayan territory. Collections were made during the 4 seasons of 2013, different grass species in pastures of the departments of Alto Paraná, Caaguazú, San Pedro and Central (Eastern Region) and Villa Hayes and Boquerón (Western Region). Symptomatic description was made in plants, location and characteristics of uredia and telios, as well as the morphology and spore types found in different grass species. The uredinals fungi found were Puccinia levis in Urochloa brizantha, Puccinia oahuensis in Digitaria eriantha, Uromyces setariae-italicae in Urochloa humidicola and ustilaginal fungus Tilletia ayresii in Panicum maximum cv. Colonial and P. maximum cv. Gatton panic.

Producción de mudas de tomate en el sistema flotante

El experimento se llevó a cabo en el invernadero de producción de mudas del Centro Hortícola de la Facultad de Ciencias Agrarias, Universidad Nacional de Asunción, Paraguay, de septiembre a octubre de 2011. Se determinó la influencia del sistema flotante y tipos de substratos sobre el crecimiento de mudas de tomate (Lycopersicon esculentum Mill). Los tratamientos estuvieron constituidos por la combinación de dos sistemas de producción de mudas (flotante y convencional) y dos tipos de substratos (comercial y humus de lombriz). Se utilizó un diseño en bloques completos al azar con arreglo factorial 2 x 2, con cinco repeticiones y 50 mudas por unidad experimental. Las variables evaluadas fueron: altura de mudas, longitud de raíz, masa seca de la parte aérea, masa seca de raíz, número de raíces secundarias, diámetro del tallo, área foliar y porcentaje de sobrevivencia a campo. Los datos fueron sometidos al análisis de varianza y las medias comparadas por la prueba de Tukey al 5% de probabilidad de error. Los resultados indican que los substratos no afectaron las variables evaluadas, a excepción del número de raíces secundarias, donde el substrato comercial fue superior. El sistema flotante fue superior para todas las variables evaluadas, excepto prendimiento a campo, que no presentó diferencias significativas. Para área foliar la interacción fue significativa, donde la combinación del substrato comercial con el sistema flotante promovió la mayor media. Estos resultados muestran que la combinación del sistema flotante con humus de lombriz es una alternativa viable para la producción de mudas de calidad en tomate.

The experiment was carried out in the greenhouse of seedling production of the Centro Hortícola of the Facultad de Ciencias Agrarias, Universidad Nacional de Asunción, Paraguay, from September to October, 2011. The influence of the floating system and types of substrates on the growth of tomato seedlings (Lycopersicon esculentum Mill) was determined. The treatments were a combination of two seedlings production’s systems (floating and conventional) and two types of substrates (commercial and vermin-compost). Randomized complete blocks with a factorial arrange 2 x 2 was used, with five replications and 50 seedlings per experimental unit. The evaluated variables were: seedling height, root length, dry mass of the aerial part, root dry mass, number of secondary roots, stem diameter, leaf area and leaf area and survival rate in the field. Data were analyzed for variance and the means were compared by the Tukey test at 5% error probability. The substrates did not affect the evaluated variables, except for the number of secondary roots, where the commercial substrate was superior. The floating system was superior for all the variables evaluated, except for the sprouting in the field, which did not present differences. For leaf area the interaction was significant, where the combination of commercial substrate with the floating system produced the highest mean. These results show that the combination of floating system with vermin-compost is a viable alternative for the production of high quality tomato seedlings.