El protista Spongospora subterranea es el patógeno del suelo causante de la sarna polvosa de la papa. Es un parásito obligado que se reproduce en raíces y tubérculos, donde produce grupos de zoosporas enquistadas, quistosoros, los cuales pasan al suelo para generar un nuevo ciclo infectivo. La prevención de esta enfermedad requiere identificar y cuantificar los quistosoros del suelo. Con el propósito de automatizar el proceso, fotografiamos digitalmente quistosoros de diferentes cultivos bajo las mismas condiciones, y caracterizamos su tamaño y forma como área y circularidad con análisis de imágenes. El rango de área fue 1086-2247 µm2 y el de circularidad fue 0.824-0.886. Con estos rangos analizamos un número creciente fotografías digitales (1-90) de un mismo suelo con quistosoros (infectado) y sin ellos (control), utilizando una rutina macro. El número de identificaciones resultó lineal, positiva y significativamente (p<0.001) correlacionado con el número de fotografías analizadas tanto en el suelo infectado (r2=0.996, y=1.679x) como en el control (r2=0.968, y=0.367x). Las identificaciones en el suelo control infectado fueron cinco veces menores y fueron sustraídas a las identificaciones del suelo infectado para cada número de fotografías analizadas. Esta sustracción resultó lineal (y=1.048x), positiva (r2=0.979) y significativamente (p<0.001) correlacionada con el promedio de quistosoros cuantificados visualmente en las mismas fotografías. Los resultados muestran que los quistosoros del suelo pueden ser cuantificados por análisis de imágenes. La automatización independiza la precisión de la cuantificación de la experiencia y habilidad de la persona que la realiza.

Título en inglés: Importance of strain and concentration range of conidia in the effect of Trichoderma asperellum on the growth of tomato seedlings Solanum lycopersicum L.Resumen El crecimiento longitudinal de tallos y raíces fue investigado en plántulas de tomate (Solanum lycopersicum L), luego de la aplicación de cuatro aislamientos de Trichoderma asperellum: T25, T46, T84 y T109. Sólo la aplicación del aislamiento T109 causó un incremento significativo (p ≤ 0,05) del crecimiento longitudinal de tallos y raíces. El peso seco de las plántulas también fue estimulado desde la primera semana luego de la aplicación de T109. El crecimiento fue estimulado significativamente (p ≤ 0,05) por la aplicación de 105 y 106 conidias/ml, pero no lo fue por la aplicación de 104, 107 y 108 conidias/ml. Estos resultados indican que el estímulo del crecimiento producido por T. asperellum en plántulas de tomate, sólo ocurre con aislamientos particulares y un rangos de concentración específicos.Palabras claves: Trichoderma asperellum, Estímulo del crecimiento, Plántulas de tomate, Aislamientos de Trichoderma, Rango de concentraciones.AbstractLongitudinal growth of shoot and roots was investigated in tomato seedlings (Solanum lycopersicum L) after application of four isolates of T. asperellum (T25, T46, T84 y T109). Only the isolate T109 caused a significant (p ≤ 0.05) increase of longitudinal growth of roots and shoots, and dry weight of seedlings was also stimulated from the first week after T109 application. The growth was significantly (p ≤ 0.05) stimulated by 105 and 106 conidia/ml, but it was not by 104, 107 and 108 conidia/ml. These results indicate that growth stimulus caused by T. asperellum in tomato seedlings, occurs only with specific isolates and at a specific concentration ranges. Key words: Trichoderma asperellum, Growth stimulation, Tomato seedlings, Trichoderma strains, concentration range.

The powdery scab is caused by the protist Spongospora subterranea (Walk.) Lagerh f. sp. subterranea Tomlinson, which is an obligate parasite that replicates in roots and tubers of potato (Solanum tuberosum). This replication results in resistant structures which are denominated cystosori. Production of cystosori was investigated in the potato variety Diacol Capiro, which was cultivated in three types of soil (Inceptisol, Entisol, and Andisol) that were infested with cystosori. Concentration of cystosori was determined at planting (Initial), at plant senescence (Harvest), and at plant disintegration (Postharvest). The experimental design was completely randomized with two treatments and three levels each. Soil type with the levels Inceptisol, Entisol and Andisol, was one treatment; and the sampling time with the initial, harvest and postharvest, was the other. Additionally, a test of simple regression to analyze correlation of the initial and final concentration of cystosori was performed. In all types of soil, cystosori concentration increased significantly (P ≤ 0.05) from planting to postharvest; the mean increase was 48%. There was no significant (P ≤ 0.05) difference among types of soil at any time sampling. The final concentration of cystosori (Postharvest) was significantly (P ≤ 0.05) which correlated with the initial concentration of cystosori (Initial). These results suggest that cystosori concentration can have a substantial increase after a single potato crop cycle, and harvest residuals, such as contaminated tubers, can contribute to this increase.

La sarna polvosa es causada por el protista Spongospora subterranea (Walk.) Lagerh f. sp. subterranea Tomlinson, un parásito obligado el cual replica en raíces y tubérculos de papa (Solanum tuberosum). Esta replicación resulta en estructuras de resistencia denominadas quistosoros. En este estudio se investigó la producción de quistosoros en papa variedad Diacol Capiro, cultivada en tres tipos de suelos: Inceptisol, Entisol, y Andisol, infestados con quistosoros. La concentración de este parásito se determinó en el suelo a la siembra (inicial), a la senescencia de las plantas (cosecha) y dos meses más tarde, cuando las plantas estaban desintegradas (poscosecha). El diseño experimental fue completamente al azar con dos tratamientos y tres niveles cada uno. Un tratamiento fue el tipo de suelo con los niveles Inceptisol, Entisol y Andisol; y el otro, el tiempo de muestreo con los niveles Inicial, Cosecha y Poscosecha. Adicionalmente, se realizó un ensayo de regresión simple para analizar la correlación de la concentración inicial y final de quistosoros. En todos los tipos de suelo la concentración aumentó (48%) (P < 0.05) desde el inicio a la poscosecha. No se observaron diferencias (P < 0.05) en la concentración de quistosoros entre los suelos durante los muestreos realizados. La concentración final de estos (poscosecha) se correlacionó (P < 0.05) con la concentración inicial (inicio). Estos resultados sugieren que la concentración de quistosoros puede sufrir un incremento significativo en un solo ciclo de cultivo de papa en todos los suelos estudiados y que los residuos de cosecha como tubérculos infectados pueden contribuir a este incremento.

Powdery scab affects most potato production zones in the world. The causal organism Spongospora subterranea f. sp. subterranea forms galls in roots and lesions on tubers during its replication. Recent researches suggest that S. subterranea could cause harmful effects on the host plant and potentially on yield. In order to quantify the disease impact on plant growth and yield, potato Solanum tuberosum ssp. andigena, cv. Diacol Capiro was grown in a soil infested with S. subterranea and compared to a healthy control soil. Data was taken at the flowering stage and at harvest. S. subterranea caused a plant length reduction of 23%, a foliar dry weight reduction of 32% and a tuber weight reduction of 30%, whereas S. subterranea did not reduce the number of tubers or stems.

Previous studies have shown that mosquito larvae retreat from the surface of water as an alarm response to sudden changes in light intensity. We investigated the effects of the insecticide fenvalerate on this alarm response in larvae of the mosquito Culix pipiens molestus and on the related vulnerability of these larvae to the predator Notonecta glauca. For the alarm response, after 1 h of exposure to fenvalerate, no immediate effects were observed. However, after a 5-h postexposure period following 1 h of exposure, the proportion of larvae that showed the alarm response decreased with increasing fenvalerate concentration. The median effective concentration (EC50) was 0.1 μg/L. After 6 h of continuous exposure, the EC50 decreased to 0.06 μg/L. In addition, vulnerability to the predator N. glauca increased after 6 h of continuous exposure. The median time needed for N. glauca to prey 50% of the larvae (PT50) decreased from 5 h 48 min in the control to 3 h 8 min at 0.3 μg/L fenvalerate. No mortality occurred after 48 h when larvae were exposed for 6 h in the absence of N. glauca. The median lethal concentration (LC50) was 0.3 μg/L after 48 h of continuous exposure. The decrease in the PT50 was related strongly to the increase in the proportion of larvae that did not exhibit an alarm response. These results show that the alarm response can be inhibited by low levels of fenvalerate, and this inhibition seems to increase larval mortality due to predation.

La sarna polvosa es una enfermedad que decrece la produccion de papa. Es causada por el parasito obligado Spongospora subterranea f. sp. subterranea, el cual produce grupos de zoosporas enquistadas llamados quistosoros. Cuando las zoosporas estan activas pueden infectar raices y tuberculos iniciando un nuevo ciclo reproductivo. Para estudiar la influencia de las condiciones de incubacion sobre la activacion de las zoosporas, suspensiones acuosas de quistosoros fueron incubadas bajo diferentes condiciones. Los quistosoros y las zoosporas activas fueron diariamente contados utilizando microscopio optico. El mayor numero de zoosporas activas se encontro al cuarto dia de incubacion, mientras que el menor numero de quistosoros se registro al quinto dia de incubacion. Esto sugiere que las zoosporas permanecen activas por un corto periodo. El numero de zoosporas activas por quistosoro fue significativamente (P<0,05) mas alto en agua de red que en agua destilada, y en presencia de luz que en oscuridad. Un mayor numero de zoosporas por quistosoro se activo a 19 °C que a 5 °C, pero la presencia de raiz de papa no tubo efecto significativo (P<0,05) en la activacion. Estos resultados muestran que las condiciones de incubacion pueden aumentar las zoosporas liberadas; sin embargo, el numero de zoosporas activas por quistosoro observado no fue mayor de cinco. Mas zoosporas por quistosoro eran esperadas, porque un quistosoro es entre 10 y 40 veces mayor que una zoospora. En consecuencia, se necesita un gran numero de quistosoros para asegurar la presencia de zoosporas activas en un inoculo.

El protozoario Spongospora subterranea f. sp. subterranea es un parásito obligado que replica en raíces y tubérculos de papa causando la sarna polvosa. Esta enfermedad se ha difundido a escala global debido al comercio de tubérculos-semilla infectados y a la ausencia de tratamientos efectivos. En este trabajo se investigó la influencia sobre la sarna polvosa de cuatro aislamientos de Trichoderma asperellum en tres tipos de suelo: Andisol, Entisol e Inceptisol. Tubérculos de Solanum tuberosum variedad Diacol Capiro fueron plantados en parcelas infectadas con 1942 ± 226 quistosoros por gramo de suelo. No se observaron diferencias entre las plantas tratadas y no tratadas con T. asperellum. La superficie de raíz ocupada por agallas fue en promedio 2,2%, sin encontrarse diferencias significativas (P<0,05) entre los tipos de suelos. La reducción del crecimiento de las plantas fue de 41, 32 y 28% en el Andisol, el Entisol y el Inceptisol, respectivamente. La reducción de la producción fue de 40, 28 y 0,1 % en el Andisol, el Entisol y el Inceptisol, respectivamente. Un porcentaje similar de superficie de raíz cubierto por agallas resultó en reducciones de la producción tan disímiles como 40% o 0,1%, indicando necesidad de utilizar otros métodos para determinar la severidad de infección. La reducción del crecimiento y la producción estuvieron inversamente asociadas a la concentración de Al3+ en los suelos, sugiriendo que los efectos de la sarna polvosa están fuertemente relacionados con las condiciones del suelo.The protozoan Spongospora subterranea f. sp. subterranea is an obligate parasite that replicates in roots and tubers of potato causing the powdery scab. This disease has disseminated on a global scale, because the commercial traffic of infected tubers used as seed and the absence of effective treatments. The present work investigated the effects of four isolates of Trichoderma asperellum in three soil types: Andisol, Entisol and Inceptisol. The soils were infected with 1942 ± 226 cystosori per gram of soil. It was used Solanum tuberosum variety Diacol Capiro. No differences were observed between treated and non treated plants with T. asperellum. The root surface affected by galls was an average of 2.2 %, and no significant differences (p<0.05) were observed among the soils. The reduction of plant growth was of 41, 32 and 28 % for the Andisol, Entisol and Inceptisol, respectively. The reduction in tubers production was of 40, 28 and 0,1% for the Andisol, Entisol and Inceptisol, respectively. Similar percent of root surface covered with galls resulted in production reduction of 40%, but also of 0,1%, indicating the necessity of other methods to determine the infection severity. The growth and production reductions were inversely associated with the Al3+ concentration in the soils, suggesting that powdery scab effects are strongly related to soil characteristics.

La sarna polvosa es una enfermedad que decrece la producción de papa. Es causada por el parásito obligado Spongospora subterranea f. sp. subterranea, el cual produce grupos de zoosporas enquistadas llamados quistosoros. Cuando las zoosporas están activas pueden infectar raíces y tubérculos iniciando un nuevo ciclo reproductivo. Para estudiar la influencia de las condiciones de incubación sobre la activación de las zoosporas, suspensiones acuosas de quistosoros fueron incubadas bajo diferentes condiciones. Los quistosoros y las zoosporas activas fueron diariamente contados utilizando microscopio óptico. El mayor número de zoosporas activas se encontró al cuarto día de incubación, mientras que el menor número de quistosoros se registró al quinto día de incubación. Esto sugiere que las zoosporas permanecen activas por un corto periodo. El número de zoosporas activas por quistosoro fue significativamente (P<0,05) más alto en agua de red que en agua destilada, y en presencia de luz que en oscuridad. Un mayor número de zoosporas por quistosoro se activó a 19 °C que a 5 °C, pero la presencia de raíz de papa no tubo efecto significativo (P<0,05) en la activación. Estos resultados muestran que las condiciones de incubación pueden aumentar las zoosporas liberadas; sin embargo, el número de zoosporas activas por quistosoro observado no fue mayor de cinco. Más zoosporas por quistosoro eran esperadas, porque un quistosoro es entre 10 y 40 veces mayor que una zoospora. En consecuencia, se necesita un gran número de quistosoros para asegurar la presencia de zoosporas activas en un inóculo.The powdery scab is a disease that decreases potato production. It is caused by Spongospora subterranea f. sp. subterranea. This obligate parasite produces cystosori, which are groups of encysted zoospores. When these zoospores are active, they can infect roots and tubers initiating a new replication cycle. To investigate the influence of the incubation conditions on the zoospore activation, suspensions of cystosori in water were incubated under different conditions. The cystosori and the active zoospores were daily counted under microscope. The higher number of active zoospores was found after four days of incubation, meanwhile the lower number of cystosori was found after five days of incubation. This suggests that zoospores are active for a short period. The number of active zoospores per cystosorus was significantly (P<0.05) higher in tap water than in distillated water, and in presence of light than in dark. More zoospores per cystosorus were activated at 19 °C than at 5 °C, but potato roots did not have a significant (P<0.05) effect on zoospores activation. These results indicate that the incubation conditions may increase the zoospores activation. However, the number of active zoospores per cystosori was not higher than five. More active zoospores were expected, because a cystosorus is between 10 and 40 times bigger than a zoospore. This shows that a large number of cystosori are needed to ensure the presence of active zoospores in an inoculum

Feeding activity and maturation were investigated in Daphnia magna exposed to fenvalerate for 24 h. The feeding activity was monitored by measuring filtration rates and 15 N‐traced food assimilation. Exposure resulted in individuals with reduced feeding activity and smaller body size at concentrations of 0.3 μg/L or greater as well as delayed maturation at concentrations of 0.6 μg/L or greater. Filtration rates recovered within 2 d of the exposure, but long‐term effects of reduced feeding activity, such as growth retardation, occurred. Because D. magna needs to reach a minimum size to mature, growth retardation may explain the observed delay in maturity. The proposed causal relationships suggest that exposure to fenvalerate reduces feeding activity, resulting in growth retardation, which leads to delayed maturity. In cases of exposure to such toxicants, the monitoring of feeding activity may predict long‐term effects on population parameters.

The aim of this study was to determine the influence of exposure duration (1 h, 24 h, continuous) to paraoxon-methyl on the magnitude of lethal and sublethal effects, the shape of the concentration-response relationships and the recovery processes in Daphnia magna. Survival was more severely reduced in the continuous than in the pulse exposure regimes. The lethal concentrations (3d median lethal concentration [LC50] values) were 233, 2.33, and 1.14 microg/L after 1-h, 24-h, and continuous exposure, respectively. The shapes of the concentration-response relationships for survival were significantly different after 1 h of exposure than after 24-h and continuous exposure. Indeed, the slopes of the curves defined by the ratios LC90/LC10 (ratio of 90 and 10% lethal concentrations) were 100, 1.74, and 1.97 for 1-h, 24-h, and continuous exposure, respectively. The large difference between 1 h and longer durations of exposure shows that the population is partially affected (10-90%) over a much broader range of concentrations when exposure is short. Negative effects on reproductive outputs occurred mostly at concentrations affecting partly the survival and therefore also over a broad range of concentrations after 1 h of exposure. However, these effects were only transient in the pulse exposure regimes as individual performances recovered. By contrast, reproductive outputs of survivors exposed continuously remained impaired. These results suggest that a refined risk assessment should consider exposure duration because it influences the magnitude of effects and recovery.

This study compares lethal and sublethal responses of Daphnia magna Straus exposed to fenvalerate continuously (21 d) and as a pulse (24 h). Survival was reduced more severely in the continuous‐ than in the pulse‐exposure regime. Complete mortality occurred at 1 μg/L for continuous exposure and at 3.2 μg/L for pulse exposure. Regarding reproductive endpoints, fenvalerate delayed the age at first reproduction. At the beginning of the reproductive phase (day 10), this delay resulted in a reduction of the neonates per living female at similar concentrations in both exposure regimes (0.3 and 0.1 μg/L for continuous and pulse exposure, respectively). The population growth rate was inhibited in continuous and pulse exposure at 0.3 and 0.6 μg/L, respectively. However, the effects of fenvalerate in the pulse exposure were transient. After 21 d, a recovery to values close to the controls occurred with respect to the total neonates per female and the population growth rate over a broad range of concentrations from 0.1 up to 1 μg/L. In contrast, no substantial recovery occurred in the continuous‐exposure regime.

Laboratory ecotoxicity tests may not adequately evaluate the effects of pesticides, because they often do not include more environmentally relevant conditions, such as pulsed toxicant exposures and low food conditions. Therefore, we tested the effects of a pulse of the pyrethroid insecticide fenvalerate (FV) on the life history and population growth rate (r) of the cladoceran Daphnia magna. The daphnids were subjected to a 24-h pesticide pulse exposure (0.03, 0.1, 0.3, 0.6, 1.0, and 3.2 microg/L) under high and low food conditions and were monitored for 21 d. Chemical analysis showed that at t = 1 h, the nominal FV concentrations were reduced by 50 to 66%. Fenvalerate decreased survival and growth in the week following pulse exposure. Age at first reproduction increased, with consequent adverse effects on cumulative reproduction per living female and, therefore, on r. Thus, a short-term exposure of FV caused a long-term reduction on r as a result of increased mortality and a delay in development. Low food conditions exacerbated the effects of the FV exposure on juvenile survival and growth during the first week. This caused a much stronger reduction in r under low food conditions. We concluded that a pulsed FV exposure may result in long-term reduction of r that can be predicted only with more environmentally relevant toxicity tests, as described in the present study.