Resistance to the Whitefly, Aleurotrachelus socialis, in Wild Populations of Cassava, Manihot Tristis

The levels of resistance in the wild species of cassava, Manihot tristis Muell-Arg. (Malpighiales: Euphorbiaceae), to the whitefly, Aleurotrachelus socialis Bondar (Hemiptera: Alelyrodidae), the most important economic pest in cassava, Manihot esculenta Crantz (Malpighiales: Euphorbiaceae) crops in South America, were estimated under glasshouse conditions. The parameters of the life history of A. socialis were studied on TST-26 and TST-18 accessions of the wild parent and compared with the susceptible (CMC-40) and resistant (MEcu-72) cultivars. The average longevity on the wild accessions (TST-26, 4.1; TST-18, 4.6 days) and oviposition rates (TST-26, 2.0; TST-18, 1.6 eggs/female/2 days) of the A. socialis females were not significantly different from those of MEcu-72 (5.1 days and 3.4 eggs/female/2days). The longevity and oviposition rates on CMC-40 were highest (11 days and 8.6 eggs/female/2days). Analyses of the demographic parameters (Ro, rm; DT) showed a significant impact of the M. tristis accessions on the potential growth of A. socialis. The average survival time of adults that fed on TST-26, TST-18, and MEcu-72 were significantly different from those recorded on the susceptible genotype. Results from this study revealed important levels of resistance to the whitefly A. socialis on the TST-26 and TST-18 accessions due to the marked differences found for longevity and reproduction, which influenced and were consistent with the differences found in the net reproduction rate (Ro), intrinsic growth rate (rm) and population doubling time (DT). The combined effect of these parameters indicated that M. tristis accessions were inappropriate hosts for A. socialis

Contribución al estudio de la guayaba coronilla, psidium friedrichsthalianum beng-niedenzu

Se colectaron semillas de Psidium friedrichsthalianum en algunos sitios de Colombia, para iniciar el establecimiento de una colección. Semilla almacenada hasta por seis meses no fue afectada en su germinación en comparación con semillas sin almacenamiento (92%). En estado de vivero, la planta presentó dos fases de crecimiento, entre los 90 y 160 días y entre los 160 y 190 días. Se halló la ecuación AF = 26.6 + 0.619 (LA - 42.2) con R2 de 95.41 para estimar área foliar (AF) con base en el producto largo por ancho de las hojas. La especie presentó mayores floraciones en julio y diciembre. Fructificación en agosto-septiembre y enero-febrero y defoliaciones altas en enero y agosto. La proporción de flores que llegó a fruto fue de 70-80 %. El modelo logístico no describió bien el desarrollo del fruto, para el cual se encontraron dos fases, crecimiento lento de los 30 a los 105 días y crecimiento rápido 105 a 135 días. Se describió la morfología de la flor antes, durante y después de floración. Se identificaron insectos asociados con la planta.In order to founding a collection, seeds of Psidium friedrichsthalianum were collected in some places in Colombia. Seeds stored up to six months were not affected in their germination in comparison to seeds that not were stored (92 %), The plant shows two stages of growth in seedling stat: from 90 to 160 days and from 1 and amp;0 to 190 days. The equation AF= 26.6 +0.619 (LA-42.2) with R2 of 95A1 for estimating foliar area (FA) based on the product, length and width of the leaves. The species showed higher flowering between july and december, fructification was august to september and from january to february. The defoliations appeared in january and in august . From 70 to 80 percent of flowers become fruit. The growth of the fruit was not well described by the logistic partnership. The fruit showed two stages: slow growth from 30 to 105 days and fast growth from 105 to 135 days. Morphological studies about the flower were made, wich were described before during and after the flowering. Associa1ed insects with the plant were identified

Recognition of potential beneficial fungi associated with chontaduro (bactris gasipaes h.b.k.) rhizosphere in the pacific region of valle del cauca, colombia

The peach palm or chontaduro (Bactris gasipaes H.B.K.) is the principal crop of the rainforest agroecosytems of the Colombian Pacific coast. This region is poorly referenced in the scientific literature despite its high biodiversity and agroecological importance. The aim of this study was to isolate and identify up to the level of genus, fungi from the rhizosphere of B. gasipaes in two areas with different crop management, Citronela and Sabanetas, both in Valle del Cauca. Roots and rhizospherical soil were sampled at three times of varying rainfall from 2006 to 2007. It is hypothesized that the size and diversity of the fungi population are negatively influenced by rainfall, as this is the dominant climatic variable in the study region. Results showed that in Citronela fungi populations were stable during the first two sampling, independent of rainfall between the sampling dates. In Sabaletas, rainfall was higher than in Citronela, which was associated with anaerobic conditions in the rhizosphere that limited fungal growth. The third sampling had higher fungal populations and diversity of fungal genera at both sites which coincides with the period of high rainfall and palm fruit production, conditions that favor the release of exudates from the roots. These factors could have favored secretion of root exudates which in turn, could favor the growth of beneficial microorganisms in the rhizosphere. The genera of fungi isolated were: Trichoderma in both sites, Fusarium and Rhizopus in Citronela only, and Penicillium y Thielaviopsis in Sabaletas only. These fungi could be beneficial and useful in programs of integrated pest management for palm peach production. Thus, the results could serve as a base for future studies in the Pacific region.El chontaduro o pejibaye (Bactris gasipaes H.B.K) es el principal cultivo de los agroecosistemas de la selva húmeda tropical de la costa pacífica colombiana. Esta región no aparece referenciada en la literatura científica a pesar de su alta biodiversidad e importancia agroecológica. El objetivo de este estudio fue aislar y caracterizar morfológicamente hasta género, hongos presentes en la rizósfera de B. gasipaes en dos sistemas de producción diferentes, localizados en Citronela y Sabaletas, Valle del Cauca, Colombia. Durante 6 meses se tomaron muestras de raíces y suelo rizosférico en tres épocas con distinta precipitación pluvial. Se planteó como hipótesis que el tamaño y diversidad de la población de hongos son influenciados negativamente por la precipitación, ya que esta es la variable climática preponderante en la región del estudio. Los resultados mostraron que en la localidad de Citronela las poblaciones de hongos permanecieron estables durante los dos primeros muestreos, independiente de los cambios ocurridos en el régimen de lluvias entre épocas. En Sabaletas, durante estos mismos periodos, los registros de lluvias fueron más altos, lo que pudo generar condiciones anaeróbias en la rizósfera y limitar la expresión poblacional fúngica. Para el tercer muestreo, en ambas localidades aumentó la población y diversidad de géneros de hongos, coincidiendo con la época de alta precipitación pluvial y llenado de frutos en las palmas, condiciones que aparentemente favorecen la liberación de exudados en las raíces y consecuentemente el desarrollo de las poblaciones microbianas benéficas de la rizósfera. Los géneros de hongos aislados en este estudio fueron: Trichoderma en ambas localidades, Fusarium y Rhizopus sólo en Citronela, Penicillium y Thielaviopsis sólo en Sabaletas. Estos microorganismos fungosos podrían presentar potencial benéfico para ser utilizados en programas de manejo integrado dentro del sistema de producción del chontaduro en la región Pacífico de Colombia

Biodiversity of Arbuscular Mycorrhizal Fungi in South America: A Review

Identification of species is crucial in understanding how diversity changes affect ecosystemic processes. Particularly, soil microbial are key factors of ecosystemic functioning .Among soil microbes, arbuscular mycorrhizal fungi (AMF, phylum Glomeromycota) are worldwide distributed and form symbiotic associations with almost 80% of the vascular plants of the earth, except for one species, Geosiphon pyriformis, which associates with the cyanobacteria Nostoc. AMF comprise around 300 morphologically defined or 350–1000 molecularly defined taxa. Since AMF associate with aboveground community, their occurrence and composition can influence ecosystemic processes either through affecting plant community composition and thus its processes rates, or soil microbial communities, which are directly involved in nutrient cycling. Soil microorganisms are considered a potentially suitable target for studying regional and local effects on diversity. The symbiosis with AMF not only increases nutrient uptake by the plant of mainly phosphorus (P) and nitrogen (N) in exchange for plant-assimilated carbon (C), but also improves the tolerance of plants to various biotic and abiotic stresses such as pathogens, salinity, and drought

Biological parameters of Bemisia tabaci (Gennadius) Biotype B (Hemiptera: Aleyrodidae) on Jatropha gossypiifolia, Commercial (Manihot esculenta) and wild cassava (Manihot flabellifolia and M. carthaginensis) (Euphorbiaceae)

Bemisia tabaci (Gennadius) is one of the most important pests of cassava in Africa and several countries of Asia due to the damage caused by direct feeding, the excretion of honeydew, and its capacity as a vector of cassava mosaic geminivirus. There is a general consensus that B. tabaci is a complex of morphologically indistinguishable populations with different biotypes. In the Americas, the polyphagous biotype B does not appear to feed on cassava. Recent studies indicate that it is possible, however, for biotype B to gradually adapt to cassava using phylogenetically related hosts. Therefore, the possibility that some wild species of cassava constitute intermediate hosts in the adaptation process may lead to the establishment of biotype B on commercial varieties of Manihot esculenta. In here, we evaluated Jatropha gossypiifolia, two wild species of cassava (Manihot flabellifolia and M. carthaginensis) and a commercial cassava variety (MCol 2063) as hosts of biotype B. The highest oviposition rate (2.7 eggs /two days) occurred on M. esculenta, although the development time (44 d) was the longest when compared to M. carthaginensis and J. gossypiifolia. About 60% of the population could reproduce on the wild cassava species vs. 55% on J. gossypiifolia and 27.5% on the commercial variety. Our data suggest that J. gossypiifolia is a suitable host and the wild species M. carthaginensis can constitute a potential intermediate host in the adaptation of biotype B to commercial varieties of cassava

Tasa intrínseca de crecimiento de Aleurotrachelus socialis (Hemiptera: Aleyrodidae) en yuca Manihot esculenta = Intrinsic rate of population increase of Aleurotrachelus socialis (Hemiptera: Aleyrodidae) in cassava Manihot esculenta

La mosca blanca Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae) es una de las plagas más importantes en el cultivo de yuca (Manihot esculenta Crantz) en el Neotrópico. En Colombia, es el principal limitante del cultivo en los departamentos del Cauca, Valle del Cauca y Tolima ocasionando pérdidas en rendimiento en campos experimentales hasta del 79%. En 1995 esta especie ha colonizado e incrementado sus poblaciones en nuevas variedades y áreas donde anterior- mente era una plaga secundaria. Con el objetivo de conocer el potencial de A. socialis para desarrollar poblaciones en nuevos materiales de yuca, se estimaron los parámetros biológicos y los principales estadísticos vitales de este insecto plaga, realizando bioensayos bajo condiciones controladas (25± 2º C, 70±5% HR, 12L:12D) sobre las variedades Chirosa (MCOL 2066), Ica Armenia (HMC1) y CMC 40. Los resultados mostraron que las hembras de A. socialis vivieron más tiempo (6,4 días) sobre el genotipo CMC-40 y presentaron un alto potencial reproductivo (33,8 huevos por hembra). Por el contrario el menor tiempo de desarrollo (32,72 días) se obtuvo en el genotipo HMC1. Los tres genotipos presentaron altas tasas de supervivencia, siendo mayor en HMC1 (89%). El mayor incremento de las poblaciones (r m ) se presentó en los genotipos HMC1 (0,167 día -1) y CMC40 (0,079 día -1). Los parámetros biológicos y poblacionales obtenidos constituyen una herramienta básica para elaborar estrategias de control de A. socialis. = The whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae) is one of the most important pests in cassava (Manihot esculenta Crantz) crops in the Neotropics. In Colombia, this is the major pest to the crop in the departments of Cauca, Valle del Cauca and Tolima, causing yield losses in experimental fields of up to 79%. Since 1995, this species has colonized and increased its populations in new varieties and areas where it was a secondary pest before. To estimate the potential of A. socialis to develop populations in new cassava varieties, the biological parameters and the main vital statistics of this pest were evaluated under controlled conditions (25± 2º C, 70±5% HR, 12L:12D) on the varieties Chirosa (Mcol 2066), Ica Armenia (HMC1) and CMC 40. The results indicated that A. socialis females lived for a longer time (6,4 days) on the genotype CMC-40 and showed a higher reproductive potential (33.8 eggs per female). On the contrary, the lowest developmental time (32,72 days) was obtained on the genotype HMC1. The three genotypes showed high survival rates, being highest on HMC1 (89%). The greatest population increase (rm) was found on HMC1 (0,167 day-1) and CMC40 (0,079 day -1). The biological and population parameters obtained constitute a basic tool to elaborate control strategies for A. socialis

Desarrollo y reproducción de Bemisia tabaci "B" (Hemiptera: Aleyrodidae) sobre genotipos de yuca (Manihot esculenta) = Development and reproduction of Bemisia tabaci "B" (Hemiptera: Aleyrodidae) on cassava (Manihot esculenta) genotypes

Los geminivirus del mosaico de la yuca (CMGs) (Geminiviridae, Begomovirus) y su vector la mosca blanca, Bemisia tabaci, ocasionan las mayores pérdidas en el rendimiento de raíces a cultivos de yuca en África y Asia. Evidencias recientes sugieren que B. tabaci representa un complejo de poblaciones indistinguibles morfológicamente con numerosos biotipos. En las Américas, aunque la yuca parece no ser un hospedero conveniente para el polífago biotipo B, se ha postulado que la ausencia de CMGs y daño mecánico están relacionados con la inhabilidad de este biotipo para colonizar eficientemente este cultivo. No obstante, resultados previos han demostrado que su adaptación a yuca, vía hospederos alternos, es un riesgo que debe tenerse siempre en mente. Este estudio tuvo como objetivo principal evaluar el desarrollo y la reproducción del biotipo B de B. tabaci al alimentarse sobre tres genotipos de M. esculenta (MEcu72, CG489-34 y CMC-40). A través de bioensayos bajo condiciones controladas (25 ± 2°C, 70 ± 5 HR. 12L:12O) se evaluó longevidad, fecundidad, supervivencia y parámetros demográficos, mediante tablas de vida. Aunque las longevidades medias para MEcu72, CG489-34 y CMC-40 fueron similares (6,3, 5,07 y 3,9 días, respectivamente), CMC-40 presentó la tasa de oviposición más baja (0,49 huevos/hembra/2días) comparada con MEcu72 (0,89) y CG489-34 (0,86). Con una tasa de supervivencia muy baja (0,03) MEcu72 fue el único genotipo donde el biotipo B completó su desarrollo de huevo a adulto, necesitando 55,1 días. Los resultados son discutidos evaluando el potencial de adaptación de B. tabaci en Sur América sobre genotipos comerciales de yuca. = The geminiviruses of cassava mosaic virus (CMGs) (Geminiviridae, Begomovirus) and their whitefly vector, Bemisia tabaci, produce the major losses in root yield of cassava crops in Asia and Africa. Recent evidence suggests that B. tabaci represents a complex of morphologically indistinguishable populations with numerous biotypes. In the Americas, although cassava seems not to be a suitable host for the polyphagous biotype B, it has being postulated that the absence of CMGs and the mechanical damage are related with incapability of this biotype to colonize efficiently this crop. However, previous studies have demonstrated that their adaptation to cassava, via alternate hosts, is a risk that must always be kept in mind. The main objective of this study was to evaluate the development and reproduction of B. tabaci biotype B feeding on three genotypes of M. esculenta (MEcu72, CG489-34 and CMC-40). Bioassays, carried out under controlled conditions (25±2°C, 70±5RH; 12:12 LD), were used to evaluate longevity, fecundity, reproduction and demographic parameters through life tables. Although mean values for longevity were similar in MEcu72, CG489-34 and CMC-40 (6.3, 5.07, and 3.9 days, respectively) CMC-40 showed the lowest oviposition rate (0.49 eggs/female/ 2days) compared with MEcu72 (0.89) and CG489-34 (0.86). With a very low survival rate (0.03), MEcu72 was the only genotype where the biotype B was able to complete its development from egg to adult, requiring 55.1 days. Results are discussed in terms of evaluating the potential adaptation of B. tabaci on commercial cassava genotypes