EFFECT OF IRRIGATION AND HYBRIDS ON MICROBIAL POPULATION DYNAMICS IN THE RIZHOSPHERE OF OIL PALM (Elaeis guineensis Jacq.)

Objective:This research was carried out to evaluate the effect of irrigation and hybrids on the population dynamics of microorganisms associated with the rhizosphere of oil palm (Elaeis guineensis Jacq.).Methods:Plots were installed under irrigated and non-irrigated conditions using three hybrids (Dura x Pisifera) of oil palm. A split-plot design was used, with three replications. Samples of soil were extracted and processed to determine the populations of functional groups of heterotrophic bacteria, actinomycetes, fungi, phosphorus (P) solubilizing microorganisms, and vesicular arbuscular (VA) mycorrhizae. Samples were taken during the wet season (June) and the dry season (August).Results:No significant differences were detected for bacterial populations (heterotrophic and actinomycetes) for irrigation and hybrids. Populations recorded for heterotrophic bacteria when water stress accounted for 28cbs were 7.43×106 CFU/g (colony forming units per g of dry soil) in irrigated plots, versus 5.86×106 CFU/g in non-irrigated plots. Fungal populations were 4.49×103 CFU/g in irrigated plots, while in non-irrigated plots were 1.81×104 CFU/g. Mycorrhizae levels ranged between 13.6% and 21.9% in irrigated and non-irrigated plots respectively. The populations of P -solubilizing microorganisms ranged from 6.64×105 CFU/g in irrigated plots, to 2.91×104 CFU/g in plots without irrigation.Conclusions:Under the conditions of this study, in the oil palm rhizosphere, there were not significant differences between the bacterial populations (heterotrophs and actinomycetes) for irrigation and hybrids.  Under the same conditions, significant differences were found among fungal populations, P-solubilizing microorganisms, and VA mycorrhizae, in the irrigation factor. The major bacterial populations were recorded in the rainy season 7centibars (cbs); meanwhile, the higher fungal populations were recorded in the dry season (28cbs). Hybrids not exert major influence on microbial populations under the conditions of this study. With some of the microorganisms isolated in this study, starting tests are needed to identify potential bio – fertilizers, and / or bio – enhancers of soil properties. Keywords: VA mycorrhizae, Phosphorus -solubilizing microorganisms, Oil palm, Heterotrophs, Irrigatio

Persistencia De Cepas De Bacillus thuringiensis Y Bacillus pumilus Potenciales Controladoras Biológicas De La Broca Del Café En Condiciones de Campo en Puerto Rico

Field trials were conducted in two years to evaluate persistence of B. thuringiensis and Bacillus pumilus under field conditions. Strains of B. thuringiensis (3971) and B. pumilus (4185) were isolated from coffee agro-ecosystem in Puerto Rico. Field trials consisted in plots of nine coffee trees arranged in a randomized complete block design, sprayed with Bt-3971 and Bp-4185 at 108, 109, or 1010 colony forming units CFU ml-1 or non-inoculated. In year 1, B. thuringiensis and B. pumilus survived up to six months after inoculation. Monitoring carried out during year 2, re-confirmed the survival of Bt-3971 and Bp-4185 inoculated in coffee trees under field conditions. Overall, Bt-3971 had significantly more recovery rates than Bp-4185. However, the higher bacterial recoveries were 1.24x1013 CFU ml-1 in coffee trees treated with Bt-3971 and 2.48x1013 CFU ml-1 in coffee trees treated with Bp-4185 in year 1 and year 2, respectively, both sprayed with 1010 spores ml-1. B. thuringiensis (3971) and B. pumilus (4185) isolated from coffee fields of Puerto Rico are well adapted to the environmental conditions of the island, and are valuable biological control agents against coffee berry borer.Ensayos de campo se llevaron a cabo en dos años para evaluar la persistencia de Bacillus thuringiensis y Bacillus pumilus. Las cepas B. thuringiensis (3971) y B. pumilus (4185) fueron aisladas del agro-ecosistema del cafeto en Puerto Rico. Los ensayos de campo consistieron en parcelas de nueve cafetos en diseño de bloques completamente aleatorizado. Los tratamientos fueron Bt-3971 y Bp-4185 a las dosis de 108, 109 y 1010 unidades formadoras de colonias por mililitro (UFC ml-1) y parcelas no inoculadas. En el año 1, B. thuringiensis y B. pumilus sobrevivieron hasta seis meses después de la inoculación (Marzo a Septiembre). Los monitoreos realizados de Marzo a Septiembre del año 2 , re-confirmaron la sobrevivencia de Bt-3971 y Bp-4185 bajo condiciones de campo en las unidades experimentales. En general, se recuperaron más aislados de los cafetos  tratados con Bt-3971 comparado con Bp-4185. Sin embargo, las tasas de recuperación de aislados más altas fueron 1.24 x 1013 UFC ml-1  en cafetos tratados con Bt-3971, y 2.48 x 1013  UFC ml-1 en cafetos tratados con Bp-4185 en los dos años respectivamente; ambos de cafetos tratados con la mayor concentración de esporas (1010 UFC ml-1). B. thuringiensis (3971) y B. pumilus (4185) aisladas del agro-ecosistema de cafeto en Puerto Rico están bien adaptadas a las condiciones de la isla, y son valiosas cepas para el control biológico de la broca del cafeto

Bacterial canker caused by Clavibacter michiganensis subsp. michiganensis in naranjilla in Ecuador

Bacterial canker of naranjilla or lulo (Solanum quitoense and Solanum pectinatum) is a new disease that could completely destroy naranjilla plants. The objectives of this study were to identify and characterize bacteria associated with canker wilt of naranjilla, and to determine the importance of wounds in the dissemination and transmission of bacterial canker.Symptoms of this disorder consist of dieback and leaves showing incurvature which was diagnostic to confirm bacterial wilt. Collapse of leaf panel on Nicotiana tabacum confirmed that the bacterium is phytopathogenic. This bacterium showed positive serological tests for Clavibacter michiganensis subsp. michiganensis, positive Gram reaction, growth on NCP 88, (ELISA+ GRAM+ NCP 88 +) as well as re-isolation through Koch postulates in Solanum cheesmanii. Aerial wounds appear to be the most important means for dissemination. More research is needed about the molecular characterization of the bacterium, and potential for the bacterium to be transmitted to other solanaceous crops. Keywords: emerging infectious crop diseases, Solanum quitoense, Solanum pectinatum, Solanum cheesmanii, Solanum hirsutu

Cancro bacteriano asociado a Clavibacter michiganensis subsp. michiganensis en naranjilla en Ecuador

Bacterial canker of naranjilla or lulo (Solanum quitoense and Solanum pectinatum) is a new disease that could completely destroy naranjilla plants. The objectives of this study were to identify and characterize bacteria associated with canker wilt of naranjilla, and to determine the importance of wounds in the dissemination and transmission of bacterial canker.Symptoms of this disorder consist of dieback and leaves showing incurvature which was diagnostic to confirm bacterial wilt. Collapse of leaf panel on Nicotiana tabacum confirmed that the bacterium is phytopathogenic. This bacterium showed positive serological tests for Clavibacter michiganensis subsp. michiganensis, positive Gram reaction, growth on NCP 88, (ELISA+ GRAM+ NCP 88 +) as well as re-isolation through Koch postulates in Solanum cheesmanii. Aerial wounds appear to be the most important means for dissemination. More research is needed about the molecular characterization of the bacterium, and potential for the bacterium to be transmitted to other solanaceous crops. Keywords: emerging infectious crop diseases, Solanum quitoense, Solanum pectinatum, Solanum cheesmanii, Solanum hirsutumLa marchitez bacteriana o cancro bacteriano de la naranjilla o lulo (Solanum quitoense y Solanum pectinatum) es una enfermedad con potencial para destruir completamente el cultivo. Los objetivos de este estudio fueron identificar y caracterizar la bacteria o bacterias asociadas al cancro bacteriano en naranjilla y determinar la importancia de las heridas en su transmisión y diseminación. Los síntomas de esta enfermedad consistieron en muerte descendente, y la curvatura de la nervadura principal que constituye un síntoma diagnóstico para la confirmación de marchitez bacteriana. El colapso del panel intervenal (propio de respuesta de hipersensibilidad) en Nicotiana tabacum permitió la confirmación de que la bacteria aislada era patogénica. Esta cepa bacteriana presentó serología positiva para Clavibacter michiganensis subsp. michiganensis, reacción Gram positiva, crecimiento en medio de cultivo semi-selectivo NCP 88 (ELISA+ GRAM+ NCP 88 +), así como re-aislamiento a partir de tejido de Solanum cheesmanii previamente inoculado para cumplir con los postulados de Koch. Heridas aéreas desarrolladas durante la poda con equipo de poda no desinfectado parece ser la forma principal de diseminación. Estudios adicionales son necesarios dirigidos hacia la caracterización molecular de la bacteria, y el potencial de diseminación de la bacteria hacia otras solanáceas. Palabras clave: enfermedades infecciosas emergentes, Solanum quitoense, Solanum pectinatum, Solanum cheesmanii, Solanum hirsutu

Epidemiology and Management of Fusarium Head Blight and Foliar Fungal Diseases of Wheat

Fusarium head blight (FHB) caused by Fusarium graminearum, the FHB-associated mycotoxin deoxynivalenol (DON), and foliar fungal diseases are significant threats to wheat production. This research 1) evaluated the effects of fungicide chemical class, application timing, and cultivar resistance on FHB and DON under field conditions; 2) evaluated the effects of field-applied fungicide chemical class, grain moisture, and time on DON under grain storage conditions; 3) evaluated the effects of field-applied fungicide chemical class and time on trichothecene-related gene (Tri5) expression under grain storage conditions; 4) determined the optimum F. graminearum spore concentration and spike bagging period following inoculation for accurately discriminating between FHB resistant and susceptible wheat cultivars under greenhouse conditions; and 5) determined the optimum timing of fungicide applications for control of foliar fungal diseases of wheat under field conditions. A triazole fungicide controlled FHB and DON more effectively than a strobilurin fungicide. A triazole applied 6 days after anthesis was as effective as an anthesis (standard timing) application, indicating a wider window of application for growers’ needed flexibility. In storage, DON decreased over time in grain of a moderately resistant cultivar treated with a triazole and increased in grain of a susceptible cultivar treated with a strobilurin. During storage, DON biosynthesis Tri5 gene expression increased over time during storage of high grain moisture grain, a significant reduction in the relative expression of the Tri5 gene and a downregulation of the gene occurred in the triazole treatment whereas expression of the gene increased in the strobilurin treatment. In the greenhouse, lower concentrations of F. graminearum inoculum (6.25 x 103 and 1.25 x 104 spores/mL) were more efficient in discriminating between a moderately resistant and a susceptible wheat cultivar compared to the standard concentration (1 x 105 spores/mL). The optimum spike bagging period following inoculation for discrimination between a moderately resistant and a susceptible cultivar was 48 hours or 72 hours (the standard). Foliar fungicide applications in field plots at the flag leaf and boot growth stages of wheat were more effective in protecting yield than later applications. Results from this research will enhance knowledge in the epidemiology and management of FHB, DON, and foliar fungal diseases of wheat. Advisors: Stephen N. Wegulo and Heather Hallen-Adam

Epidemiology and Management of Fusarium Head Blight and Foliar Fungal Diseases of Wheat

Fusarium head blight (FHB) caused by Fusarium graminearum, the FHB-associated mycotoxin deoxynivalenol (DON), and foliar fungal diseases are significant threats to wheat production. This research 1) evaluated the effects of fungicide chemical class, application timing, and cultivar resistance on FHB and DON under field conditions; 2) evaluated the effects of field-applied fungicide chemical class, grain moisture, and time on DON under grain storage conditions; 3) evaluated the effects of field-applied fungicide chemical class and time on trichothecene-related gene (Tri5) expression under grain storage conditions; 4) determined the optimum F. graminearum spore concentration and spike bagging period following inoculation for accurately discriminating between FHB resistant and susceptible wheat cultivars under greenhouse conditions; and 5) determined the optimum timing of fungicide applications for control of foliar fungal diseases of wheat under field conditions. A triazole fungicide controlled FHB and DON more effectively than a strobilurin fungicide. A triazole applied 6 days after anthesis was as effective as an anthesis (standard timing) application, indicating a wider window of application for growers’ needed flexibility. In storage, DON decreased over time in grain of a moderately resistant cultivar treated with a triazole and increased in grain of a susceptible cultivar treated with a strobilurin. During storage, DON biosynthesis Tri5 gene expression increased over time during storage of high grain moisture grain, a significant reduction in the relative expression of the Tri5 gene and a downregulation of the gene occurred in the triazole treatment whereas expression of the gene increased in the strobilurin treatment. In the greenhouse, lower concentrations of F. graminearum inoculum (6.25 x 10 3 and 1.25 x 104 spores/mL) were more efficient in discriminating between a moderately resistant and a susceptible wheat cultivar compared to the standard concentration (1 x 105 spores/mL). The optimum spike bagging period following inoculation for discrimination between a moderately resistant and a susceptible cultivar was 48 hours or 72 hours (the standard). Foliar fungicide applications in field plots at the flag leaf and boot growth stages of wheat were more effective in protecting yield than later applications. Results from this research will enhance knowledge in the epidemiology and management of FHB, DON, and foliar fungal diseases of wheat

Effects of field-applied fungicides, grain moisture, and time on deoxynivalenol during postharvest storage of winter wheat grain

Fusarium head blight, caused mainly by Fusarium graminearum Schwabe, results in major losses in wheat. In two separate field experiments, spikes of winter wheat cultivars ‘Overland’ (moderately resistant) and ‘Overley’ (susceptible) were sprayed at anthesis with the triazole fungicide Prosaro (prothioconazole + tebuconazole) or the strobilurin fungicide Headline (pyraclostrobin) or not sprayed. Following harvest, deoxynivalenol (DON) concentrations were monitored during 120 d of grain storage at 10 °C, 40% relative humidity, and 10%, 16%, or 20% grain moisture. In ‘Overland’, DON decreased significantly at P = 0.05 from an average of 3.6 to 3.0 μg g−1 in the check and decreased from 2.7 to 2.2 μg g−1 in the Prosaro treatment. DON did not significantly decrease (4.4–4.1 μg g−1) in the Headline treatment. DON concentrations did not differ between 16% (3.1 μg g−1) and 20% (3.0 μg g−1) grain moisture. In ‘Overley’, DON increased significantly from 3.1 to 3.6 μg g−1 in the check and from 2.9 to 3.5 μg g−1 in the Headline treatment, but remained the same at 2.2 μg g−1 in the Prosaro treatment. DON concentrations were not different between 16% (3.2 μg g−1) and 20% (3.1 μg g−1) grain moisture but were significantly lower (2.7 μg g−1) at 10% grain moisture. These results indicate that the effects of fungicides applied at anthesis in the field can impact DON concentrations through grain storage. Triazoles are recommended over strobilurins to achieve this extended postharvest protection from DON, and grain moisture during storage should be below the maximum safe level of 13.5% at 10 °C.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author