Screening tropical maize lines for resistance to downy mildew by Peronosclerospora sorghi (Weston & Uppal) C. G. Shaw. J. M. ALEZONES, A. D. González, V. R. Barrientos, and A. A. Chassaigne. Fundación Danac, Carretera Panamericana, encrucijada Marín – San Javier, vía Guarataro, Estado Yaracuy, Venezuela, CP 3201.
Downy mildew of maize is a serious disease in tropical countries. Techniques used for screening germplasm on field conditions are inconsistent and inefficient, due to environmental conditions and pathogen behaviour. Therefore, the identification of sources of resistance using a reliable screening technique is mandatory. For that reason, a controlled inoculation method was established to detect resistance in maize under controlled conditions. For its validation we used 80 Venezuelan maize inbred lines developed by Danac Foundation breeding program and a highly susceptible cultivar. The technique consisted in the inoculation of maize seedlings, using infected Sorghum verticilliflorum plant tissue releasing conidias of Peronosclerospora sorghi. This tissue was positioned in a manner that, conidias fell from above over young maize seedlings in a inoculation room at 17°C and 95% of RH. The day after the plants were located under greenhouse conditions for a 9 days incubation period. Then the seedlings were evaluated using a disease index that included number of infected leaves and severity of the injury. The analysis showed differences between genotypes and allowed us to detect a group of highly resistant lines (D35, D20, D10, D19, and D57). We conclude that the technique is reliable to identify genetic resistance in maize.
Correlations among fatty acids content, fungal infection and mycotoxin production by Aspergillus flavus and Fusarium moniliforme in Venezuelan corn hybrids. J. M. ALEZONES (1), C. Mazzani (2), V. R. Barrientos (1), A. A. Chassaigne (1), and O. Luzón (2). (1) Fundación Danac, Carretera Panamericana, encrucijada Marín – San Javier, vía Guarataro, Estado Yaracuy, Venezuela, CP 3201; (2) Universidad Central de Venezuela, Maracay, Estado Aragua, Venezuela.Worldwide, preharvest contamination of food commodities by mycotoxins is considered a serious health problem. Aspergillus flavus (AF) and Fusarium moniliforme (FM) grow and produce aflatoxins (AFL) and fumonisins (FMN), respectively, in grains of several crops. Unsaturated fatty acids (i.e. linoleic acid) and their derivatives are known to affect growth and mycotoxin production of AF. In order to determine the effect of five fatty acids on fungal contamination and mycotoxin production, 29 commercial white maize hybrids were sown at three localities of Venezuela. Grain samples were evaluated for AF and FM incidence, and for AFL, FMN and fatty acids content. Non parametric correlations revealed that palmitic acid concentration was positively correlated with FM incidence (r = 0,62**), AFL (r = 0,24*) and FMN (r = 0,27*) production, and that oleic acid was negatively correlated with FM incidence (r = –0,29*), and FMN production (r = –0,25*), likewise, and as we expected, AF and FM incidence were positively correlated with AFL (r = 0,57**) and FMN (r = 0,32**) production, respectively. We didn’t find a relationship between AFL content and linoleic acid concentration as other authors have reported. We predict that breeding schemes for better fatty acids profiles could have an incidence on mycotoxin production.
Yield losses caused by Maize dwarf mosaic potyvirus (MDMV), in genotypes of maize, inoculated mechanically, in the Department of Caldas, Colombia. C. M. Arango and G. Martínez. Universidad de Caldas, Manizales, Colombia.In order to generate information on the magnitude of the losses associated with MDMV in the Colombian Coffee Growing Area, the reduction in the production in three genotypes of maize was evaluated: ICA V-305, DEKALB 888 and SYNCO, all of which have been adopted by the farmers of this region. The study was carried out in the Montelindo Farm, municipality of Palestina, Caldas. The plants were inoculated mechanically in six different developmental stages: first leaf, fourth leaf, sixth leaf, eighth leaf, tenth leaf, and twelfth leaf; the development of the symptoms was evaluated, as well as the weight of the seeds at harvest time, in order to determine, according to the age of the plant at the moment of inoculation, the effect on the yield. The results showed that the disease caused higher losses when the inoculation occurred in the first developmental stages, being less severe as the plants were inoculated in the later stages. On average, in the three evaluated genotypes the losses reached 75.72% when the virus was inoculated in the first leaf; but these losses decreased to 69.58%; 48.41%; 36.98%; 11.08% and they were just of 6.12%, when the plants were inoculated in the fourth, sixth, eighth, tenth and twelfth leaf respectively. These results confirm the importance of implementing preventive control practices of MDMV, especially during the first stages of development of the crop. The implementation of these practices is more important when materials that do not present characteristics of genetic resistance to the virus are sowed. Keywords: Virus, inoculation, symptoms, yield.
Differential induction of PAL and PFO in stems and roots of carnation (Dianthus caryophyllus L.) during the interaction with Fusarium oxysporum f. sp. dianthi race 2. H. ARDILA, B. Baquero, and S. Martínez. Universidad Nacional de Colombia, Química.The Vascular wilting caused by Fod race 2, is one of the major incidence diseases in the carnation production. The aim of this research was studying the biochemical mechanisms that regulate the response of defense in this model. In the present study, the modulation and differential induction of Polyphenol oxidase (PFO) and Phenylalanine Ammonium Liase (PAL) was evaluated at level of stem and root. Therefore, some kinetic parameters of these enzymes were partially characterized in extract from stems and roots. An in vivo assay was carried out with cuttings of two varieties of carnation and different levels of resistance. The induction was done by inoculation with the pathogen and elicitation with an extract of cell wall obtained from the same one. At root level in the resistant variety, the PAL was induced by inoculation at 48 h and the PFO at 24 h. In stem the induction of the PFO was found at 48 h post inoculation, whereas for the PAL the levels did not turn out to be affected. However, 12 h after the elicitation with cellular wall, this enzyme presented a significant increase in its activity.
Exotic citrus diseases of concern for the Caribbean. R. H. BRLANSKY. University of Florida, Plant Pathology, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850.Exotic citrus diseases continue to be a threat for introduction into many countries in the Caribbean area. In the last 10 years some new diseases have already been found in many countries and have continued to spread to new areas. This presentation will discuss some of the most important exotic citrus diseases that have the potential or have already been introduced into the Caribbean area. It also will discuss some criteria that can be used to assess them as to their importance for introduction and establishment. Finally, the importance of budwood certification and education programs to mitigate the spread of these diseases will be presented.
Evaluation of the mitochondrial COI gene as a useful genetic marker for Myndus crudus and other Myndus spp. J. K. BROWN (1) and M. Dollet (2). (1) Department of Plant Sciences, The University of Arizona, Tucson, AZ 85721 USA; (2) CIRAD, Campus International de Baillarguet, 34398 Montpellier, Cedex 5 France.
In the Americas and Caribbean, the lethal yellowing (LY) phytoplasma causes a disease of palms transmitted by the leafhopper Myndus crudus (family, Cixiidae), which may not be the sole vector. In Vanuatu and Ghana LY-like diseases also are rampant in coconut palm but M. taffini is thought to be a vector. Recently, high mortality in disease-resistant palms has occurred widely. The availability of a molecular marker would make possible the tracking of distribution and dispersal behaviors of Myndus species in relation to epidemic and non-epidemic areas. We employed PCR and mtCOI primers [F-C1-J-2195, R-L2-N-3014] to amplify from DNA extracts a 780 bp fragment. Phylogenetic analysis sorted putative Myndus spp. into three main clades: adiopodoumeensis (Ghana), crudus (Caribbean), and taffinii (Vanuvatu), the latter which comprised two sister groups. A fourth Myndus spp. from Oaxaca MEX grouped uniquely from other New World collections and herein has been identified as a new, putative vector species.
Polyphenoloxidase and peroxidase induction in the Lulo fruit (Solanum quitoense L.) by infection with Colletotrichum acutatum. O. CAICEDO and B. Higuera. Univ. Nacional de Colombia, Química, Bogotá.The anthracnosis caused by Colletotrichum is a problem among the Lulo growers and consumers. On the fruit, the illness starts with a black patch on the peel and it extends to the pulp provoking an unpleasant flavor. The behavior of peroxidase POD and polyphenoloxidase PPO on lulo fruits peel, healthy or infected with C. acutatum, was evaluated. Methodologies for extraction and activity measure were implemented. We determine that the best extraction buffer system is phosphate 100 mM, PVPP, SDS, using acetone dust. For the activity measure there were established pH 7 and 6,5; 27 and 55°C; substrates cathecol 40 mM and H(2)O(2) 10 mM plus guaiacol 15 mM, respectively. The enzymes were evaluated for healthy green G, semi mature SM and mature M fruits, finding a progressive PPO increase from G to M, while the major POD activity was found for G fruits, followed by M and SM. Lulos were inoculated (C. acutatum) 1 × 10(^5) conidias mL(^–1)) and enzymes were measured. The results showed that it produced an important PPO activation in M fruits after inoculation, then, this enzyme could be related with the fruit-pathogen interaction.
Evaluation of some biochemical responses in resistant and susceptible plants of yam (Dioscorea spp.) by interaction with Colletotrichum gloeosporioides f. alate. L. CERÓN (1), B. Higuera (1), H. Ardila (1), and G. Buitrago (2). (1) Dept. Química; (2) Inst. Biotecnología Univ. Nacional de Colombia, Bogotá.
The yam, a basic and traditional cultivar of the Atlantic Colombian region, has been affected due to the anthracnose disease caused by C. gloeosporioides. This fact, and the lack of studies about this model, constitutes a serious limitation for the disease control. We examined the callose content and the peroxidase (POD), polyphenoloxidase (PPO), and beta-1,3-glucanase (GLU) activities in this interaction, using a resistant D. alata var. TDA and susceptible D. rotundata var. Espino species, and the treatment with elicitors derived from the pathogen in the susceptible var. It was observed that the resistant specie induced biochemical responses as the POD activity and the callose content within 4 h. In contrast, the susceptible exhibited low levels of those parameters. The elicitor application by aspersion induced increased level of GLU and POD while the application by injection induced PPO and callose. This research may postulate the use of fungal elicitor as an alternative that became during to the disease control.
Antimicrobial activity of Minthostachys mollis (Lamiaceae) essential oil. N. CHICA (1), J. Sánchez (1), A. K. Carrascal (2), and L. M. Melgarejo (1). (1) Biology Department, Physiological Stress and Plant and Microorganisms Biodiversity Group, Sciences Faculty, Universidad Nacional de Colombia, Bogotá, Colombia, Universitary City; (2) Food Microbiology Laboratory, Environmental Biotechnology and Microbiology Group Sciences Faculty, Pontificia Universidad Javeriana, Bogotá, Colombia. firstname.lastname@example.org, email@example.comThe antimicrobial activity of Minthostachys mollis essential oil at different concentrations (3.5 to 100 µg/ml, and pure) was tested against the plant pathogens, Erwinia amylovora, Pseudomonas syringae, Colletotrichum acutatum, C. gloeosporioides, and Alternaria alternata, by antimicrobial disk susceptibility test for bacteria and the well method for fungi, using oxytetracycline and Acrobat™ (Dimetomorf and Mancozeb) as controls. The effect on count of viable of E. amylovora and A. alternate was tested by exposure to the essential oil. All microorganisms were susceptible to the oil and there was a direct relation between concentration and size of the growth inhibition zone. Strong antimicrobial activity was observed for C. acutatum, with 100 percent susceptibility for all concentrations, the bacteria were susceptible at 50 µg/ml and higher. Effect of the oil at 100 µg/ml was 2.5 and 3.5 times as strong as that of the oxytetracycline and Acrobat™. A total reduction in the count of viable (6 LU) for A. alternate, and a bactericide effect for E. amylovora were observed. Chemical composition of the oil was determined by gas chromatography-mass spectrometry. The main components of the essential oil were carvacril acetate, carvacrol, pulegone and mentone; antimicrobial activity was attributed to their way of action in the cell. This is the first report from M. mollis essential oil exhibiting antimicrobial activity against plant pathogens.
Control of white mold and web blight on lima bean grown for processing. K. L. Everts (1,2) and X. G. Zhou (1). (1) University of Maryland, Salisbury, MD 21801; (2) University of Delaware, Georgetown, DE 19947.Several diseases limit yields of lima and snap beans grown in Maryland and Delaware. White mold (Sclerotinia sclerotiorum), which is endemic in coastal regions and along the Delaware Bay, causes yield losses of 20%. Web blight (Rhizoctonia solani) also is a frequent cause of discolored seed in lima bean. Fungicides available for management of white mold became limited due to changing U.S. pesticide regulations, and little data existed on efficacy of newly registered alternatives. Multi-year experiments were conducted on the efficacy of reduced-risk fungicides and foliar- and soil-applied biofungicides. The soil-applied biofungicide Coniothyrium minitans and the fungicide boscalid reduced the number of white mold-infected pods and increased yields. The fungicides cyprodinil + fludioxonil, fluazinam, and thiophanate-methyl gave an intermediate level of white mold control. Boscalid also reduced the amount of white mold sclerotia and infected pods remaining on the soil surface at the end of the growing season. The biofungicide Bacillus subtilis reduced the number of discolored seed, but only in one year.
First report of Rhizoctonia zeae in Cynodon dactylon in Cuba. MARLENY GONZÁLEZ GARCÍA, Elda Ramos Ramos, y Rebeca Ramírez. Plant Health Institute, Cuba.Rhizoctonia is a soilborne fungus of considerable importance not only in Cuba but in the world, due to the losses that it causes in several crops, the wide host range and its distribution. In Cuba, the record of species for this genus is poor, due to difficulties with the taxonomic classification. In the last years Rhizoctonia occurrence has been increased in the western part of the country, it shows the ability of adaptation to different conditions such as: soil, temperatures and humidity. In the present work it is informed the presence of Rhizoctonia zeae causing patches in golf fields sowed with Bermudagrass (Cynodon dactylon) in Matanzas. The observed symptoms were necrotic lesions in the stems and leaves. It was achieved the isolation and identification of Rhizoctonia zeae in seven of 11 samples tested. The pathogenic tests were carried out and the symptoms were reproduced. This is the first report of this species as causal agent of patches in bermudagrass, and olso C. dactylon is a new host for R. zeae in Cuba. Keywords: Rhizoctonia zeae, Cynodon dactylon, patches.
The complete sequence of the Cytoplasmic citrus leprosis virus (CCLV) and its genome organization. A. S. GUERRA (1), K. L. Manjunath (2), R. H. Brlansky (1), and R. F. Lee (2). (1) University of Florida, Plant Path Dept., CREC, Lake Alfred, FL 33850; (2) USDA ARS, Riverside, CA 92507.Leprosis, an emerging invasive disease of citrus in Central America, has been present in South America for several years. Leprosis does not occur in the U.S. or the Caribbean Islands, but these regions are threatened by the disease. We have described the association of a bipartite, positive-sense RNA virus associated with the cytoplasmic citrus leprosis. The CCLV RNAs were identified from a cDNA library created from citrus naturally infected with the cytoplasmic leprosis disease from Panama. Here we report the complete sequence of the CCLV bipartite genome. RNA 1 possesses two open reading frames (ORFs). ORF 1 in RNA 1 encodes a putative 276 kDa polyprotein containing domains similar to the Sindbis-like virus super group having putative methyltransferase, cysteine protease, RNA helicase and RNA dependent RNA polymerase motifs. ORF 2 in RNA 1 shows no similarity with other sequences in the Genbank. RNA 2 has three ORFs. While ORFs 1 and 3 of RNA 2 show no similarity with sequences in the Genbank, ORF 2 encodes a putative 30.6 kDa viral movement protein.
Infectivity of Merremia mosaic virus clones: A bipartite begomovirus from Puerto Rico. A. M. Idris (1), J. Bird (2), and J. K. BROWN (1). (1) Department of Plant Sciences, The University of Arizona, Tucson, AZ 85721 USA; (2) College of Agricultural Sciences, University of Puerto Rico, Rio Piedras, PR 00928.Merremia mosaic virus (MeMV) is a bipartite begomovirus (family, Geminiviridae). MeM disease symptoms and its transmissibility by B. tabaci were reported by Bird (~1958) from indigenous Merremia quinquefolia and M. aegyptia in Puerto Rico (PR). Until now, the MeMV DNA-A and -B components had been cloned only from symptomatic tomato from PR. Total DNA extracted from symptomatic tomato plants, and from leaves of M. quinquefolia and M. aegyptia weeds were used in rolling circle amplification (RCA) to obtain full-length genome-size fragments (~2.6 kbp). Based on the PR tomato isolate sequence, unique restriction sites were identified to enable cloning the DNA-A (Hind III) and DNA-B (Nco I) components. The DNA sequence was determined for the A (2557 bp) and B (2492 bp) component, which each shared >98% identity with MeMV-tomato components. Clones were biolistically inoculated to tomato and M. quinquefolia and symptoms that developed (14 days PI) were indistinguishable from those of natural infections.
Papaya ring spot virus affects tomato plants in west Mexico. J. L. MARTÍNEZ, P. Posos-Ponce, C. M. Duran-Martínez, and J. Santillán-Santana. Universidad de Guadalajara, CUCBA, Zapopan, Jalisco, México. C.P. 45110.Various laboratory and field studies were conducted in 2003 and 2004 with the objective of determining the incidence and distribution of Papaya Ring Spot Virus (PRSV) affecting the tomato crop. Various fields were sampled to determine the incidence and distribution of the disease. We collected samples of weeds growing near the planting area and samples of plantas mostrencas of other crops. There were a total of 19 sampling sites in six locations of the region. The presence of PRSV in the samples was confirmed in the laboratory though serological tests (DAS-ELISA, AGDIA). PRSV was identified in all the sampling sites and the virus was in combination with other viruses. The incidence of the virus in the plants ranged from 3% to 100%. PRSV was found in combination with Potato Leaf Roll Virus (PLRV) in plantas mostrencas of Physalis filadelfica. In wild plants, PRSV was found alone in a bush known as “Taziste” (Genus Montanoa, Family Compositae). The presence of PRSV in this bush may be important since the incidence of PRS was strongly associated with the presence of Taziste near the planting area.
Serological analysis of Colombian Citrus tristeza virus isolates. S. Martínez and M. Guzmán B. Universidad Nacional de Colombia, Bogotá.Citrus tristeza virus (CTV) causes stem pitting (SP) in some citrus. Symptomless field trees were analyzed for SP isolates using serology. The major virus coat protein (p25) of virus isolates from 44 oranges and 22 Tahiti limes was detected with Agdia antibody using DAS-ELISA and for strain discrimination with MCA13 antibody with coating antibodies (Agdia or Spanish 3CA5+3DF1) using ELISA-DASI. Two antibody combinations, 110/109 or 109/10E3, reported as promising for the detection of SP isolates also were used. All the oranges and 21 of the limes were CTV positive. The use of MCA13 with Spanish coating antibodies was sensitive for identifying 6 additional severe samples. The sandwich 109/10E3 detected some MCA13 negative orange isolates that were confirmed later as SP by CPG sequence comparison. The two antibody combinations used showed no correlation between them. This study increases the information on CTV in Colombia, confirming the existence of severe strains with the antibody MCA13 that recognized a large spectrum in the presence of Spanish 3CA4+ 3DF1 antibodies and detection of SP isolates with 109/10E3 antibodies. Not everything that is MCA13-negative is mild CTV.
Contribución a la clasificación sexológica de algunos aislamientos colombianos, del virus de la tristeza de los cítricos por medio de la proteína de la cápside. S. T. MARTINEZ y M. Guzmán. Universidad Nacional de Colombia (Departamento de Química, Instituto de Biotecnología) Bogotá, Colombia.El virus de la tristeza de los cítricos (CTV) es un patógeno deletéreo para la citricultura mundial. Causa diversos síntomas como decaimiento rápido de la planta y acanalamiento del tallo (SP) que son severos y reducen la producción de frutos y pueden causar la muerte del árbol. El objetivo del presente trabajo fue buscar cepas SP por caracterización serológica de aislados de cítricos recolectados en campo de tres regiones de Colombia, para lo cual se utilizaron anticuerpos que detectan el virus (Casa Agadia), un anticuerpo para diferenciar cepas severas de suaves (MCA13)y dos pares de anticuerpos (110/109 y 109/10E3) informados como promisorios para reconocer cepas SP en muestras cultivadas en invernadero. En total 66 cítricos entre naranjas y limones de las regiones de Quindío, Meta (Corpoica) y Antioquia. se analizaron por la técnica de ELISA DAS, donde se encontró 100% de positividad en naranjas de Quindío y Meta y 98% en limones de Antioquia. Posteriormente, se utilizó la técnica ELISA DAS-I con el anticuerpo monoclonal secundario MCA13, sobre dos ensayos: con anticuerpo de cubrimiento de la casa Agdia o con cubrimiento con los anticuerpos españoles (3DF1+3CA5). Este último ensayo mostró mayor sensibilidad ya que se reconocieron 6 muestras severas más que en el ensayo con el anticuerpo Agdia. Para detectar posibles aislados tipo SP en naranjo se utilizaron los pares de anticuerpos cubrimiento/detección 110/109 y 109/10E3. Entre ellos no se encontró una correlación similar a la informada en la literatura para plantas en invernadero, sin embargo, el anticuerpo 10E3 permitió seleccionar aislados que se caracterizaron posteriormente por secuenciamiento y presentaron una alta homología con cepas severas SP. El presente trabajo amplió el conocimiento de las regiones colombianas en las cuales esta presente CTV, confirmando la existencia de cepas severas con el Ac MCA13 el cual reconoce un espectro mayor de cepas en presencia de los anticuerpos 3DF1 + 3CA5. No todo lo que es MCA 13 negativo es CTV suave.
Biochemical study of enzymes induced in carnation as a response to Fusarium oxysporum f. sp. dianthi. R. MAYORGA and B. Higuera. Univ. Nacional de Colombia Química, Bogotá.Over the last years the Colombian carnation production has been affected with the presence of Fusarium oxysporum f. sp. dianthi (FOD), which causes vascular wilt. In spite of alternatives for the disease control the problem has not been resolved. The study of the biochemical responses that are activated for defense in carnations, has been developed by our research group and has allowed us to determine that changes are produced in enzymatic activities as Polyphenoloxidase PPO and beta-1,3-Glucanase GLU, enzymes that have been associated with resistance in other models. We proceeded for its isolation, purification and biochemical characterization, once they were induced by stems inoculation of a tolerant var. The purification was made by chromatographic processes, after that, they were characterized as: MW 30 and 40 KDa, IP 8.8 and 5.0; Vmax 55 and 322 U min(^–1), Km 0.70 mg mL(^–1) and 249 mM, for GLU and PPO respectively. The purified proteins or its products (PPO) showed in vitro inhibition of FOD, obtaining at 24h 58% (PPO) and 75 (GLU). This allows postulating that they are possibly associated with defensive responses of carnation to FOD.
Sustratos para bacterias líticas en la filosfera de banano y plátano en el control de sigatoka negra. L. F. PATIÑO (1), L. M. Salazar (2), J. C. Collazos (3), R. A. Piedrahita (3), y E. Bustamante (3). (1) Politécnico Colombiano Jaime Isaza Cadavid. Carrera 48 N° 7-151 Medellín-Colombia; (2) Bacterióloga, Inst. Col. de Medicina Tropical; (3) Augura-Cenibanano.El control de la Sigatoka Negra (Mycosphaerella fijiensis Morelet), se fundamenta en fungicidas químicos, a los cuales el patógeno ha desarrollado resistencia, aumentándose los costos de control y el impacto negativo sobre el ambiente, sumado a la exigencia de los consumidores por una fruta con menor uso de plaguicidas. La biorregulación, una alternativa escasamente investigada, podría contribuir eficazmente al manejo de la enfermedad. Debido a esto, se desarrolló una estrategia basada en el estudio y manipulación de algunos de los factores bióticos y abióticos que interactúan en la filosfera de banano y plátano. La caracterización química (contenido de nutrimentos) y microbiológica parcial, reveló lo crítico de las necesidades nutricionales para la microflora de interés, lo cual fundamentó la formulación de diferentes sustratos foliares que fomentaran las poblaciones naturales de estos agentes biológicos, y verificó la presencia de poblaciones bacterianas quitinolíticas y glucanolíticas, las cuales tienen potencial de regulación de M. fijiensis (principalmente, bacilos gram-negativos). Los sustratos disponían de una solución mineral base, quitina coloidal [4%], harina de cebada [2,5%] y urea [1%], solos o en combianciones. Posteriormente se evaluó el efecto de estos sustratos foliares sobre el control de la enfermedad, en plantas adultas de banano y plátano en condiciones de campo, logrando una reducción entre un 43–46% en el número de ciclos de fungicidas convencionales, cuando los sustratos fueron aplicados en mezcla y rotación con los fungicidas. Los resultados de esta investigación pueden significar altos beneficios económicos, ambientales y de competitividad para la fruta exportada.
Host number increase for Erysiphaceae family and its relationships with Erysiphaceae family temperature. Y. Pérez (1), D. López (1), M. O. López (1), G. Gómez (1), M. Veitía (1), R. Vega (2), and O. Solano (2). (1) Plant Protection Institute Research; (2) Meteorology Institute, Cuba.Erysiphaceae family comprise the fungal genera that cause powdery mildew disease. The higher incidences have been occurred in dry season with temperatures between 20 and 26°C in Cuba. A search was performed in all official publications recording fungi in Cuba including the most recent papers. In 2004 and 2005 were collected plants with symptoms of the disease in several provinces. The genus and some species were determined by stereomicroscopy and microscopic studies. A possible correlation between the number of hosts for Erysiphaceae family recorded and temperature increase since 1918 to 2005 was studied. It was found for the first time new hosts of this family which comprises plant species such as Anethum graveolens, Brassica nigra, Chenopodium ambrosoides, Eryngium foetidum, Impatiens sp., Jatropha gossypifolia, Matricaria recutita, Mentha nemorosa, Physalis sp., Rosmarinum officinalis, Stachytarpheta jamaicencis, Tamarindus indica, and Thymus vulgaris. Keywords: Powdery mildew, host, temperatures.
Alternative management of damping-off (Fusarium sp., Rhizoctonia sp., Sclerotium sp.) in tomato in Jocotepec, Jalisco, Mexico. P. POSOS, J. L. Martínez, C. M. Duran, and J. Santillán. Universidad de Guadalajara, CUCBA, Zapopan, Jalisco, México, C.P. 45110.We conducted field and laboratory studies during the fall/winter 2005 season with the objective of determining the efficacy of the fungicide-bactericide Rhizomarr 18% SL (potassium permanganate 18%) to control damping-off Fusarium sp., Rhizoctonia sp., Sclerotium sp.) in tomato (Lycopersicon esculentum L. cv. Río Grande) in Jocotepec, Jalisco, México. Rhizomarr was applied as a drench, at the base of the stem. The treatments were: Rhizomarr at 1, 2 or 3 liter/ha (180, 360 or 540 gram i.a./ha); Bunema (Metam sodium) 55 at 185 liter/ha (83 kg i.a./ha) (conventional treatment), and an untreated control. The variables measured in the field were incidence and severity of the disease and those in the laboratory were the number of colony-forming units in treated soil. Metam sodium controlled damping-off at 86% compared to an average of 88% with Rhizomarr 18%. There were no differences in the control of damping-off as affected by the rate of Rhizomarr 18%. The results of the laboratory were similar to those of the field.
Phytopathology and food webs: About elephants and earthworms? R. Quiñones. Applied Biology, U. Militar Nueva Granada, Colombia.Using detrivorous arthropods as potential ecosystemic intermediaries between beneficial microorganisms and phytopathogens, is an interesting research hypothesis. Preliminary conclusions of a taxonomic food web study in a kikuyu (P. clandestinum) dairy pasture in a tropical mountain plateau, showed the detritivores as a meaningful food web compartment. Members of this web knot may act as incubating bioreactors, transporting media, dispersal and inoculating agents within a crop. The detritus found at the Horizon “O” of almost any terrestrial ecosystem, derives from primary biomass fixation; it is also a habitat that contains this important food web compartment. Phytopathologically, the horizon “O” is also a hypothetical source for microflora diversification; ecologically, should provide biodiversity to agroecosystems, particularly as potential source for preys and hosts for beneficial control agents, but also may be source of natural dispersal agents, which may act as natural “gut incubators” or bioreactors for the microflora. In consequence, the agricultural new developments should consider explicitly the importance of the forgotten Horizon “O” and its associated detritivores, as central elements for present and future agroecological and phytopathological research on microflora diversity for agriculture.
Coconut lethal yellowing: Current situation, research and future perspectives for Mexico, Central America, and the Caribbean. M. M. ROCA (1), C. Oropeza (2), and W. Myre (3). (1) Escuela Agrícola Panamericana, Zamorano, Po.Box. 93, Tegucigalpa, Honduras; (2) C. Oropeza Centro de Investigación Científica del Yucatán, Mérida, México CP 97200; (3) Coconut Industry Board, 18 Waterloo Road, Kingston 10, Jamaica W1.Lethal yellowing (LY) of coconut (Cocos nucifera L.) caused by a 16SrIV-A subgroup phytoplasma and transmitted by insect vectors has been present in the Americas since the 19th century. Thousands of palms were destroyed in Jamaica and Florida in the 60’s and 70’s before the epidemic spread to México in the 80’s and to Central American countries in the 90’s. In 2006, LY is present in most Caribbean Islands, including Cuba, Jamaica, Dominican Republic and Haiti, México, Honduras, Guatemala and Belize, where it continues to pose serious problems to coconut production and the tourist industry. Recent surveys in the Atlantic regions of Nicaragua, Costa Rica, confirmed that the disease has not spread to these countries. A high mortality of the tolerant Maypan hybrids and Malayan Dwarf varieties, replanted since the 70’s have been experienced in several “hotspots” throughout the region. As a response, a regional 5-year initiative, “Sustainable Coconut Production through the Management of Coconut Lethal Yellowing” was initiated in 2005 with financial support from The Common Fund of Commodities (CFC) with an emphasis on: replanting with Mexican tall varieties that have shown appropriate tolerant levels to the disease, identifying new resistant germplasm, improve the detection methods for the LY phytoplasma and other coconut diseases and pests through RT-PCR, multiplex systems and field ELISA tests, characterize the possible pathotypes that are causing the break in the resistance in hotspots through RFLP’S and sequencing analysis, and study the epidemiology of the diseases and possible spread through alternate hosts, embryo transmission and other insects other than the reported vector, Myndus crudus. Parallel efforts from the International community in genomics, tissue culture allow some promise in the long and difficult road towards managing LY.
Determinación de la presencia de geminivirus y fitoplasmas en tomate en Guatemala, El Salvador, Honduras y Nicaragua. M. M. ROCA y T. Escuela Toruño. Agrícola Panamericana Zamorano, P.O. Box. 93, Tegucigalpa, Honduras.Las infecciones virales en cultivos hortícolas en Centro América son el principal problema en la producción. En las últimas dos décadas se ha abusado de los agroquímicos para controlar a los insectos vectores, creando problemas de resistencia, contaminación ambiental y daños a la salud humana. Asimismo, en los últimos años, el cultivo de papa (Solanum tuberosum L.) ha sido afectado por una nueva enfermedad denominada “punta morada de la papa”, causada por un fitoplasma que disminuye la calidad de los tubérculos. Desde el 2000 se han promovido campañas en México y Centro América para hacer aplicaciones de antibióticos en cultivos de tomate, ya que los daños se atribuyen a fitoplasmas (susceptibles a antibióticos), que no han podido ser controlados por los insecticidas tradicionales utilizados para manejar infecciones virales. Estas recomendaciones se han hecho sin ningún análisis previo para establecer la etiología de estas enfermedades. El objetivo de este estudio fue establecer si los daños observados en zonas productoras de tomate (Lycopersicum esculentum) en Guatemala, El Salvador, Honduras y Nicaragua, donde se ha recomendado el uso de antibióticos agrícolas, es causado por geminivirus o por fitoplasmas. Se realizó una evaluación de campo, seguida por la recolección de muestras representativas y un análisis molecular en el laboratorio, para detectar la presencia de geminivirus o fitoplasmas. El análisis molecular se realizó utilizando la técnica de la Reacción en Cadena de la Polimerasa (PCR, por sus siglas en inglés) utilizando primers universales para fitoplasmas (P1, P7), y los primers para geminivirus (514, 1048). La sintomatología observada en plantaciones de tomate en las zonas muestreadas de los 4 países coincidió con infecciones virales, incluyendo aquellas causadas por geminivirus y no con los síntomas clásicos causados por fitoplasmas como el “stolbur” reportado en tomate en Europa, pero no en México o Centro América. De un total de 112 muestras recolectadas, el 64% resultaron positivas a geminivirus (94% Guatemala, 83% Honduras, 59% El Salvador y 26% Nicaragua) y en ninguna se detectó la presencia de fitoplasmas. El 36% de los otros daños pueden atribuirse a otros virus y/o a factores abióticos. El estudio concluye que el uso de antibióticos agrícolas no es justificado en las zonas del estudio ya que no se detectó la presencia de fitoplasmas.
Fusarium wilt of watermelon: The challenges of disease management and multiple pathogen races. X. G. Zhou (1) and K. L. Everts (1,2). (1) University of Maryland, Salisbury, MD 21801; (2) University of Delaware, Georgetown, DE 19947.Fusarium wilt of watermelon (Fusarium oxysporum f. sp. niveum) has become more prevalent in the mid-Atlantic region of the U.S. as the production of triploid (seedless) watermelon increases and use of methyl bromide is phased-out. A survey of watermelon acreage found that race 1 was the most common race, although race 0 or the highly aggressive race 2 also were present in more than 20% of fields surveyed. In addition, two isolates were more aggressive and caused significantly more vascular discoloration and stem colonization than race 2. These isolates, which were vegetatively compatible with each other but not race 2, are proposed as race 3. Experiments were conducted to evaluate management of Fusarium wilt with cultivar resistance and use of suppressive cover crops. No commercially grown triploid watermelons have an adequate level of resistance to Fusarium wilt. However, when triploid watermelons are grown following a green manure of hairy vetch (Vicia villosa) cover crop, losses were minimized. Use of hairy vetch to manage Fusarium wilt of watermelon is being tested in commercial production.