EFECTO DEL SOMBRÍO SOBRE LA SIGATOKA NEGRA (Mycosphaerella fijiensis MORELET) EN CULTIVO DE PLÁTANO cv HARTÓN (Musa AAB SIMMONDS)

La sigatoka negra en el cultivo del plátano es considerada como una de las enfermedades más limitante de la producción, a nivel mundial, siendo manejada con fungicidas, ocasionando contaminaciones ambientales e incremento de los costos de producción. Como estrategia no contaminante, algunos investigadores recomiendan cultivar en condiciones de sombrío, para reducir la enfermedad. El objetivo de este trabajo fue evaluar el efecto de diferentes porcentajes de sombrío en la incidencia de la enfermedad y en la producción, bajo condiciones del Caribe húmedo colombiano. En condiciones de campo, se estableció el cultivar '˜Hartón', en un diseño de bloques completos al azar y cuatro porcentajes de sombrío, 20, 35 y 50%, teniendo como testigo plantas cultivadas a libre exposición solar 100%. Las evaluaciones, se realizaron durante el periodo de floración del cultivo, cuantificando el número de hojas funcionales NHF, la hoja más joven con síntomas HMJS, la hoja más joven enferma HMJE, el índice de severidad IS y rendimiento. Los tratamientos con 20, 35 y 50% de sombrío no presentaron diferencias estadísticas entre sí; más sí, con el testigo en las variables NHF, HMJE, IS y rendimiento. Los tratamientos con sombra manifestaron menor IS de la sigatoka negra, de 13 al 15%, mientras el testigo fue del 18%; además, los rendimientos se incrementaron en 400kg ha-1. Se concluye, que el cultivo de plátano '˜Hartón', manejado a partir del 20% de sombrío, fue suficiente para reducir la severidad de la sigatoka negra e incrementar significativamente los rendimientos.

Black sigatoka in plantain cultivation is considered one of the most limiting production diseases worldwide. It is managed with fungicides, causing environmental pollution and increased production costs. As a nonpolluting strategy, some researchers recommend cultivating shade conditions to reduce the disease. The aim of this study was to evaluate the effect of different shade percentages in the incidence of disease and production under the Caribbean Colombian humid conditions. Under field conditions it was established to cultivate the '˜Harton' in a completely randomized block design and four shade percentages 20, 35 and 50%, having as control plants growing in 100% sun exposure. Evaluations were performed during the flowering period of the crop, quantifying the number of functional leaves NFL, the youngest leaf with symptoms YLS, the youngest diseased leaf YDL, the severity index SI and yield. Treatments with 20, 35 and 50% shade were not statistically different from each other; but with the witness in the NFL, YLS, SI and yield. Treatments with shade had lower SI of black sigatoka, between 13 to 15%; while the witness was 18%; also the yield increased in 400kg ha-1. It is concluded that growing '˜Harton', managed from 20% shade was enough to reduce the severity of black sigatoka and significantly increase yields.

Chemical management in fungicide sensivity of Mycosphaerella fijiensis collected from banana fields in México

The chemical management of the black leaf streak disease in banana caused by Mycosphaerella fijiensis (Morelet) requires numerous applications of fungicides per year. However this has led to fungicide resistance in the field. The present study evaluated the activities of six fungicides against the mycelial growth by determination of EC50 values of strains collected from fields with different fungicide management programs: Rustic management (RM) without applications and Intensive management (IM) more than 25 fungicide application/year. Results showed a decreased sensitivity to all fungicides in isolates collected from IM. Means of EC50 values in mg L-1 for RM and IM were: 13.25 ± 18.24 and 51.58 ± 46.14 for azoxystrobin, 81.40 ± 56.50 and 1.8575 ± 2.11 for carbendazim, 1.225 ± 0.945 and 10.01 ± 8.55 for propiconazole, 220 ± 67.66 vs. 368 ± 62.76 for vinclozolin, 9.862 ± 3.24 and 54.5 ± 21.08 for fludioxonil, 49.2125 ± 34.11 and 112.25 ± 51.20 for mancozeb. A molecular analysis for β-tubulin revealed a mutation at codon 198 in these strains having an EC50 greater than 10 mg L-1 for carbendazim. Our data indicate a consistency between fungicide resistance and intensive chemical management in banana fields, however indicative values for resistance were also found in strains collected from rustic fields, suggesting that proximity among fields may be causing a fungus interchange, where rustic fields are breeding grounds for development of resistant strains. Urgent actions are required in order to avoid fungicide resistance in Mexican populations of M. fijiensis due to fungicide management practices.

Diversidade genética de isolados de Mycosphaerella musicola obtidos de bananais do norte de Minas Gerais, Brasil por meio de marcadores RAPD / Genetic diversity of Mycosphaerella musicola isolates obtained from bananas of north of Minas Gerais, Brazil by using RAPD markers

Onze primers RAPD foram utilizados para avaliar a variabilidade genética de 31 isolados de M. musicola coletados a partir de folhas de bananeiras 'Prata Anã' e 'Nanica', cultivadas no Norte de Minas Gerais. Foram amplificados um total de 83 bandas sendo 73 polimórficas, dando uma média de 6,6 bandas polimórficas por primer. As distâncias genéticas observadas variaram de 0,56 a 0,06 entre os isolados, com distância média de 0,25. O dendrograma construído com base no método UPGMA revelou a formação de 8 grupos, não sendo observada correlação entre a diversidade genética dos isolados e as origens geográficas dos isolados avaliados.

Eleven primers RAPD were used to estimate the genetic variability between 31 isolates of M. musicola collected from 'PrataAnã' and Nanica bananas that were cultivated in northern Minas Gerais, Brazil. A total o 83 fragments were amplified, of which 73 were polymorphic, corresponding to an average of 6.6 polymorphic fragments per primer. The genetic distances ranged from 0.06 to 0.56 and the average distance of 0.21. A dendrogram constructed based on the UPGMA clustering method revealed 8 and no correlation between molecular grouping and geographical origin was observed.

Modelagem geoestatística da sigatoka-negra e sua relação com a fertilidade do solo / Geostatistical modeling of black-sigatoka and relation to soil fertility

Objetivou-se, com a realização do presente trabalho, caracterizar a variabilidade espacial da sigatoka-negra, utilizando-se metodologia de análise geoestatística para verificar sua relação com a fertilidade do solo na cultivar Grande Naine. O experimento foi realizado no município de Registro, SP. Demarcou-se, no campo, uma malha regular de 30 x 30 m, totalizando-se 30 pontos amostrais georreferenciados com aparelho de GPS. Foram realizadas avaliações da severidade da sigatoka-negra, com auxílio de uma escala diagramática. Coletaram-se amostras de solo na camada de 0-20 cm, para análise de fertilidade. Com base na análise do semivariograma isotrópico, verificou-se a forte dependência espacial da severidade da doença, com alcance de 25,28 m. Os mapas de krigagem demonstraram um padrão agregado e da relação negativa da severidade da doença com os teores de potássio e positiva com teores de enxofre no solo.

The objective in this research was to characterize the spatial variability of the Black Sigatoka disease, using the geostatistic analysis methodology to identify its relation to soil fertility in the Grande Naine cultivar. The experiment was conducted in the city of Registro, São Paulo state, Brazil. A regular 30 x 30m field mesh was demarcated, using a Geographical Positioning System in the experimental field, composed of a total of 30 sampling points or georeferences. Evaluations of the severity of the Black Sigatoka were conducted using a diagrammatic scale. Soil samples were collected in the 0 - 20cm layer for fertility analysis. Based on the isotropic semivariogram, a clustered spatial dependence of the disease severity, with a range of 25.28m was verified. The kriging maps demonstrated an aggregate pattern and negative relationship of the severity of the disease to potassium and positive with levels sulphur in the soil.