Gilberto Manzo-Sánchez

The development of mating type-specific primers for Mycosphaerella fijiensis, the causal agent of black Sigatoka of banana, and analysis of the frequency of idiomorph types in Mexican populations

A multiplex-PCR method was developed to identify the distribution and frequency of the mating types of the fungal banana leaf pathogen Mycosphaerella fijiensis in Mexico. PCR amplification identified different sized fragments for mat1-1 and mat1-2 genes. The same primers were also used to amplify fragments of the idiomorphs of Mycosphaerella musicola, another important banana pathogen closely-related to M. fijiensis. These were sequenced and were highly similar to M. fijiensis. Single conidial isolates of M. fijiensis were obtained from different fields in regions of Mexico not previously sampled, and from different banana and plantain cultivars, to determine the frequency and distribution of the mating types within natural populations. The multiplex primers and methods used for population analysis in M. fijiensis could also be applied to M. musicola populations andmay also be applicable to determine mating types in other closely related species, for a better understanding of the Mycosphaerella complex of pathogens and saprophytes associated with banana leaves. Additional keywords: epidemiology, fungal hybridisation, genetic mapping, virulence.

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.

El Barrenador de la Semilla Caryedon serratus Oliver (Coleoptera: Bruchidae) en Tamarindo en el Trópico Seco de México — Una Revisión

Abstract. Tamarind, Tamarindus indica L., is an economically important crop in the dry tropical region of Western Mexico. For more than a decade, damage caused by an insect borer in seeds has been observed. Since 2006, taxonomical identification, biology, hosts, and integrated management of the insect have been studied. In this review, current knowledge of the tamarind seed borer is presented. The beetle is 4 to 6 mm long, with a brown-colored body with pubescence, large hind legs, and large serrated antennae. Its elytra do not cover the last abdominal segments. The larvae are 7 to 8 mm long, pinkish-white in color, and slightly mobile. In the Western region of Mexico, tamarind is the main host. The insect oviposits on different legumes; however, only on tamarind (followed by peanut and chickpea) can it complete its life cycle. According to these characteristics, the insect was identified as Caryedon serratus Oliver and affects tamarind pods at pre-and postharvest. Its control should be oriented to damage reduction in the field and storage. The use of insecticides (deltamethrin and paraffinic oil) before harvest is suggested. Also, all the fruits on the tree must be cut during harvest, because this insect is able to complete its life cycle in them. The fumigation of the pods with aluminum phosphide can reduce damage during storage.

The Long-Jawed Longhorn Beetle (Coleoptera: Cerambycidae) in Tamarid Trees in the Dry Tropic of Mexico — A Brief Revision

Abstract. Tamarind (Tamarindus indica L.) is an economically important crop in the dry tropical region of Western Mexico. During more than one decade, damage caused by a borer insect in tree branches and trunk have been observed. Until recently, the taxonomy and generalities of this pest were unknown. In this brief review, current knowledge of the tamarind borer is presented. The insect is a large beetle, 18 to 33 mm, glossy, of fusiform black- or brown-colored body with yellow/black alternate sections in tarsus and antennal segments. The adult is characterized by extremely long antennae as long as or longer than the body of the beetle. Each elytra has two yellow spots. The larvae are cerambyciform, whitish in color, and its head is wider than the rest of the body. The insect was identified as Trachyderes (Dendrobias) mandibularis Dupont. In this region, the borer has been observed affecting only tamarind, in spite of other hosts such as Mexican lime, orange, and mango. The borer attacks young plants and adult trees. Its control consists of cultural practices (irrigation and fertilization) to reduce damage. For infested trees, pruning of damaged branches is recommended and then killing the larvae to break its life cycle. The application of insecticides (painted) to the trunk of the trees is a preventive measure to control the borer.

Uso de Aceites y Extractos Vegetales para el Control de Diaphorina citri Kuwayama1 en Lima Mexicana en el Trópico Seco de México

Resumen. El psílido asiático de los cítricos (PAC; Diaphorina citri) es la plaga más importante que afecta a la lima mexicanao (Citrus aurantifolia) en el trópico seco de México y es el vector de la enfermedad del Huanglongbing. Su control se basa en el uso de insecticidas sintéticos. La búsqueda de alternativas sustentables y eficaces es una prioridad en el manejo del PAC. En este estudio, se evaluó el efecto de diferentes tipos de aceites y extractos de plantas en el control de ninfas del PAC en el estado de Colima, México. Las pruebas fueron conducidas en árboles de lima mexicana y plantas de vivero infestadas con la plaga. Se realizó una aplicación foliar de cada tratamiento sobre brotes vegetativos de 5 a 7 días de edad. Las evaluaciones del número de ninfas vivas se hicieron antes y después de la aplicación de los aceites y los extractos de plantas. En la primera prueba, el aceite parafínico (99% de residuos no sulfonados) a concentraciones de 1, 2, y 3%, redujeron la población del PAC entre un 77 a 98% en comparación con el testigo sin control. En las otras pruebas, los diferentes aceites (parafínicos, de cocina y de cítricos) mostraron una baja infestación del PAC con relación al testigo. También, los extractos de neem, ajo y cebolla mostraron una reducción significativa de ninfas después de la aplicación. El aceite de semilla de Jatropha curcas tuvo una buena efectividad en el control del insecto. No se observaron signos de fitotoxicidad en los árboles tratados con cualquiera de los aceites durante el invierno, pero si los hubo durante el verano, principalmente con los aceites de cocina. Estos resultados demuestran que los aceites y extractos vegetales pueden ser incluidos en un programa de control del PAC en lima mexicana para reducir el uso de insecticidas sintéticos (organofosforados), los cuales están teniendo problemas de resistencia de D. citri.