No abstract

No abstract

The objective of this study was to identify a pathogen observed in wheat in the Texcoco area (Mexico). The symptoms induced by this pathogen are consistent with those caused by a virus. Identification was based on host range, symptoms, mode of transmission, and on serological and morphological characterization. The pathogen was mechanically transmitted to Triticum aestivum, T. durum, Secale cereale, × Triticosecale, Avena sativa, and Hordeum vulgare. The virus particles were flexuous rods, 700 nm long that produced cylindrical inclusions seen as pinwheel inclusions under the electron microscope. The pathogen reacted with Wheat streak mosaic virus (WSMV) antibodies in enzyme-linked immunosorbent assay. An eriophyoid mite associated with this virus was identified as Aceria tosichella and found to transmit the virus efficiently. Based on its characteristics, the pathogen was identified as WSMV. During this study, the virus appeared sporadically in test plots without causing significant yield losses.

a partir del sexto día de la inoculación y el desarrollo de la enfermedad se explicó por un modelo de regresión lineal simple (Y = 1.123 + 0.1133X). No se detectó la formación de apresorios pero sí la síntesis de una capa mucilaginosa asociada con los tubos germinativos. El proceso infectivo del hongo se manifestó con la penetración de las hifas intra e inter-celularmente y con la producción de acérvulos a partir de los 12 días después de la inoculación. Los síntomas de la antracnosis se asociaron con la degradación de polifenoles, plasmólisis, necrosis y desintegración celular Palabras Clave: Persea americana L., antracnosis, patogenicidad, patogénesis. ANALYSIS OF Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. INFECTION OF AVOCADO FRUITSABSTRACT -The pathogenesis of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. from the state of Michoacán, México was characterized in avocado (Persea americana L.) fruits cv. 'Hass'. The fungus caused typical disease symptoms of 'anthracnose' ten days after inoculation. Fungal infection rate was significantly different (p≤0.05) between treatments since the sixth day after inoculation and the disease development was explained by one simple linear regression model (Y = 1.123 + 0.1133X). No appresoria were found but one mucilagous layer associated to germ tubes was detected. Fungal infective process started with intra and intercellular penetration by hyphae and after, acervuli were produced twelve days after inoculation. Anthracnose symptoms were associated with poly-phenol degradation, plasmolysis, necrosis and cell disintegration

The epiphytic plant Hylocereus undatus , locally known as pitahaya, is endemic to Mexico. Recently, small-scale farming of this plant has begun and the harvested fruit exported to distant markets. In 2001 and 2002, samples of H. undatus with stem spots were collected from Mecapalapa, Xochitlan and Dolores Hidalgo in the state of Puebla. Early symptoms were small, chlorotic specks, which enlarged as they matured to a maximum of 0·5 cm in diameter. A fast-growing, mouse-grey-coloured fungus was consistently isolated from these diseased stems. After 8 days, under continuous fluorescent light at 22 -25 ° C, pycnidal fruiting bodies (180 × 150 µ m) formed on potato dextrose agar (PDA). The conidia observed in these bodies were one-celled, hyaline, ellipsoidal to fusoid with distinctly truncate bases and measured 12·15 -19·44 × 4·86 -8·51 µ m (av. 16·49 × 5·90 µ m). The isolated fungus conformed to the anamorphic Fusicoccum state of Botryosphaeria dothidea . The teleomorph was never observed in culture, but was seen on infected plants. Healthy, detached H. undatus stems were inoculated with the Fusicoccum isolate, while three control stems were inoculated with sterile PDA discs. After incubation for 3 days at 25-30 ° C, under high humidity and a 12-h day length, disease symptoms similar to those observed on naturally infected plants were observed. All inoculated stems were infected and turned brown, in contrast to the negative controls which remained unaffected. The anamorphic Fusicoccum state of B. dothidea was re-isolated from the inoculated plants, thus satisfying Koch's postulates. This fungus has been previously reported to cause panicle and shoot blight and

No abstract

No abstract

Las semillas ortodoxas cerca de la madurez adquieren tolerancia a la desecación; sin embargo, durante el proceso de imbibición-germinación ésta se pierde. El tiempo en que ocurre entre especies, incluso entre lotes de la misma especie es variable. Se determinó el momento en que ocurre la pérdida de tolerancia a la desecación en semillas de maíz durante la imbibición-germinación, además se observó el comportamiento y relación de cuerpos lípidos con la pérdida de tolerancia. Semillas de maíz de la línea 231 fueron imbibidas en agua y con diferentes concentraciones de polietilenglicol 8 000. La cinética de imbibición se cuantifico en periodos de ocho horas hasta las 40 h y la pérdida de tolerancia a desecación se estimó con pruebas de germinación estándar, conductividad eléctrica y envejecimiento acelerado. Ejes embrionarios fueron procesados y observados en el microscopio electrónico de transmisión. La pérdida de tolerancia a la desecación se presentó a las 32 h de imbibición a contenidos de agua de 300 g H2O kg1 y 520 g H2O kg1 en semilla y embrión respectivamente. En este momento la conductividad aumenta de 7.26 a 15.63 μSm-1g-1 mientras la germinación y viabilidad se redujeron 27 y 84% respectivamente. El movimiento de los cuerpos lípidos durante la imbibición-germinación se presenta entre las 24 h y 32 h, provocando alteraciones a la membrana con los secados, por lo que el papel que juegan éstos, además de ser fuente de energía durante la germinación, proveen de protección a las membranas durante la desecación.