Abstract: Sugarcane mosaic virus (SCMV) is one of the main viral agents that infect sugarcane (Saccharum spp.). SCMV detection in Mexico has been based on typical symptomatology of the disease, which is not conclusive. Additionally, there is limited information about their phylogenetic origin. The objective of this work was to detect the presence and distribution of SCMV in the sugarcane growing areas of the Mexican Pacific using RT-PCR, and to determine the phylogenetic origin of one isolate from Jalisco. The results showed the wide distribution of SCMV in sugarcane areas of the Mexican Pacific. The virus was found in 33 of the 242 samples analyzed, corresponding to 13.63%. The varieties Mex 69-290 and CP 72-2086 presented the most severe mosaic symptoms. Phylogenetic analysis using partial HC-Pro sequences of SCMV isolate from Jalisco (JalMex-126) suggests a close relationship with isolates from India, Australia, China and Argentina, and thus likely share a common genetic origin and have been dispersed to through infected sugarcane germplasm.

Resumen: El virus de mosaico de la caña de azúcar (SCMV) es uno de los principales agentes virales que infectan a caña de azúcar (Saccharum spp.). En México la detección del SCMV se ha basado en sintomatología típica de la enfermedad, por lo que la información no es concluyente, además hay poca información sobre su origen filogenético. El objetivo del trabajo fue detectar mediante RT-PCR la presencia y distribución del SCMV en las zonas cañeras de los estados de Colima, Jalisco y Nayarit, México y determinar el origen filogenético de un aislado de Jalisco. Los resultados obtenidos demuestran la amplia distribución del SCMV en la región cañera del Pacífico de México. De las 242 muestras analizadas se detectó al virus en 33 de ellas, lo que corresponde a un 13.63%. Las variedades Mex 69-290 y CP 72-2086 fueron las que presentaron los síntomas de mosaico más severos. El análisis filogenético con la secuencia parcial HC-Pro del SCMV aislado de Jalisco (JalMex-126) sugiere una estrecha relación con aislados de la India, Australia, China y Argentina, por lo que probblemente compartan un origen genético común y se hayan dispersado a través de germoplasma de caña de azúcar infectado.

External pH constitutes one of the most important environmental factors that control growth, metabolism and differentiation in microorganisms, including fungi. We have analyzed the effect of external pH on sterigmatocystin biosynthesis in Aspergillus nidulans. It was observed in repeated experiments that alkaline pH, in opposition to acid pH, increased sterigmatocystin production and the transcript levels of aflR, the master gene that regulates expression of the sterigmatocystin cluster in A. nidulans. It is known that pH effects in fungi operate mostly through the Pal/Pac signaling pathway, originally described in Aspergillus nidulans. Accordingly, we studied the role of this signaling pathway in ST biosynthesis. It was observed that aflR transcript levels were increased in the "alkalinity mimicking" mutant pacCc14 and were minimal in the "acidity mimicking" mutant palA1. No sterigmatocystin was produced by palA1 or pacC- mutants at neither acid or alkaline pH of incubation. Finally, fluG and flbA, genes known to regulate both conidiation and sterigmatocystin synthesis upstream in the regulatory cascade, were up-regulated at alkaline pH.