Variations in the Molecular and Physiological Characteristics and the Virulence of Monilinia fructicola, M. fructigena and M. laxa Isolates

Twenty-three Monilinia isolates of various origin were identified and compared by morphological means and by biomolecular protocols based on random amplified polymorphic DNA (RAPD) analysis, and on PCR detection by species-specific primer pairs. The identification of most Monilinia isolates by PCR and RAPD confirmed the identification by morphological criteria, although two isolates initially identified as M. fructigena by morphological means were attributed to M. fructicola by the biomolecular techniques. Monilinia isolates were also compared in terms of their in vitro pectolytic activity and isoenzyme patterns. All the isolates produced polygalacturonase and pectin methylesterase, but pectin lyase activity was found only in M. fructicola and M. fructigena, and not in most M. laxa isolates. The Monilinia isolates differed significantly in their isoenzyme patterns. Based on RAPD-PCR and PCR amplification and pectolytic isoenzymes, the isolates analysed clustered in three major groups, each corresponding to a Monilinia species. Artificial inoculations in peach and pear fruits revealed differences in virulence between the Monilinia species and within isolates. No correlation was found between the amount of pectolytic enzymes produced in vitro and virulence. Variations between and within the Monilinia species may depend at the physiological level on variations in the isoenzyme patterns of the pectolytic enzymes

Primera cita de Sawadaea bicornis (Wallr.) Miyabe, causante del oidio del acer en la provincia de Mendoza, Argentina

A strong defoliation of Acer negundo L. specimens was observed during the 2001-2002 vegetative cycle in the Province of Mendoza (Argentina). It was further noted that the leaves had chlorotic spots covered with a whitish powdery coating, which afterwards necrotized and pierced the leaf tissue. When a high percentage of the surface of the leaf was affected, the leaf would drop prematurely. The sign observed was produced by fungal fructifications of the genus Oidium. Morphometric measurements and bibliographic searches led us to conclude that the agent was Sawadaea bicornis (Wallr.); this being the first time the microorganism is cited for MendozaDurante la estación vegetativa 2001-2002 en la provincia de Mendoza, se observó una marcada defoliación de ejemplares de Acer negundo L. Estudiando el problema, se observó en las hojas manchas cloróticas cubiertas por una pulverulencia blanquecina, estas lesiones coalecían abarcando gran superficie de los folíolos lacerándolos. Cuando un alto porcentaje del área foliar era afectada, se producía la caída anticipada de las hojas. El signo observado era producido por las fructificaciones de un hongo del género Oidium. El estudio morfométrico de las estructuras miceliares halladas, acompañado de la investigación bibliográfica correspondiente, permitieron concluir que el microorganismo responsable de la sintomatología y los signos observados era Sawadaea bicornis (Wallr.). Ésta es su primera cita para la provincia de Mendoz