Marcela Gally

Pectinolytic enzyme production by Colletotrichum truncatum, causal agent of soybean anthracnose

BACKGROUND Colletotrichum truncatum is the most common pathogenic fungus associated with soybean anthracnose, a prevalent disease in Argentina. Pectinolytic enzymes are involved in the pathogenicity of a wide range of plant pathogenic fungi. OBJECTIVES To explore pectinolytic enzyme production in Argentinian Colletotrichum strains isolated from diseased soybean plants from different geographic locations, as a preliminary step to establish the biological role of the pectinolytic enzymes in the Colletotrichum spp.-soybean system, yet unknown. METHODS Ten strains were screened for in vitro pectinolytic enzyme production on a defined medium based on pectin as carbon source. RESULTS All isolates were able to grow in this medium and polymethylgalacturonase (PMG), polygalacturonase (PG) and pectin lyase (PL) activities were detected. On the whole, the peak of polygalacturonases activities preceded the day of maximum growth, while PL activity reached its highest level afterwards. Strain BAFC 3097 (from Santa Fe province) yielded high titles of the three enzymes (1.08U/ml PG, 1.05U/ml PMG, 156U/ml PL), after a short incubation period (7-10 days). Low synthesis of polygalacturonases in cultures containing glucose as unique carbon source suggests that these enzymes are constitutive in contrast with PL, which was not detected. CONCLUSIONS The disparity observed in enzyme production among strains cannot be related to fungal growth, since no major differences in mycelial yield were found; it was not connected with their geographic origin, but might be associated with differences in virulence among strains not yet evaluated.

In vitro growth and cell wall degrading enzyme production by Argentinean isolates of Macrophomina phaseolina, the causative agent of charcoal rot in corn

Macrophomina phaseolina is a polyphagous phytopathogen, causing stalk rot on many commercially important species. Damages caused by this pathogen in soybean and maize crops in Argentina during drought and hot weather have increased due its ability to survive as sclerotia in soil and crop debris under non-till practices. In this work, we explored the in vitro production of plant cell wall-degrading enzymes [pectinases (polygalacturonase and polymethylgalacturonase); cellulases (endoglucanase); hemicellulases (endoxylanase) and the ligninolytic enzyme laccase] by several Argentinean isolates of M. phaseolina, and assessed the pathogenicity of these isolates as a preliminary step to establish the role of these enzymes in M. phaseolina-maize interaction. The isolates were grown in liquid synthetic medium supplemented with glucose, pectin, carboxymethylcellulose or xylan as carbon sources and/or enzyme inducers and glutamic acid as nitrogen source. Pectinases were the first cell wall-degrading enzymes detected and the activities obtained (polygalacturonase activity was between 0.4 and 1.3U/ml and polymethylgalacturonase between 0.15 and 1.3U/ml) were higher than those of cellulases and xylanases, which appeared later and in a lesser magnitude. This sequence would promote initial tissue maceration followed by cell wall degradation. Laccase was detected in all the isolates evaluated (activity was between 36U/l and 63U/l). The aggressiveness of the isolates was tested in maize, sunflower and watermelon seeds, being high on all the plants assayed. This study reports for the first time the potential of different isolates of M. phaseolina to produce plant cell wall-degrading enzymes in submerged fermentation.

Molecular characterization of Colletotrichum species causing soybean anthracnose in Argentina

Twenty-six isolates obtained from soybean crops (Glycine max) with typical anthracnose symptoms were identified as Colletotrichum truncatum (73 %) and C. destructivum (26 %). Their genetic relationships were studied using the AFLP method. A UPGMA phenogram divided the strains into two clusters corresponding with the two species. Genetic distances based on association coefficient were 0.71–0.89 among the 18 C. truncatum strains and 0.67–1 among the eight C. destructivum strains. Genetic variability within species, measured in terms of percentage of polymorphic loci, was high (<90%). Only two isolates showed 100% similarity, suggesting high intraspecific variability.

Uso de mezclas de azoxistrobina y triazoles para controlar enfermedades de fin de ciclo de la soja

Widely spread in Argentina, late season diseases (LSD), cause yield losses and seed quality changes. Leaf application of fungicides is an effective procedure to manage LSD under the current cropping conditions (monocrop and no-till system). The aims of the present study were 1) to determine causal agents of LSD, 2) to evaluate yield reduction caused by LSD and 3) to evaluate the efficiency of mixtures containing triazoles and strobirulins, sprayed during R3 or R5 reproductive stages to control LSD. Four experiments were carried out in a randomized complete block design, with four replicates in Armstrong, Santa Fe, Argentina, in a soybean cultivation area in the Pampeana Region. Two assays were performed in 2004/2005, and the remaining ones in 2005/2006 growing seasons. Two azoxystrobin mixtures, one with cyproconazole and the other with difenoconazole, and a mixture of the latter two were tested. The following pathogens were detected : Cercospora kikuchii, Colletotrichum truncatum, Septoria glycines, Glomerella glycines y Phomopsis sojae. All treatments presented higher yield than control, with 5% of statistic significance. It can be concluded that, under the present experimental conditions, characterized by frequent rains between R1 and R5.5, the tested mixtures efficiently controlled LSD.

Functional groups of plant pathogens in agroecosystems: a review

The concept of functional groups (set of species having similar physiological, ecological or life-history traits) has been largely used for plants, microorganisms, nematodes or insects in agroecosystems. However, this concept has been rarely applied to describe assemblages of plant pathogens. Yet, classification systems in plant pathology resemble this functional approach, as they address different disease processes or life history traits. In this review, we discuss advantages and drawbacks of current classification systems in relation to their application to the ecological management of crop diseases. Then, we propose to reorganize one of the classical plant-pathogen systems in a dichotomous key of functional groups obtained by combining two life-history traits: dispersal and survival strategies. The six functional groups proposed here are soil inhabitants; soil survivors; debris-seed-borne; air-borne; seed-borne, and vector-borne pathogens. We applied these groups to characterize pathogens of two major crops, wheat and tomato, grown in temperate climate regions. Our contribution intends to provide a comprehensive conceptual framework for the design of crop disease management strategies based on ecological principles, as well as to facilitate the interpretation of the occurrence of epidemics in response to the agricultural practices applied in real-world agroecosystems.

AFLP characterization in pathogenic and coprophilous fungi.

Fil: Cinto, Isabel Esther. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Micologia y Botanica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Micologia y Botanica; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biologia Experimental; Argentina