Argentina is one of the top 10 world producers and exporters of wheat. In routine surveys of wheat (Triticum aestivum L.) in Buenos Aires Province, Argentina, a new disease was observed in 2012 on seeds of wheat cv. Buck Meteoro. Symptomatic grains (black points) and leaves (chlorosis and spots) were collected during the spring of that year. The objectives of the present study were to identify the causal agent, to investigate its pathogenicity in relation to nine wheat cultivars and to identify the secondary metabolites produced by fungus. Symptomatic grains were plated on potato dextrose agar (PDA). Morphological characterization of colonies and sequencing of the ITS region after DNA extraction identified it as Pseudopithomyces chartarum. For pathogenicity tests, two different isolates, P221 and P224, were inoculated on seedlings of nine wheat cultivars, which showed different disease symptoms, % of grain germination (GG), % of grain discoloration (GD) and % of weak seedlings (WS), suggesting different levels of response against Pseudopithomyces chartarum. Particularly B. Meteoro, Buck Guapo and Klein Proteo cultivars demonstrated major infection tolerance for GD and WS. In contrast, Sy 100 and Klein Pantera were most affected showing weakness, chlorosis, or reduced length of coleoptile, and 50% of necrotic symptoms. Pseudopithomyces chartarum isolates produced secondary metabolites including alternariol, alternariol mono-methyl ether, altertoxin I and altertoxine II. The fungus is a new pathogen of wheat in Argentina that can cause diseases on different cultivars as well as produce mycotoxins.

Agronomy for Sustainable Development, An International Journal in Agriculture and Environment

A nivel mundial, Laetiporus sulphureus es un importante patógeno causante de pudriciones castañas en el arbolado urbano. En la ciudad de La Plata, dicho hongo fue hallado en ejemplares de álamo blanco, fresno americano, eucalipto y paraíso gigante. El objetivo del trabajo fue analizar las alteraciones estructurales y químicas ocasionadas por L. sulphureus en el leño de álamo blanco, fresno americano, eucalipto y paraíso gigante con el propósito de dimensionar el riesgo que implica su deterioro para los habitantes, sus bienes y la diversidad arbórea de la ciudad. Los estudios anatómicos fueron realizados con microscopios óptico y electrónico de barrido. Los análisis químicos se llevaron a cabo en muestras de fresno y paraíso, según normas TAPPI. En todos los ejemplares el daño se localizó en el duramen, registrándose caracteres típicos de estadios avanzados de pudrición castaña. En cada especie se registraron alteraciones particulares a nivel anatómico y químico, compatibles con las diferencias estructurales entre ellas. Esta es la primera contribución regional sobre el tipo y grado de deterioro registrados en especies infectadas naturalmente por L. sulphureus, de utilidad para la comprensión de los riesgos que ello implica en el contexto urbano.

During March, 1997, a leaf rust was observed on Vaccinium corymbosum L. cv. Bluegold in Argentina. Leaf lesions began as chlorotic flecks that expanded and developed into necrotic spots with several uredinia. The typical orange pustules of the disease developed mostly on the abaxial sides of leaves. Urediniospores were elliptical to obovate (17 to 28 × 11 to 23 μm) and finely verrucose. Telia were round, covered by the epidermis, slightly elevated, and brown to black. Teliospores were sessile and oblong to columnar (7 to 11 × 14 to 17 μm) with two or more vertical cell walls, and were smooth and brown. Urediniospore and teliospore morphology and dimensions were consistent with the description of Pucciniastrum vaccinii (G. Wint.) Jørst (syn. P. myrtilli Arth.) (1). A pathogenicity test was conducted with 18-month-old cv. Bluegold plants. Fully expanded leaves were sprayed, using a hand-held sprayer, with freshly collected urediniospores (1 mg of spores per ml of 0.05% water solution of Tween 20), covered with plastic bags, and placed in a growth chamber at 20°C for 48 h with 12 h of light per day. The plastic bags were then removed and the plants mantained in a greenhouse. After 10 days, orange rust pustules similar to the original symptoms developed on all plants. As the rust was not reported on ornamental Ericaceae in Argentina, and hemlock, the alternate host, is not present in the area, it is suggested that P. vaccinii is cycling on blueberry. This is the first report of P. vaccinii on blueberry in Argentina. Reference: (1) P. R. Bristow and A. W. Stretch. 1995. Pages 20–22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN.

Tan spot caused by Pyrenophora tritici-repentis is an economically important disease of wheat (Triticum aestivum L.) in Argentina. The success of local breeding programs for resistance to the disease depends to a large extent on the genetic variation within the pathogen population. To assay this variability, 155 isolates of P. tritici-repentis obtained from leaves of wheat and Festuca sp. of different localities were assayed and compared for isozyme polymorphisms. Isozyme analysis was performed with polyacrilamide gel electrophoresis in the systems estearase, phosphatase and peroxidase. Variation in the number and relative mobility of the bands by each system was detected in this collection of isolates. Intraspecific polymorphisms were identified in the three systems assayed. The cluster analysis based in bands patterns defined 86 electromorph types among the 155 isolates evaluated according with the Jaccard’s coefficient (CCC = 095). The isozymes patterns were not correlated with the geographic and/or wheat cultivars origin of the P. tritici-repentis isolates.