En raíces de plantas adultas de tomate se observó una lesión castaña de aspecto húmedo, que se extendía 2-4 cm por encima del suelo. Las plantas atacadas se marchitaron y murieron. El objetivo del trabajo fue aislar e identificar al organismo causal de esta sintomatología. Se usaron medios de cultivos generales y selectivos. A las 24 horas desarrollaron colonias con micelio blanco algodonoso. Se evaluó la morfología de la colonia y la producción, morfología y dimensiones de estructuras reproductivas. El rDNA del micelio de un aislamiento fue extraído de cultivos puros con 7-10 días de crecimiento en medios agarizados. La región ITS se amplificó usando primers ITS4 e ITS5, se secuenció y comparó en banco de genes del servidor BLAST- NCBI para verificar su similitud con las secuencias tipo u holotipo disponibles. Al microscopio se observó micelio cenocítico, esporangios esfericos-globulados y oosporas apleroticas característicos del género Pythium. Se efectuaron pruebas de patogenicidad con resultados positivos reaislándose un microorganismo de características idénticas. La caracterización lograda por las técnicas tradicionales, los estudios moleculares y el resultado de las pruebas de patogenicidad permiten concluir que Pythium aphanidermatum es el causante de la Podredumbre basal de plantas adultas de Tomate.

Since 1995 severe losses were recorded on the production of Chamelaucium uncinatum in the vicinity of La Plata. In 2010, with the aim to confirm the identity of the causal agent of Geraldton waxplant basal rot, molecular studies were added to the morphological observations of the pathogen. P. nicotianae was identified as the causal agent of the disease.

Root and stem rot of rooted cuttings of young poinsettia plants were observed in a soil-less culture system in Buenos Aires Province, Argentina. Pythium aphanidermatum was identified as the causal agent of these symptoms. This is the first report of P. aphanidermatum affecting poinsettia in Argentina.

Kikuyu grass (Pennisetum clandestinum) is a perennial plant that belongs to the Poaceae family. In Argentina, it is used in warm areas as tropical pasture, forage and grass in gardens and sports fields. Species of Pythium have a cosmopolitan distribution and are important pathogens of a wide range of plant hosts. In the spring of 2009, a new disease affected areas cultivated with kikuyu grass in different parks located near the city of Buenos Aires. The symptoms were an evident chlorosis of leaves, which got circular as the affected area expanded, followed by severely rotten roots and blighting. The aim of this study was to identify the causal agent of kikuyu yellows in Argentina. An oomycete was consistently isolated from diseased tissues. The pathogen was identified as Pythium graminicola based on cultural characteristics and the morphology of vegetative and reproductive structures. Phylogenetic analyses were performed based on combined sequence datasets of the internal transcribed spacer of the nuclear rDNA and the beta tubulin gene. Pathogenicity tests were carried out and Koch's postulates were fulfilled. This is the first report of P. graminicola causing kikuyu yellows in Argentina and in the world.

Poinsettia (Euphorbia pulcherrima Will. ex. Klotzsch) is a worldwide potted or landscape ornamental plant that belongs to the Euphorbiaceae family. During 2003 and 2004, several symptoms were observed on poinsettia potted plants in nurseries and crops near Buenos Aires. Symptoms included irregular, brown, water-soaked spots on adult plants and leaf spots that extended causing stem blight in seedlings. Small pieces of diseased tissues were surface disinfected for 2 min in 2% sodium hypochlorite, plated on 2% potato dextrose agar (PDA), and incubated at 22°C for 48 h. Dense, whitish mycelia developed on PDA and then turned gray when asexual structures were formed. The fungus conidia were ellipsoid, hyaline, nonseptate, and were formed on botryose heads. The pathogenicity test was carried out on 10 plants using a conidial suspension (2 × 106 spores per ml) that was sprayed on leaves with and without injuries. All plants were incubated in a moist chamber at 22 ± 2°C for 48 h and then maintained in a greenhouse. After 3 days, symptoms similar to the original were observed on the inoculated plants. Control plants sprayed with distilled water remained symptomless. Koch's postulates were confirmed by reisolating the same fungus from diseased plants. In accordance with conidial and cultural characteristics, the pathogen was identified as Botrytis cinerea Pers: Fr. (1). To our knowledge, this is the first report of B. cinerea causing leaf spot and stem rot on poinsettia in Buenos Aires, Argentina. Reference: (1) M. V. Ellis and J. M. Waller. No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1974.

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Background and aims: The genus Phytophthora includes plant pathogens that affect a wide host range and cause severe damage and economic losses. The aim of this study was to achieve a more comprehensive knowledge of Phytophthora in Argentina. To this end, a review was carried out from the first reports in the late nineteenth century until March 2019. M&M: Information was taken from printed and on-line primary and secondary sources such as Proceedings of National and International Scientific Meetings, Bulletins from National Institutions and Universities, periodical Journals, books and data bases, and then analyzed and categorized. Results: The revision allowed updating the status of Phytophthora species recorded in the country, considering their geographical distribution, groups of crops affected, host-pathogen relationships, symptoms and nomenclature changes, as well as presenting a quick and comparative access to different subjects related to these pathogens. The results showed that, to date, 20 Phytophthora spp., one species affinis and one taxon affect 223 host-pathogen relationships in Argentina. The diversity of Phytophthora species in the world suggests that a larger number of species, still not cited, could be present in Argentina. Conclusions: Researchers specialized in the genus Phytophthora, molecular techniques and phylogenetic studies, may allow progressing in the accurate identification of the species and knowledge of their genetic variability.

In the North region of Buenos Aires Province, 2-year-old Phoenix canariensis plants showed severe wilt of some lower leaves and tip death, followed by eventual plant death. Cross-sections of vascular tissues showed dark discoloration. A pathogen was isolated from stem sections with symptoms following surface sterilization for 2 min in 2% NaOCl, transfer to potato dextrose agar (PDA) and incubated at 24 ± 2 ° C. Pure cultures formed white rose cottony colonies that developed a purplish tint visible from the underside. Abundant single-celled microconidia and some macroconidia with two to three partitions (27-50 × 3-5 µ m) were observed. Abundant chlamydospores were formed on water agar (WA). Pathogenicity tests were carried out on 2-year-old P . canariensis plants. Prior to inoculation, the basal rachis was wounded with a sterile needle. Ten plants were sprayed with a water suspension of 1 × 10 6 conidia mL. Simultaneously three mycelial plugs per plant from 10-day-old PDA cultures were placed below the collar on another 10 plants. Control plants were inoculated with sterile distilled water and agar-only discs. Plants were covered with plastic bags for 48 h and incubated at 23 ° C and 100% relative humidity, before being transferred to growth chambers at 25 ° C with natural light for 15 days. Symptoms first appeared on plants 10 days after inoculation.Initially, rachis lesions developed in proximity to the wounds and chlorotic leaves were observed. In the course of 1 month, the basal leaves died and the apex showed symptoms of infection. Cross-sections through the base revealed darkened vascular tissue. Control plants remained healthy.Morphological and micrometrics studies of the fungus isolated from inoculated palnts (Booth, 1977; Nelson et al ., 1983) indicated the pathogen to be Fusarium oxysporum f. sp. canariensis which was first observed in 1970 in France (Mercier & Louvet, 1973). This is the first report of this pathogen on P. canariensis in Argentina. References First report of Pestalotiopsis macrochaeta on Carapa guianensis B. A. Halfeld-Vieira* and K. L. NechetEmbrapa Roraima, BR 174, km 8, Distrito Industrial, CP 133, Brazil Carapa guianensis (Meliaceae) is a tree that occurs naturally in Central and South America, but is also planted as an ornamental. It has attracted much attention because its seeds contain an oil with medicinal properties. The common name of C. guianensis in Brazil is ' andiroba ', hence andiroba oil, while in Guyana it is known as ' karaba ' (crabwood oil) (Lorenzi, 1992). In 2003 a foliar blight was observed in the lower canopy of trees in the state of Roraima, Brazil. Closer examination revealed punctiform acervuli, which contained conidia typical of Pestalotiopsis (Nag Raj, 1993). These were smooth, long-fusiform, 4-septate, with three intermediate cells almost concolorous and 2-3 apical appendages. They measured 24-34 × 5-8 µ m, with median cells 16-21 µ m, apical appendage 16-34 µ m long and a single basal appendage 5 -8 µ m long. Mycelial growth on potato dextrose agar w...