In April 2002, Phakopsora pachyrhizi Sydow was observed for the first time in L. N. Alem, in the Province of Misiones, Argentina. Misiones is nearly surrounded by Paraguay and Brazil, where P. pachyrhizi was discovered recently (2) and where it is a serious disease (3). Symptoms were observed on leaves in the upper half of plants at the R6 stage in a soybean research field trial. Symptoms included reddish-brown lesions on leaves especially on the abaxial surface, and uredinias were observed in the lesions with a 10× lens. Leaf defoliation was observed due to the disease after the R5 stage, and the enviroment (high humidity and air temperatures) was particularly conducive to the disease. The field trial area was 2,500 m2 and included soybean genotypes of maturity groups V to IX. Symptoms were detected in the later maturity groups. Field trials were surrounded by kudzu (Pueraria sp.), which is a common weed introduced in South America as a forage plant by Asian farmers, and it was reported as the main host of this pathogen in Paraguay (2). To confirm the identity of the pathogen, leaf samples from the middle part of plants were collected and sent to the Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD. Samples were analyzed using a real-time polymerase chain reaction assay (1). Identification of P. pachyrhizi was confirmed the last week of May, 2002 (R. Frederick, personal communication). The soybean production area in Misiones is a small area in Argentina lying 600 km northeast of the main soybean area in the north central part of the country. SENASA (Servicio Nacional de Sanidad Vegetal [Nacional Service of Plant Health]) and SAGPYA (Secretary of Agriculture) were formally informed about these results on June 19, 2002. A program to assess the risk of disease spread is under development. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) W. Morel Paiva. AnaisII Congresso Brasilero de Soja e Mercosoja. Foz de Iguazu, Brazil, 2002. (3) T. Yorinori. Anais II Congresso Brasilero de Soja e Mercosoja. Foz de Iguazu, Brazil, 2002.
Stewart's wilt is a serious disease of corn (Zea mays L.) caused by the bacterium Pantoea stewartii subsp. stewartii (Pss). Typical symptoms of infected fields and dent corn are longitudinal streaks with irregular or wavy margins, which are parallel to the veins and may extend the length of the leaf. These pale to green yellow lesions become dry and brown as the disease progresses producing a leaf blight (4). During the growing seasons 2010 to 2011 and 2011 to 2012, symptoms of bacterial leaf blight of corn were observed in central Argentina maize fields, with an incidence of 54% in Córdoba province. To identify the pathogen, leaves from 10 symptomatic maize plants per field were collected from 15 fields covering a representative geographical area. High populations of morphologically uniform bacteria were isolated from leaf tissues by conventional methods using King's medium B agar (2). Ten representative facultatively anaerobic gram-negative, non-fluorescing, non-motile, catalase positive and oxidase negative rod-shaped and yellow-pigmented bacterial isolates were evaluated further. The biochemical profile obtained was: fermentative metabolism, negative indol, acetoin and hydrogen sulfide production, negative gelatin hydrolysis (22°C), positive acid production from D-glucose and lactose, negative gas production from D-glucose, and negative nitrate reduction (1). All the isolates produced a 300-bp band with PCR using the species specific primer pair PST3581/PST3909c (3). The Pss ATCC 8199 and Pseudomonas fluorescens ATCC 13525 strains were used as positive and negative controls for the PCR assays, respectively. The pathogenicity test was performed by stem inoculation of five to ten P2069 YR maize plants (one to two leaf growth stage) grown in growth chamber. Plants were inoculated by syringe with a 107 to 108 cell/ml bacterial suspension and kept in a humid chamber at 25 to 27°C. Plants inoculated with Pss ATCC 8199 or with sterile water were used as positive and negative control treatments, respectively. The development of symptoms similar to those originally found in the field was observed on all the plants inoculated with the different isolates at 7 to 10 days post inoculation. In addition, symptoms on inoculated plants were similar to those observed for the positive control treatment. No symptoms were found on negative controls. Koch's postulates were fulfilled since bacteria isolated from symptomatic tissue had identical characteristics to isolates used to inoculate plants and to the reference Pss strain for biochemical tests and PCR reaction mentioned above. To our knowledge, this is the first report of P. stewartii subsp. stewartii isolated from diseased maize in Argentina. References: (1) J. G. Holt et al. Page 179 in: Bergey's manual of determinative bacteriology. Williams and Wilkins, Baltimore, MD, 1994. (2) OEPP/EPPO. Bulletin OEPP/EPPO Bulletin, 36: 111, 2006. Pantoea stewartii subsp. stewartii diagnostic. (3) A. Wensing et al. Appl. Environ. Microbiol. 76:6248, 2010. (4) D. G. White Page 4 in: Compendium of corn disease. The American Phytopathology Society, 1999.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.