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Poster Presentations


Poster Presentations


Effect of low temperatures on the survival of Phakopsora pachyrhizi urediniospores in overwinter volunteer soybean plants in Entre Ríos Province, Argentina

Presenter: C. Godoy

All authors and affiliations: J. de Souza (1), N. Formento (1), T. Boca (2), C. GODOY (3), and A. del C. Ridao (4). (1) Factores Bióticos y Prot. Vegetal, INTA EEA Paraná, Entre Ríos, Argentina; (2) Instituto de Clima y Agua, CIRN INTA Castelar, Buenos Aires, Argentina; (3) Embrapa Soja, Londrina, Brazil; and (4) Facultad de Cs. Agrarias, Univ. Nac. de Mar del Plata, Buenos Aires, Argentina

Temperature is probably the most important of the environmental factors affecting Phakopsora pachyrhizi survival over the winter and it has been reported that there is no spore germination below 7°C. However, erumpent uredinia of Asian soybean rust (ASR) were observed in volunteer soybean plants during the overwintering periods of the 2004–2005 and 2005–2006 growing seasons in Entre Ríos province (ER). This situation may generate a new risk for Argentina. The objective of this study was to analyze the effect of low temperatures on the survival of Phakopsora pachyrhizi urediniospores under controlled conditions. Soybean leaflets with ASR and free urediniospores were exposed to temperatures between –10 and 25°C during 1, 3, 5, 7, and 24 h in a controlled environment chamber. The germination rate was evaluated as an indicator of urediniospores to resist stress conditions due to frost during the overwintering period. Then, water agar plates (2%) were incubated for 6 and 22 h, and the percentage of germinated spores was assessed by counting (n = 200). Up to –10°C, germination was observed, and a greater effect of low temperature was registered with prolonged exposure periods. If optimal conditions occurred during the 22 h after the exposure to coldness, germination was increased by approximately 50%. Low temperatures would therefore not constitute a limiting factor for P. pachyrhizi survival in ER and urediniospores may remain active on the volunteer soybean plants until the establishment of new soybean lots. Commercial cultures and volunteer soybean plants would represent the main reservoirs of the disease in ER.

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