Efeito de baixas temperaturas e do binomio temperatura-umidade relativa sobre a viabilidade dos uredosporos de Hemileia vastatrix Berk. et Br. e Uromyces phaseoli typica arth. :
The effect of liquid nitrogen (-196°C), Freezing temperatures (-18 to -16°C), and several combinations of temperatures and relative humidities on germination and infectivity of uredospores of Hemileia vastatrix and Uromyces phaseoli typica was studied. Uredospores of H. vastatrix kept at room temperature did not germinate after 60 days; after 20 days of storage they were not able to infect coffee seedlings inoculated under greenhouse conditions. Uredospores of U. phaseoli typica after 40 days of storage at room temperature were able to infect bean plants inoculated under greenhouse conditions; they lost viability completely after 60 days. H. vastatrix uredospores stored at 10° and 15°C lost viability after 80 days, no matter the relative humidity in which they were kept: 20-24 percent, 50 percent, 74-75 percent, 80-83 or 50-80 percent. U. phaseoli typica under the same conditions were able to cause infection after 100 days. The best conditions found to store uredospores of H. vastatrix in low temperature was to keep them in containers with 50-80 percent of relative humidity mantained at 5°C in refrigerator. In the case of U. phaseoli typica, the best combination was 50-75 percent of relative humidity and 5°C of temperature. When stored at freezing temperature (-18 to -16°C), bean rust uredospores kept their viability after 180 days; under the same conditions uredospores of H. vastatrix did not germinate after 120 days. Storage in refrigerator at 5°C and 50 percent relative humidity compared with storage in freezer (-18° to -16°C) was shown to be more effective. Nevertheless, storage of uredospores of both organisms in liquid nitrogen (-196°C) gave the best results, keeping their viability for at least 150 days. It was also found that the uredospores of U. phaseoli typica can be taken out from the freezer or liquid nitrogen directly to room temperature without any reduction in the percentage of germination. On the other hand, H. vastatrix uredospores stored in freezer or liquid nitrogen seem to become dormant. Thermic treatment in water bath at 40°C for 5 to 15 minutes broke the dormancy of uredospores allowing their normal germination. H. vastatrix uredospores percentage of germination was satisfactorily correlated with infectivity in all cases; the same did not happen in the case of U. phaseoli typica.
| Main Authors: | , |
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| Format: | biblioteca |
| Language: | eng |
| Published: |
1974
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| Subjects: | HEMILEIA VASTATRIX, UROMYCES PHASEOLI, ENFERMEDADES FUNGOSAS, ESPORAS, TEMPERATURA, HUMEDAD RELATIVA, |
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