Resumen

GARCES FIALLOS, Felipe Rafael  y  FORCELINI, Carlos Alberto. Temporal progress of rust and reduced leaf area and yield components in soybean grain. Acta Agron. [online]. 2011, vol.60, n.2, pp.147-157. ISSN 0120-2812.

The harvest of the year 2009-10 of soybean crop in Southern Brazil occurred under higher intensity of soybean rust (Phakopsora pachyrhizi Sydow y Sydow), which allowed studies on disease progress and crop reduction. A field experiment with 64 plots (2.7 x 5 m) of the cultivar Glycine max L. (Nidera 5909 RG) sown on 5/Dec/2009 was used for the evaluations. Disease gradients were obtained by spraying the fungicides tebuconazol or epoxiconazol + pyraclostrobin once, twice or three times, at different plant growth stages. Disease progress was assessed as number of lesions and urédias and later converted into percent severity (%). The leaf area index (LAI) was measured at the full pod filling stage and the grain yield components at the harvest. The final disease severity was over 50% on non-sprayed plots. There were differences in disease severity among plant parts (lower, medium, and upper thirds), which were caused by varying initial disease, since the rates of disease progress determined by Logistic and Gompertz models were similar among thirds (0.13 to 0.14 to Logistic and 0.1 to 0.11 to Gompertz). The LAI varied from 1.96 on non-treated plots to 4.4 on the standard treatment with four sprays of epoxiconazol + pyraclostrobin. Disease control programs with two or three sprays began at the phenological stage V9 resulted in higher LAI and higher grain weight on the upper third. The number of pods or grains per plant and the number of grains per pod did not differ among treatments. There was only difference in weight of the upper grain, when fungicides were applied two or three times from phenological stage V9.

Palabras clave : Crop yield; fungus diseases; Glycine max; Gompertz; leaf area index; Logistic; severity; Uredinales.

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