Germinação de uredosporos e período latente de phakopsora pachyrhizi determinado por tempo cronológico e unidades de calor

Abstract

Soybean [Glycine max L. (Merr. )] is the main oleaginous crop cultivated in Brazil. Asian soybean rust caused by the Basidiomycete fungus Phakopsora pachyrhizi is considered the main crop disease. In experiments carried out in incubators the basal, optimal and the maximum temperatures were determined in soybean leaf extract-agar in petry dishes. It was assessed spore germination and germ tube length. Accumulated degree-days were used to estimate the latent, infectious period, and sporulation potential using detached soybean leaflets under different temperatures. The best substrate for uredosporos germination was 4.0 g.L-1 of soybean leaf extract. Lower thermal threshold, optimum temperature and upper thermal threshold were 6, 21 and 36oC respectively. By MONTEITH s (1977) formula, were calculated 182, 293, 569, and 765 accumulated degrees days for the temperatures 10, 15, 20 and 25 ºC respectively. On the other hand,using Russele s et al. (1984) formula, accumulated degrees days were 157,5; 332,5; 507,5 and 682 for the same temperatures respectively