Relationship between climate and the progress of the asian soybean rust (Phakopsora pachyrhizi) in two micro-regions of Paraná State

Abstract

The objective of the work was to study the influence of the climate on the progress of the soybean rust (Phakopsora pachyrhizi) under field conditions. Two assays were carried out during the 2005/2006 season in Castro and Arapoti regions, Paraná. The epidemic was divided in three periods: sowing until first symptoms of disease; beginning of the disease until severity of 20% and severity of 20% until maximum severity. The rust symptoms occurred in Castro at 78 days and in Arapoti at 82 days after the sowing. The biggest duration of leaf wetness period - Dpm (18 hours) was observed in Castro. During the second period of the epidemic, Arapoti presented apparent infection rate-r (0.18), higher than observed in Castro (0.12). During same period were observed greater rainfall values and greater index of number of days of rain – Indr compared with Castro. The final disease severity was 99.9% in Arapoti and 96% in Castro 96%. It was observed a relation between Dpm with the appearance of the first symptoms and was also observed and relation between precipitation data and Indc with the progress of the epidemic. The ambient conditions had been more favorable to the disease in Arapoti, where bigger value of AACPDp (38.2) was observed and less favorable for Castro (30.4).