The asian rust (Phakopsora pachyrhizi Sydow) which has been reported in areas of tropical and subtropical climates around the world, causes significant soybean [Glycine max (L.) Merr.] yield reduction. The disease progress is influenced by biotic factors as interaction pathogen-host and abiotic factors of the environment. The objective of this work was to study the effects of temperature and leaf wetness period in the asian rust progress in the cultivars Conquista, Savana and Suprema. The experiment was conducted at the Department of Plant Pathology at Federal University of Lavras, in growth chamber at temperatures of 15, 20, 25 and 30 °C and leaf wetness periods of 0,6, 12, 18 and 24 hours. The plants were inoculated by spraying a suspension of inoculum of P. pachyrhizi at concentration of 10(4) urediniospores.mL-1. Severity and incidence data were integrated by the area under disease progress curve for severity (AUDPCS) and incidence (AUDPCI). Non-linear regression models were adjusted for the disease severity (AUDPCS) and incidence (AUDPCI). Volume under the response surface of temperature and leaf wetness was calculated for incidence (VURSI) and severity (VURSS) to detect differences between cultivars. Higher soybean rust intensity occurred with leaf wetness above 15 hours and temperatures close to 20 ºC, for the three tested cultivars. Temperatures above 30 ºC and below 15 ºC reduced the disease progress. Disease intensity was reduced in leaf wetness below 6 hours. All cultivars were susceptible, but higher VURSI and VURSS occurred in Conquista cultivar, followed by Savana and Suprema cultivars. Disease intensity was not statistically different between Savana and Suprema cultivars. Temperature and leaf wetness were different among cultivars for AUDPCI.
severity; incidence; epidemiology