The rust Puccinia abrupta var. partheniicola, a potential biocontrol agentof Parthenium weed: Environmental requirements for disease progress

The rust fungus Puccinia abrupta var. partheniicola, a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination te mperatures as well as dew period durations and temperatures were investigat ed to determine some of the environmental requirements for disease establis hment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20 d egrees C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26 degrees C or 18/13 de grees C; day/night). Urediniospores germinated best at 12 +/- 1 degrees C, with lower germination rates at 5 degrees C or above 20 degrees C. No infec tion occurred when the plants were exposed to dew periods of less than or e qual to 3 h, regardless of the incubation temperature. The disease progress ed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 +/- 1 degrees C. The disease progre ssed most slowly following inoculation at dew periods of 6 h or less. Disea se progress was more rapid when the plants were exposed to a cool-temperatu re regime (18/13 degrees C) than when exposed to a warm-temperature regime (30/26 degrees C). This suggests that good infection of parthenium weed cou ld be obtained when the urediniospores arrive on the plants during the afte rnoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected. (C) 1999 Academic Press.