Uredospore Germination and Development of Some Cereal Rusts from South‐central Chile at Constant Temperatures

The minimum and maximum temperatures for germination of uredospores of Puccinia striiformis, P. recondite, P. coronata and P.gramnis isolates from south‐central Chile were 0°C and 26°C, 0°C and 32°C, 8°C and 30°C, and 4°C and 34°C, respectively, whereas the shortest latent period was 8.5 days for P. struformis at 20°C, 5 days for P. recondite at 26°C, 5.5 days for P. coronata at temperatures, reaching the minimum and maximum threshold temperatures at 0.006°C and 23°C for P. strüformis, 0.31°C for P. recondita, 2.87°C and 30°C for P. coronata, and 1.72°C and 32°C for P. graminis. rspectively. The cardinal temperatures give no explanation as to the observed sequential appearance of these rusts during the growing season. Other phenomena like the systemic mycelial growth of P.striiformis might be involved here. At temperatures between 19°C and 22°C, the average daily increase of the area of sporulation of P.striiformis in wheat leaves varied between 9.05 and 22.48 mm2/infection site. This variation was due to substrate (plant) history and environmental factors.