Studies on Sunflower Rust: Ii. Longevity of Urediospores of Puccinia Helianthi

Urediospores of Puccinia helianthi Schw. collected from sunflower plants in the field and stored in glass vials at 5° C in a refrigerator survived for 846 days. In a freezer at −10° to −22 °C their ability to infect plants and to germinate on agar appeared unimpaired after 1652 days' storage. Storage under mineral oil decreased spore longevity at both refrigerator and freezer temperatures. Viable spores dispersed in oil germinated well on agar and induced heavy infections on sunflowers.The longevity of dry spores of P. helianthi stored at −10 °C to −22 °C and the high level of viability retained greatly exceed those reported for other species of rusts.