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Axenic Culture of the Mononucleate Stage of Cronartium ribicola. A. E. Harvey, Plant Pathologist, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah 84401, stationed at Forestry Sciences Laboratory, Missoula, Montana 59801; J. L. Grasham, Biological Technician, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah 84401, stationed at Forestry Sciences Laboratory, Missoula, Moscow, Idaho 83843. Phytopathology 64:1028-1035. Accepted for publication 23 February 1974. DOI: 10.1094/Phyto-64-1028.

Cultures of Cronartium ribicola were established on media containing (g/liter) calcium nitrate 0.5, magnesium sulfate 0.14, potassium phosphate (monobasic) 0.14, ammonium sulfate 0.025, ferric sulfate 0.014, manganese sulfate 0.0035, glucose 10.0, and Difco agar 10.0, plus any one of the following: (i) vitamin-free casein acid hydrolysate 10.0; (ii) yeast extract 1.0; (iii) Bacto peptone 1.0; (iv) Evan’s peptone 1.0; (v) a combination of alanine 3.0, aspartic acid 3.0, and glutathione (reduced) 2.0; or (vi) as in v but substituting cystine 2.0 for glutathione. Excellent growth was obtained on the basal medium plus a combination of 1.0 yeast extract, 1.0 Evan’s peptone, and 10.0 defatted Bovine serum albumin. Addition of CaCO₃ 10.0 increased growth, up to 300%, on all media. Inocula consisted of infected parts of tissue cultures of Pinus monticola or mycelium derived therefrom. Rust fungus transferred from five cultures reinfected pine tissue cultures and produced haustoria after 40 days in axenic culture (five subcultures). Subsequently, colonies from the five cultures were reestablished on artificial media. After 10 mo of continuous propagation, rust colonies from three cultures infected stems of germ-free Pinus monticola seedlings. All cultures intermittently produced immature spores. Homogenates of colonies from three cultures infected Ribes nigrum leaves and produced uredia and subsequently teliospores. Some cultures produced haustorialike structures.