Parts from correspondence with a Prairie Rosarian,
"Percy Wright would put his seeds in tin cans of soil and keep them in a cold cellar until March. Then, he'd take them outside and bury them in a snow drift until spring."
(Riku's note) ... based on the frost in aiti's cold cellar (concrete block with 2x1" air vents to outside and under front concrete steps ... cold cellars can be "cold" (0C+) ... but potatoes did not "black decay" but would sprout.
... another view, Dr. Svejda from book" Canadian Explorer Roses",
"We found that the most effective treatment for breaking dormancy in R rugosa seeds was the combination of 8 weeks at 20C, followed by 12 weeks at 4C."
... "Throughout the program we treated the seeds, which were mixed with moist peat moss, wrapped in plastic and properly labelled, to warm-cold periods of 8 weeks .... For the warm treatment, where temperature level should be constant the seed parcels were placed in an incubator and then transferred to a household refrigerator. The after-ripened seeds in the peat were placed on top of seed flats, covered with soil, and the resulting seedlings were potted before field plantation. The soil used was a mixture of soil, perlite and peat, generally used in our greenhouses."
To zero I go next winter, ... after cleaning, shucking and drying followed by a brief period at room temp.
A meeting place for rose breeders.