SEED DORMANCY IN ROSA AS A FUNCTION OF CLIMATE

Abstract

THE SEEDS of many plants are known to be dormant at maturity, and to require a period of exposure to low temperature to enable them to germinate under subsequent suitable conditions. In Rosa, and in several other rosaceous genera, this lowtemperature after-ripening is widely regarded as a fixed and characteristic prerequisite to further development of the embryonic plant. Joseph (1929) pointed out that rosaceous seeds require low temperature stratification to prepare them for germination. Haut (1938) found that apple, cherry, peach and pear seeds must be after-ripened before germination will occur. Crocker (1927) reported that seeds of temperate-zone roses germinate well only following a period at low temperature, and Crocker and Barton (1931) determined the after-ripening requirements of hybrid and species rose seeds, as well as those of several other rosaceous seeds. The ubiquitous nature of the low-temperature after-ripening requirement of rosaceous seeds is apparently unquestioned in recent literature, with the exception of a report by Calvino (1930) stating that hybrid rose seeds grown at San Remo, Italy, germinated readily with no prior low-temperature treatment. This report was accorded little significance, and the results were logically explained by Crocker and Barton (1931) by supposing that the seed were inadvertently exposed to winter temperatures sufficiently low and prolonged to allow afterripening to occur. More recently, however, there have been unpublished reports from southern France, and from some of the inland valleys of California, claiming successful germination of hybrid rose seed without resort to low-temperature treatment. These reports have been partially substantiated in this laboratory by the collection or import of seed from several localities, and in the course of the investigation it has become apparent that the dormancy of hybrid rose seed of a given genetic origin may vary widely from year to year, and from one region to another. The present paper deals with the quantitative aspect of the dormancy, and with the relationship between the dormancy and the pre-harvest climatic environment. MATERIALS AND METHODS.Temperature data were obtained in the experimental field from shielded maximum and minimum registering thermometers. Sunlight data were calculated from the Local Climatological Data of the U. S. Weather Bureau station at Portland, Oregon. This station is