Title: Cytogenetics and Evolution in American Fragaria
Abstract: Fragaria × ananassa Duch., the modern cultivated octoploid strawberry (2n = 8x = 56), is the culmination of all strawberry evolution as we know it.It was derived from the two American octoploid species: F. virginiana L., native to North America north of Mexico (primarily the Atlantic seaboard, Great Plains, and westem mountain ranges); and F. chiloensis Duch., native to west coastal North America and the west coast and Andes Mountains of South America.Both natural species are products of ancient polyploidization and natural selection.The modern cultivated strawberry (F.×ananassa) is of recent origin [in Europe between 1714 and 1759, according to Staudt (1962)], resulting from human intervention in the evolutionary process (Darrow, 1966).There is no convincing evidence that any of the lower ploidy level Fragaria spp. of Europe, Asia, or elsewhere were directly involved in the synthesis of the modern octoploid cultivars, as suggested by some (Wilhelm and Sagen, 1974).In this paper, I attempt to establish that the evolutionary forces that gave rise to the present polyploids (particularly polyploidization and introgression), are still active in the narrow and fragile coastal fog belt of California today.Unless the evolutionary process is terminated by the imprudent destructive activities of humans, new ploidy levels may yet evolve with greater breadth of adaptation than that-of the present coastal octoploids.In addition, a significant amount of introgressive gene flow from the diploids into the octoploids without long-term changes in chromosome number is also likely.