Cytological Studies on Polyploids Derived from Tetraploid Fragaria Vesca and Cultivated Strawberries.

REVIOUS workers have obtained hybrid seedlings from diploid Fragaria P vesca x cultivated strawberry, but they were always sterile so that new types never became established. -4 colchicine-induced autotetraploid of F. vesca L. (DERMEN and DARROW 1938) when used in a series of crosses with the octoploid cultivated strawberry ( x F. ununassa Duch.) has given hybrids varying in fertility from completely sterile types to fully fertile ones. Fruits of some of the fertile seedlings have a pleasing, high aroma similar to that of F. vesca. Since aroma is a desirable character to incorporate into cultivated strawberry varieties, the fertile new types may be of economic importance. Since the new hybrids involving tetraploid F. vesra and cultivated strawberry gave progenies with both fertile and infertile forms, questions arose regarding the chromosome numbers of these plants, their meiotic behavior, their pollen production, and the procedure to use in a practical breeding program. Consequently, a cytological study dealing with this material seemed necessary to answer the above questions and to supply a basis for further hybridization work. This is a report of such a study. A comprehensive review of literature on strawberry breeding up to 1937 was given by DARROW (1937). Hence, only those papers that are pertinent to the present cytological report will be considered here. DUCHESNE (1766) accurately described many different species of strawberries. The chromosome numbers of the different species were unknown iintil ICHIJIMA (1926), KIHARA (1926), and LONCLEY (1926) reported on them. LONGLEY (1926) pointed out that there were three natural groups, diploid, hexaploid, and octoploid, with a basic number of x = 7. He considered Fraguria vesca one of the most primitive species. The diploid species with 14 somatic chromosomes are represented today by F. vesca L., F. nilgerrensk Schlecht., F. daltoniana J. Gay, and F. viridis Duch. There is only one hexaploid, F. moschata Duch. ; but there are three octoploid species, F. virgivriana Duch., F. chiloensis (L.) Duch., and F. ovalis (Lehm.) Rydb. The cultivated strawberry (x F. anunwsa Duch.) is believed to have resulted from hybridization of F. virginiana and F. chiloensis, as first noted by DUCHESNE (1766).