rel="nofollow" href="#fb3_img_img_e2846c25-e2a6-5406-8571-882d433a59d2.jpg" alt="Image"/>); cultivated F. chiloensis f. chiloensis (○), and cultivated F. × ananassa (⊗). Note that the white forms of the wild forms cluster closely with domesticated F. chiloensis. (Adapted from Lavín, 1997, and del Pozo, Muñoz, Lavín and Maureira, unpublished.)
Native hybridizations between F. vesca and F. chiloensis in coastal California have resulted in persistent 5x, 6x and 9x colonies (Fig. 1.7) (Bringhurst and Senanayake, 1966). These have been named Fragaria × bringhurstii after their discoverer R.S. Bringhurst (Staudt, 1989). Their leaves are intermediate between F. chiloensis and F. vesca with regard to thickness, colour, profile, pubescence and the appearance of the upper leaf surface. They are mostly sterile at 2n = 35, 42 or 63, but small percentages of aneuploid gametes are produced that are interfertile with octoploid material.
Fig. 1.7. The morphological and cytogenetic traits distinguishing F. chiloensis, F. vesca and their pentaploid hybrid at Point Sur, California. (Adapted from Bringhurst and Khan, 1963.)
Fragaria virginiana Duch.
The scarlet or Virginia strawberry is found in meadows throughout central and eastern North America. Plants are slender, tall and profusely runnering (Fig. 1.8). Leaves are coarsely toothed and obovate to oblong. The terminal tooth of the terminal leaflet is usually shorter than the adjacent lateral teeth. The inflorescence is variable, basal to high branching and flowers are small to large (0.6–2.5 cm) and dioecious. The fruit is soft and round, up to 3 cm in diameter (although most fruit is much smaller). It is light red with white flesh, aromatic and has deeply embedded seeds. F. virginiana can be distinguished from F. chiloensis by a number of morphological traits (Table 1.3).
Fig. 1.8. Duchesne’s drawing of Fragaria virginiana. This species is the North American progenitor of the cultivated strawberry, F. × ananassa. (From Darrow, 1966.)
Table 1.3. The characteristics that separate F. chiloensis from F. virginiana. (From Darrow, 1966.)
| Character | F. chiloensis | F. virginiana |
|---|---|---|
| Leaves | Thick, leathery | Thin |
| Deep set stomata | Shallow set stomata | |
| Strongly netted | Not strongly netted | |
| Glossy | Dull | |
| Dark green | Bluish to light green | |
| Evergreen | Deciduous | |
| Short teeth | Coarse teeth | |
| Petioles | Thick | Slender |
| Not channelled | Broadly channelled | |
| Runners | Robust | Slender |
| Red | Green | |
| Persistent | Ephemeral | |
| Crown | Thick | Less thick |
| Flowers | Large | Small |
| Large stamens | Small stamens | |
| Fruit | Dull red | Scarlet to crimson |
| Seeds slightly sunken | Seeds sunken in pits | |
| Late ripening | Early ripening | |
| Large | Small | |
| Firm | Soft |
Populations of F. virginiana vary from being completely dioecious to trioecious. In western populations of F. virginiana, all three sexes are found in similar proportions, whereas in eastern populations, only hermaphrodites and females are observed, again in relatively equal proportions (Staudt, 1968; Luby and Stahler, 1993). Levels of fertility in hermaphrodites are highly variable, with large ranges of fertility being found in natural populations from pure males to pure hermaphrodites (Hancock and Bringhurst, 1979a, 1980; Stahler, 1990). In general, females are more fertile than hermaphrodites (Dale et al., 1992). Environment probably plays a role in the fertility of hermaphrodites (Stahler, 1990; Dale et al., 1992), but most of the control is genetic. The level of fertility in hermaphrodites appears to be polygenic as large ranges of fertility are generated in crosses of native males with cultivated hermaphrodites (Scott et al., 1962) and fruit set in native hermaphrodites can be greatly enhanced through recurrent selection (Luby et al., 1995).
F. virginiana has undergone considerable genetic differentiation like the other octoploid species, F. chiloensis. Staudt (1962) described four subspecies: (i) ssp. glauca (Wats.) Staudt – southern Rocky Mountains to north-west Canada and central Alaska; (ii) ssp. platypetala (Rydb.) Staudt – Rocky Mountains from Wyoming to Colorado, west to Sierra Nevada and Cascades Mountains; (iii) ssp. grayana (E. Vilmorin ex Gay) Staudt – meadows and forest margins from New York to Alabama, Louisiana and Texas; and (iv) ssp. virginiana Duch. – meadows and forest margins from eastern USA, Newfoundland and Yukon Territory. Staudt felt that ssp. virginiana
