Strawberries. James F Hancock
evidence of a third unmapped locus influencing sex phenotype. The gene on LG6 in F. vesca is on the same chromosome as the one regulating sex in F. chiloensis but at a different position. However, these two genes are likely not homologous, as the one in F. chiloensis is dominant while the one in F. vesca is recessive.
DESCRIPTION AND LOCATION OF STRAWBERRY SPECIES
Diploids (2n = 2x = 14)
Fragaria bucharica Losinsk.
This species is similar to Fragaria nubicola except it has sympodial rather than monopodial runners (Staudt, 2006; Hummer et al., 2011). Two subspecies are recognized based on the size of their bractlets: F. bucharica ssp. bucharica(larger) and F. bucharica ssp. darvasica (smaller). Fragaria nubicola can be crossed with F. mandshurica, F. vesca and F. viridis, resulting in mostly heterotic plants with the morphological characters of F. bucharica. Crosses with Fragaria nipponica produce dwarf plants. F. bucharica is distributed from Tadjikistan to Afghanistan, Pakistan and Himachal Pradesh in India.
Fragaria chinensis Losinsk.
This species is a slender plant about 8–15 cm in height with monopodial branching runners (Lei et al., 2014). Its leaves are trifoliate, elliptic or obovate and nearly sessile. Its runners and peduncles are glabrous or covered with sparse appressed hairs. There are two to six flowers per inflorescence with a calyx that is wide lanceolate to triangular. Its fruits are pale red to red and mostly flavourless, with light yellow to brown seeds that are deeply sunken in the fruit. F. chinensis is native to western and south-western China.
Fragaria vesca L.
The wood or alpine strawberry is cultivated to a limited extent in North America and Europe. It has thin, light-green, sharply serrated leaves borne on slender petioles (Fig. 1.3). The branching of its stolons is sympodial. The terminal tooth of the terminal leaflet is usually longer than the adjacent lateral teeth and the calyx is reflexed. The plant is erect and 15–30 cm tall. Flowers are bisexual, approximately 1.3 cm wide; inflorescences are about the same length or taller than the leaf petioles. Most plants are short day, but everbearing types exist (F. vesca f. semperflorens). Fruits are long ovate, bright red in colour and highly aromatic. The fruit has very soft flesh and raised or superficial seeds. Runnerless and white-fruited forms exist.
Fig. 1.3. Duchesne’s drawing of Fragaria vesca. Cytogenetic studies suggest that this species may be a diploid progenitor of the octoploid strawberries. (From Darrow, 1966.)
There are four subspecies found in the group (Staudt, 1962, 1999): (i) F. vesca ssp. vesca – woods of Europe and Asia; (ii) ssp. americana (Porter) Staudt – woods of eastern North America to British Columbia; (iii) ssp. bracteata (Heller) Staudt – woods of western North America; and (iv) ssp. californica (Chamisse and Schlechtendal) Staudt – California. Several ecotypes have been described within ssp. californica including headland scrub, coastal forest and Sierran forest (Table 1.2). All of these subspecies are hermaphroditic and self-fertile, except for ssp. braceata which has both hermaphrodites and occasional females (Staudt, 1989).
Table 1.2. Ecotypes of F. vesca and F. chiloensis found in California. (From Hancock and Bringhurst, 1979a, b.)
Fragaria viridis Duch.
This is a slender, upright species with dark-green leaves with smaller serrations than F. vesca (Fig. 1.4). It is native to Europe and central Asia, and found in open grassland hills, steppes, at the edge of forests and among brush. It produces only a few nodeless runners with monopodial branching. Flower numbers per inflorescence are smaller than F. vesca, but it has perfect flowers that are larger than F. vesca. The petals overlap and are often yellowish-green when opening. Fruit is small but larger than F. vesca, firm, green to pink in colour, and aromatic. The scapes lie along the ground when the berries are ripe. Seeds are set in pits. The calyx is clasping and hard to separate. F. viridis can be distinguished from F. vesca by its phosphoglucose isomerase isozyme pattern (Arulsekar and Bringhurst, 1981).
Fig. 1.4. Duchesne’s drawing of Fragaria viridis. (From Darrow, 1966.)
Fragaria daltoniana J. Gay
This species is vigorous, with petiolulate leaves that have few teeth along the margins. Runners are slender and sympodial branching; flowers are solitary and self-compatible (Bors and Sullivan, 1998). Fruit range from ovate to cylindrical, are relatively long (2–2.5 cm), bright red, spongy and tasteless. It has shiny, coriaceous leaves. Staudt (2006) suggests that it can be crossed with Fragaria iinumae, Fragaria nilgerrensis, and F. nipponica, producing morphologically intermediate hybrids. It is distributed in the Himalayas from India to Myanmar at elevations of 3000–4500 m.
Fragaria nilgerrensis Schlecht.
This species is vigorous and spreading with pubescent, dark-green and heavily veined leaves. The petioles and peduncles are covered with long, stout hairs. The leaflets are petiolate, round to ovate, with small serrations, dull green and very pubescent. Branching of stolons is sympodial. It produces a small inflorescence with three or four large bisexual flowers. The flowers have a pink blush. The fruit are small, subglobose, pale-pink, tasteless to unpleasant and have many small, sunken seeds. Staudt (1989) describes it as having a banana-like flavour. The subspecies F. nilgerrensis ssp. hayatai from Taiwan has anthocyanin in all parts of the plant, including the berries.
Fragaria nubicola Lindl. ex Lacaita
This species closely resembles F. viridis. It is around 4–10 cm in height and its leaves are obovate with very sharp teeth (Lei et al., 2014). Appressed hairs cover its petioles, runners and peduncles. Its stolons are filiform and monopodial branching. Fruits are globose or elliptic with an appressed, persistent calyx. It is found in Tibet at elevations of 1500–4000 m.
Fragaria pentaphylla Losinsk.
This species has penniform, thick leaves, reflexed sepals and elongated calycules at fruit maturity. They are self-incompatible (Bors and Sullivan, 1998) and the fruit is ovoid–globose. It is 6–15 cm height with monopodial branching runners; the leaves have five leaflets and the central one is elliptic with large serrations and long petioles, nearly glabrous above and purplish-red beneath (Lei et al., 2014). Often there are 2~3 auriculate leaves on petioles. The petioles and runners are covered with spreading hairs, while the peduncles have few hairs. There are both white and red coloured fruited forms.