G.M. Darrow, The Strawberry: History, Breeding and Physiology
IN THE PRECEDING CHAPTER, results of genetical research with the strawberry are given; the four chromosome groups of species are described; and hybrids derived in various ways but having other chromosome numbers also are discussed. The subject of the two parts of this chapter is one of a narrowing scope of concern: the eleven species, placed in the four chromosome groups, are described in terms of gross morphology, then attention is focused on the three species out of the eleven, which compose the genetic source of the modern strawberry. Much of the material in this discussion of necessity must be of a technical nature. The modern strawberry is chiefly the result of crosses between two octoploids, with slight infusion of some characters of a third. These octoploids presumably came from ancient diploids, whether by doubling with unreduced gametes to tetraploid, and then doubling again to octoploid, or by some other process. Certainly the strawberry was not always the highly heterozygous plant that it now is. A trend to greater complexity and adaptability associated with higher polyploidy is evident. Out of the array of technical detail, patterns can be drawn; the causes of present weaknesses and reasons for the modern strawberry's strength can be traced to earlier sources.
* By Clyde F. Reed, botanist, Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland.
The genus Fragaria Linn. belongs to the Rose Family (Rosaceae, subfam. Rosoideae, tribe Potentilleae) along with its closest allies, Duchesnea Smith and Potentilla L. The wild species of strawberries fall into four groups, cor related with their chromosome numbers, these being five diploids, two tetraploids, one hexaploid and three octoploids. Until recently (Ellis, 1961, Nature 190: 968) when sterile plants resulted from crosses with species of Potentilla, no certain hybrids with other plants had been obtained (though Burbank reported crosses with raspberries, Rubus).
The cultivated varieties of commercial strawberries are almost all octoploids and are derived chiefly from the octoploids F. chiloensis and F. virginiana, usually recognized as F. x ananassa. A few have octoploid F. ovalis in their ancestry. A few "musk" varieties from the hexaploid F. moschata are grown very slightly, chiefly in Europe. A few of the very small-fruited, highly aromatic diploid varieties, derived from the European F. vesca and its everbearing form F. semperflorens, also are grown slightly. No cultivated varieties have come from the two tetraploid species, F. orientalis and F. moupinensis of Asia; none from the diploid species F. daltoniana, F. nubicola and F. nilgerrensis of India and Southeast Asia; none from the diploid F. viridis of Europe. The diploid species are the least variable and the octoploid, the most variable.
Many other strawberries have been described as new species, but most of them fall within the ranges of variability for the eleven species described below. The genetics and hybridity is unknown for most of these "species" at the present time and the exact placing of these species must await more extensive study and breeding.
F. vesca L., 1753. (Sp. Pl., 494, Fig. 8-1). Wood Strawberry, Frais. des bois. This is the common wild woodland strawberry of Europe and Asia. It is the most widely distributed species of the genus, being circumpolar, appearing throughout Europe, northern Asia, North America and northern Africa. At present at least it is found Southward in its botanical varieties at the higher elevations in the mountains of the West Indies, Mexico and South America. Map 8:1.
Plants are erect, 15-30 centimeters high, with runners; leaves are thin and light green with slender petioles, glabrous or becoming so above, lighter colored and lightly silky-hairy beneath, at least on the veins; leaflets are nearly sessile, rather small, relatively narrow, cuneate-ovate to rhombic-ovate with large sharp serrations; petioles and peduncles have few but generally spreading soft hairs; inflorescence is small, on usually tall inflorescences, equaling or exceeding the leaves, forking; flowers are about 1.3 centimeters in diameter, bisexual; fruit is hemispherical (in the type and seedling raised) flesh extremely soft, pulpy, generally aromatic to highly aromatic; seeds are small, raised, very prominent; calyx is reflexed, widely spreading.
Many allied species or varieties have been proposed, but they vary from the type only slightly: var. californica (Cham. & Schlecht., 1827) Staudt, 1962, with leaves silky below; F. mexicana Schlecht., 1839, with cuneate or oblong-obovate leaflets; ssp. bracteata (Heller, 1898) Staudt, 1962, and F. insularis Rydb., 1908, with the calyx spreading; ssp. americana (Porter) Staudt, 1962, with ovoid or subconic fruit red, occasionally white, with sub-appressed hairs on the peduncles and pedicels; var. eflagellis (Duch.) Ser., in DC., 1825, runnerless; F. semperflorens (Duch.) Ser. in DC., 1825, both runnered and runnerless (Alpine), flowering all summer; var. monophylla (Duch.) Ser. in DC., 1825, with a single leaflet; var. muricata (Duch.) Ser. in DC., 1825, with petals, stamens and pistils leafy (may be due to Aster yellows virus); var. multiplex (Duch.) Ser. in DC., 1825, with petaloid stamens.
Some forms, as semperflorens, helleri (Holz in Coult., 1896, Fig. 8-2) and monophylla, are known to differ by single genes from the typical vesca. Though not greatly variable genetically, Fragaria vesca is very adaptable and is the most widely native and naturalized of all the species of strawberries. The three most notable qualities for this strawberry are its adaptable plant, its highly aromatic fruit and its everbearing character. Its most undesirable characteristic is its extremely soft fruit, with large intercellular air-spaces throughout the berry. Map 8:1-1.
F. viridis Duch., 1766. (Hist. Nat. Frais., 135). (Syn.: F. collina Ehrh., 1792, F. bifera Duch., 1790, Fig. 5-5 ). Capitan, Breslinge, Green strawberry. This species is native to most of Europe and to eastern (Caucasus) and central (Siberia) Asia; Canary Island, in open grassland hills, steppes, small forest areas and in brush. Map 8:2-10.
Plants are slender, with no or very few, short runners without nodes; leaves are deep green, silky beneath, thin, ovate to elliptic with curved and smaller teeth than vesca; inflorescence is erect, small; flowers are perfect, much larger than those of vesca, the petals are overlapping, usually somewhat yellowish-greenish when opening; stamens are longer and the anthers are larger than in vesca; fruit is green, greenish-white to red (in the sun) when ripe, small, the flesh firm, aromatic; achenes are set in pits; calyx is relatively large, long, hard to separate and clasping as in chiloensis, epicalyx spreading.
This species is native to grassy meadows and steppes and forest edges. Plants resemble F. vesca in general appearance. It commonly reflowers in fall. Though slightly variable, it seems rather distinctive and has no apparent characters that would improve present cultivated sorts, unless it may have a different everbearing or photoperiod response. Its firmness should be surveyed for new genes for that character. It is said to thrive on calcareous soils better than most species. Map 8:2-10.
F. nilgerrensis Schlecht., 1857. (ex J. Gay, Ann. Sci. Nat. IV, 8:206, Fig.8-3). This vigorous species is native to southeast Asia from the mountains of the Philippines and central southern China (Yunnan, Hupeh, Szechman, Mingtsze) across to India, especially the hill region of southern India. Map 8:1-2.
Plants are often very robust; runners, petioles and peduncles are covered with long stout spreading hairs; leaflets are petiolulate, thick and rugose, round to obovate, small to medium, small serrations, very pubescent on leaves and petioles, dull green; inflorescence is small, three to four large flowers, white with a pink blush; stamens are short, pistils are very numerous; receptacle is large, flat; fruit is subglobose or depressed, white with a pale pink tint, tasteless to unpleasant, small, borne on erect pedicels; seed is small, numerous, set close together and in pits; calyx-lobes are large, often clasping, entire, spreading or suberect in fruit; forms with scarlet instead of white flowers and large instead of small fruits are known.
Little is known of the physiological characters of this species, such as its photoperiod and temperature responses. Its native distribution suggests it as one possible parent of Duchesnea indica, the false strawberry. Its large number of small seeds per fruit also suggests its value in breeding for large fruit, using as the other parent a variety with large fruit to furnish the most hormone per seed for swelling. Attempts to cross this have usually resulted in failure or in dwarf plants that do not fruit. However, in 1941 Nuremberg (1959) crossed vesca and nilgerrensis and obtained eleven normal and seven dwarf plants. Backcrossed to nilgerrensis he obtained seventeen hermaphrodites, four pistillate and seven male or sterile plants.
This diploid seems to have a tetraploid counterpart in most of its morphological characteristics in F. moupinensis from farther north and eastward (in China mainly). Some specimens from China (W. Hupeh) are huge (up to one foot tall with larger leaves and runners two feet long) and may prove to be octoploids of F. nilgerrensis.
F. daltoniana J. Gay, 1857. (Ann. Sci. Nat. IV, 8:204, Fig. 8-4). This species is native of Sikkim Himalayas at 10,000 to 15,000 feet. Map 8:2-9.
Plants have filiform runners, slender, hairy to nearly glabrous; leaflets are petiolulate, with few teeth; flowers are solitary; calyx lobes are toothed and bracteoles toothed, spreading in fruit; fruit is elongate-ovoid, or fusiform, often nearly 2.5 centimeters by 1.3 centimeters broad, bright scarlet, but with little flavor. Map 8:2-9.
This species seems to have only its relatively large fruit size and possible hardiness to recommend it to breeders.
F. nubicola Lindl., ex Lacaita, 1916. (Jour. Linn. Soc. Bot. 43:467). This species is native of the temperate Himalayas, 5,000-13,000 feet elevation. Map 8:2-8.
This species is described as being nearest F. viridis, although the specimens seen resemble F. vesca. Hooker (1879, Fl. Brit. India, 2:344) considered this species as a variety of F. vesca. Staudt (1959) by experimentation showed that nubicola was incompatible with vesca, and considered it a separate species.
Plants are slender, silvery, nearly glabrous, runners filiform, hairs on the petioles and the few-flowered peduncles densely silky appressed; calyx-lobes are narrow, spreading in the fruit.
No desirable characteristics for breeders have been noted.
F. moupinensis (Franch.) Card., 1916. (Bull. Mus. Nat. Hist. Paris, 22:397- 398). Based on Potentilla moupinensis Franch., 1885 (1886). This is a species of eastern Tibet (Moupine), Yunnan and western China. Map 8:2-7.
The range of this species lies between that of F. orientalis to the north, of F. nilgerrensis to the south and of F. nubicola and F. viridis (F. collina) to the west. In leaf characteristics it is very similar to F. nilgerrensis and may represent a tetraploid form of that diploid species. Franchet had suggested that it resembled F. collina (F. viridis, a diploid), in which case it may be a tetraploid of that species. In this case the distribution of F. viridis would be extended eastward from central Siberia into western China.
Plants are slender; rhizome is short, stoloniferous; radical leaves are trifoliate, sometimes pinnately quinquefoliolate, with smaller leaflets on the petiole below, sericeous beneath, glabrous above; floriferous stem is more or less longer than the leaves, hirtellous, often two-flowered, sometimes as many as four-flowered, the peduncles are often with a smaller simple leaf or subtended by a bract, appressed sericeous; calyx is laciniate, the lobes are lanceolate-linear; petals white, subrotund, about twice as large as the calyx.
Although we know this species to be a tetraploid, its culture and cultivation in China is not too well known. More study and breeding of this species is needed before it can be properly evaluated.
F. orientalis Losinsk., 1926. (Bull. Jard. Bot. Princ. U.R.S.S.. 25:70-72, Fig. 8-5a, 8-5b). This species lives in the forests and open mountain slopes, frequently in stony soil, of western Siberia, Mongolia, Manchuria and Korea. Map 8:2-6.
Plants (in type) are only 3.8 centimeters high, the runners, long and slender; leaflets are ovate, rhomboid-shaped, with silky hairs below, almost sessile, with six to nine large, deep teeth on each side; inflorescence is few-flowered, bract at base of two to three leaflets; flowers are large, 2.5 to 3 centimeters, usually perfect, pedicel thick with thick spreading hairs; petals are up to 1 centimeter long, rounded, overlapping; sepals are tightly haired, lanceolate, outer sepals linear-lanceolate, shorter than the petals, clasping; fruit is conical or round, red; seeds are sunken.
Its distribution in the cold dry areas of Asia suggest its hardiness and drought resistance. It is sometimes fall-fruiting in Maryland. Petrov, who found this species to be a tetraploid, later obtained an octoploid by colchicine treatment. This strawberry is used fresh in the Far East, but its culture is unknown.
F. moschata Duch., 1766. (Hist. Nat. Frais., 145, Fig. 8-6). (Syn.: F. elatior Ehrh., 1792). Musk, Capron, Capiton, Hautbois Strawberry. This species of strawberry grows in forests, under shrubs, in shaded places, in tall grass. It is found from Scandinavia and Atlantic Europe, eastward through central and eastern Europe (Volga, Dnieper, Don regions), and into Russia, Siberia (Region of Amur). Map 8:2-11.
Plants are vigorous, 10 to 40 centimeters tall, runners none or very few, even more vigorous than many virginiana and chiloensis clones; plants are dioecious but cultivated varieties usually perfect-flowered; leaves are broad, rhombic, strongly veined, rugose and very hairy; inflorescence is tall, umbel-like usually above the foliage; flowers are large, 20 to 25 millimeters in diameter; fruit is larger than in vesca, light red to dark dull brownish or purplish red, even greenish-red, irregular-globose (to ovoid), aromatic, strongly vinous or musky; achenes are raised; calyx is strongly reflexed.
Schiemann (1937) reported that hybrids of moschata and viridis are tetraploid and fully fertile and can hardly be distinguished from moschata. Most hybrids with the octoploid virginiana are completely sterile, but a small percentage of the seedlings produces fruit and a few seed, and such seedlings look like moschata. This species is very hairy, has great plant vigor, very large flowers and the most aromatic fruit of all. It has been cultivated to some extent since about A.D. 1600 for its vinous flavored fruit, liked by some, disliked by many. It is like the muscat grapes, which, with a slight muskiness, are considered by many the most delicious of grapes, but seedlings of which may have such a strong flavor as to be inedible. Notably most of the berries ripen together in F. moschata.
F. virginiana Duch., 1766. (Hist. Nat. Frais., 204, Fig. 5-6). Scarlet or Virginian strawberry. This is the meadow strawberry of eastern North America from Louisiana and Georgia to Hudson Bay and the Dakotas. It is an octoploid with fifty-six chromosomes while the only other species of eastern North America is the diploid, F. vesca ssp. americana (Porter) Staudt, 1962 (Canad. Jour. Bot. 40:872) found in woodland and shady places from Newfoundland and Manitoba south to Virginia, a much more slender plant. Map 8:2-3.
Plant is from a subsimple caudex at end of a simple rhizome, making runners early; leaves are relatively thick, medium to dark green, usually petiolate, coarsely toothed, obovate to oblong; petioles are with spreading hairs; terminal leaflet is 1.5 to 10 centimeters long, with four to eight pairs of teeth; inflorescence is variable, basal to high branching, hairy; flowers are large, dioecious, occasionally polygamous, the strictly pistillate flowers much smaller than the staminate, 0.6 to 2.5 centimeters broad; borne below, with or above the foliage; calyx-lobes are 4 to 11 millimeters long; fruits are 0.5 to 2 centimeters in diameter, about twice the size of vesca, subglobose to ovoid, light to deep red, mostly scarlet, flesh usually white, pulpy, acid, aromatic, sometimes astringent; achenes are 1.3 to 1.6 millimeters long, sunk in deep pits below the surface.
The Virginian strawberry is quite a variable species and several botanical varieties have been described: var. australis Rydb., 1898, with nearly sessile leaflets; var. illinoensis (Prince) Gray, 1867, (var. grayana (Vilm.) Rydb., 1898), very vigorous, with spreading hairs on pedicels, terminal leaflets 5 to 10 centimeters with eight to fifteen pairs of teeth; var. canadensis (Michx.) Farw. with oblong-conic fruits; F. multicipita Fern., 1908 (many crowned), may be virus-affected plants (Gaspé); var. terrae-novae (Rydb., 1898), Fern. & Wieg., leaflets with short petiolules, scapes and petioles appressed to strigose-pubescent to glabrous; var. glauca S. Wats., 1871, with sparse pubescence.
Many notable characteristics appear in the various regional wild clones: from northern North America comes extreme resistance to low temperatures as well as to high temperatures; from southern United States comes the adaptation to short photoperiods: from the northern Great Plains comes drought resistance. Furthermore, the flowers range from susceptible to very resistant to frost. It has generally aromatic, rather acid, soft fruits, but firm selections can be obtained. Many selections cap very easily; many ripen all their berries nearly at the same time.
F. x ananassa Duch., 1766 (Hist. Nat. Frais., 190, Fig. 8-7). (Hybrid between F. chiloensis andF. virginiana; F. x ananassa nm. cuneifolia (Mitt. ex Howell) Staudt, 1962, is a nothomorph). (Syn.: F. chiloensis var. ananassa (Duch.) L.H. Bailey, 1925; F. grandiflora Ehrh., 1792).
Most of our common cultivated strawberries with large fruits belong here. Duchesne (1766) had suggested ananassa as a hybrid between F. virginiana and F. chiloensis. F. x ananassa strongly resembles F. virginiana var. illinoensis but has heavier and slightly rugose foliage, coarser and blunter teeth, and more superficial pits of the larger fruit. It is often found escaped from cultivation along woodsides and railroads. Specimens have been seen from Europe, North America, Russia, Hawaii, Japan and China.
F. chiloensis (L.) Duch., 1766. (Hist. Nat. Frais., 165, Fig. 8-7). This species is based on cultivated plants taken from Concepción, Chile, to France in 1714. This very variable species is abundant along the beaches of the Coast of Chile (but often somewhat inland) and in the Andes Mountains from the latitude of Concepción south 700 miles to below Coyhaique, even on the eastern slope in Argentina; in North America it is confined to the beaches from near Santa Barbara, California, north 3,000 miles to the Aleutian Peninsula of Alaska, but never inland off the beaches, as in Chile; in Hawaii it is on the mountain tops at 5,000 feet elevation up. Though cultivated in Peru and Ecuador and formerly in Mexico, the cultivated varieties of F. chiloensis were all from Chile and differ from most of the species in being more hairy, in having dull leaves that are glossy only at times, and in often having perfect flowers and large fruits. All these characters can be found in wild plants both in Chile and occasionally in California. Map 8:2-5.
Plants are low, stocky, usually entirely silky, runners Stout, short to long often perennial, mostly forming after fruiting; petioles are stout, 2 to 20 centimeters long; leaves are very thick and leathery, usually glossy, dark green, tending to be evergreen, large to small; leaflets are broadly obovate and the margin crenate with short rounded teeth above the middle, pale and silky beneath, petiolulate to nearly sessile; inflorescence is extremely variable, mostly silky haired, basal to high branching, few to many flowered, dioecious with occasional hermaphrodites, especially in Chile; flowers are mostly very large, 20 to 35 millimeters broad, borne below, with and above the foliage; petals are broadly obovate; calyx is clasping after petal-fall, quite silky; fruit is dull brownish red (especially on the sunny side) to pale translucent pink, flesh white, firm, mild, usually lacking in flavor, hemispherical to oblate, 15 to 20 millimeters in diameter, separating from the calyx very easily in most, usually larger than in other species; achenes are mostly raised above the surface, but may be in shallow pits, dark.
Many variants can be found along the coast and in the mountains of Chile, along the Pacific coast of North America and in the mountains (above 5,000 feet) of Hawaii: ssp. chiloensis. f . chiloensis Staudt, 1962, cultivated in South America, especially in Chile; ssp. chiloensis f. patagonica Staudt, 1962, in Chile and Argentina; ssp. lucida (E. Vilm.) Staudt, 1962, Washington to California; ssp. Pacifica Staudt, 1962, California to Aleutian Islands; ssp. sandwicensis (Decaisne) Staudt, 1962, Sandwich Isl., Hawaii. (This name cannot stand because of F. chiloensis var. sandwicensis Deg. &.- Deg., Fl. Hawaii, 1961).
This species is notable for its drought tolerance; adaptability to low temperatures (although some plants are not); adaptability both to long and to short photoperiods; resistance to cold when in flower and fruit in the Andes Mountains of Chile. Also notable, the inflorescences are often very large in Hawaii, the fruits usually cap easily, and are often quite firm. The limiting characters are susceptibility to leaf-scorch, plants usually tender to very tender to both cold and heat; berries dull red to white, with white flesh, dark seeds and very little flavor. Some clones found in California are reported as being highly flavored.
F. ovalis (Lehm.) Rydb., 1906. (Bull. Torr. Bot. Club, 33:143, Fig. 8-8). Based on Potentilla ovalis Lehm., 1849. This species includes all the pasture and meadow strawberries from northern New Mexico in the mountains to Montana west to the beaches of California, and north to Alaska. It is fully fertile with F. virginiana to the East and with F. chiloensis of the beaches to the West and merges with those species on both boundaries. Map 8:2-4.
Plants are more or less glaucous; leaves are usually thicker than in virginiana, but much thinner than in chiloensis, usually with a bluish sheen, silky beneath; leaflets are subsessile, or short-petiolulate, oblong or cuneate, 2 to 3 centimeters long coarsely toothed above the middle; inflorescence is rather short, not over 5 centimeters high, usually below the leaves, flowers 1 to 1.5 centimeters in diameter, petals obovate, exceeding the sepals by a half; fruit is pale red, usually soft to extremely soft, subglobose, about 1 centimeter in diameter.
This species is as variable as chiloensis and virginiana are. Introgression of characters of chiloensis such as thicker leaves, firm, dark-seeded, dull fruit and clasping calyx can be found in ovalis as much as 100 miles from the beaches inland in Oregon, and of the characters of virginiana such as the thin leaves with toothing below the middle, with bright scarlet berries with reflexed calyx in Colorado and Wyoming, west of the range of virginiana. Hybrids between chiloensis and ovalis and backcrosses and segregates are abundant where ovalis meets chiloensis at the beaches. F. ovalis is notable for its drought tolerance, its resistance to low- winter temperatures, its reflowering and everbearing character in very many clones, its early ripening, its flower-resistance to frost and its earliness, and can contribute these qualities to future strawberries.
By 1920 strawberry breeders in the United States were interested generally in the systematic crossing of varieties and the use of qualities of the native species in breeding. In his breeding, A.F. Etter in northern California was using F. chiloensis (Clausen, 1915) which he had collected along the California coast (Etter's catalogue 1920), as well as a South American chiloensis; in 1900, Hansen and Haralson had begun their crossing of cultivated varieties with selected wild Virginians from Manitoba and North and South Dakota; Fletcher had recently published his book, The Strawberry in North America (1 917) and also his monograph "North American Varieties of the Strawberry" (Va. Tech. Bul. 11, 1916); at the old U.S. Department of Agriculture Research Farm across the Potomac River in Virginia, W.F. Wight, during the years just before 1920, had established for study a planting of Fragaria species from various botanic gardens and other places of the world; D.N. Shoemaker, about 1916, selected superior wild plants of virginiana in the mountains of western North Carolina, and others made selections in Michigan, Minnesota, and elsewhere for Wight's collection; Georgeson, beginning in 1905, was using selected chiloensis and ovalis in his Alaskan breeding work; in 1920-1921 Popenoe surveyed the Chilean strawberries of Ecuador and Chile (Jour. Her. 1921) and sent plants to the United States; and Hedrick and associates were working on the monograph The Small Fruits of New York (1925).
By this time it seemed quite clear from Fletcher's book that F. chiloensis and F. virginiana were the two chief, if not the only, parent species of the cultivated strawberry. Then came the questions. Had the strawberry during the hundred years of breeding and selection in North America evolved toward chiloensis or toward virginiana, and had we lost valuable qualities in the process? Were there other qualities in the wild parent species which might be of value in cultivated varieties; qualities such as resistance to "black root" and leaf spots, to the humid semi-tropics, and to drought, resistance of flowers to frost, and of berries to rot? Could wild species furnish such qualities as hardier crowns to make mulching unnecessary, or flowers with more pollen and less sterility, to reduce nubbins and produce larger berries? Later, questions arose as to possible sources of resistance to red stele, Verticillium wilt, and viruses both in wild species and in cultivated varieties.
For the breeding work of the U.S. Department of Agriculture begun in 1920 at Glenn Dale, Md., the selections of virginiana made by Shoemaker proved especially interesting, for there were very productive pistillate and perfect-flowered selections among them. Crosses of these selections with cultivated varieties yielded seedlings which fruited as early as 1922 with some as large as the cultivated parent. Fifty or more of his varieties and hybrids, derived in part from chiloensis selections, were obtained from Etter and grown at Glenn Dale. A considerable population of crosses of many of these with eastern varieties was fruited at Glenn Dale, also as early as 1922. In 1923 as many as 1,268 seedlings with one parent chiloensis were set in the field. In addition many varieties were imported from Europe and used in breeding beginning in 1923. Some of these varieties, such as Louis Gauthier, White Pineapple, and La Constante quite evidently were derived in large part from chiloensis. During the years 1927 and 1928 through the courtesy of the Forest Service, forest rangers collected and sent about seventy-five lots of selected plants of F. ovalis from many parts of Western United States. Some of these were used in breeding. Before 1930, Prof. Schuster, at the Corvallis Station in Oregon, made many crosses of F. chiloensis and F. ovalis with cultivated varieties. From July 1930 to June 1932, further collections by Darrow were made of chiloensis along the coast of California, Oregon, and Washington, and of ovalis from the inland areas, to be grown at the Oregon State Station. Later, selections of ovalis were obtained and used from the extensive collections at the federal station at Cheyenne, Wyoming (Plate 8-1). G.F. Waldo (of the U.S.D.A.), who has been stationed at Corvallis since 1932, has made many additional collections of chiloensis and has used them in his breeding ever since. Of 765 selections made by him in his breeding between 1941 and 1956, 443 (about 60 per cent) were only two or three generations removed from the wild. A collection of virginiana selections from the wild in different areas of North Dakota was furnished by A.F. Yeager, and has been used in breeding both for frost-resistant flowers and basal flower-cluster branching habit. In 1957 over one hundred collections of selected clones and many seed collections were made by Darrow in Chile and some of these were used (Plate 8-1b). Many state and provincial stations have made selections of these species, especially, California, Washington, Alaska, British Columbia, Alberta, North Dakota, South Dakota, Iowa, Minnesota, New Hampshire, Louisiana, and Missouri.
The commonly accepted classification of the wild octoploid strawberries is that of three species -- F. virginiana, the meadow strawberry of eastern North America, from the Atlantic seaboard west to about the western boundary of the Dakotas; F. ovalis (includes also most of glauca, cuneifolia and platy-petala) from Montana, Wyoming, Colorado, and northern New Mexico west to the beaches of the Pacific and to Alaska; and F. chiloensis along the Pacific beaches, rarely half a mile inland, from Alaska to south central California, along the beaches of south central Chile, and eastward into the Andes Mountains, extending to include their Argentine side; and on the volcanoes of the Hawaiian Islands.1 F. ovalis is completely interfertile with both chiloensis and virginiana and there has been an introgression of characters of virginiana into ovalis in its eastern range and of chiloensis into ovalis from the Pacific coast inland. Where the latter two species meet along the beaches of the Pacific coast the characters of chiloensis are most in evidence, while inland those of ovalis predominate. It would seem that some characters of ovalis prevented it from becoming dominant on the beaches, and some characters of chiloensis prevented it from becoming dominant inland. All three octoploid species in the wild are almost entirely dioecious, but as early as 1624 perfect-flowered virginiana were selected and taken to Europe. The Indians of Chile also had selected perfect-flowered plants of chiloensis which they were growing when the Spanish came to the Concepción area of Chile in 1557. In Chile, besides the many "staminate" or male chiloensis that set from one to several berries to the inflorescence, a wild variant has been found at various places, in form much like the cultivated Red and White Chilean, which are grown in Chile today, but with duller, very hairy, thinner leaves and often perfect flowers. This variant also has been found in the south-central coastal area of California.
In the last sixty years, F. ovalis has entered into cultivated strawberries through the work of Georgeson in Alaska, Etter in California, Powers in Wyoming, and the federal-state work in Oregon. The Washington variety (one parent of Robinson) is considered to have ovalis as one parent. The Molalla of Waldo in Oregon and the Ogallala of Powers in Wyoming also have ovalis in their parentage.
The plants of F. chiloensis and of F. virginiana are very different in appearance, chiefly due to the glossy, dark green, thick, leathery leaves of the former (Fig. 8-9) and the non-glossy, light green, hairy, thin, coarsely toothed leaves of the latter (Fig. 8-10). The leaves of chiloensis are relatively evergreen; its crowns, petioles, peduncles, and runners are usually relatively stout, while those of virginiana more slender. Chiloensis has silky fine hairs, while virginiana has coarse hairs. Chiloensis usually blossoms much later (twenty to forty days); its flowers are usually larger; its stamens are larger with more pollen; the ripe berries (Plate 8-1b) have a clasping calyx, are larger, with dull purplish-red skin, white flesh and dark seeds that are raised, or at most slightly imbedded; the berries have only slight flavor and aroma. Fruit of virginiana has a recurved calyx, is aromatic, scarlet to crimson in color, often red-fleshed with seeds sunken in pits ((Plate 8-1c). Virginiana is quite tolerant to both cold and the humid heat of the Eastern United States, while chiloensis usually cannot survive this heat and cold. In general, most chiloensis seem much more susceptible to cold, even though the species is very abundant in the fields about Cohaique, Chile, and other places in the Andes Mountains, as well as along the coast of Alaska, where very low temperatures in winter are the rule. On the other hand, chiloensis seems to endure drought far better than most virginiana varieties and survives the dry spells in dunes and sandy beaches of the Pacific Coast (Fig.8-11). Chiloensis leaves seem adapted to drought conditions, for the thickness of their upper surface cuticle and epidermal cell wall runs about 6.9m (Fig. 8-12), while that of the virginiana is 4.3m. The thickness of the cell wall or the lower epidermal surface is 3.9m for chiloensis and 1.6m for virginiana. In chiloensis the entire wall of the upper epidermis is thickened.
Fragaria ovalis characters are in general so intermediate between chiloensis and virginiana that comparisons of contrasting characters are not so easily listed. Its characteristic bluish green foliage is rarely seen in virginiana and either is masked by the deep green or is not present in chiloensis. Its leaflets are much more wedge-shaped than is usual of those of the other two species. Two notable characteristics are the especially everbearing character of many of the ovalis at lower elevations and the drought resistance and hardiness of its plants.
The characters of the three species may be contrasted as follows:
|Leaves - thick, leathery||thick to thin||thin|
thick cuticle and epidermal
|thin cuticle and epidermal cell-wall|
|deep-set stomata||shallow-set stomata|
|strongly netted||not strongly netted|
|dark green||bluish green||light green|
|evergreen||dying with cold||dying with col|
|silky||silky to hairy||hairy|
|short teeth||coarse teeth||coarse teeth|
|Petioles - thick||slender||slender|
|not channeled||broadly channeled|
|Crown - thick||less thick||less thick|
|Flowers - large||medium||medium to small|
|large stamens||medium stamens|
|Fruit - dull red||medium red||scarlet to crimson|
|seeds slightly sunken||sunken in pits||sunken in pits|
|calyx clasping when ripe||clasping to reflexed||reflexed|
|slight flavor||mostly strong flavored||strongly flavored and fragrant|
|Plant - drought resistant||drought resistant||less resistant to drought|
|heat susceptible||heat resistant||heat resistant|
low temperature susceptible
(except in Andes)
|low temp. resistant||low temperature resistant|
|non-everbearing||often everbearing||rarely everbearing|
It would seem that during the past hundred years the wild strawberry of much of eastern North America has become extensively hybridized with the cultivated. Birds have carried seed of cultivated varieties to the wild, where the best adapted of the seedlings survive. Bees have carried pollen from cultivated to wild strawberries. Hybrids growing from such seed often have larger leaves and fruit than the pure wild virginiana. Some characters of cultivated sorts can be found in wild strawberries quite widely. Relatively, large-fruited and thick-leaved clones are common among wild strawberries of Eastern North America; many of these have been transplanted to gardens; and many varieties have been named from wild plants. Even a recent "Register of Fruit Varieties" (Brooks & Olmo, 1960) lists eight varieties as chance seedlings and five others as of unknown parentage. All of these thirteen would certainly have more characters of virginiana than of chiloensis in their ancestry, but to have large enough and firm enough berries for naming none could be entirely virginiana. Even in Western Oregon and Washington some natural hybrids between cultivated varieties and ovalis are being found (Fig. 8-13).
When large numbers of seedlings are grown at one place as in Maryland, those selected to be tested as varieties will naturally be the ones best adapted to that environment. Most strawberry breeding has been done in eastern North America where virginiana is native or, if in Western States, it has been done inland from the beaches and not where chiloensis is native. Hence it is to be expected that selections for naming contain more virginiana than chiloensis. Few American varieties resemble chiloensis closely; many are close to virginiana; all seem intermediate in some respects.
A chart estimating the characters of these two species as they appear in a number of cultivated varieties will illustrate the differences in their genetic makeup in respect to the two species. F1 seedlings, if grown both in Maryland and along the beaches of the Pacific Coast, would probably show this contrast of some characters, as well as the masking of others and the intermediateness of still others. The best test to show the true characters of varieties in relation to the species would be to compare plants grown on the Pacific beaches with the same kinds grown inland. Judging the characters as they appear in our plots is the best we can do now. The following table gives ratings of five varieties for several characters of chiloensis.
|Fruit color exterior||70||20||20||20||30|
|" " interior||0||0||0||20||20|
|Plant drought resistance||50||50||80||50||50|
|Plant heat susceptibility||30||20||0||50||0|
|Plant cold susceptibility||20||10||10||10||20|
According to this rating Fairfax expresses 57 percent of the characters of chiloensis; Earlidawn, 28 percent; Blakemore, 31 percent; Howard, 17, 31 percent; and Missionary, only 27 percent. This would seem to confirm the idea that, due to selection in an environment best suited to virginiana, North American varieties have more characters of virginiana in them than of chiloensis. Yet Fairfax, which seems to have the most chiloensis in its characteristics of eastern varieties succeeds well in a rather wide area and it has been successfully used as a parent in North America, Japan, and Europe. Greater use of chiloensis in breeding for superior varieties seems indicated.
1 Staudt (1962) does not give ovalis specific rank but keeps only two octoploid species. On Hawaiian Mts. a form sandwicencis may be a hybrid or a separate species; a visit to Hawaii (Dec. 1965) suggests this to be derived from chiloensis x ovalis and carried by birds from Alaska. It has sharply toothed leaves and often at least very large inflorescences with relatively large berries.