Index | Search | Home | Morton

Morton, J. 1987. Sundry Hybrids and Rootstocks. p. 185–186. In: Fruits of warm climates. Julia F. Morton, Miami, FL.

Sundry Hybrids and Rootstocks



TRIFOLIATE ORANGE (Poncirus trifoliata Raf., syn. Citrus trifoliata Linn.) grown for thousands of years in central and northern China; from the 8th Century in Japan if not earlier; a small, fast-growing, deciduous tree, with palmate leaves usually having 3 leaflets, rarely 4 or 5; flowers showy, white, 5-petalled; fruits round to pear-shaped, 1 1/4 to 2 in (3.2-5 cm) wide; peel fragrant, dull-yellow, minutely downy, rough, with numerous oil glands, thick; pulp scant, sour, with a little acrid oil in the center; seeds ovoid, plump, numerous. Immature fruits and dried mature fruits used medicinally in China. In southern Germany, fruit juice after 2 weeks' storage used to make a flavoring sirup, the peel is candied and used as a spice, and is a source of pectin. The plant is much grown as an ornamental in cool areas of Europe, Asia and North America. In Brazil, it is valued as a protective hedge against animals and human trespassers. Seedlings are important in most citrus-growing areas as rootstocks for various Citrus and related species.

CITRANGE (X Citroncirus Webberi J. Ingram & H. E. Moore); a trifoliate orange X sweet orange hybrid created by Dr. Walter Swingle or under his direction, beginning in 1897. Tree is evergreen or semi-deciduous, usually trifoliolate, deciduous; not as cold-resistant as the trifoliate orange. Fruits more or less aromatic, outwardly orange-like; 2 to 3 in (5-7.5 cm) wide; peel yellow to deep-orange, may be hairy or non-hairy, wrinkled, ribbed, or smooth; thin; pulp often very juicy and tender, richly flavored, highly acid, slightly bitter; seedless or with a few, mostly polyembryonic, seeds. Certain cultivars, 'Coleman', 'Morton', 'Rusk' and 'Savage', especially 'Rusk', yield juice valued for ade and mixed drinks. They are also desirable for pie, jams and marmalade. 'Troyer' ('Carrizo'), a 'Washington Navel' X trifoliate orange hybrid created by Dr. Walter Reuther in 1909, named 'Troyer' by Swingle in 1934 and renamed 'Carrizo' in 1938, has become a very important rootstock, particularly in California. When budded onto trifoliate orange, can be grown in Georgia.

In early 1985, citrange hybrids 'C35' and 'C32' ('Ruby' orange X trifoliate orange) were released by the Citrus Research Center, Riverside, California, for trial as rootstocks because of their resistance to the citrus nematode, also to Phytophthora spp. and the tristeza virus.

CITRANGEQUAT (Fortunella sp. X citrange). The first crosses were made by Dr. Swingle at Eustis, Florida, in 1909. Tree is vigorous, erect, thorny or thornless, with mostly trifoliolate leaves; highly cold-resistant. Fruit resembles the oval kumquat, mostly very acid. One cultivar, 'Thomasville', becomes edible when fully mature, though it is relatively seedy. It is very juicy, valued for eating out-of-hand, for ade and marmalade. The tree is strongly resistant to citrus canker and is very ornamental. Two other cultivars, 'Swinton' and 'Telfair', have few seeds, but are less desirable; have limited use for juice and as ornamentals.

LIMEQUAT (X Citrofortunella spp.)–Mexican lime X kumquat hybrids made by Dr. Swingle in 1909, described and named in 1913. Tree vigorous, evergreen, the single leaflets having narrowly-winged petioles; nearly spineless or with a few short thorns; more cold-tolerant than the lime but not as hardy as the kumquat; very resistant to withertip. Fruit much like the Mexican lime. There are three named cultivars:

'Eustis' limequat
Fig. 46: 'Eustis' limequat (X Citrafortunella floridana), a cross between a Mexican lime and the Marumi kumquat.

'Eustis' (X C. floridana J. Ingram & H. E. Moore)–Mexican lime crossed with round kumquat; oval or round, 1 1/8 to 1 1/2 in (2.8-4 cm) wide; peel pale-yellow, smooth, glossy, with prominent oil glands, thin, edible; pulp light greenish in 6 to 9 segments, tender, juicy, very acid, with 5 to 12 small seeds. Of excellent quality, nearly everbearing but mainly in fall-to-winter. Tree has small spines and pure-white buds and flowers; prolific.

'Lakeland' (different seed from same hybrid parent)–oval, 1 1/4 to 2 1/4 in (4.5-7 cm) wide; peel bright-yellow, smooth, thin; pulp in 5 to 8 segments, pale-yellow, juicy, pleasantly acid, with 2 to 9 large seeds. Tree nearly spineless; flowers white with pink streaks.

'Tavares' (X C. Swinglei J. Ingram & H. E. Moore)–a Mexican lime X oval kumquat hybrid; obovate to oval, about 1 1/4 to 1 7/8 in (3.2-4.75 cm) wide; peel pale orange-yellow, smooth, thin, tender, edible; pulp buff-yellow, in 7 to 8 segments, juicy, very acid, with 6 to 11 large seeds. Tree vigorous with short spines and pink flower buds.

Limequats are cultivated as dooryard trees to a limited extent in central Florida; are more commonly grown in California as potted ornamentals.

VOLKAMER LEMON is described and illustrated in great detail by H. Chapot as Citrus volkameriana Pasquale, though the author views it as a hybrid between the lemon and possibly the sour orange. Tanaka and others suggest that it may be a variety of mandarin lime.

The tree is a little smaller than the average lemon tree. Young seedlings bear a few spines 1/2 to 3/5 in (12.5-15 mm) long, but these disappear with age and are produced only occasionally on older specimens. The leaves are short-petioled, ellipsoid, more or less toothed, 3 3/4 to 6 in (9.5-15 cm) long. The flowers, only slightly fragrant, short-stalked, 3-to-6-petalled, 1 3/8 in (3.5 cm) wide, are borne in small clusters all along the branches and at the tips. The fruit, borne profusely, is lemon-shaped, 2 1/4 in (5.7 cm) long, 2 1/8 in (5.4 cm) wide, rough, bright-reddish-orange. The yellow-orange pulp, in 7 to 11 segments, is very juicy, acid, faintly bitter, of agreeable odor and flavor, with few seeds. The fruiting tree is exceptionally ornamental and the fruit can be used as a substitute for the lemon.

The Volkamer lemon has been known for more than 3 centuries. In the mid-1950's, it was reported in Italy to be a promising rootstock for lemon because of its high resistance to malsecco (Deuterophoma tracheiphila) and foot-rot (Phytophthora sp.). Trials in Morocco in 1972-1973 with scions of sour orange, sweet orange, mandarin orange, grapefruit, lemon and rough lemon, and inoculated Volkamer rootstock, showed it to be highly susceptible to gummosis caused by Phytophthora citrophthora in contrast to 'Carrizo' citrange rootstock's high resistance. The degree of necrosis varied somewhat with the scion. (See Chapot in Bibliography).

During tristeza studies on Reunion, workers noted on several trunks of the Volkamer lemon woody galls associated with a wood-bark-socket stem-pitting, according to Aubert et al. Protopapadakis and Zambettakis have reported that, in Crete, Volkamer lemon has proved to be second only to sour orange in resistance to mal secco.