FIG. 50.—Fruits of the Thomasville citrangequat. The gooseneck stem attachment and clawlike calyx points are characteristic of this hybrid
Trifoliate Orange Valuable
CITRANGES and Some Related Hybrid Fruits
The breeding of cold-resistant citrus fruits suitable for culture in the southern part of the Cotton Belt has been in progress for many years. A large group of hybrids known as "citranges” were first produced by crossing the commercially worthless trifoliate orange of Japan with the ordinary orange. The citranges are unlike either parent, and serve chiefly as hardy substitutes for the lemon. The Rusk citrange has been more widely distributed than the others, its prolific nature, evergreen_habit, and handsome appearance, especially when carrying a full crop of bright orange-red fruits, giving it value as an ornamental in addition to its fruits.
In 1909, crosses were made between the citrange and kumquat, resulting in the creation of the citrangequat. Of these, the best known is the Thomasville, a tree of compact, upright habit, evergreen, and which starts bearing at an early age, carrying its fruit from late summer into the winter months. These fruits resemble in shape a large oval kumquat, but have an acid, limelike juice, making them excellent for marmalade, preserves, and ade. The gooseneck fruit spur and clawlike calyx points (fig. 50) are unique characters which make the fruit easy to identify. The citrangequat inherits the kumquat’s habit of sustained winter dormancy, with resulting hardiness, and so may be grown in regions much too cold for ordinary citrus varieties. It has, too, the unique immunity to citrus canker possessed by its kumquat parent, and so meets the need for a home-grown fruit that will not help in spreading this most serious of all citrus diseases should there be another infestation in the Gulf States.
The trifoliate orange, while worthless for fruit production, is an important rootstock for citrus, especially the Satsuma orange. It has a number of serious disadvantages, however, since it is susceptible to citrus canker, fails to grow in very light sandy soils or the black waxy and heavy silt soils of southern Texas, and dies at the root when the budded top happens to be killed by a severe freeze such as sometimes visits the Gulf coast region. The Rusk citrange and Thomasville citrangequat, on the other hand, produce vigorous sprouts from the old roots after a freeze and the trees may be re-budded and a grove reestablished in two or three years. Both show, in budding experiments, a perfect compatibility with the Satsuma orange, and buds grow readily on these stocks. Both are sufficiently hardy to be proof against cold injury in the Gulf States and have a wide range of adaptability to soils not suited to the trifoliate orange. The quality of fruit thus far produced on these stocks is in no way inferior to that grown on the trifoliate.
Both the Rusk and Thomasville, however, produce few seed, so that although they come true to seed their rapid propagation is something of a problem. This problem has apparently been solved by the discovery that cuttings may be rooted in a “solar propagating frame”—a rooting bed using sunlight for bottom heat. Fine twig cuttings with leaves attached may be rooted in six to eight weeks and the root systems so developed are in no way inferior to those of seedling plants. The use of cuttings, furthermore, insures a uniformity not possible with seedlings, while the saving of time as compared with planting seed will more than offset the expense and trouble of rooting the cuttings. Field tests of these stocks are being made, though it will require a few seasons before all factors that enter into their successful commercial use can be determined with certainty.