Citrange

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Citrange
Genus × Citrocirus
Hybrid parentage Citrus sinensis × Poncirus trifoliata
Cultivar Rusk, Troyer, Carrizo
Breeder Herbert John Webber & Walter Tennyson Swingle
Origin USA

The citrange (Citrus sinensis × Poncirus trifoliata or C. sinensis × C. trifoliata) is a citrus hybrid of the sweet orange and the trifoliate orange. The purpose of this cross was to attempt to create a cold hardy citrus tree (which is the nature of a trifoliate), with delicious fruit like those of the sweet orange. However, citranges are generally bitter.

Citrange is used as a rootstock for citrus in Morocco, but is not successful to prevent dry root rot, neither for exocortis.[1]

Cultivars[edit]

There is a carrizo citrange[2] and there is a troyer citrange.[3] Both are resulting of a hybrid between the trifoliate orange and the Washington navel orange. There is also a cultivar called Rusk which is resulting from a cross between a Ruby orange and a trifoliate orange. [4]

Excerpts[edit]

The following is a message from Herbert John Webber, one of the botanists that were responsible for the development of Troyer:

When I visited the tree of this in Field 8A with Swingle on 12/04/34, he was much pleased with its vigor and numerous plump seeds and told me to put down the name Troyer for it as the first fruits came to him from a Mr. Troyer at Fairhope, Alabama. It thus becomes the Troyer citrange and I will describe it under that name in my Variety manuscript.[5]

And here is what he actually wrote in what he called his variety manuscript, which grew out to be The Citrus Industry (book) Volume I:[6]

The Citranges (Poncirus X C. sinensis).— The influence of the trifoliate orange is strongly marked in the "citranges" as evidenced by the trifoliolate nature of their leaves, the acidity and bitterness of their fruits, and the cold-hardiness of the trees. The influence of the sweet orange is shown, however, in the evergreen nature of the trees, though a few are semi-deciduous, and in their greater vigor. Additionally, the fruit is usually much larger and more orange-like in appearance. In general, however, the citranges exhibit some degree of intermediacy between the parental species. Of great horticultural importance in connection with their use as rootstocks is the fact that with few exceptions they come remarkably true from seed. They are highly polyembryonic and apparently rarely develop zygotic embryos (Swingle, 1927).

The term citrange was announced and the first variety named and described in 1904 (Webber and Swingle, 1905) and subsequently a dozen or more have been added. For descriptions of most of them the reader is referred to Webber (1943, pp. 656-65) and the literature he cites.

In Webber's opinion, the citrange varieties that most closely approach the sweet orange in size, appearance, and edibility in the fresh state, and hence may be useful as juice fruits for dooryard planting in regions too cold for oranges and mandarins, are Morton, Coleman, and Savage. He also recommends them as ornamentals.

Since, in general, the citranges exhibit some of the most desirable features of the trifoliate orange combined with the greater vigor and wider range of soil adaptation of the sweet orange, some of them are currently of promise or already have achieved importance as rootstocks. Principal among these are Carrizo, Rusk, and Troyer, which are described below.

Carrizo - Carrizo is indistinguishable from Troyer and of the same parentage. Savage and Gardner (1965) have recently presented convincing evidence that Carrizo and Troyer are in fact a single clone which originated as the zygotic seedling (CPB 4-5019) from a cross of Washington navel and trifoliate orange made by the senior author in 1909 under the direction of W. T. Swingle of the U.S. Department of Agriculture instead of two sister seedlings as had been assumed (Mortensen, 1954).

In 1923, Swingle had 200 seedlings of this then unnamed clone sent to the Winter Haven substation (No. 19) near Carrizo Springs, Texas. In 1938, he suggested it be named Carrizo, either forgetting that he had already given it the name Troyer in 1934, which seems unlikely, or because he failed to recognize its identity, which seems surprising.

Bitters reports that its field performance has differed somewhat from Troyer, which is difficult to understand in light of the conclusions set forth above.

Rusk (fig. 4-97) - Fruit rather small, oblate to spherical; smooth and virtually glabrous; color deep orange with reddish flush. Rind thin and tightly adherent; segments about 10. Flesh color orange-yellow; very juicy; flavor sprightly acid and only slightly bitter. Seeds few and highly polyembryonic. Early in maturity. Tree vigorous, tall-growing, productive, and hardy; foliage evergreen to semi-deciduous and dense, consisting of moderately large trifoliolate leaves.

Rusk, a Ruby orange and trifoliata hybrid, is one of the oldest citranges, having been created by Swingle in 1897 and described and released in 1905 (Webber and Swingle). It was named in honor of J. M. Rusk, the first Secretary of Agriculture of the United States.

The tree is an attractive ornamental and the fruit is juicy and approaches edibility more closely than most citranges. Its low seed content mitigates against use as a rootstock.

Rusk is currently of greatest interest and importance in Florida.

Troyer (fig. 4-98) - Fruit small, oblate to spherical; smooth and nearly glabrous; color light orange. Rind medium-thick, with numerous oil glands; tightly adherent. Segments 9 to 10 and axis solid. Flesh color light yellow; juicy; flavor strongly acid and bitter. Seeds numerous, plump, and highly polyembryonic. Season of maturity early. Tree vigorous, upright-spreading, and medium-large with rather slender, thorny branchlets; foliage moderately dense, evergreen to semi-evergreen. Leaves dark green, medium in size, and mainly trifoliolate, occasionally unifoliolate. Productive and hardy.

This variety originated as a hybrid of the Washington navel orange crossed with trifoliate orange pollen (hence is actually a citruvel) that was made by E. M. Savage, under the direction of W. T. Swingle of the U.S. Department of Agriculture, at Riverside, California, in 1909. In 1934, Swingle named it for A. M. Troyer, on whose place at Fairhope, Alabama, it was first fruited. The rise of this rootstock to prominence in California has been spectacular. Within less than twenty-five years from the first field trial it has become the rootstock most employed and is much in demand elsewhere.

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