THE PUERTO RICAN CHIRONJA - A new type of citrus

SCIENTIFIC NAME: Citrus paradisi x Citrus sinensis (?)
FAMILY: Rutaceae

The chironja, a new type of citrus, was found by the author in 1956, in the central mountains of Puerto Rico. This new fruit appears to combine desirable characteristics of the orange and grapefruit. It is generally similar to a grapefruit in size, although slightly more elongated. At maturity the outer rind is bright yellow and glossy and the pulp is orange colour. The flavour is best described as a combination of sweet orange and grapefruit, without the acidity of the former or the bitterness of the latter.

The chironja is a versatile fruit of various table uses having a vast commercial potential. It may be eaten as a grapefruit, cut in half, or peeled and eaten as a tangerine, or it may be utilized for juice, the average chironja yielding the equivalent of 2 medium-sized Valencia oranges. The average chironja weighs 500 grams, the number of seeds per fruit varying from 7 to 15. It is nucellar.

Field experiments have been conducted over a period of ten years with seedling and grafted trees. Some ever­bearing trees have been observed. Chironjas were found easy to process in canning experiments reported in 1965. No difficulties were experienced in removing the peel or in separating the sections. Some research has been conducted on adaptation to various environments, grafting and behaviour of progeny from selected material. Research has been conducted on adaptation to various selected material. Research now in progress proposes to elucidate the true nature of the chironja through botanical and cytogenetical studies, comparing characteristics of this fruit with grapefruit, Citrus paradisi Macf And orange, C. sinensis (L) Osbeck.

The Puerto Rican Chironja is a delicious new addition to the citrus family. This new fruit which was discovered in 1956 (Moscoso, 1958) growing wild in the mountains near Utuado, Puerto Rico, appears to combine very desirable characteristics of orange, Citrus sinensis (L) Osbeck, and grapefruit, Citrus paradisi Macf In fact, these characteristics are so notable that the name 'Chironja' selected for the fruit is a combination of the Puerto Rican names for orange and grapefruit, i.e., 'China' and Toronja' respectively.

In February, 1956, while in charge of the Citrus Marketing Project at the Agricultural Experiment Station of the university of Puerto Rico (Moscoso, 1957) the writer made many field trips to the coffee zone of the island to look for new and promising varieties of oranges. On one of these field trips the tree to which the name 'Puerto Rican Chironja' was given, was first observed.

While inspecting an orchard in the vicinity of Utuado Puerto Rico, high up in the mountains, the writer was impressed with the appearance of one particular tree. It was unusually large and laden with bright, glossy, yellow fruit, quite different in appearance from the orange and grapefruit trees surrounding it. The taste of the fruit was a fascinating combination of both orange and grapefruit flavours. Upon questioning the farmer on whose land this tree was growing, it was learned that this particular tree and a number of others like it growing on neighboring farms had all been propagated from seed. It was stated that the few farmers who possessed these unusual trees had rarely marketed the fruit, but rather, in view of the superior flavour, size and keeping qualities, had preferred to keep the fruit for the use of their own immediate families.

Seed and vegetative propagating material for making grafts were collected, and early in 1957 propagation of this new citrus for experimental purposes was begun. The fruit of the chironja may be compared with the average grapefruit in size. At maturity the peel becomes a bright glossy yellow while the inner flesh is orange in colour. The flavour of the juice and pulp is a combination of orange and grapefruit, but with neither the acidity of the orange nor the bitterness often characteristic of the grapefruit (Moscoso 1958).

When the chironja is grown in partial shade the trees tend to be large and columnar. However, chironja trees grown in full sunlight have the typical rounded form of citrus. Branches are irregular and on the young twigs and shoots of some trees there are thorns similar to those produces by young seedling grapefruit trees. In general the foliage of the chironja tree is quite dense, the leaves being a deep bright green. Branches are rounded and generally smooth, although on some trees a slight pubescence has been observed on the under surface on the union on the trunk and smaller branches. The average height of the chironja tree is approximately 8.3 m.

The leaves are quite similar in appearance to those of the grapefruit, and are usually large with prominent veins. Leaf texture is thick and strong. They are irregularly undulated, shiny, even waxy in appearance. When bruised, an aroma similar to that of grapefruit leaves is noticeable. On a mature tree the average length of leaves is 140.6 mm with an average width of 70 mm, The fruits of the chironja are borne singly or in bunches at the ends of branches. Fruits vary in shape from globose to pyriform being somewhat obloid. The fruit is usually larger than the grapefruit, although occasionally smaller fruits about the size of a large orange are produced. The base or stem is slightly to prominently collared and depressed. The collar is often longitudinally furrowed or ridged. The apex has a very small stylar scar surrounded by a prominent grey to tan area approximately one-half inch in diameter. This peculiar circular area is a characteristic the writer has observed in all chironjas which he has examined. The diameter of the fruit varies from 92 to 110 mm, with an average diameter of 101 mm. Height ranges from 90 to 134 mm, with an average height of 111 mm (Moscoso 1964).

The bright yellow outer rind of the fruit is similar to the grapefruit in aroma. Thickness of the rind varies from 5 to 8 mm with an average of 6.8 mm, the rind representing 24% of the total weight of the fruit. Texture varies from smooth to slightly rough. Although the rind is thick, it is as easy to peel as a tangerine. Fruit sections also separate very easily.

The edible portion of the chironja contains nine to thirteen segments, with an average of eleven. The septa or thin covering of each segment is very tender and may be eaten without distaste. The clear, sweet juice of the chironja is light orange in colour. The size of segments varies from 39 to 44 mm in width, with an average of 40.2 mm and length varies from 79 to 90 mm, with an average of 84.5 mm.

The fruits are easy to process and no difficulties were experienced in removing the peel or in separating sections. Shelf­life studies showed that the canned product kept very well in storage at 85°F for over one year (Benero and Carlo Velez, 1965).

The chironja is nucellar. Its seeds are light ivory-coloured with a slight pinkish tint. Fairly large, they compare in size and shape with the seeds of the grapefruit and the orange. The number of seeds in each fruit varies between seven and fifteen, with an average number of eleven seeds. However, a few trees have fruits containing only two seeds. (Moscoso 1964).

In field trials conducted with 500 seedlings chironga trees none reverted back to either orange or grapefruit, but rather maintained true to-type. characteristics of this new citrus. Undoubtedly this is a form of apomixis.

It is possible that the chironja may be the result of a natural cross of orange and grapefruit. If this is true, it is evident that such a cross has become sufficiently stabilized to permit the development of this new type of citrus capable of reproducing its characteristics by means of propagation by seed (Moscoso 1964).

The flowers of the chironja are white. They develop singly or in bunches at the ends of the branches. The flower contains 5 sepals and 5 petals and has from 10 to 25 stamens with fairly large anthers. Flowers are produced on different trees during all seasons of the year in Puerto Rico, generally in greater abundance during late spring and early summer. This means that it is possible to harvest fruits at any given time of year on selected trees. A few ever-bearing chironja trees occur.

During more than ten years of field research more that twelve selections of chironja have been made, three of which are considered to be outstanding; M-1, with good appearance, shape and productivity; M-2, which is a late-yielding line; and M-3 which has good appearance and is a very heavy yielder.

A current project places emphasis on the botanical differences between the chironja, on the one hand, and orange and grapefruit on the other, including cytogenetical aspects and chemical analyses. Results of these studies will be published upon completion of the project. Cytogenetic studies indicated that the chironja, as most other varieties of citrus, contains nine pairs of chromosomes. Its pollen is very fertile but its chromosomatic ration does not confirm whether or not the chironja is a cross between and orange and a grapefruit. The possibility is not however, eliminated (Vikki, 1964).

Chemical analyses showed that the chironja is much less acid and much richer in sugars than the other two fruits.

It is noteworthy that the chironja and the orange showed the same ascorbic acid content, 39 mg of ascorbic acid per 100 ml of juice for both fruits.

The high sugar and low acid of the chironja was confirmed by work at the Biochemical Laboratory.

C G Moscoso,
Agricultural Experimental station, Rio Piedras, Puerto Rico

DATE: December 2001

* * * * * * * * * * * * * **