Several species of Opuntia, notably 0. Ficus-indica, Mill., and 0. megacantha, S. D., are extensively grown in tropical and subtropical countries for their fruits, commonly known as tunas, prickly-pears, or Indian figs.
Among the aboriginal inhabitants of tropical America, the tuna (using this term in a comprehensive sense) has long been held in high esteem. It was early introduced into southern California by the Franciscan monks, and is now found abundantly in many places, particularly around the old missions. From America it was carried to Spain by the early voyagers, and from that country it spread along the Mediterranean littoral and finally to many other regions. It is now cultivated and naturalized throughout the tropics and subtropics.
The edible-fruited opuntias are erect or spreading plants, growing from 10 to 25 feet in height. They have large flattened branches made up of more or less rounded joints, which in popular language are called leaves. Usually these joints bear long sharp spines, although in some species they are almost spineless. The flowers, which are produced toward the upper part of the joints, are yellow or red and rather showy. The oblong to pear-shaped fruits, commonly 2 to 3 inches in length and green to deep maroon in color, contain soft, whitish, translucent pulp intermixed with numerous large bony seeds. The pulp is juicy with a pleasant, although not pronounced, flavor. The principal objection to the tunas is the great quantity of hard seeds which they contain.
0. Ficus-indica has fewer spines and somewhat differently colored fruit from 0. megacantha; both these species are cultivated in the southwestern United States as well as in Mexico, the Mediterranean region, and elsewhere. Several other species produce edible fruits, but their cultivation is not extensive.
A considerable quantity of tunas is shipped annually to the United States from Sicily, and an important trade could be developed betweeen the United States and Mexico.
Because of its rather high nutritive value, the tuna forms an important article of diet in many regions. It is eaten fresh, dried, or prepared in various ways. Griffiths and Hare have discussed this subject fully in "The Tuna as Food for Man." 1 The ripe fruit contains: Total solids 19.66 per cent, ash 0.40, acids 0.18, protein 0.98, total sugars 13.42, fat 0.23, and fiber 2.79.
J. W. Tourney, writing in Bailey's "Standard Cyclopedia of Horticulture," says: "It has been ascertained that some of the best varieties are capable of producing on lean, sandy or rocky soil, ill-suited for growing ordinary crops, as much as 18,000 pounds of fruit to the acre. When it is considered that this is equal to 2500 pounds of sugar, as well as other valuable food constituents, it may be readily seen that the food value from the standpoint of nutrition is considerable."
Little cultural attention is usually given to the opuntias in the regions where they are grown for their fruit. To quote Tourney again : "Plantations are usually made on dry slopes of hills, as the plants do not thrive where there is much moisture or on heavy clay soils. Joints, cut or broken from the plants, are used instead of seeds, and are planted at distances of 6 to 8 feet in furrows from 6 to 15 feet apart. No tillage is practiced, as they grow rapidly, and in a few years smother out all other growth. Before planting, the cuttings are exposed in half sunlight from seven to fifteen days, that they may partially wither, in order to facilitate rooting.
"An important advantage in the culture of these plants is the regularity of the yearly crop. They begin to bear in about three years after planting, and continue in bearing for many years."
Numerous varieties or forms, usually local in their distribution, are distinguished in Mexico and elsewhere. In spite of the attention given in recent years to the improvement of this fruit by breeding, still further advances must be made before varieties are obtained which will become popular as table-fruits among North Americans.
1 Bul. 116, Bur. Plant Industry.